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Micro and Nanocrystalline Silicide - Refractory Metals FGM for Materials Innovation in Transport Applications

Final Report Summary - SILTRANS (Micro and Nanocrystalline Silicide - Refractory Metals FGM for Materials Innovation in Transport Applications)

Executive Summary:
The main idea of the SILTRANS project was to develop a functionally gradient material (FGM) able to withstand complex loading usually combining several factors like high temperature (HT), high heat flux, corrosion (oxidation) attack and multiaxial dynamically changing forces and this all should be accomplished using manufacturing techniques enabling cost efficient production of net shape (also very complex) structural parts. Such material is inevitable for further development of high-tech applications working in extreme conditions and environments such as aircraft and automobile engines, space vehicles, high temperature or high pressure fusion or chemical reactors, etc.

After 48 months of project performance a consortium consisting of 7 partners from 5 European countries has developed a new class of structural HT composites consisting of a continuous refractory metal framework (Nb, Mo) embedded in a silicide matrix that offers excellent oxidation resistance at HT (forming self healing silica), while continuous refractory metal skeleton provides efficient tool against crack propagation, thus improving strength, ductility and toughness of composite at both high and low temperatures.
The developed Mo/Mo-silicide FGM has shown significantly improved oxidation resistance at HT in comparison with standard Mo alloy and much higher fracture toughness at low temperatures if compared to traditional silicides. The obtained mechanical properties at high temperatures combined with good oxidation resistance bring the developed material into a group of very promising high temperature structural materials, able to outperform currently used Ni based superalloys.
The industrially viable method for cost acceptable manufacturing of complex shaped parts from developed materials has been developed together with novel reactive infiltration technique for manufacturing of dense woven Mo wire based silicide matrix composites for special applications and laser beam sintering technique for manufacturing of complex shape parts from Mo powders, enabling rapid manufacturing of prototypes from developed materials
The performance of developed materials and manufacturing technique was demonstrated on three selected demonstrators in transport related applications; in particular on stationary turbine blade in automobile engine turbocharger (high volume production at low price), on space related structure, e.g. mounting stands-off elements for holding of thermal protection sheets (low volume – price insensitive) and multichannel catalyst part (rapid prototyping of complex shape). The mounting stands-off element for space structure made of developed composite survived successfully standard thermal shock resistance test simulating re-entry conditions. A few other potential applications and spin-off products utilising developed materials were identified.
Models describing reaction kinetics in Mo-Si system both in liquid and solid states were suggested and experimentally verified; the potential effect of various barrier coatings on this reaction kinetics was evaluated.

Two research institutes (IMSAS, FRAUNHOFER), 2 universities (EPFL, TUW), 2 industrial SME partners (ATL, KE) and one multinational industry partner (EADS) from 5 European countries (A, D, CH, SK, UK) covered all necessary competencies needed for successful performance of the SILTRANS project (for contact details see attached list of partners). High industrial participation in this project (50%) reveals strong interest of industrial partners in the results of this project and guarantees their quick and efficient implementation into practical use.

Project Context and Objectives:
The further development of many technical fields is strongly restricted by the limits of current structural and protection materials. This is especially true for high-tech applications working in extreme conditions and environments such as aircraft and automobile engines, space vehicles, high temperature or high pressure fusion or chemical reactors, etc. Their reliable and efficient performance requires revolutionary improved materials able to withstand complex loading usually combining several factors like high temperature (HT), high heat flux, corrosion (oxidation) attack and multiaxial dynamically changing forces and this all should be accomplished using manufacturing techniques enabling cost efficient production of net shape (also very complex) structural parts.

Designers, who must cope with high temperature (HT) have a limited selection of materials:
Graphite and other carbon-based materials are widely used as high temperature structural materials because they are dimensionally stable, strong at high temperature, easy to machine, lightweight, and relatively inexpensive. However, they degrade rapidly at temperatures above 800°C in oxidizing atmospheres. Coatings that protect carbon-based materials from oxidation are an attractive option, but thermal expansion differences between coatings and the substrates, along with high temperature reactions, make this an impractical solution for many applications.
In recent years, a renewed interest has developed in diborides and carbides of the early transition metals (e.g. Zr, Hf, Ta). These materials have melting temperature above 3000°C, retain their strength at temperatures above 1200°C, exhibit good thermal shock and erosion resistance, and can be modified with additives such as SiC to promote oxidation resistance. The major limitation to their use is a lack of an affordable, reproducible manufacturing process.
Other candidate materials include ceramic oxides, nitrides, refractory metals or their silicides. Although oxides are inherently stable in an oxidizing environment and can be fabricated by manufacturing-friendly processes such as powder forming and sintering, they suffer from lack of thermal shock resistance, low fracture toughness, and poor creep resistance at elevated temperature.
Refractory metals are readily formed to shape, have high thermal shock resistance and have high fracture toughness, but they undergo active oxidation in these applications and are limited by creep resistance at elevated temperatures. In addition, most of them have high densities and cost.
Refractory metal (Mo, Nb) silicides are able to create stable and renewing oxide at a surface and thus protect material from further corrosion. Their main problem is high DBTT ~1100 K, limited creep resistance above 1500 K, low oxidation resistance at moderate temperatures (pesting behaviour) and in sulphuric environments. Manufacturing of complex parts is also difficult.

Despite extensive R&D activities on abovementioned materials in last decades, Ni based superalloys (5th generation) still remain as the most reliable and widely used material systems for many HT applications. Their exhibit excellent creep strength, oxidation resistance, and fracture toughness. However, nickel-base superalloys are approaching one fundamental limitation– their melting point. Since advanced superalloys melt at temperatures about of 1350°C, significant strengthening can be obtained only at temperatures below 1150°C, what is as much as 150 K lower than current requirements defined by designers of efficient and clean aircraft or modern industrial turbines.

The main idea of the SILTRANS project was to develop a new class of HT composites consisting of a continuous refractory metal framework (Nb, Mo) embedded in a silicide matrix, whereas:
- continuous (percolating) porous skeletons of refractory metal (Nb, Mo) is infiltrated with molten silicon or silicon based alloy using gas pressure infiltration technique (GPI)
- during GPI partial reactions between melt and refractory metal take place, forming silicides at the surface of porous precursor, leaving less free silicon for formation of silicides inside the porous structure, thus making in situ FGMs (functionally graded materials) with gradiently increasing metal content towards the core of composite
- the amount of molten silicon is controlled to form required thickness and composition of silicides at the surface of refractory metal, but retain continuous metallic skeleton
- Mutual reaction between refractory metal and silicon is controlled via infiltration parameters (pressure-temperature-pore size) or optionally via utilisation of barrier coatings applied on precursor by chemical vapour infiltration method (CVI)

Final composites do not contain any free silicon - all is converted into silicides, whereas the metallic skeleton still remains as percolating structure. In such composites the silicide matrix provides excellent oxidation resistance at HT (forming silica), while refractory metal reinforcements is utilised for HT strength, ductility and creep resistance enhancement. The continuous metallic skeleton provides efficient tool against crack propagation, thus improving toughness of material at both high and low temperatures.

