Mechanical alloying of L21 phase Ni–Ti–Al alloy with high hardness: Influence of multiple process control agents

Abstract

Cold welding becomes easier during mechanical alloying in alloy system with ductile and low melting point components. Here, effects of multiple process control agents (PCAs) including volatile PCAs, non-volatile PCAs and no PCA on mechanical alloying of Ni–Ti–Al powders was investigated. It is found that L21 phase Ni–Ti–Al alloys milled with volatile PCAs and no PCA show superior hardness that is much higher than the non-volatile PCAs samples, but all exist serious cold welding. However, the alloy milled with non-volatile PCA exhibits almost identical high hardness as the volatile PCAs and no PCA samples with prolonging milling time. Moreover, cold welding phenomenon is completely avoided by using non-volatile PCAs properly. The particle morphology changes from large flaky at the initial stage to uniform ultrafine particles during milling process. Uniform composition distribution greatly reduces the alloying temperature, which facilitates the formation of L21-Ni2TiAl phase with high hardness.