HiGh spEed TuRbinE cAsing produced by powDer HIP technologY

Project Information

GETREADY

Grant agreement ID: 641594

Closed project

Start date 1 September 2014

End date 29 February 2016

Funded under

• Specific Programme "Cooperation": Joint Technology Initiatives

Total cost € 886 158,81

EU contribution € 531 484,00

Coordinated by

CONSORZIO INTERUNIVERSITARIO NAZIONALE PER LA SCIENZA E TECNOLOGIA DEI MATERIALI
Italy

Final Report Summary - GETREADY (HiGh spEed TuRbinE cAsing produced by powDer HIP technologY)

Executive Summary:
The next generation of aeronautic engines aims at continuously improving performances and efficiency, reducing at the same time emissions. However, increasing this temperature severely stresses the turbine constitutive materials. Current casing constitutive materials are designed to work at ca. 650° C and superalloys like Inconel 718 or Waspaloy are typically used. Different aeronautic propulsion producers have different strategies to develop more efficient turbines, but they are all trying to find materials and manufacturing routes capable to provide casings which can readily operate at 700 to 800° C. Besides the requirement on maximum operating temperature casing constitutive materials are also requested to have high stiffness, so as to guarantee the maintenance of accurate clearances between the rotatory and stationary parts of turbines. Materials capable to provide such characteristics are indeed available on the market, e.g. Astroloy, but with major problems in terms of workability.
Astroloy is characterized by an higher amount of Ti + Al alloying elements with respect to Waspaloy and the increased content of these elements gives the possibility to develop a higher fraction of gamma prime precipitates which are responsible for the improved properties at high temperature. At the same time increased Ti and Al additions provide poorer forgeability for Astroloy material. Therefore, although appealing service performances can be achieved by designing with Astroloy, there is of course a strong industrial interest to apply alternative near net shape processing routes to form such an alloy, so as to increase cost efficiency of manufacturing and reduce the environmental impact of the overall component processing.
Within this project the Consortium:
1) Has successfully applied the powder Near Net Shape Hot Isostatic Pressing (NNSHIP) manufacturing route to the fabrication of two Astroloy turbine casings for high speed turbine.
2) Has optimised the material usage reducing material waste: the NNSHIP to design process has been optimised so as to provide a semi-finished part very close to the final casing profile component (1.5 mm overstock) thus reducing as much as possible the machining efforts.
3) Has fine tuned a post heat treatment to fully exploit the Astroloy potential thermal/mechanical resistance for casing application and done a complete and certified mechanical characterization.
4) Has developed a modelling of thermal densification and rheological properties of the powders with simulation tools to simulate the NNSHIP process and being able to adapt the process when component change its design.

Project Context and Objectives:
The next generation of aeronautic engines aims at continuously improving performances and efficiency, reducing at the same time emissions. The major service parameter affecting turbine efficiency is the operating temperature, which has a direct proportional relation with it. However, increasing this temperature severely stresses the turbine constitutive materials. Current casing constitutive materials are designed to work at ca. 650° C. Superalloys like Inconel 718 or Waspaloy are typically used. Different aeronautic propulsion producers have different strategies to develop more efficient turbines, but they are all trying to find materials and manufacturing routes capable to provide casings which can readily operate at 700 to 800° C. Besides the requirement on maximum operating temperature casing constitutive materials are also requested to have high stiffness, so as to guarantee the maintenance of accurate clearances between the rotatory and stationary parts of turbines. Materials capable to provide such characteristics are indeed available on the market, e.g. Astroloy, but with major problems in terms of workability.
Astroloy is characterized by an higher amount of Ti + Al alloying elements with respect to Waspaloy and the increased content of these elements gives the possibility to develop a higher fraction of gamma prime precipitates which are responsible for the improved properties at high temperature. At the same time increased Ti and Al additions provide poorer forgeability for Astroloy material. Therefore, although appealing service performances can be achieved by designing with Astroloy, there is of course a strong industrial interest to apply alternative near net shape processing routes to form such an alloy, so as to increase cost efficiency of manufacturing and reduce the environmental impact of the overall component processing.
In this project we evaluate Near Net Shape Hot Isostatic Pressing (NNSHIP) as processing route for Astroloy casings:
- The manufacturing process was assessed as well as the heat treatment.
- A complete and certified mechanical characterization has been performed and revealed to be higher than the requirements given by our Topic Manager.
- The cross contamination between Astroloy part and steel capsule is less than 500 micrometers.
- A modelling of thermal densification and rheological properties of the powders with simulation tools have been developed to simulate the NNSHIP process; to this purpose this tool demonstrated to be very accurate allowing to predict with a very low discrepancy the final shape and dimension of the casing.
- The final overstock material of NNSHIP casing is around 1.5 mm
- Two full scale NNSHIP casing have been produced (maximum diameter of the casing is approximately 1,200 mm).
According to the Topic Manager with this project we reached TRL4 and MRL3 for Astroloy casing fabricated via NNSHIP. The potential of the work done within this project is high and the Consortium intends to continue to pursue this application and are actively looking for suitable funding sources.