The following bodies were used as continuous (percolating) porous skeletons of refractory metals (Mo, Nb):
- perforated Mo metal sheets
- woven structures of refractory Mo or Nb wires
- sintered powders of Mo or Nb with controlled open porosity to allow subsequent infiltration
- sintered complex shape porous Mo structures made according to novel patented process (EP 1 268 105 B1) comprising simultaneous reduction and sintering of fine grained refractory oxides cast into required complex shapes
- complex shape porous prototypes with gradiently changing porosity made of Mo- and Mo powder mixtures sintered by means of newly developed laser beam sintering technique

Objectives of the project

The main objectives of the project included:

- development of new class of structural HT composites consisting of a continuous refractory metal framework (Mo, Nb) infiltrated by a silicide matrix and possessing enhanced properties needed for their use under extreme loading conditions in particular:

- creep strengths at high temperatures
- sufficient fracture toughness
- good oxidation resistance
- low density - especially for moving structures
- very low ductile to brittle transition temperature (DBTT should be below room temperature)
- suggestion of industrially viable method for cost acceptable manufacturing of complex shaped parts from developed materials
- evaluation of the performance of developed materials on two carefully selected demonstrators in transport related applications; in particular on stationary turbine blade in automobile engine turbocharger (high volume production at low price) and on space related structure, e.g. mounting stands-off elements for holding of thermal protection sheets (low volume – price insensitive)
Benchmarking materials are Ni-base superalloys – i.e. the main challenging aim of the project was to develop materials beyond Ni-base superalloys (with respect to operation temperature), which can be used for structural purposes similarly as superalloys.

Main deliverables of the projects are:
- Novel FGM composite material based on refractory metal reinforced silicide with enhanced creep and corrosion resistance if compared to currently used superalloys possessing acceptable fracture toughness and DBTT as well as corresponding manufacturing techniques
- Novel (micro)porous refractory metal material made by cost efficient manufacturing technique
- Models describing reaction kinetics between Si melts and refractory metals, role of barrier coating and alloying elements
- Database of mechanical properties of developed materials with respect to HT applications in oxidising environments
- Two demonstrators made of developed materials including evaluation of their performance in extreme loading conditions.

The workplan for 48 months duration of the SILTRANS project was divided into 7 workpackages (WPs). Four WPs were devoted to RTD activities, and the three others to demonstration activities, management and knowledge dissemination.
The main objective of first three RTD WPs was to elaborate the knowledge needed for better understanding of processes which were then used for manufacturing of FGM in further project performance:
- WP1 was assigned to the development of porous preforms from refractory metals (Mo, Nb) via sintering of fine metallic powders and alternatively via reduction of compacted metal oxides. The special attention has been given to the development of the process enabling to obtain fine grained material with controllable porosity gradiently changing from the surface to the core
- In WP2 the infiltration of molten silicon into Mo porous body was studied in order to understand the reactions between molten silicon and solid refractory metal as well as their kinetics and suggest the way for efficient control of infiltration process
- In WP3 the reactions which may have negative influence on the long term stability of the developed gradient and thus non equilibrium composites were parallelly investigated in solid state at high temperatures HT, with an aim to suggest optimum composition of formed silicide layers. Simultaneously, an effect of barrier CVD (CVI) coatings on the surface of refractory metal particles on the reaction kinetics was examined.

All three WPs started parallelly at the beginning of the project. The knowledge obtained in WP2 and WP3 was continuously transferred to WP1 in order to optimize porosity of developed preforms and on the other hand developed performs were used for optimization of infiltration process. The optimized materials were tested in WP4 at targeted conditions, i.e. at high temperature in oxidizing environment. The determination of oxidation resistance and mechanical properties at room and high temperatures was of the prime interest. Finally three carefully selected demonstrators were manufactured from the developed materials for application oriented test, in order to demonstrate material performance in real operation conditions. According to the obtained results plan of use and dissemination of foreground was elaborated including identification of market opportunities as well as measures needed to bring developed materials to large industrial exploitation.

The novelty and breakthroughs expected from the SILTRANS project are mainly related to:

- novel composite material comprising a continuous metallic skeleton fully embedded in a silicide-matrix, whereas continuous refractory metal will improve the fracture toughness, ductility and creep resistance and silicide matrix the oxidation resistance at high temperatures
- a self-healing silica or complex oxide coating which is automatically formed at the surface of composite in oxidising environment at HT
- a cost efficient technique for manufacturing of complex near-net shape silicides, since the infiltrated body follows the shape of a porous preform, which is relatively easy to make utilizing standard powder metallurgical techniques
- lower processing temperatures needed for silicon infiltration than for casting of silicides and thus lower equipment and energy costs
- fine grained final structures without large phases which negatively influence mechanical properties (especially in case of presintered fine grained powders or thin wires from refractory metals)
- an original approach for in situ formation of FGM structures utilizing controlled kinetics of interfacial reaction between the Si-alloy and metal during GPI, as well as gradually changing the porosity of the metallic perform

Two research institutes (IMSAS, FRAUNHOFER), 2 universities (EPFL, TUW), 2 industrial SME partners (ATL, KE) and one multinational industry partner (EADS) from 5 European countries (A, D, CH, SK, UK) covered all necessary competencies needed for successful performance of the SILTRANS project (for contact details see attached list of partners). High industrial participation in this project (50%) reveals strong interest of industrial partners in the results of this project and guarantees their quick and efficient implementation into practical use.
Project Results:
The total duration of the SILTRANS project was 48 months. S&T work was performed in four workpackages (WPs).

WP1 (Development of porous perform) was assigned to develop the preform with controllable open porosity made of continuously bonded refractory metal powders (Mo, Nb) suitable for further infiltration with molten silicon alloys. The special attention has been given to the development of the process enabling to obtain fine grained material with controllable porosity gradiently changing from the surface to the core. The possibility to use the cost efficient technique for mass production of porous Mo performs from Mo oxide powders according to patented process (EP 1 268 105 B1) comprising simultaneous reduction and sintering of fine grained refractory oxides cast into required complex shapes has also been investigated

WP2 (Optimisation of infiltration process) was aimed to optimise technology and parameters for successful infiltration of porous refractory (Mo, Nb, W) preforms with molten silicon, whereas enabling a controllable mutual reaction between refractory metal and silicon

WP3 (Optimisation of solid state processing) was aimed ot optimise technology and parameters for successful completion of the silicide forming reaction after infiltration of porous refractory (Mo, Nb, W) preforms with molten silicon and minimise possible residual porosity. The reactions running at high temperatures HT which may have negative influence on the long term stability of the developed gradient composites were parallelly investigated, with an aim to suggest optimum composition of formed silicide layers. Simultaneously, an effect of barrier CVD (CVI) coatings on the surface of refractory metal particles on the reaction kinetics was examined.

WP4 (Testing of FGM) was devoted to testing of the properties of developed materials under targeted conditions

According to the results obtained in S&T workpackages, three carefully selected demonstrators from the developed materials were suggested for application oriented test, in order to demonstrate material performance in the real operation conditions. The demonstrators were then manufactured and evaluated in WP5 (FGM compounds) devoted to demonstration activities.

