Periodic Report Summary - MATRANS (Micro and nanocrystalline functionally graded materials for transport applications)
Project context and objectives:
MATRANS aims at the development of novel metal-ceramic Functionally graded materials (FGMs) for aerospace and automotive applications in: (i) exhaust and propulsion systems; (ii) power transmission systems; and (iii) braking systems with the main objective to enhance the mechanical properties of these materials through spatial variations of material composition and microstructure.
MATRANS deals with two groups of FGMs, i.e. FGM I: ceramics (Al2O3)-copper / copper alloys, and FGM II: ceramics (Al2O3)-intermetallics(NiAl). Within FGM I two distinct systems are being investigated: FGM I-L (with low alumina contents; target application - thruster) and FGM I-H (with high alumina contents; target application - brake disk). The FGM II systems are intended for the valve application. The MATRANS graded materials have not yet been used for the applications in question.
The MATRANS methodology is problem oriented combining interrelated activities of material processing (core of the project), characterisation, modelling and demonstration. The processing encompasses preparation of starting materials (i.e. composite micro- and nanopowders; composite cast foils, porous ceramic preforms) and the resulting FGMs obtained by: (i) powder metallurgy methods; (ii) spraying techniques; and (iii) infiltration of molten metals into ceramic preforms. Characterisation of the FGMs includes detailed description of microstructure, measurements of physical / mechanical properties and residual stresses. Modelling is carried out at a design phase and of material properties and behaviour under service conditions. Extensive use of multiscale models and numerical simulations is being made.
The project addresses joint design of the FGM and the structural component it is intended for. Economic and ecological aspects of processing are included. Risk aspects of material non-performance are tackled, too. MATRANS has mobilised a critical mass of interdisciplinary expertise and highly specialised research infrastructure. The consortium includes leading groups from materials science, physics, chemistry, mechanical engineering and computer science. The industry and SMEs involvement in the project is essential. As the exploitation measures, the industrial partners will define business plans and start pilot cases during the project followed by upscaling activities after the project end.
Project results:
During the first two years of the project activities the research work has been concentrated on the starting materials and processing of the composite layers for the FGM I and FGM II including characterisation of their properties and microstructure. Importantly, the first design samples of FGMs have already been manufactured for the three target applications (thruster, valve, brake disk). In parallel, modelling of the FGM I and FGM II was carried out leading to some significant results of scientific value and of practical importance for the processing of the MATRANS materials. The main results obtained so far are as follows:
Starting materials
FGM I (copper-alumina). The processed alumina-copper composite powders intended for FGM I-L show good particle distributions in copper with no agglomeration of the reinforcement. Bulk samples with densities around 100 % of the theoretical density were fabricated and characterised in terms of microstructure and mechanical properties. Porous ceramic preforms for FGM I-H were successfully manufactured by foil casting and slip casting techniques. Lamination and sintering of packages of ceramic foils with different porosities were successfully completed and delivered for infiltration. FGM II (intermetallics-alumina). A selection of different matrix compositions was tested for the fabrication of the target nickel-aluminide composites. NiAl and NiAlFe matrices were selected for FGM II. High-energy milling route of elemental powder mixtures was developed. A homogeneous distribution of the alumina reinforcement up to10 vol. % was achieved.
Processing of FGMs
For preparation of FGM I and FGM II several techniques are under investigation. For thruster application FGM I-L with low alumina contents is prepared by powder metallurgy (SPS) and by thermal spraying. The brake disk application is approached by applying metal infiltration in order to get FGM I with high amount of alumina. For the valve application FGM II have to be used due to the high temperature and wear resistance required. The thermal spraying technology, powder metallurgy technologies and reactive infiltration are under investigation for the valve application.
Thruster: FGM I samples with a thickness of about 1 mm were fabricated by powder stacking and subsequent Spark Plasma Sintering (SPS). A four-layered copper composite with alumina reinforcement with a good spatial distribution of the components was obtained. Properties of the composite layers were promising but the optimisation of the oxidation is a crucial task when using Cu alloys. After the quality gate at the project mid-term milestone the High velocity oxygen flame spraying (HVOF) was selected as the leading FGM I-L processing technology owing to its best performance in terms of deposition on the substrate, remaining porosity and other parameters. No inclusions, pores or voids were found between the layers of the obtained FGM I-L. The adhesion of the FGM system to the substrate is good and homogeneous. On the other hand the SPS yielded good results for FGM I-L but due to shape limitations of the samples it may be less suitable for the thruster demonstrator.
