Microstructure, brittle–ductile transition temperature and elevated temperature compressive behavior of the directionally solidified NiAl–Cr(Mo)–Hf alloy

Abstract

The directionally solidified NiAl–27Cr–5.6Mo–0.4Hf (at.%) alloy was hot isostatically pressed at 1573 K, 100 MPa for 2 h and then annealed at 1323 K for 40 h. Microstructure examination revealed that the present alloy was mainly composed of three phases, i.e. the NiAl matrix, the lamellar Cr(Mo) and Heusler phase (Ni 2 AlHf). The interfaces between the NiAl–Cr(Mo), the NiAl–Ni 2 AlHf were atomically flat. The mechanical properties including the brittle–ductile transition temperature and the high temperature compressive behavior were also tested. The BDTT of the alloy was about 1233 K at a strain rate of 1.04 × 10 −4 s −1 and dependent on strain rate. This strain-rate dependent BDT can be explained by the cooperative dislocation generation model. The investigation on the high temperature compressive behavior between 1200 and 1300 K showed that the deformation behaviors of the alloy could be adequately described by the standard power-law. The possible strengthening mechanism was discussed.