The project performance aimed to develop new FGM has resulted in many new S&T findings/foreground that can be summarised in following groups:

A. Novel processing technologies:
A1 manufacturing of sintered porous performs with gradiently changing porosity from Mo (Nb powders)
A2 manufacturing of complex shaped porous parts with required gradient porosities from Mo powders using laser beam sintering technique
A3 cost efficient technique for manufacturing of complex shaped porous Mo performs from Mo oxide powders via simultaneous reduction and sintering of fine grained oxides cast into required complex shapes
A4 reactive infiltration of Mo precursors (woven wires, shaped perforated sheets, sintered porous preforms) with molten silicon or silicon alloy
A5 chemical vapour infiltration aimed to form barrier coatings on the pore surfaces of porous Mo precursors

B. Understanding of reactions
B1 reaction kinetics in liquid silicon solid Mo system
B2 reaction products and their long term stability at high temperatures in solid Mo-Si system
B3 possible role of barrier coatings on Mo precursors in the control of interfacial reaction in Mo- Si system

C. Properties of developed materials
C1 - oxidation resistance at high temperatures
C2 - mechanical properties as a function of testing temperature
C3 - ductile to brittle transition temperature (DBTT) for developed materials

D. Performance of selected demonstrators
D1 - high temperature stand-off connector between heat shields and the base structure to transmit different elongations generated during re-entry heating
D2 - turbo charger stator blade
D3 - multichannel catalyst part

A. Novel processing technologies:

Preparation of Mo performs:

The standard press-and-sinter route enabled production of metal bodies with varying, if desired also stepwise graded, porosity, depending on the compacting pressure. The focus was on manufacturing of specimens with lower specific surface and higher mechanical stability, i.e. stronger sintering contacts that are less prone to be attacked and broken up by the silicon melt.
Lower specific surface was attained through using coarse starting powders; the resulting wider pore channels enabled deeper penetration of Si into the pore space and thus a rough substrate-silicide interface with better interfacial strength than the fairly plane interface attained with the fine materials.
As there is no suitable coarse Mo powder available on the market, the preparation route for such powder has been established at TUW. The powder was proved to be tricky to process by pressing, the green and also the sintered compacts being very weak, but adding a defined amount of fine powder as “sintering aid” eliminated this problem. Here the proper balance between coarse and fine powder has been found to ensure processability and strength while retaining the attractive infiltration behaviour of the coarse structures. Strength of the compacts was also markedly enhanced by increasing the sintering temperature up to 1800°C.
Preparation of Mo preforms from bimodal powders finally yields preforms with regular coarse porosity and sufficient strength for infiltrability. This method is easy to implement in industrial production; nevertheless commercial source for coarse Mo powder needs to be established.
In addition to molybdenum, also niobium was used for manufacturing the porous preforms through the press-and-sinter route, processing of Nb proving to be similar to that of Mo, with the exception that Nb has to be sintered in vacuum compared to H2 as standard for Mo.

A very attractive and promising approach to obtain preforms with coarse and well defined pore structure is additive manufacturing, also known as rapid prototyping. Partner KE developed a laser sintering/melting process that enables e.g. grid-type structures which possess well defined void structure and thus infiltrability. The generation of 3-dimensional Mo structures by laser processing proved to be a very difficult task, the results being extremely sensitive to the processing, mainly the laser, parameters, but currently bodies many mm tall and with clearly defined void geometry can be produced. In this case, addition of some Si to the Mo powder proved to be helpful; the silicide content in the preforms positively affected the controllability of the subsequent Si infiltration process.
The laser beam sintering process has been successfully developed for manufacturing complex compounds from Mo powders with well defined architecture of internal porosity. The developed technique has a big potential for rapid manufacturing of prototypes or small series from Mo (alloy) powders. The manufacturing of several complex shape parts has been tried using this technique; a patent application has been filled for the part to be applied in solar heaters.

The patented Kochanek process (EP 1 268 105 B1) based on the injection moulding procedure that includes manufacturing a feedstock from oxide powder, shaping, debinding and then a reducing sintering procedure has been for the first time adopted and optimised for the production of Mo parts (a new patent application AT 509526 B1 has been filled covering this topic). The process yielded Mo compacts with high and extremely fine and regular porosity with large application potential in many industrial fields. Several problems needed to be solved to enable subsequent infiltration of such material with molten silicon alloy in the project, incl. the unwelcome shrinkage during heating up to the infiltration temperature and/or vigorous reaction of very fine Mo structure with molten silicon. The novel approach enabling alloying of nanosized Mo particles during preform manufacturing helped to overcome these difficulties and after optimisation ended up with large, defect free porous preforms of high geometric accuracy. It can be concluded that the “Kochanek process” was successfully adapted to the Mo oxide powders, thus enabling low cost production of porous fine-grained Mo perform from relatively cheap Mo oxides

Reactive infiltration of Mo precursors

The development of the technology for reactive infiltration of porous Mo with molten Si under controllable conditions was very challenging task and required a lot of unexpected additional effort. Success in these activities was crucial for the further work in all other project activities (testing of properties, demonstration of performance).
The challenge was to keep the interfacial reaction under control and to allow only limited amount of silicon to enter the structure. After completing the reaction, all silicon must be spent for formation of silicides. However, a continuous refractory framework must still remain as a reinforcing percolating body within whole infiltrated sample (at least within the core of the sample).
The main target of the research was to optimise technology and parameters for successful infiltration of porous refractory (Mo, Nb) preforms with molten silicon, whereas enabling a controllable mutual reaction between refractory metal and silicon. The infiltration experiments performed within the project have revealed that:
- MoSi2 and Mo5Si3 are typical reaction products;
- intense dissolving of Mo takes place in a presence of excessive Si melt;
- powder preforms due to their high specific surface facilitate the intense mutual reaction leading to their disintegration;
- Mo-Si reaction is accompanied by forming of pores and cracks due to volume changes, internal stresses arising from irregular substrate surfaces and mismatch in CTE;

Following main parameters were found to control the process:
- Si-content available for the reaction
- size and shape of pores of the Mo perform
- size of Mo particles/wires coming into the reaction with molten silicon
- the reactivity of the surface of Mo particles

The optimum Mo grain size and Si to Mo ratio have been defined for successful infiltration. Although the Mo-Si reaction rate is still difficult to control via technological parameters i.e. temperature or infiltration time, it has been found, that the extent of reaction can be conveniently controlled via the amount of Si allowed to react with the preform. As soon as the silicon is consumed, the reaction is over. In this way successfully infiltrated Mo/silicide FGM could be prepared.
If compact pore free Mo/Mo - silicide structures are required additional post infiltration treatment needs to be employed. However Mo silicides are too strong and therefore difficult to deform. Even hot pressing at 1800 °C/3 hours/30 MPa was not sufficient to remove the pores. This is why the originally planned post compaction via hot isostatic pressing could not be successfully applied. It was shown that consolidation of infiltrated Mo/Mo silicide composite can be improved via applying Ni as bonding agent whereas secondary infiltration with excessive Ni leads to dissolving of Mo and Mo silicides and forming of new phases with low melting temperature (NiSi). Subsequent hot isostatic pressing at 1250 °C can partially eliminate the undesired NiSi phase and improve the interfacial bonding, however higher temperatures can further contribute to the consolidation process.
Nevertheless the best results were achieved applying newly developed procedure based on mechanical loading during reactive infiltration. The core of Mo perform was fully densified due to the mechanical loading, the surface was converted to thick pore free silicide layer. A true FGM specimen could be produced in this way.
This procedure was then finally used for manufacturing of demonstrators in the project.