Valve:
Of several technologies tested in the first half of the project to manufacture FGM II (NiAl(Fe) + 0, 5, 10, 20, 30 vol-% Al2O3) for the valve application the following two have yielded the best results and will be further refined in the optimised design phase: (i) reactive infiltration of Ni powders with molten Al as primary FGM technology for the valve head; and (ii) powder stacking technology for the graded valve tip. Joining technologies are envisaged to obtain a complete FGM valve.
Brake disk:
The FGM I-H for the brake disk application is a metal-ceramic material with high Al2O3 content to ensure proper frictional wear and temperature resistance. The metal (Cu) besides the mechanical strength and fracture toughness is used to ensure effective heat transfer out of the braking system. The FGM I-H for the brake disk application are processed in MATRANS exclusively by the infiltration technique of molten metal into porous ceramic perform. A number of variants of the infiltration technique were investigated: (i) pressure-assisted; (ii) pressureless; (iii) with and without additions to improve wettability of the perform by copper, (iv) with different routes of obtaining the porous ceramic performs. The gas pressure assisted infiltration has yielded the best results and will be the primary technology used for the FGM I-H brake disk demonstrator manufacturing.
Characterisation of FGMs
Characterisation of microstructure, testing of mechanical and physical properties, and screening of resistance to service conditions of MATRANS materials are necessary to assess their usefulness for the three target applications as compared to reference materials. Microstructure and residual stresses. Analysis of the chemical and phase composition of Cu-based composites for FGM I and NiAl based composites for FGM II was done. The microstructure and morphology of the Cu-Al2O3 composite samples was also investigated using synchrotron radiation micro-CT at the European synchrotron radiation facility (ESRF) in Grenoble. Residual stresses in FGM I-L composite samples were measured by X-ray diffraction method (XRD). Measurements of residual stresses by neutron / synchrotron radiation diffraction method are in progress.
Mechanical, physical properties and non-destructive testing. The determination of Young's modulus, Poisson's ratio, thermal expansion coefficient, thermal conductivity, hardness, microhardness, fracture toughness, bending strength, ductility was done on the constituent composite layers of FGM I and II.
Resistance to service conditions. Screening tests of resistance to erosion, thermal shocks, frictional wear, oxidation / corrosion, thermal fatigue and blanching applied on FGM I-L and its constituent layers were done showing superior performance of MATRANS materials in a number of cases.
Modelling
Modelling of graded profiles of FGM I and FGM II. The desired properties (e.g. thermal resistance, toughness, cost) are the objectives related to microstructural parameters (or design variables), e.g. number and thickness of layers, grain size, volume fraction. The multi-objective optimisation is used on those relationships to achieve the desired properties. The numerical implementation of the multi-objective optimisation algorithm was achieved for particular geometry and parameters of the valve application.
Modelling of microcracking during processing. The main loading during the processing is caused by the temperature difference which results in residual thermal stresses due to the inhomogeneous distribution of material properties. The temperature induced residual stresses are computed using a FEM model of FGM accounting for the microstructure and material data of the individual phases. The computed stress distribution is used to identify and to assess microcracking at phase interfaces. The model is based on a grid of voxels representing metal and ceramic phases. This microstructural data comes from micro-CT scans or is assumed as randomly distributed. Different concentrations of copper have been tested.
Effective elastic and thermal properties. The effective elastic constants of interpenetrating FGM I-L were modelled using analytical models of Voigt, Reuss, Hashin-Shtrikman, Tuchinskii and Feng. Numerical models were developed for real FGM microstructures using three-dimensional (3D) images obtained with computer micro-tomography. Effective thermal conductivity and thermal expansion coefficient were calculated at room temperature with random and real microstructure (micro-CT images). The effective thermal conductivity turned out to be influenced considerably by the microstructure, while the effective thermal expansion coefficient did not.
FEM models of residual stresses. An effective FEM model was developed for prediction of thermal stresses in FGM I-L for the thruster application but can be used for any MATRANS material if the required material input data is available. The model is capable of making use of microstructural data from micro-CT images and of predicting thermal stresses with a good accuracy as compared with the measurements by the XRD method. The micro-CT digital data is fast processed and respective FE mesh is produced automatically by a software enabling fast computation of the thermal residual stresses. This is essential for practical applications. A concrete result of this model was the predicted graded structure of FGM I-L comprising four layers with 0 /2 /3.5 /5 vol. % Al2O3 used in further FGM I-L processing.
