Ti-4.5Al-0.5Fe-0.2C-(Cr, Mo, V) 合金の引張特性に及ぼす高温加熱の影響

抄録

Recently, Ti-4.5Al-4Cr-0.5Fe-0.2C has been developed. This alloy has excellent hot workability superior to the most widely used Ti-6Al-4V and comparable good mechanical properties, and contains only eutectoid-type beta stabilizers such as Cr and Fe in composition. Generally, eutectoid-type beta stabilizers embrittle the alloy after high temperature exposure because of the precipitation of intermetallic compounds such as TiCr₂. In this study, we investigated the tensile properties of Ti-4.5Al-4Cr-0.5Fe-0.2C after exposure at various elevated temperatures for various times. It is found that the precipitation of TiCr₂ makes this alloy brittle and that it takes place faster at 773 K than 523 K; embrittlement occurred after 8 h when exposed at 773 K while the alloy maintained good ductility even after 1000 h when exposed at 573 K. In order to suppress the precipitation of TiCr₂, after exploring alloy compositions for both good ductility after exposure and good hot workability, Ti-4.5Al-2Cr-1.7Mo-1.3V-0.5Fe-0.2C, where Mo and V substitute Cr in Ti-4.5Al-4Cr-0.5Fe-0.2C, has been obtained. The new alloy has shown to be able to suppress precipitation of TiCr₂ and to maintain much better ductility than Ti-4.5Al-4Cr-0.5Fe-0.2C after long time exposure at 773 K.