Chemical vapour infiltration for preparation of barrier coatings on Mo substrate

The main objective of this work was to find a proper coating onto Mo preform with an aim to control vigorous reaction between molten Si and Mo. The trials have been carried out on the surface of Mo/Nb wires, coatings have been infiltrated into porous preforms and trials have also been conducted on two grades of Mo powder. It has become apparent that simple diffusion based infiltration of process gases into the fine pores of the materials available had led to limited conversion of the surface regions. For this reason ATL has introduced the Forced Chemical Vapour Infiltration’ (FCVI) - a technique which involves pushing the process gas through the preform to expose the majority of the surface area inside the preform to the coating mixture. This technique has proved to be far more successful than previous one and some applications of barrier coatings have showed some promise in tests with liquid silicon. Two different arrangements were used; for process in vacuum or in air. Both were adopted for potential demonstrators.
According to the results Si has been suggested as most promising coating, because it facilitates silicide forming reaction at the surface of the Mo preform. Silicide layer formed provides a barrier for direct contact of liquid silicon and Mo in subsequent infiltration, thus helping to control the mutual reaction. Another objective for Si coating was a possibility to introduce Si deeply into the preform without starting a mutual reaction (because of low temperature), which stops a paths for Si in the case of fine pores. According to previous results Si has been suggested as most promising coating, because it facilitates silicide forming reaction at the surface of the Mo preform. Silicide layer formed provides a barrier for direct contact of liquid silicon and Mo in subsequent infiltration, thus helping to control the mutual reaction. Another objective for Si coating is a possibility to introduce Si deeply into the preform without starting a mutual reaction (because of low temperature), which stops a paths for Si in the case of fine pores. Many tests have been applied to Mo components using the vapour of chlorosilanes as the Si source at different temperatures, pressures and gas flow rates. From all analysis performed it appeared that forced Si CVI has not been effective in infiltrating Mo preforms with fine pores beyond a few hundred microns and thus the effectiveness in reducing the rate of reaction of these preforms with liquid Si has not been reduced to a level that is significant enough to allow the overall reaction to be controlled. However, with preforms with larger pores such as those found in laser sintered samples it appears that far better conversion to Mo silicides is taking place on the interior of the preforms. Best application may be a high surface area catalyst.
A similar CVD type process has been used for boronising. Although this process has only had a limited success within the project and has not been able to slow the liquid silicon reaction sufficiently for the required applications, the knowledge gained through experimentation with many forms of the process has been invaluable to ATL in winning industrial research projects which are working in similar fields (see section concerning impact of the project).

B. Understanding of reactions
Reaction kinetics in liquid silicon - solid Mo system

Kinetics of the mutual reaction was studied as a function of infiltration parameters (pressure, immersion time, melt and preform temperature) as well as a function of pore size on unidirectionally aligned Mo wire bundles. The mutual reaction was studied and the developed phases and corresponding volume changes due to reaction were identified.
It appeared that the main products obtained from the reaction between molybdenum and liquid silicon are layers formed by columnar crystals of MoSi2 growing perpendicular to the Mo surface with poor bonding to the substrate and a thinner layer of Mo5Si3 between this layer of MoSi2 and the Mo, exhibiting outstanding bonding to Mo metallic substrate. The growth of these layers follows a parabolic law, typical of diffusion controlled processes with the activation energy of 177 kJ/mol for MoSi2 and 347 kJ/mol for Mo5Si3.

It was observed that just in the first 5 seconds of the reaction between Mo and Si (l) there is an effective reduction of the Mo particle size of 4-12 µm. The particle size of the porous preforms and, even more important, the size of the bonds between these particles must be above this limit to allow the sample to survive the direct immersion in Si (l). This fact excluded successful infiltration of many Mo performs made by sintering of Mo powders with pure liquid Si. In order to restrict the intense Mo-Si reaction, infiltration with Cu-Si or alternatively with Mg-Si alloys was experienced and studied. It appeared that the main product of the reaction between Mo and the alloy is Mo5Si3.The infiltration rate of the alloy into Mo porous bodies is much lower than the rate using pure silicon. The porous samples resisted the infiltration without important deformations.
The use of Mg-Si alloy for infiltration of powdered Mo performs resulted in successful conversion of pore surfaces into silicides without any damage of the original preform. However, free Mg (Cu) retaining in the pores in this way limited the mechanical properties of the part, especially at high temperature. Nevertheless, free Mg (Cu) can be easily removed by evaporation giving porous Mo/Mo-silicide parts suitable e.g for filter or catalyst applications working at HT.
The knowledge obtained in SILTRANS concerning Mo(s) - Si(l) reaction can be efficiently used in the design of such components. The kinetics of reaction and pore filling process during infiltration of molten silicon (alloy) into porous Mo body were clarified and are now well understood. It has been found that the reaction always leads to residual porosity or to remaining free Mg or Cu in the material. This leads to necessity of subsequent treatment of materials after infiltration or to simultaneous mechanical compaction of the component during infiltration.

Reaction products and their long term stability at high temperatures in solid Mo-Si system

This study was to optimise technology and parameters for successful completion of the silicide forming reaction in solid state after infiltration of porous refractory (Mo, Nb) preforms with molten silicon and simultaneously minimise possible residual porosity. Another important objective was to determine the stability of non equilibrium microstructure during HT performance and thus to determine and understand kinetics of reactions between silicon and Mo as well as between Mo and temporary reaction products (Mo silicides) in solid state.
Reactions in solid state were studied (Fraunhofer) with respect to temperature and time. Main conclusions drawn from these investigations are:
- at around 800-900 °C solution of Si in Mo starts. This process is not affected by Si particle size and amount of Si
- silicide forming reaction starts at ~900 °C and its intensity is the higher the higher is Si content and the lower is Si particle size
- below 1350 °C the reaction in solid phase has not been completed and all silicides were observed as intermediates
- Mo diffusion can be neglected, Si diffusion prevails, but strongly differs in Mo, MoSi2, Mo5Si3 and Mo3Si
- silicide forming reaction between Mo and Si is strongly exothermic leading to a thick MoSi2 layer on the thinner Mo5Si3 interlayer which is on almost not detectable Mo3Si layer placed directly on Mo. All silicides grow simultaneously
- MoSi2 will be decomposed in direct contact to Mo resp. Mo5Si3 leading to silicides with lower Si content (Mo5Si3, Mo3Si); this is accompanied also with volume changes
- the decomposition of MoSi2 cannot be inhibited, however in the case of thick MoSi2 layer it is able to survive more than 100h at 1400 °C
- MoSi2 shows self passivating behaviour (SiO2 scale), this ability decreases with decreasing Si content, Mo5Si3 and Mo3Si lead to formation MoO3 which evaporates already at temperatures below 1000°C
Mo particles embedded within (porous) MoSi2 do not oxidise in air, but Mo particles near surface region do

Solid state reactions in Mo-Si binary system were successfully characterized. The reactions in solid state and their kinetics are now well understood. It has been found that the FGM system always tends to equilibrium giving limits for long term performance, depending on the size of particular phases and working temperature. The knowledge obtained in SILTRANS is thus very useful for the design of components aimed for high temperature applications.

