Effect of solidification rate on microstructure and crystal orientation of ferromagnetic shape memory alloys Co–Ni–Al

Abstract

Effect of solidification rate on the solidified microstructure and crystal orientation based on a new type ferromagnetic shape memory Co–Ni–Al alloys have been studied by the liquid metal cooling directional solidification. The results show that at the lower rate of 5 μm/s for the Co 32Ni 40Al 28 alloys, worm-like γ′ phase precipitated in martensite matrix and faceted γ particles were introduced under the rate of 10 μm/s. For a rather faster growth rate of 150 μm/s, interdendritic β + γ eutectic lamella appears after the dendritic β formed. The single austenite phase was observed in the Co 38Ni 34Al 28 alloy at the rate of 5 μm/s. At the same time, the preferred orientations changed with the variation of the solidification conditions. It is found that 〈1 1 1〉 oriented martensite crystal can be obtained in the Co 32Ni 40Al 28 alloy at the rate of 5 μm/s, while 〈1 1 0〉 and 〈1 0 0〉 orientations become stronger at the rate of 10 μm/s. But the preferred orientation degree at 150 μm/s is very poor. The Co 38Ni 34Al 28 rod with 〈1 1 0〉 oriented austenite can be prepared at the rate of 5 μm/s.