Project Results:
1) Setting up of the Astroloy Near Net Shape Hipping (NNSHIP) process and heat treatment with microstructural and chemical analysis

Preliminary studies on powders (dimensions and distributions, chemical composition, morphology) have been done to assess the proper powder characteristic for NNSHIP process.
NNSHIP process parameters (temperature and pressure) have been assessed in order to achieve full density. A billet 100x100x1000 mm has been produced for heat treatment set up and cut up to obtain specimens for the characterization.
Mould design was developed identifying the potential critical manufacturing process.
Heat treatment conditions have been assessed. On specimens obtained with the defined process parameters microstructural and chemical analysis has been done to assess the effect of heat treatment on the microstructure as well as creep and tensile properties. Solutioning temperature and time, cooling rate, aging temperature, time and number of were used as parameters to define the optimal HT recipe.
Studies have been carried out in order to define the depth of alteration provided by elements inter-diffusion at the interface between the NNSHIP casing and the steel capsule (used for HIPping process). By determining the type of alteration provided and the related, the actual potentials for performing Near-Net-Shape or Net-Shape design for casing manufacturing were defined. It resulted that the crossed contamination Astroloy part - steel capsule is less than 500 micron.

2) Complete and certified mechanical characterization

The mechanical tests agreed with the Topic Manager have been assessed:
- tensile tests at room temperature and at high temperature up to 820 °C;
- creep tests at high temperature up to 820 °C;
- low cycle fatigue tests at high temperature up to 820 °C;
- high cycle fatigue tests at room temperature;
- fatigue crack growth tests at room temperature and at high temperature up to 760 °C.
Thermal stability of the material has been assessed and tensile tests at room temperature and at high temperature up to 820°C have been performed on material previously subjected to a prolonged exposition to air and high temperature (200 h at 820°C)
All these mechanical properties revealed to be higher than references provided by Topic Manager and higher than Topic Manager requirements for the application.
All the samples for such characterization was removed by another HIP billet fabricated using always the same batch of powder (the same batch that was used for all the research activities) and the same HIP conditions.

3) Manufacturing of the first casing for the demonstrator

All aspects of work required for the production and assessment of the NNSHIP casing has been defined.
The design of the NNSHIP casing has been agreed with the Topic Manager, the maximum diameter of the casing is approximately 1200 mm.
A modelling of thermal densification and rheological properties of the powders with simulation tools have been developed to simulate the NNSHIP process.
The NNSHIP casing has been produced and the post processing operation in order to perform heat treatment and mould removal avoiding dimensional changes and distortions have been performed thus producing a NNSHIP part that as only 1.5 mm of overstock material. This means that final machining has been reduced as much as possible.
Mechanical properties have been repeated on specimens obtained from bars accompanying the NNSHIP casing in all its production steps and revealed to be in perfect agreement with the complete mechanical characterization performed on samples removed from the first billets produced.
According to project proposal, this first NNSHIP casing should have been cut-up, but the CAD design of the part has been sent to the Topic Manager because the resulting component has dimensions that may be directly acceptable for its final machining and the related casing production. The Topic Manager confirmed that it was suitable to follow this solution, so it was agreed to delay the cut up of the part after second NNSHIP casing production. In this way if something would have gone wrong with the second production we would have been in a safe situation to have at least a good NNSHIP casing as demonstrator.

4) Manufacturing of the final casing for the demonstrator

After some process improvements according previous experience the second NNSHIP casing has been produced. The CAD design of the part has been sent to the Topic Manager in order to evaluate if the resulting component has dimensions that were adapt for final machining and casing production. The Topic Manager confirmed that it was possible to use such part to fabricate the final casing and it was agreed to delay the cut up of one of the two NNSHIP casings postponing it after Topic Manager final machining and final casing production. In this way if something would have gone wrong with machining, Topic Manager would have the possibility to repeat the machining on the second part and use the previous one for cut up thus being again in a safe situation.
Mechanical properties have been repeated on specimens obtained from bars accompanying the NNSHIP casing in all its production steps and revealed to be in perfect agreement with the complete mechanical characterization performed on samples removed from the first billets produced.
At the end of the activity Technology readiness level (TRL) Material readiness level (MRL) have been assessed. According to Topic Manager metrics thanks to this project the NNSHIP Astroloy casing product and process have reached TRL4 and MRL3.

Potential Impact:
We have successfully built Near Net Shape Hipped (NNSHIP) Astroloy casings for high speed turbine and generated a complete and certified characterization of the mechanical properties of the material with which it is made. The casing design was agreed with the topic Manager as well as the certification needed for the mechanical properties and the list of the mechanical properties.
At the beginning of the project, according to the proposal, one small NNSHIP casing and a full size demo one should have been produced, but we were able, indeed, to produce two full size NNSHIP casings. Both parts provided to have the right geometry for Topic Manager final machining and casings production. As regards mechanical properties, the material has properties well above Topic Manager requirements.
The Topic Manager made some estimation of the future scenario that can be:
1. Ramp up in 3 years to 500 casings per year
2. Ramp up in 3 years to 1000 casings per year
Of course both these scenarios are very ambitious and impose to have a huge amount of further development work. This work is in particular requested in order to further increase TRL and MRL of material and process before serial production is viable.
The consortium and the Topic Manager intend to continue to work together to pursue this application and are actively looking for suitable additional funding sources.
The project was very short in duration with very high demanding technical activities that the collection of results for external dissemination activity revealed to be a difficult matter to be addressed. However now that the project is concluded the Consortium is working on different dissemination activities such as the preparation of several scientific papers on the project topics, conference participations and what is considered particularly interesting by the Consortium and the Topic manager is the participation to the Powder Metallurgy Component Awards 2016 (see the following link: http://componentawards.epma.com/). Of course, even if the project is closed, all of these activities will be done in full agreement among the Consortium and with Topic Manager approval.

List of Websites:
In agreement with topic manager a public website was not opened. A web ftp area has been created within the web services of Politecnico di Torino to be used as data exchange space and to distribute the documents with the level of security agreed with the other partner and the Topic Manager. For this reason the site is an area restricted to partners and Topic Manager only and it is possible to access to this area only through the use of a username and a password.