Martensitic transformation behaviour of non-equilibrium heat treated Ni50·9Ti49·1 alloys

Abstract

Ni50·9Ti49·1 specimens were heat treated using a thermal simulator. The martensitic transformation behaviours of selected areas of the thermal simulating treated specimens were studied with resistivity temperature measurements. In the thermal simulating process specimens were heated by a large electric current to a given peak temperature (400, 500, 600, 800, 900 or 1100°C respectively) and immediately water cooled to room temperature. As the two ends of a NiTi alloy specimen were fixed in copper jigs, unequal heat treatment effect areas were formed in the specimen segments near its two ends. In the unequal area of an 800°C thermal simulating treated sample, a wide transformation temperature range phenomena appeared. The experimental results indicate that non-equilibrium heat treatment proves to be an effective method to fabricate transformation temperature gradient shape memory materials.