Abstract

Superelastic Ti–50·8 at.%Ni alloy wires were tested under ultrasonic conditions using a self-designed ultrasonic fatigue tester. Different heat treatment processes were carried out to Ni–Ti wires, and the mechanical properties of the wires were investigated. Experimental results indicated that the longest fatigue life of Ni–Ti wire under ultrasonic conditions was obtained when it was annealed after cold drawing. Proper thermomechanical treatment increased the fatigue life of Ni–Ti wire due to the adjustment of microstructure in Ni–Ti alloys as well as the workhardening effect. The strengthening effect of heat treatment and cold drawing was attributed to the fine Ti3Ni4 precipitated phase and the high density of dislocations respectively. The SEM results showed smooth fractured faces with dimples existed in the propagation region of the fatigue cracks, indicating the excellent ductility and better resistance to propagation of fatigue cracks of NiTi wires.

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