On the development of Ni powder metallurgy alloys

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Sintered powder metallurgy (PM) alloys are an attractive material for the aerospace and automotive industries as high strength/low weight substitutes for traditional products. For the aerospace industry pressure has been placed on the metallurgical community to develop new routes for processing Ni and Co-based Superalloys for gas turbine use due to the necessity to improve performance and reduce noxious emissions. Attempts to develop new materials using the attractive mechanical properties of intermetallics have been only marginally successful due to their inherent brittle nature. However PM is used to produce turbine disks and the fine grain nature along with near net shape capability of PM should be attractive for afterburner and combustor liners. PM formed Superalloys can also possess a more uniform microstructure thereby improving low cycle thermo-mechanical fatigue. Unfortunately, only a limited number of prealloyed/master alloy Superalloy powders are available and at times these have been found to suffer from heterogeneity in powder grain composition. As well, poor compressibility and associated residual porosity on sintering have plagued the development of new Ni PM alloys and applications. Thus the two objectives of this proposal are to continue research on development of a Ni-Cr-Fe based PM Superalloy similar to IN600 with minimal residual porosity and improved compressibility and to improve the oxidation resistance of the optimised Ni PM alloy by rare earth additions and/or additions of Y. The novelty is the development of a laboratory scale Ni-PM based process to correctly simulate industrial practice and using this to produce new reliable Ni-based PM products. Techniques include press/sinter, microstructural characterization SEM, TEM, EDS, DSC. The significance is in the development of Ni-based PM components for the aerospace sector thereby providing an economical near-net-shape process for producing parts with enhanced elevated temperature and oxidation resistance.