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

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 (Ni2AlHf). The interfaces between the NiAl–Cr(Mo), the NiAl–Ni2AlHf 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.