Effect of process control agent on alloying and mechanical behavior of L2^sub 1^ phase Ni–Ti–Al alloys

In this paper, we manufacture Ni50Ti25Al25 alloys dominated by L21-Ni2TiAl phases using mechanical alloying (MA) technique. The effects of process control agent (PCA) on MA process and mechanical properties of the Ni–Ti–Al alloys are investigated. It is found that the present L21-Ni50Ti25Al25 alloy exhibits high hardness, low reduced modulus and excellent pseudoelasticity. The PCA directly affects the MA process, microstructure and mechanical properties of the alloys. The MA sample without adding PCA has higher strength and much lower alloying temperature than that with PCA. Based on the nanoindentation tests, hardness of the both alloys showed obvious indentation depth dependence. Meanwhile a transition from normal indentation size effect of nano-hardness to reverse indentation size effect is observed.