A model of wear in FGM I-H (brake disk) system has been developed for pertinent wear mechanisms based on the micromechanics. Progressive wear during reciprocating ball-on-flat test has been modelled basing on asymptotic wear states so that detailed analysis of contact was avoided. The model which is highly efficient as compared to the usual approach employing repeated 3D contact analysis is combined with shape updating.
Potential impact:
The expected final results of MATRANS are novel metal-ceramic composites with graded microstructure (FGMs) for the three target applications: thrusters, valve, brake disks to replace the currently used reference materials for their enhanced mechanical and physical properties. Lightness with high frictional wear resistance and high thermal conductivity are the main target properties of infiltrated FGM I-H (target application: brake disk). Reduction of thermal stresses through graded profile, improved lifetime, better oxidation and erosion resistance as well as high temperature strength are the main target properties of FGM I-L processed by spraying (target application: thruster). Low weight combined with enhanced strength in high temperature and high resistance to wear, corrosion, oxidation are the main target properties for FGM II (target application: valve). The potential technological impact of MATRANS FGMs can be substantial in automotive and aerospace sectors as they will contribute to longer materials life-time, enhance materials performance limits and durability while reaching desired functionalities at a lower or at least a reasonable cost.
As regards societal impact the novel FGMs and their processing technologies developed in MATRANS will generate a larger market share for European products. Consequently, an increasing market for material production in Europe may arise with emerging and new companies. The quantitative increase in highly skilled workforce together with the knowledge stemming from the project activities, will contribute to knowledge-based European economy and will thus enhance the competitiveness of European industry in comparison to the resource intensive approaches pursued elsewhere. The society will profit from the reduced use of raw materials and energy, extended lifetime of industrial infrastructure and lowered cost of decommissioning, which are the outcomes of the lifecycle approach. On a project-scale one may expect that about 50 new, highly skilled young engineers and scientists will emerge from the MATRANS project. This dynamic and skilled workforce, together with the knowledge produced, will contribute to the competitiveness of the European Union industry.
MATRANS aims at the development of novel metal-ceramic Functionally graded materials (FGMs) for aerospace and automotive applications in: (i) exhaust and propulsion systems; (ii) power transmission systems; and (iii) braking systems with the main objective to enhance the mechanical properties of these materials through spatial variations of material composition and microstructure.
MATRANS deals with two groups of FGMs, i.e. FGM I: ceramics (Al2O3)-copper / copper alloys, and FGM II: ceramics (Al2O3)-intermetallics(NiAl). Within FGM I two distinct systems are being investigated: FGM I-L (with low alumina contents; target application - thruster) and FGM I-H (with high alumina contents; target application - brake disk). The FGM II systems are intended for the valve application. The MATRANS graded materials have not yet been used for the applications in question.
The MATRANS methodology is problem oriented combining interrelated activities of material processing (core of the project), characterisation, modelling and demonstration. The processing encompasses preparation of starting materials (i.e. composite micro- and nanopowders; composite cast foils, porous ceramic preforms) and the resulting FGMs obtained by: (i) powder metallurgy methods; (ii) spraying techniques; and (iii) infiltration of molten metals into ceramic preforms. Characterisation of the FGMs includes detailed description of microstructure, measurements of physical / mechanical properties and residual stresses. Modelling is carried out at a design phase and of material properties and behaviour under service conditions. Extensive use of multiscale models and numerical simulations is being made.
The project addresses joint design of the FGM and the structural component it is intended for. Economic and ecological aspects of processing are included. Risk aspects of material non-performance are tackled, too. MATRANS has mobilised a critical mass of interdisciplinary expertise and highly specialised research infrastructure. The consortium includes leading groups from materials science, physics, chemistry, mechanical engineering and computer science. The industry and SMEs involvement in the project is essential. As the exploitation measures, the industrial partners will define business plans and start pilot cases during the project followed by upscaling activities after the project end.