Role of barrier coatings in the control of interfacial reaction in Mo- Si system

Wires, powders and powder preforms were coated with Si, SiC, TiC, B, BxC, BN, SiC/Si, C, Er2O3 coatings in order to produce barrier for the excessive interfacial reaction with molten silicon. The coated precursors were dipped into molten silicon to test their protective potential. It appeared that no of used barriers was sufficiently resistant to prevent Si penetration, mostly because of the surface cracking which allows entry of the Si under the coating. It had to be concluded that barrier coatings made by CVD (CVI) did not shown sufficient protection of porous Mo samples. The most compatible ‘coatings’ have been Si or SiC which actually pre-convert the surface and slow the reaction with liquid Si rather than preventing it.
It should be noted, that boron appeared as very useful element forming MoB2 that has been recognized as very effective diffusion barrier surpressing the decomposition of MoSi2 silicide in solid state.

C. Properties of developed materials

Oxidation resistance at high temperatures

Good oxidation resistance is one of the crucial characteristics expected from the Mo silicides. To establish the oxidation resistance of developed materials the thermogravimetric analysis was implemented. The investigations have revealed following results:
- only MoSi2 is stable in oxidative environments due to SiO2 scale formation
- other silicides decompose leading to MoO3 and SiO2 formation
- MoSi2 / Mo5Si3 mixtures are rather stable, if the Mo5Si3 amount does not exceed more than 19% (literature data)
- the sample density controls the stability to great amount; even MoSi2 is not stable if the sample is too porous
- Nb silicides are significantly less resistant to oxidation if compared with MoSi2

In the case the MoSi2 layer is covering the surface of the material the mass change due to oxidation is remarkable low, even when small cracks or porosity exist in the layer.
In case of FGM made from Mo wire preforms the exposure to oxidising atmosphere at the temperature of 1100 °C for 3 hours revealed encouraging low mass loss of about 1.55 %. The microstructural studies performed on these samples revealed no visible degradation due to the effect of oxidation.

Mechanical properties as a function of testing temperature

The testing of mechanical properties of FGM is speculative because of gradiently changing composition. FGM should be tested rather as components. Nevertheless some mechanical tests were performed on developed materials based on silicon infiltrated Mo wires with following conclusion:
- 3-point bending tests of unidirectional wire reinforced FGM at room temperature and 850°C resulted in a bending strength of 342 and 352 MPa
- bending strength at 850°C is higher than tensile strength of PM1000 reference
- use of additional Mo cloth (2nd generation) resulted in even higher bending strength values at room temperature.
- there is no brittle fracture due to the Mo wires
- the material has significant damage tolerance at room and high temperature

Ductile to brittle transition temperature (DBTT) for developed materials

Mechanical tests have shown that the Mo/Mo silicide composite exhibits a plastic behavior in the whole examined temperature range from 20 °C to 1150 °C. This confirms a positive role of Mo wires as the stoppers of crack growing in brittle silicide matrix. DBTT of developed materials lies well bellow room temperature.

D. Performance of selected demonstrators

Discussion on potential applications for developed material started already before submission of the project proposal and continued during whole project implementation. Based on the results obtained in testing of first material specimens and developed manufacturing possibilities the compounds for final testing of material performance were carefully selected to demonstrate beneficial properties of developed material and technologies and satisfy the main objectives of the project. The aim was to find a wide variety of applications based on the expected performance of the material under development as well as suitable compounds representing such applications but having a geometry that can be realized and tested within the project frame with the developed processes and tools.
Following demonstrators have been identified, covering a wide variety of automotive and aerospace applications:

Demonstrator 1 – high temperature stand-off connector between heat shields and the base structure to transmit different elongations generated during re-entry heating.

This thin walled part was produced from Si infiltrated Mo-cloths and perforated Mo sheets.
Several re-entry stand-off components based on drilled Mo sheet of 0.35 or 0.80 mm thickness with converted MoSi2 surface were subjected to thermal shock resistance tests accrding to standard procedure using adapted ERBURIG test device with a H2/O2 burner at EADS. The peak temperature at the top side was set to 1600 °C for 7 min, which is typical during 20 min re-entry. The test was repeated for 4 cycles in total (full qualification) with intermediate investigation.
All the components showed a very low weight loss in the range of 0.02 g (about 0.3 %) and minor surface damage with similar appearance as original non tested component. It can be concluded that all tested components survived the test successfully.

The Si infiltrated drilled Mo sheet samples were also subjected to modified thermal shock resistance test at TUW. They were preheated by flame torch to the temperature of 1300 °C and 1600 °C respectively. The structural studies confirmed that rapid heating to 1300 °C didn´t affect the structure seriously. MoSi2 protective layer retained at the surface of the drilled sheet, protecting it from oxidation. The preheating to 1600 °C resulted in the transformations of the continuous layer of MoSi2 to composite layer consisting of MoSi2 islands embedded in Mo5Si3 matrix. The thickness of pure Mo5Si3 interlayer (between composite surface layer and the Mo core increased. In any case the adherence to the Mo core and thus protection ability remained very good.

Demonstrator 2 – turbo charger stator blade based on powder preforms prepared by “KE process” and infiltrated with MgSi alloy.

The main aim of this part was to demonstrate the possibility of use of cost efficient manufacturing technique for production of shaped porous Mo parts by “KE process”. Such technique gives a good potential for mass production of developed materials for cost sensitive applications. The stator blade was therefore made using Mo perform made by “KE process”. This preform was then sintered (1700 °C, 24 h, Ar), resulting in the significant shrinkage and porosity reduction. The residual open pores were then subsequently infiltrated with Mg-Si alloy, whereas Si reacted with Mo forming protective silicide layer. The residual Mg was evaporated from the structure leaving small residual porosity.

Demonstrator 3 – multichannel catalyst part based on Mo powder preforms produced by LBS process and coated with silicon via CVI to create MoSi2 on the whole active surface without closing porosity.
This part proved the advantages of LBS technique for rapid prototyping, in particular extreme complexity available by LBS comprising straight and complex (spiral) internal “drillholes” 2 mm diameter along total height of 60mm (see attached picture)

As a potential spin-off product, copper infiltrated Mo preform made by “KE process” was manufactured and tested with an aim to be applied in high temperature applications which require high thermal conductivity, such as welding or plasma electrodes and other HT heat sinks.

Summary

The results obtained in SILTRANS project have shown that the shaped porous Mo and Nb preforms with gradiently changing porosity can be reliably prepared by standard sintering techniques. The novel proprietary process, which has a very good potential for large volume industrial application, has been developed enabling low cost alternative for production of porous fine-grained Mo performs from relatively cheap Mo oxides. It has been shown, that porous Mo preforms with controllable architecture, including gradiently changing porosity can be efficiently manufactured also via laser beam sintering process, which may be useful for rapid prototyping purposes.

The kinetics of reaction between molten silicon and Mo during infiltration was analyzed and determined. The simple model has been developed for description of reaction rate and reaction product formation. Several techniques were proposed to bring apparently vigorous reaction into controllable manner and to minimise the residual porosity. The mechanical loading (compression) of porous Mo perform during reactive infiltration with molten silicon appeared as most promising approach in the reduction of residual porosity.

