Effect of Multiple Forging on Microstructure and Mechanical Properties of Powder Metallurgy FGH4096 Superalloy

FGH4096 is an important damage-tolerance-type powder metallurgy (PM) superalloy, which is also the optimized turbine material for high performance aero-engine. To turbine disc, bore and rim are used in high temperature-low stress condition and low temperature-high stress condition, and dual-microstructure is introduced. Coarse-grained microstructure is suit for rim region and fine-grained is no doubt most suitable for bore region. But fine-grained ingot can not make by PM technique, so that gradient heat treatment can not be developed to coarsen the grain of rim region. Under the confine of PM technique, several treatment processing should be taken place to refine the coarse grains of PM alloy. Multiple forging with large accumulate deformation was carried c-it on PM FGH4096 superalloy, and fine grains of 3.5 mu m were obtained by this treatment processing. Mechanical properties testing were ake carried out on both fine-grained and other statuses alloys. Microstructure evolution was observed by optical microscopy, scanning electron microscopy and transmission electron microscopy. As a result of repeated dynamic recrystallization, coarse grains could be completely refined into fine grains. And the increase of strength was mainly attributed to refinement effect and improvement of defects such as previous particle boundaries. Successful development of fine-grained treatment processing will promote the research of dual-microstructure turbine disc.