| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 100 === In this study, the property improvement of shape memory effect (SME) and pseudoelasticity (PE) exhibited in Ni-rich Ti49Ni51 shape memory alloy (SMA) solid-soluted(SS) and aged at 250℃~500℃ for various time is investigated. The hardness of specimen at 900℃x 1 hr SS and water quenched is 303HV. Among all aged specimens, the maximum hardness is 374 HV for specimen aged at 250℃x25 hrs. From DSC tests, B2↔R transformation mainly appears in specimens aged at 250℃~350℃, but both B2↔R and R↔B19’/B2↔B19’ transformations occur in specimens aged at 400℃~500℃. The Rs temperature and ∆HR value of B2↔R transformation reach their maxima for specimens aged at 300℃. In the early aging, the curve of the specimen hardness at room temperature v.s. aging time has the 1st maximum, the minimum and the 2nd maximum , in which the 2nd maximum is also the highest hardness possessed in aged alloy. From DSC results and TEM observations, the formation of R phase and nano-precipitates is closely related to the hardness maximum and minimum exhibited in specimens aged at 250℃~400℃. The specimens with two step aging have 100% SME and higher damping capacity even though their the maximum hardness is 348HV. The tensile tests for specimens aged at 300℃x50 hrs (hardness 360HV) and at 250℃x5 hrs+400℃x1 hr (hardness 341HV) indicate their SME and PE properties are better than those of Ti49.3Ni50.7 due to the former has higher SS strengthening and precipitation hardening.
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