(85-X)Ti-XNi-15Hf(X=48-51at.%) 형상기억합금의 상변태거동 = Phase Transformation Behavior of (85-X)Ti-XNi-15Hf(X=48-51at.%) Shape Memory Alloys

다국어 초록 (Multilingual Abstract)

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.