Synthesis of NiAl intermetallics from cold-extruded samples

In a previous study, we described the phenomenological densification behavior of Ni–Al mixtures, up to a pressure of 100 MPa. The following use of Differential Hydrostatic Extrusion, forcing on the sample non-isotropic plastic deformations allowed a final densification of 98.4% on the stoichiometric mixture. Due to this plastic deformation, the contact area between Ni and Al was improved, with the possible destruction of intermediate oxide layers. Following this idea, the reactivity of these samples was studied under argon at 450 °C, 550 °C and 800 °C. The formation of intermetallics was observed from 450 °C by solid state diffusion, while at 550 °C, the mechanical activation provided by differential hydrostatic extrusion allowed the sample to undergo Thermal Explosion. Using a low heating rate, this phenomenon could be avoided, and we were able to recover high density NiAl with a strong preferred orientation by a heat treatment at 800 °C.