Application of microscopy and X-ray Diffraction in optimization of the production of NiTi alloy by powder metallurgy

Abstract

This paper describes the dependence of microstructure of NiTi shape memory alloy on the conditions of nonconventional powder metallurgy processing routes-reactive sintering of compressed Ni+Ti powder mixture and mechanical alloying with consequent compaction by Spark Plasma Sintering. First method was chosen as the process enabling to yield the high-purity NiTi alloy, while the second one aimed to reach the ultrafine-grained microstructure. The microstructure and phase composition of the products are compared in this work. The positive effects of high heating rate (> 300 K.min-1) and high temperature (at least 900 °C) on the reactive sintering process were recognized. Microstructure of the product is composed by NiTi matrix with dispersed Ti2Ni particles. Similar microstructure can be also obtained by mechanical alloying for at least 120 min and consequent compaction by Spark Plasma Sintering.