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

A vacuum induction melted and drop cast ingot of NiAl-28Cr-5.5Mo-0.5Hf (at. %) was directionally solidified under Ar atmosphere in an Al2O3-SiO2 cerami c mold by the standard Bridgman method, then was hot isostatically pressed (HIP) at 1300 degreesC/100 MPa for 2 h and aged at 1050 degrees 'C for 40 h . The composite was mainly composed of three phases, i.e. the lamellar Cr(N o), the NiAl matrix and Heusler phase, and the interface between NiAl and C r(Mo) was atomically flat. The mechanical properties of the composite were also tested. It was found that the brittle-to-ductile transition temperatur e (BDTT) of the composite was dependent on strain rate and the apparent act ivation energy is approximately 596 kJ/mol, which may be responsible for th e high BDTT. (C) 2001 Elsevier Science B.V. All rights reserved.