Influence of Ni/Ti ratio and Nb addition on martensite transformation behavior of NiTiNb alloys

Abstract Based on the designed Ni x Ti y Nb z (x/y = 1, 1.0210, 1.0425, 1.0645, 1.0869/x-y≈0, 1, 2, 3, 4; z = 0, 2, 4, 6, 9) alloys, influence of Ni/Ti ratio and Nb addition on martensite transformation behavior of NiTiNb alloys is elaborately examined. The microstructure evolution and valence electron concentrations ( c v ) were analyzed with increasing Ni/Ti ratio and Nb addition. The Ms of NiTiNb alloys are mainly determined by microstructure and c v of B2-NiTi matrix. Different Ni/Ti ratio and Nb addition result in the variation of microstructure and c v of B2-NiTi matrix, and thus influence Ms. For instance, when x/y ≤ 1, the Ms decrease with increasing Nb addition then reach a steady state; when x/y>1, the Ms first increase and then decrease with increasing Nb addition, and finally also reach a steady state.