Investigation of a directionally solidified NiAl/Cr(Mo) composite alloyed with Hf

Abstract

A NiAl/Cr(Mo) composite alloyed with Hf was directionally solidified under a Ar atmosphere in Al2O3-SiO2 mold by the standard Bridgman technique. The as-grown composite was composed of NiAl matrix, lamellar Cr(Mo), and semicontinuously distributed Ni2AlHf. The G phase (Ni16Hf6Si7) formed in the presence of Si, which was a contamination resulting from the ceramic mold. The interfaces were atomically flat with no transition layer. After hot isostatic pressing (hipping) and aging treatment, the G phase completely disappeared and the amount of intercellular Ni2AlHf phase was partially reduced. The compressive yield stress and tensile strength of the composite were higher than those of many NiAl-based alloys. Embrittlement existed at high temperatures, induced by hipping and aging. The effect of the G phase and Heusler phase on the mechanical property of the composite was also discussed.