Project results:
During the first two years of the project activities the research work has been concentrated on the starting materials and processing of the composite layers for the FGM I and FGM II including characterisation of their properties and microstructure. Importantly, the first design samples of FGMs have already been manufactured for the three target applications (thruster, valve, brake disk). In parallel, modelling of the FGM I and FGM II was carried out leading to some significant results of scientific value and of practical importance for the processing of the MATRANS materials. The main results obtained so far are as follows:
Starting materials
FGM I (copper-alumina). The processed alumina-copper composite powders intended for FGM I-L show good particle distributions in copper with no agglomeration of the reinforcement. Bulk samples with densities around 100 % of the theoretical density were fabricated and characterised in terms of microstructure and mechanical properties. Porous ceramic preforms for FGM I-H were successfully manufactured by foil casting and slip casting techniques. Lamination and sintering of packages of ceramic foils with different porosities were successfully completed and delivered for infiltration. FGM II (intermetallics-alumina). A selection of different matrix compositions was tested for the fabrication of the target nickel-aluminide composites. NiAl and NiAlFe matrices were selected for FGM II. High-energy milling route of elemental powder mixtures was developed. A homogeneous distribution of the alumina reinforcement up to10 vol. % was achieved.
Processing of FGMs
For preparation of FGM I and FGM II several techniques are under investigation. For thruster application FGM I-L with low alumina contents is prepared by powder metallurgy (SPS) and by thermal spraying. The brake disk application is approached by applying metal infiltration in order to get FGM I with high amount of alumina. For the valve application FGM II have to be used due to the high temperature and wear resistance required. The thermal spraying technology, powder metallurgy technologies and reactive infiltration are under investigation for the valve application.
Thruster: FGM I samples with a thickness of about 1 mm were fabricated by powder stacking and subsequent Spark Plasma Sintering (SPS). A four-layered copper composite with alumina reinforcement with a good spatial distribution of the components was obtained. Properties of the composite layers were promising but the optimisation of the oxidation is a crucial task when using Cu alloys. After the quality gate at the project mid-term milestone the High velocity oxygen flame spraying (HVOF) was selected as the leading FGM I-L processing technology owing to its best performance in terms of deposition on the substrate, remaining porosity and other parameters. No inclusions, pores or voids were found between the layers of the obtained FGM I-L. The adhesion of the FGM system to the substrate is good and homogeneous. On the other hand the SPS yielded good results for FGM I-L but due to shape limitations of the samples it may be less suitable for the thruster demonstrator.
Valve:
Of several technologies tested in the first half of the project to manufacture FGM II (NiAl(Fe) + 0, 5, 10, 20, 30 vol-% Al2O3) for the valve application the following two have yielded the best results and will be further refined in the optimised design phase: (i) reactive infiltration of Ni powders with molten Al as primary FGM technology for the valve head; and (ii) powder stacking technology for the graded valve tip. Joining technologies are envisaged to obtain a complete FGM valve.
Brake disk:
The FGM I-H for the brake disk application is a metal-ceramic material with high Al2O3 content to ensure proper frictional wear and temperature resistance. The metal (Cu) besides the mechanical strength and fracture toughness is used to ensure effective heat transfer out of the braking system. The FGM I-H for the brake disk application are processed in MATRANS exclusively by the infiltration technique of molten metal into porous ceramic perform. A number of variants of the infiltration technique were investigated: (i) pressure-assisted; (ii) pressureless; (iii) with and without additions to improve wettability of the perform by copper, (iv) with different routes of obtaining the porous ceramic performs. The gas pressure assisted infiltration has yielded the best results and will be the primary technology used for the FGM I-H brake disk demonstrator manufacturing.
Characterisation of FGMs
Characterisation of microstructure, testing of mechanical and physical properties, and screening of resistance to service conditions of MATRANS materials are necessary to assess their usefulness for the three target applications as compared to reference materials. Microstructure and residual stresses. Analysis of the chemical and phase composition of Cu-based composites for FGM I and NiAl based composites for FGM II was done. The microstructure and morphology of the Cu-Al2O3 composite samples was also investigated using synchrotron radiation micro-CT at the European synchrotron radiation facility (ESRF) in Grenoble. Residual stresses in FGM I-L composite samples were measured by X-ray diffraction method (XRD). Measurements of residual stresses by neutron / synchrotron radiation diffraction method are in progress.
Mechanical, physical properties and non-destructive testing. The determination of Young's modulus, Poisson's ratio, thermal expansion coefficient, thermal conductivity, hardness, microhardness, fracture toughness, bending strength, ductility was done on the constituent composite layers of FGM I and II.