A comprehensive investigation of the reactions in Mo-Si system in solid state at high temperature has revealed the limits for structural stability of various combinations of silicide matrix and Mo reinforcements. The kinetics of the Mo-Si reactions in solid state is now well understood; the reaction products have been identified and characterized. Various approaches improving structural stability of FGM were proposed and investigated.

The most important properties of developed materials have been experimentally verified, incl. bending strength, fracture toughness, oxidation and thermal shock resistance. The properties were evaluated at various temperatures from RT up to 1600 °C. The developed Mo/Mo-silicide FGM has shown significantly improved oxidation resistance at HT in comparison with standard Mo alloy and much higher fracture toughness at low temperatures if compared to traditional silicides. The obtained mechanical properties at high temperatures combined with good oxidation resistance bring the developed material into a group of very promising high temperature structural materials, able to outperform currently used Ni based superalloys
in some applications.

Finally, the proper compaction method has been found enabling manufacturing of Mo/Mo silicide composites with minimal porosity and without formation of any ternary compound that could put the higher temperature stability of Mo/Mo silicide composites into danger. First demonstrators were prepared and spin-off products were identified.

The mock of protective tile holder for space vehicle has been manufactured from developed FGM and tested under environmental parameters close to real re-entry conditions. No damage has been observed after four subsequent thermal cycles, which confirmed the high potential of developed materials in this application field. A few other potential applications and spin-off products utilising developed materials were identified.

Finally a training oriented workshop ”Advanced Materials for High Temperature Applications” has been organized in order to train participants from industrial companies, universities and R&D institutions in the development and use of advanced engineering materials for applications working at extremely high temperatures.

If the results obtained in SILTRANS project are compared with originally planned objectives it can be concluded, that most of them were successfully achieved:

- a new class of structural HT composites consisting of a continuous refractory metal framework (Mo, Nb) infiltrated by a silicide matrix has been developed possessing unique combination of properties needed for their use under extreme loading conditions in particular:

- sufficient fracture toughness at all tested temperatures
- good oxidation resistance at HT at least for short term exposure
- lower density than Mo reference (less than 25%)
- low ductile to brittle transition temperature (DBTT below room temperature)
- industrially viable method for cost acceptable manufacturing of complex shaped parts from developed materials has been developed and its feasibility was demonstrated on turbocharger stator blade prototype
- beside this novel reactive infiltration technique has been developed for dense woven Mo wire based silicide matrix composites for special applications
- laser beam sintering technique has been adopted for manufacturing of complex shape parts from Mo powders, enabling rapid manufacturing of prototypes from developed materials
- the performance of developed materials and manufacturing technique was demonstrated on three selected demonstrators in transport related applications; in particular on stationary turbine blade in automobile engine turbocharger (high volume production at low price), on space related structure, e.g. mounting stands-off elements for holding of thermal protection sheets (low volume – price insensitive) and multichannel catalyst part (rapid prototyping of complex shape)
- the mounting stands-off element for space structure made of developed composite survived successfully standard thermal shock resistance test simulating re-entry conditions
- a few other potential applications and spin-off products utilising developed materials were identified
- models describing reaction kinetics in Mo-Si system both in liquid and solid states were suggested and experimentally verified; the potential effect of various barrier coatings on this reaction kinetics was evaluated.
Potential Impact:
The potential impact of the SILTRANS project can be seen in various levels:
- impact of potential applications of developed materials (unique Mo silicide matrix composites)
- impact of developed novel manufacturing techniques
- impact of developed knowledge concerning the kinetics of the reactions in Mo-Si system, the properties of developed composites, the effect of various barrier coatings
- impact of skills developed in the projects
- impact of improved qualification of PhD students working on the project
- impact of established cooperation and improved relations among participating partners

Potential applications of developed materials can be derived from the unique combination of material properties which offers “metal–like” characteristics in terms of mechanical properties, fracture toughness, plasticity, manufacturing costs, shape complexity etc. and “ceramics-like” characteristics in terms of high melting point, high temperature strength, creep resistance, oxidation resistance, thermal shock resistance etc.
These properties in association with industrially viable manufacturing technique allow expecting radical improvements in many industrial applications. The project results yield a new potential for substantial improvements in many industrial applications working at very high temperature in oxidizing environment and contribute so to lower fuel consumption; reduction of carbon dioxide emissions and improved life extension of most critical parts in aircrafts and automotive engines.
The overall efficiency improvements in turbines in engines or energy generators are recognized to be the result of the thermal efficiency improvements mostly related to several technology opportunities. These can be grouped into improvements to current simple cycle bypass designs or new, more complex engine cycles. Improvements to current approaches include the following:
- Further increases in the pressure ratio of compression systems
- Higher temperature hot sections with reduced (or eliminated) cooling requirements
- Improved component efficiencies.
Studies suggest that total gains of 10-20% in the thermal efficiency of the engine might be achievable by pursuing these options (Hill, 1996).
There are, of course, alternative or modified thermodynamic cycle approaches to future engine design, such as incorporation of an inter-cooler and/or a recuperator. Some of these technologies are used in land-based gas turbines, with large potential gains in thermal efficiency. However, they invariably employ heat exchangers, which increase engine weight to an extent that they are currently impractical for aircraft applications.
There is a growing awareness, however, of the potential for reducing the weight of aircraft engines by 20-40%. This general approach offers particular attractions for application to long-range transport aircraft. One unit of engine weight generally saves between 1.5 and 4 units of aircraft empty weight, with a concomitant decrease in fuel burn. Enabling technologies required to achieve significant engine weight reductions include the following:
- Improved materials (composites and high-temperature materials in particular)
- Improved aerodynamics (to reduce the number of turbine and compressor stages)
- Increased turbine entry temperatures (to reduce airflow thus core engine size required for a given power output).
The higher efficiency in jet engines and gas turbines can reduce CO2 emission, thus contributing significantly to the prevention of global warming. The 1450-1500 °C-class combined cycle power generation system can contribute significantly to reducing CO2 emission from fuel consumption by substituting coal firing steam power plants. In Japan an ultra-efficient (60 % HHV) combined-cycle power generation system with higher operating temperature as high as 1700 °C is planed.
To achieve this goals, it is essential to improve the properties of high temperature materials so that a higher inlet gas temperature is reached. It is fair to say that Ni-base superalloys are expected to play a major role in near future although substantial improvements are related to the introduction of new family of high temperature materials.
Since advanced superalloys melt at temperatures on the order of 1350°C, significant strengthening can be obtained only at temperatures below 1150°C, what is as much as 150 K lower than requirements defined by designers of efficient and clean aircraft or modern industrial turbines. The melting points of the silicide containing composites based on Mo silicides are in excess of 1750 °C yielding dramatic increase of operational temperatures for HT applications.
The improvement of operational temperature will undoubtedly address the most important system performance requirements of turbines for both – air or surface applications. These include fuel efficiency in producing power or thrust (increasing the combustion temperature generally leads to efficiency improvements), weight, and reliability. Reducing the cooling air increases the efficiency, since less of the work done in compressing the air for combustion is lost to cooling. If the airfoil mass can be reduced significantly, the centrifugal stress on the rotor is reduced, and a smaller, lighter rotor can be employed. This can have a major impact on the thrust-to-weight performance of the turbine. An increase in component-temperature capability can generally be exploited by life extension, by a higher combustion temperature, or by a combination of higher combustion temperature and life extension.
Developed silicide matrix FGM are promising candidates to fulfil part of these expectations. Their performance exceeds the performance of current nickel-based superalloys in terms of maximum operating surface temperatures (~ 150 K higher), density (~ 20 % lower), rupture resistance and oxidation resistance.
Increasing the combustion temperature allows reducing the cooling air thus increasing the efficiency, since less of the work done in compressing the air for combustion is lost to cooling. If the airfoil mass can be reduced significantly, the centrifugal stress on the rotor is reduced, and a smaller, lighter rotor can be employed. This can have a major impact on the thrust-to-weight performance of the turbine.
An increase in component-temperature capability can generally be exploited by life extension, by a higher combustion temperature, or by a combination of higher combustion temperature and life extension. Turbine blades are usually used with a ceramics coating and inner air cooling system. With the improvement of temperature capability of 50°C, the turbine inlet gas temperature could be increased by about 2 times the improved temperature difference (i.e. 100°C).
If the temperature capability is improved by 50 °C (from 1100 to 1150 °C), the cooling air inside the turbine blades, for example, can be reduced to improve thermal efficiency and thus the specific fuel consumption. The 50 °C improvement corresponds to the improvement of about 6 times longer creep rupture life, provided that the alloy is used at the same condition. Subsequently, in this way the reliability of the parts will also be much improved.

