STRUCTURE AND PERFORMANCE ACROSS THE MARTENSITIC TRANSTION IN Co-Ni-Al MAGNETIC SHAPE MEMORY ALLOYS

摘要

As a potential magnetic shape memory alloy, Two-phase structure Co-Ni-Al has good mechanical properties and high phase transformation temperature. In this study, the microstructure and performance across the martensitic transition in Co-Ni-Al alloys were investigated. The results revealed that specimens exhibited the matrix and dendrite-type y phase. A self-accommodation martensite, whose transformation from β phase, is tetragonal Ll_0 structure. With Ni/Al atomic ratio increase, y phase grows up to be a coarse network dendritic structure at the grain boundaries. Element Ni had solid solution in the matrix and y phase, which significantly improved the magnetic properties. The introduction of the y phase is significantly improved the ductility of alloys and the volume fraction of y phase was increasing with Ni/Al atomic ratio rise. Both compressive and hardness tests indicated that the specimens containing more y phase have better ductility.