Search

The effects of different forming process on the microstructure, martensitic transformation, and mechanical properties of the Ni50Mn34In14Co2 (numbers indicate at.%) alloys were investigated in detail. The results show that the microstructure of Ni50Mn34In14Co2 alloy consists of the matrix and the second phase by powder hot forging technology under the forces in different directions and spark plasma sintering (SPS), and the prepared sample has obvious preferred orientation by applied force in the three directions. The grain and the second phase of prepared sample were obviously refined by the hot forging technology. The martensitic transformation behavior was almost unchanged by different forming process. In addition, the shape memory effect of prepared Ni50Mn34In14Co2 alloy was significantly enhanced by different forming processes. [ABSTRACT FROM AUTHOR]

A Heusler Ni50Mn29Ga16Gd5 alloy with a high transformation temperature has been obtained by substituting 5 at% Gd for Ga in a ternary Ni50Mn29Ga21 ferromagnetic shape memory alloy. The microstructure and phase transformations in the Ni50Mn29Ga16Gd5 alloy have been investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and differential scanning calorimetry. It is shown that the microstructure of the Ni50Mn29Ga16Gd5 alloy consists of matrix and hexagonal Gd (Ni,Mn)4Ga phase, which indicates a eutectic structure composed of these two phases. One-step thermoelastic martensitic transformation occurs in this quaternary alloy. Ni50Mn29Ga16Gd5 alloy exhibits a martensite transformation start temperature up to 524 K, approximately 200 K higher than that of Ni50Mn29Ga21 alloy. At room temperature, non-modulated martensite with twin substructure is observed in Ni50Mn29Ga16Gd5 alloy. [ABSTRACT FROM AUTHOR]

In the present work, 1 at% Y was added to Ti-50.7at%Ni alloy to prepare Ti-50.2Ni-1Y alloy and the effects of rare earth Y addition on the microstructure and martensitic transformation behavior of Ti-50.7at%Ni alloy was investigated by optical microscope, scanning electronic microscope (SEM) X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results show the microstructure of Ti-50.2Ni-1Y alloy is different with that of Ti-50.7at.%Ni alloy, and its microstructure consists of B19′martensite and the Y-rich phase, which may be YNi phase. One-step martensitic transformation occurs in Ti-50.2Ni-1Y ternary alloy. The phase transformation temperatures increase rapidly with Y addition, and the increase of Ms is about 85°C. [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]