These improvements should significantly help to reach the given goal of 10% propulsion production average fuel-efficiency increase in the time period to 2015. In the longer term (2050) compared to 1997, a total aircraft production average fuel-efficiency improvement of 40-50% is considered feasible (ICCAIA, 1997g). These levels of efficiency improvement are assumed in the 2050 technology scenarios. The ratio of airframe to propulsion production average fuel-efficiency improvement over the period 1997 to 2050 is projected to be 55/45 in favour of airframe technology developments.

A truly breakthrough development would result either (A) in a significant increase in performance or (B) in a substantial reduction material/process cost. The latter should be the targeted goal for the low cost segment, the former a target for the high performance segment.
Increase in performance is very interesting from the application point of view since there is a high potential for cost savings through either reduced fuel consumption or a prolonged operation of the satellite. Pt-based alloys are considered as baseline, but even higher costs could be justified with a substantial increase of performance.
The demand for satellite propulsion systems is naturally strongly linked to the number of satellites being launched. More than a dozen positioning thrusters (low price segment) are normally mounted on a satellite. Estimating a market for again up to 15 satellites per year, a market for 200-300 engines can be imagined.
Considering the size of satellite 10 N engines (total height of about 60 mm; the outside diameter of the combustion chamber less then 10 mm) only a few kg, maybe a few hundred kg considering raw material or ingot sizes are requested.

Heat shields are critical for the success of a re-entry mission. They have to withstand high temperature in oxidizing atmosphere and need to be lightweight, as they have to protect large areas of the spacecraft module. A typical design is a low thermally conductive ceramic or CMC shell at the hot outside, locally connected with the metallic fuselage with a specific stand-off distance to allow for clamping a lightweight thermal insulation in the gap. Such “Stand-off” connectors are usually made of high temperature resistant metals because they require enough ductility to compensate the thermal expansion mismatch of the outer shell and the fuselage during re-entry heating up. In the past, PM1000 or PM2000 (cold-workable oxide dispersion strengthened (ODS) Ni based material with a high Cr content) were frequently used due to their well fitting properties, but both materials are not produced anymore and no other materials are available that can replace them perfectly. Therefore Astrium is interested in having an alternative cost effective high temperature resistant material for re-entry components.

The industrial application of developed FGM and compounds in space technologies will allow Europe a significant lead in technology and result in enhanced materials safety for re-entry objects and cost reduction in space propulsion.
The main part of the currently exploitable foreground goes to the EADS product portfolio of HT applications, like thrusters, re-entry, shielding, that need continuous optimisation in terms of cost, weight and performance to improve competitiveness. This is dedicated to a general knowledge about existing challenges, potential materials, processes to produce, resulting products and measures to investigate the performance.
The foreground might be exploited by the EADS divisions within their products after an internal development following a strict TRL (Technology Readiness Level) review procedure with a progress that is difficult to foresee especially in the case of potential show stoppers coming up. Highest application probability is the use as stand-off component for re-entry vehicles that are used to mount high temperature protective tiles, e. g. CMC (Ceramic Matrix Composites) plates, on the conventional metallic substructure to transmit mechanical loads coming from the atmospheric pressure and the thermal expansion mismatch between (hot) ceramic tile and (cold) metallic substructure during re-entry.
For the current know-how status, no IPR measures were taken or are intended. The possibility for creating own IPR is continuously evaluated during the further research work that is still necessary to reach a reproducible material quality with the expected properties in terms of cost and performance.
The potential impact of this new development is strongly influenced by the future plans for developing a new European space vehicle, e. g. REX freeflyer. Depending on the size of the vehicle, a huge number of protective tiles (50-100) have to be mounted to the substructure using 4 stand-off components each. This means 200 to 400 components per vehicle that might be replaced after each mission. At the moment it is not clear whether the European space vehicle program will be realized and how many vehicles will be manufactured. Thus it is currently not possible to further quantify the demand.

The impact on transport applications are not restricted only to space and aviation. Significant improvements are to be expected also in the field of terrestrial applications where the high temperature materials are strongly demanded.

The efficiency of burner for diesel particulate filter also strongly depends on the temperature of regeneration process. In this process the trapped scoot is heated and after reaching the scoot igniting temperature is oxidised with additional oxygen, coming from a blower unit, into CO2. The efficiency of the process, the quality of the exhaust gases and the lifetime of the burner depend on the high temperature properties and the oxidation resistance of the applied burner material.
Even more significant contributions are expected by replacing most critical parts of current turbochargers with new high temperature materials resulting in more efficient fuel consumptions and more environmental friendly exhaust gases.

The introduction of Mo silicide FGM composites into the design of future turbochargers will meet the demands for the increase of charging pressures and the air flow rate range. The increase of exhaust temperature of turbocharged gasoline engines by about 50 to 100 °C what is within the scope of refractory silicides has the potential of fuel savings up to 20 %. Finally the thermal inertia and the surface area of the turbine housing can be smaller what helps to keep emissions low. A reduction in the weight in this context also benefits the total weight of the vehicle.
HT materials with enhanced corrosion and thermal shock resistance are inevitable for new devices for solar energy conversion and related hydrogen production. In H2 generation plants, extensive use of inert high temperature composites and of H2 permeation barrier technology will drastically enhance operational safety and will allow the location of H2 generation plants in populated zones. The main aims are to avoid explosions by confining the H2 and to avoid the emission of poisonous fumes and toxic products by confining the sulphuric acid and the hydrogen iodide (HI), which has an inventory of tens of tons in the case of HI.

