Electrical resistivity of Ti–Ni binary and Ti–Ni–X (X = Fe, Cu) ternary shape memory alloys

The electrical resistivities of Ti–Ni binary and Ti–Ni–X (X = Fe, Cu) ternary shape memory alloys (SMAs) are investigated. Experimental results reveal that the Ti–Ni and Ti–Ni–X SMAs exhibit different electrical resistivity (ρ) characteristics due to their different martensitic transformation behaviors. The increase of ρ during the B2 → R transformation of Ti–Ni SMAs is about 10–16 μΩ cm, which is a change of about 12–20%. For a two-stage transformation of B2 ↔ R ↔ B19′, there is a sharp increase of ρ during B2 → R transformation, and then a rapid decrease of ρ during R → B19′ transformation. However, for the Ti-40 at.%,Ni-10 at.%,Cu alloy, which exhibits a B2 ↔ B19 ↔ B19′ two-stage transformation, there is a small variation of ρ during B2 → B19 transformation, but a significant variation of ρ during B19 → B19′ transformation. These phenomena may be ascribed to their different structures, deformation defects, accommodated twin variants and crystal distortions.