INFLUENCE OF HIGH TEMPERATURE HEAT TREATMENT ON MICROSTRUCTURE AND MICROHARDNESS OF (DS)NiAl-Cr(Mo)-Hf EUTECTIC ALLOY
Influence Of High Temperature Heat Treatment On Microstructure And Microhardness Of (Ds)Nial--Cr(Mo)—Hf Eutectic Alloy

The influence of high temperature heat treatment on microstructure and microhardness of (DS)NiAl-Cr(Mo)-Hf eutectic alloy fabricated with directional solidification under high temperature gradient was investigated. The results indicate that there is little change in the morphology of NiAl and Cr(Mo) phases after high temperature heat treatment. But the semicontinuous Heusler phase which is originally located on the grain boundaries is partially reduced and fine Heusler particles re-precipitated within NiAl matrix. Furthermore, NiAl precipitates coarsen in the Cr(Mo) phase and dislocation appears in the Cr(Mo) phase. Microhardness of as-fabricated (DS)NiAl-28Cr-5Mo-lHf alloy is much higher than that of (DS)NiAl-28Cr-6Mo and basically unchanged after heat treatment.