Microstructural change and martensitic transformation in a rapidly solidified Cu-Al-Ni based SMA ribbons with heat treatment

Abstract

The effects of flash-heating and aging on the microstructure and transformation characteristics has been studied in Cu-Al-Ni based melt-spun ribbons. When the as-spun ribbon, stabilized due to higher Al content and fast cooling, is flash-heated at 750 degrees C, the beta(1) parent phase is partially retained. Even though flash-heating temperature is increased upto 850 degrees C, a little beta(1) parent phase with lager grains above 10 mu m is still retained. The M-s temperature is increased with increasing flash-heating temperature due to the decrease of grain constraint within grown grains. However, the greater part of P, parent phase with smaller grains of 2 similar to 3 mu m is transformed to martensite in the initial stage of aging at 200 degrees C. The M-s temperature of the ribbon with smaller grains is higher than that of the ribbon with larger grains. It is considered that the increase of M, temperature is caused to the disappearance of lattice defects introduced during melt spinning by aging at 200 degrees C rather than grain growth.