Effect of hot isostatic pressing on microstructure and mechanical property of NiAl/Cr(Mo,Hf) composite

Abstract

A vacuum induction melted and drop cast ingot of NiAl–28Cr–5.5Mo–0.5Hf (at.%) was directionally solidified under Ar atmosphere in an Al 2O 3–SiO 2 ceramic mold by the standard Bridgman method, then was hot isostatically pressed (HIP) at 1300°C/100 MPa for 2 h and aged at 1050°C for 40 h. The composite was mainly composed of three phases, i.e. the lamellar Cr(Mo), the NiAl matrix and Heusler phase, and the interface between NiAl and Cr(Mo) was atomically flat. The mechanical properties of the composite were also tested. It was found that the brittle-to-ductile transition temperature (BDTT) of the composite was dependent on strain rate and the apparent activation energy is approximately 596 kJ/mol, which may be responsible for the high BDTT.