Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Powder metallurgy processing routes for the production of main line bearings for aero gas turbine engines

Powder processing is an attractive alternative to casting and hot working for production of the mainline bearings for gas turbines owing to a fine microstructure, a uniform distribution of fine carbides and an improved homogeneity. 2 commercial high speed steels T1 and M50 were considered and processed along various routes.

For T1 a satisfactory process route has been developed on the laboratory scale and validated on the 300 kg scale relying on water atomization (with filtering of liquid metal and magnetic separation of nonmetallic inclusions) and vacuum sintering to greater than 96% total density (td) hot isostatic pressing or hot working. For M50 nitrogen atomization (600 kg) hot isostatic pressing route is the only viable route. Both materials exhibit the fine microstructure expected from powder metallurgy. For T1 the carbide size may be adjusted between 1 and 5 um.
Levels of static mechanical properties equal or superior to those of optimized reference materials have been measured in bend testing (3 or 4 point) and the interaction of carbides with cracking has been studied on the various materials. The inclusion contents of the conventional materials can be matched by both powder metal routes and the performance of the fully densified powder metal high speed steels with an optimized microstructure under fatigue and also under rolling contact fatigue conditions is encouraging.

As envisaged at the outset the material cleanliness problem dominated the final stages of the research programme to produce inferior quality bearings. However, the scientific knowledge acquired has created interest in other applications of high speed steels, for which the tolerance for defects is not as low as for aeroengine bearings (eg wear parts in combustion engines).
Among the positve results achieved have been:
process methods for water atomized powders sintering and hot forging leading to refined microstructure;
process methods for gas atomized poeders deformation assisted densification.
Scientific knowledge has been gained on microstructural control by controlling the process parameters and composition, especially for the mechanisms operating in high temperature sintering.

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