Impact of developed novel manufacturing techniques can be demonstrated on the cases SME partners KE and ATL.
In SILTRANS project ATL developed a couple of novel processes for manufacturing of various barrier coatings necessary for Mo protection. So far the projects where ATL made use of knowledge gained during the Siltrans project have been worth over 200k€:
- Simulation of Vapour siliconising of furnace components - Understanding the influence of trichlorosilane on the siliconisation of refractory metals has been useful in developing reactor components for silicon growth furnaces for customers in the silicon processing and solar silicon industries. ATL has been able to perform exposure trials in many relevant atmospheres for various high temperature materials for a major US customer.
- Deposition of silicon in the solar silicon industry - As a potential route to recycling waste silicon from the solar industry, ATL has been asked to experiment with growing silicon onto small particles with a defined surface structure.
- Deposition of silicon in the battery industry - The experience of treating powders has led to the ability to coat fine C and SiC powders with Si for development of ultra high capacity batteries with a UK customer
- Use of non-standard chlorosilanes for deposition of SiC and Si3N4 -Added experience with other chlorosilanes has enabled us to produce both SiC and Si3N4 coatings using lower temperature processes.
- Development of Si doped BN as an interface for CMCs - The aerospace industry is interested in BN interfaces for SiC/SiC CMCs and ATL been using chlorosilanes to modify the oxidation resistance of the BN by doping precursor mixtures.
- Boron coatings for the nuclear industry - boron coatings are useful in the nuclear industry due to their neutron absorption properties. Working at a variety of new B coating conditions within Siltrans has helped us understand the process better for coating different substrates.
- Silicide coating replacements for European Space Agency - Many current rocket thrusters are made from silicide coated niobium alloys. ATL has a contract with ESA to look at replacing this materials combination with other suitable materials and this has necessitated an understanding of the Nb/Si interaction chemistry which Siltrans has provided. Without this background knowledge from Siltrans it would have been very difficult to win this contract.

In the SILTRANS project KE start to work with an Additive Manufacturing Method- the Selective Laser Melting (or Selective Laser Beam Sintering - LBS). Know How has been generated in the field of Laser Beam Sintering of molybdenum powders and of alloyed Mo powders. With a help of this knowledge KE started to manufacture all kinds of demonstrators and prototypes which could be useful in different areas of applications, mainly Catalysis; Solar Heat exchangers; Rapid Prototyping; Rapid Tooling.
A newly developed solar heat exchanger was filled for patent application as it is promising for beneficial knowledge transfer. LBS technique enabled to evaluate its properties on rapidly manufactured prototype. Thanks to gained knowledge KE was invited to join a research project on Additive Manufacturing of different Ironaluminides (Radikal/DE/BMBF). KE plans to raise a spin-off company that will exploit all research results in the Area of Additive Manufacturing. This will include LBS of unconventional materials as well as rapid tooling. Meanwhile Additive Manufacturing is one of the most prominent R&D topics worldwide. The amount of users is growing constantly as well as the market. Without SILTRANS this market would remain closed for KE.

Impact of developed knowledge concerning the kinetics of the reactions in Mo-Si system, the properties of developed composites, the effect of various barrier coatings etc. will help research institutes and universities involved to remain or become competitive through the transfer of knowledge from research to application.
The knowledge developed in the course of the project will be an additional benefit of the project promoting further attempts to use silicides in future HT applications which will be based on deep fundamental understanding of structure (composition) / property relations, and degradation mechanism. The knowledge generated in the project will help industry to adopt these unique materials in tailored made solutions for other potential applications where high temperature, radiation, erosion and corrosion create dominated working environment.
Most of this kind of knowledge has been or will be published in peer reviewed journals (5 journal papers have been published so far). Unpublished know-how and gained expertise will be used in future follow up research projects.

The partners will definitely benefit from the skills of researchers developed in the SILTRANS projects – both theoretical and practical. Two dissertations have been directly elaborated within Siltrans (Lucia Sencekova – IMSAS, Ewa Dadal - TUW).


Impact on society

The synergetic effect of the expected contributions will impose a positive impact on some of most sensitive aspects of social space including living as well as working conditions.

The main benefits from the proposed project are expected from the performance of novel Mo based FGM with enhanced working temperature, oxidation resistance and lower density if compared with currently used superalloys. They become interesting especially if they are made by industrially viable techniques. If this goal is achieved revolutionary changes in whole high temperature sector (mainly in turbines) will follow, bringing Europe a leading world position in this field. The new materials and processes developed in SILTRANS can create a higher market share for highly sophisticated European products in the overall world and thus an increasing market for material production in Europe with emerging and new companies. Related industry like machinery production can also benefit from successful market development contributing thus positively to the employment in Europe.

About 20 highly skilled engineers and scientists emerged from SILTRANS. This skilled workforce, together with the knowledge stemming from the project activities, will contribute to the transformation of the European industry from a resource intensive to a knowledge-based one. This will further enhance the competitiveness of European industry in comparison to the resource intensive approaches pursued e.g. in India, China, Russia, and the US.

The focus of SILTRANS applications on zero-CO2 energy technologies (fusion, H2 generation), the improvement of energy production (turbines, solar energy converters) and the improved efficiency of aerospace structures may lead to positive changes in the emission of gases and the consumption of carbon based fuel, harmful for the atmosphere (greenhouse effect), as well as in he release of harmful ingredients, being beneficial for the overall environment.

The EU and global society will profit from the reduced use of raw materials and energy, enhanced lifetime of industrial facilities as well as lowered cost of decommissioning, which are the outcomes of the lifecycle approach. Most importantly, the zero-CO2 energy technologies at the focus of SILTRANS will provide sustainable electricity and mobility maintaining the high quality of life of EU citizens.

In order to ensure industrial relevance and impact of the research effort 3 of 7 project partners are coming from industrial sector. The interest in sophisticated high added value materials (though made at high cost level) has attracted the attention of 2 SMEs, that await significant benefits from project results. This is fully in accordance with the EU politics that expects a particular attention to be paid to ensure the adequate participation of SMEs, in particular knowledge-intensive SME, in transnational cooperation. Investment in RTD in EU transport industries is a prerequisite for ensuring a technological competitive advantage in global markets. Activities at European level will also stimulate the restructuring of the industry, including the integration of the supply chain and, in particular, SMEs.

Support for longer term cooperation programmes between organisations from academia and industry, in particular SMEs and including traditional manufacturing industries, will aim at stimulating intersectoral mobility and increasing knowledge sharing through joint research partnerships, supported by the recruitment of experienced researchers to the partnership, by staff secondments between both sectors, and by the organisation of events.

Strengthening the innovation capacity of European SMEs and their contribution to the development of new technology based products and markets by helping them outsource research, increase their research efforts, extend their networks, better exploit research results and acquire technological know how, bridging the gap between research and innovation.

SMEs are at the core of European industry. They should be a key component of the innovation system and in the chain of transformation of knowledge into new products, processes and services.

SILTRANS project provided an environment for fruitful cooperation among organisations from academia and industry, in particular SMEs. It stimulated intersectoral knowledge sharing, which now continues through joint research partnerships, supported by the staff secondments between academia and industry, and by the joint organisation of events. In this sense SILTRANS contributed to the bridging the gap between research and innovation.
List of Websites:
The address of the project public website is:
http://siltrans.sav.sk/