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The effects of aging on martensitic transformation and microhardness were investigated for Ni53Mn23·5Ga18·5Ti5 ferromagnetic shape memory alloy. The results show that precipitation has obvious effect on martensitic transformation temperature and the microhardness increases with increasing aging temperature up to 973 K, and then decreases gradually with the further increase in aging temperature. [ABSTRACT FROM AUTHOR]

Microstructural aspects and interfacial characteristics of deformed martensite variants in a compressed Ni[sub55]Mn[sub20]Ga[sub25] (at.-%) alloy have been investigated using transmission electron microscopy. It is shown that the undeformed specimen exhibits a well accommodated morphology and a straight and well defined interfacial boundary. After deformation, reorientation of martensite variants occurs at the expense of unfavourable martensite variants, and the interfacial boundary changes from sharp and straight to curved and irregular. Meanwhile, lattice defects are formed inside the variants even in slightly compressed samples. With increasing deformation, high density lattice defects are generated and rearranged inside the variants as well as in the interfacial boundaries between variants. [ABSTRACT FROM AUTHOR]

The effect of annealing treatment and thermal cycling on the phase transformation behaviour of Ni-Mn-Ga alloy prepared by arc melting technology has been investigated. The results show that the main transformation parameters decrease in a few initial thermal cycles, and then stabilise with further cycling. The transformation temperature interval decreases with an increase of annealing temperature. As cast material exhibits a columnar grain microstructure, while annealed material exhibits coarsened grains with clearly martensitic plates. When the alloy is annealed at 1073 K, both the martensite start temperature M[sub s] and the austenite finish temperature A[sub f] decrease, while the martensite finish temperature M[sub f] and the austenite start temperature A[sub s] increase with an increase in annealing time. This implies that the chemical order degree of the parent phase increases with increasing annealing time, which causes the chemical driving force for martensitic transformation to decrease. [ABSTRACT FROM AUTHOR]