| In the previous study, the highest phase transformation temperature among Ti-Ni-Hf alloys has been obtained in the alloy containing 15at.%Hf. In the present study, the Ni-content dependence of phase transformation behavior and microstructures in Ti-Ni-Hf shape memory alloys containing 15at.%Hf is investigated by means of differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. Transformation temperatures decreased with increasing Ni-content and a martensitic transformation did not occur in a 51at.%Ni alloy. In alloys whose Ni-content is less than 51at.%, both the B19(orthorhombic) and the B19`(monoclinic) martensites coexisted over the temperature ranges between 77K and 623K, indicating that the B2-B19 and the B19-B19` transformations were not separated. The (001) twin existed in the B19` martensite as an internal defect and became finer with increasing Hf-content, while did not exist in the B19 martensite. |
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