Microstructure and mechanical properties of NiAl produced in the SHS process induced by low-temperature hydrostatic extrusion

Abstract

A stoichiometric nickel aluminide intermetallic alloy produced by self-sustained high-temperature synthesis (SHS) induced to the green compacts of the mixture of elemental Ni and Al powders by mechanical heavy deformation during low-temperature hydrostatic extrusion has been investigated. The process was performed with the high strain rate (>102 s−1) at the low temperature (∼500°C). To reduce the porosity, grain size and non-homogeneity of the obtained material a further high-temperature (∼950°C) hydrostatic extrusion was applied. Mechanical properties of the material were measured on the samples cut out from extruded rods in the longitudinal and transverse directions. Elastic anisotropy (elastic tensor) was determined using a resonant ultrasound spectroscopy (RUS) method applied to small cylindrical samples of the material. Its value described as the ratio of the coefficients of linear compressibility in transverse and longitudinal directions was at the level of 2 for extruded material even after annealing. Plastic anisotropy of the material was determined in uniaxial compression tests using an acoustic emission (AE) method for monitoring early stages of microcracking process in the samples under investigation. The phenomenon of the yielding point was observed for the samples compressed in the direction of extrusion.