Microstructure Refinement and Work-Hardening Behaviors of NiAl Alloy Prepared by Combustion Synthesis and Hot Pressing Technique

Most methods used to synthesize and prepare NiAl intermetallics and their alloys have the disadvantages of complexity and high cost. In this paper, the NiAl alloy was prepared by a Combustion Synthesis and Hot Pressing (CSHP) technique under rapid solidification. The grain size of the NiAl alloy is significantly refined to 60–80 μm, which reduces the stress concentration during deformation and improves the fracture strength and fracture hardness. Moreover, the large internal stress and greater amount of dislocations in the as-cast microstructure are produced by their formation under pressure due to the fast cooling rate in the solidification process. The high dislocation density strengthens the NiAl alloy, giving it higher strength, hardness, and work-hardening ability. The high compression properties are also present in the NiAl intermetallics at room temperature, in which the fracture strength is around 1005 MPa and the fracture strain reaches 21.6%. The compressive fracture strength at room temperature is higher than that of the pure NiAl alloy prepared by the Hot-Pressing-Aided Exothermic Synthesis (HPES, about 632 MPa), while it is slightly lower than that of pure NiAl alloy treated by HPES and Hot Isostatic Pressing (HIP, 1050 MPa). The fracture strain is significantly higher than that of the NiAl alloy prepared by other methods. This study can provide guidance for the successful preparation of the NiAl alloy with high strength and toughness.