Resistance to service conditions. Screening tests of resistance to erosion, thermal shocks, frictional wear, oxidation / corrosion, thermal fatigue and blanching applied on FGM I-L and its constituent layers were done showing superior performance of MATRANS materials in a number of cases.
Modelling
Modelling of graded profiles of FGM I and FGM II. The desired properties (e.g. thermal resistance, toughness, cost) are the objectives related to microstructural parameters (or design variables), e.g. number and thickness of layers, grain size, volume fraction. The multi-objective optimisation is used on those relationships to achieve the desired properties. The numerical implementation of the multi-objective optimisation algorithm was achieved for particular geometry and parameters of the valve application.
Modelling of microcracking during processing. The main loading during the processing is caused by the temperature difference which results in residual thermal stresses due to the inhomogeneous distribution of material properties. The temperature induced residual stresses are computed using a FEM model of FGM accounting for the microstructure and material data of the individual phases. The computed stress distribution is used to identify and to assess microcracking at phase interfaces. The model is based on a grid of voxels representing metal and ceramic phases. This microstructural data comes from micro-CT scans or is assumed as randomly distributed. Different concentrations of copper have been tested.
Effective elastic and thermal properties. The effective elastic constants of interpenetrating FGM I-L were modelled using analytical models of Voigt, Reuss, Hashin-Shtrikman, Tuchinskii and Feng. Numerical models were developed for real FGM microstructures using three-dimensional (3D) images obtained with computer micro-tomography. Effective thermal conductivity and thermal expansion coefficient were calculated at room temperature with random and real microstructure (micro-CT images). The effective thermal conductivity turned out to be influenced considerably by the microstructure, while the effective thermal expansion coefficient did not.
FEM models of residual stresses. An effective FEM model was developed for prediction of thermal stresses in FGM I-L for the thruster application but can be used for any MATRANS material if the required material input data is available. The model is capable of making use of microstructural data from micro-CT images and of predicting thermal stresses with a good accuracy as compared with the measurements by the XRD method. The micro-CT digital data is fast processed and respective FE mesh is produced automatically by a software enabling fast computation of the thermal residual stresses. This is essential for practical applications. A concrete result of this model was the predicted graded structure of FGM I-L comprising four layers with 0 /2 /3.5 /5 vol. % Al2O3 used in further FGM I-L processing.
A model of wear in FGM I-H (brake disk) system has been developed for pertinent wear mechanisms based on the micromechanics. Progressive wear during reciprocating ball-on-flat test has been modelled basing on asymptotic wear states so that detailed analysis of contact was avoided. The model which is highly efficient as compared to the usual approach employing repeated 3D contact analysis is combined with shape updating.
Potential impact:
The expected final results of MATRANS are novel metal-ceramic composites with graded microstructure (FGMs) for the three target applications: thrusters, valve, brake disks to replace the currently used reference materials for their enhanced mechanical and physical properties. Lightness with high frictional wear resistance and high thermal conductivity are the main target properties of infiltrated FGM I-H (target application: brake disk). Reduction of thermal stresses through graded profile, improved lifetime, better oxidation and erosion resistance as well as high temperature strength are the main target properties of FGM I-L processed by spraying (target application: thruster). Low weight combined with enhanced strength in high temperature and high resistance to wear, corrosion, oxidation are the main target properties for FGM II (target application: valve). The potential technological impact of MATRANS FGMs can be substantial in automotive and aerospace sectors as they will contribute to longer materials life-time, enhance materials performance limits and durability while reaching desired functionalities at a lower or at least a reasonable cost.
As regards societal impact the novel FGMs and their processing technologies developed in MATRANS will generate a larger market share for European products. Consequently, an increasing market for material production in Europe may arise with emerging and new companies. The quantitative increase in highly skilled workforce together with the knowledge stemming from the project activities, will contribute to knowledge-based European economy and will thus enhance the competitiveness of European industry in comparison to the resource intensive approaches pursued elsewhere. The society will profit from the reduced use of raw materials and energy, extended lifetime of industrial infrastructure and lowered cost of decommissioning, which are the outcomes of the lifecycle approach. On a project-scale one may expect that about 50 new, highly skilled young engineers and scientists will emerge from the MATRANS project. This dynamic and skilled workforce, together with the knowledge produced, will contribute to the competitiveness of the European Union industry.