| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 101 === In this study, the properties of shape memory effect (SME), pseudoelasticity (PE) and stress-strain (σ-ε) cycling exhibited in Ni-rich Ti48.7Ni51.3 and Ti48.4Ni51.6 shape memory alloys (SMAs) are investigated. These SMAs are solid-soluted(SS) at 900℃x 1 hr, water quenched, and then aged at 250℃~500℃ for various time. The hardnesses of as-SS Ti48.7Ni51.3 and Ti48.4Ni51.6 SMAs are 362HV and 386HV, respectively. The maximum hardness for SS and aged specimens is 415 HV for Ti48.7Ni51.3 SMA aged at 300℃x10 hrs, and is 455HV for Ti48.4Ni51.6 SMA aged at 350℃x3 hrs. In the early aging, the curve of hardness at room temperature v.s. aging time for Ti48.7Ni51.3 SMA aged at 250℃ has two maxima, but that for Ti48.7Ni51.3 SMA aged at 300℃~500℃ and that for Ti48.4Ni51.6 SMA aged at 250℃~500℃ have only one maximum. From DSC tests of Ti48.7Ni51.3 and Ti48.4Ni51.6 SMAs, B2↔R transformation mainly appears in specimens aged at 250℃~350℃, but B2↔R↔B19’ transformation occurs in specimens aged at 400℃~500℃. The tensile tests indicate that, in specimens of Ti48.7Ni51.3 and Ti48.4Ni51.6 SMAs aged at 500℃x10 hrs, their SME, PE and σ-ε cycling properties are better than other aging conditions due to Ti3Ni4 precipitates grow larger and the resistance for B19’ transformation is less.
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