Microstructure and transformation temperatures of Si-added Ni–Ti–Cu and Ni–Ti–Zr shape memory alloys

The effect of Si on the martensitic transformation in Ni 44 Ti 50 Cu 6 and Ni 50 Ti 30 Zr 20 was investigated in the present study. The martensite transformation temperature of the two alloys decreased with the increase of Si content. In particular, a large decrease was observed for Ni 50 Ti 30 Zr 20 . With the addition of 0.5 at% Si, the initial martensite temperature of Ni 50 Ti 30 Zr 20 decreased by 238.2 K, compared to that of Ni 44 Ti 50 Cu 6 , which decreased by only 16.4 K. This significant decrease is attributed to the high sensitivity of the valence electron concentration and the decrease in the lattice parameter caused by the addition of Si, leading to the very large increase of stability of B2 with addition of Si in Ni 50 Ti 30 Zr 20 . Graphical abstract