| In order to investigate the effect of Hf-content on phase transformation behavior and the microstructures of Ti-Ni-Hf shape memory alloys, differential scanning calorimetry, X-ray diffraction and transmission electron microscopy were performed. The one stage B2(cubic)-B19`(monoclinic) transformation occurred in the alloys whose Hf-contents are less than 10 at%, while both the B19(orthorhombic) and the B19` martensite coexisted in the alloys whose Hf-content is more than 10 at%, indicating that the B2-B19 and the B19-B19` transformations were not separated. Transformation temperatures decreased with increasing the Hf-content for the alloys whose Hf-contents are less than 5 at%, and then increased for those whose Hf-content is more than 5 at% and less than 15 at%. Further increasing Hf-content, however, the decrease in transformation temperatures which may be attributed to an unknown phase was observed. The (001) twin as an internal defect existed in the B19` martensite, while did not exist in the B19 martensite. |
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