Brittle-to-ductile transition in multiphase NiAl alloy

The microstructure of a directionally solidified (DS) NiAl/Cr(Mo,Hf) alloy was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This alloy was composed of NiAl, Cr(Mo) and Ni2AlHf phases. Tensile testing of this multiphase NiAl alloy was performed from room temperature to 1323 K at various strain rates from 1.04×10−4 s−1 to 1.04×10−2 s−1. It was found that the brittle-to-ductile transition temperature (BDTT) of this alloy was higher than values reported for many of NiAl-based alloys and dependent on the strain rate. Regardless of strain rate, at temperatures just above the BDTT, the fracture morphology changed from NiAlʹs cleavage and debonding along the NiAl/Cr(Mo) interface to completely ductile in nature. It was also found that the apparent activation energy responsible for BDT is 463 kJ mol−1, which may be responsible for the higher BDTT.