HREM observation of interface between precipitates and martensite of reversible shape memory alloy Ni-Ti
Since the reversible shape memory (RSM) alloys were found in 1960, a number of investigations and applications have been carried out and the mechanism have been discussed extensively. Ni-Ti is one of the typical RSM alloys. Many researches were concentrated on martensite structure and the relationship between martensite and austenite. However, the interface structures between martensite and precipitates have been rarely studied. In the present paper, the interface structures between precipitates ( NiTi2 and Ni3Ti) and martensite were investigated in atomic scale by using nigh resolution electron microscopy.49.5at%Ni-50.5at%Ti alloy whose martensitic transformation temperature is 75°C was annealed at 900°C for 2 hours to allow the components to become uniformly distributed, then quenched into water at room temperature. The specimens for electron microscopy observation were prepared by spark cutting and electropolishing. A JEM-2000EX and JEM-4000EX operated at 200kv and 400kv, respectively were used in the present observations.