Influence of Sc addition on microstructure and transformation behaviour of Ni24.7Ti50.3Pd25.0 high temperature shape memory alloy |
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| Affiliation: | 1. Materials Science Division, National Aerospace Laboratories, Council of Scientific and Industrial Research (CSIR), Bangalore 560 017, India;2. Department of Materials Science & Engineering, Indian Institute of Technology, Kanpur 208 016, India;1. California Institute of Technology, 1200 E California Blvd., Pasadena, CA 91125, USA;2. NASA Glenn Research Center, 21000 Brookpark Rd., Cleveland, OH 44135, USA;3. University of Kentucky, 151 Ralph G. Anderson Building, Lexington, KY, 40506, USA;4. University of Toledo, 2801 West Bancroft Ave., Toledo, OH 43606, USA;5. Tomsk State University Siberian Physical-Technical Institute, Novosobornay Sq. 1, Tomsk 634050, Russia;1. School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150001, China;2. Guangdong University of Technology, Guangzhou, 510006, China;3. College of Mechanical and Electrical Engineering, Northeast Forestry University, Harbin, 150001, China;1. Division of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan;2. Center of Excellence for Advanced Materials Research, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia |
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| Abstract: | Vacuum-arc melted Ni24.7Ti50.3Pd25.0 and Ni24.7Ti49.3Pd25.0Sc1.0 (at.%) alloys were investigated to study effect of Sc micro-addition on microstructure and transformation behaviour of NiTiPd alloy. Study showed that microstructure of homogenized NiTiPd alloy consisted of NiTiPd matrix interspersed with Ti2(Ni,Pd) precipitates. In contrast, NiTiPdSc alloy showed a single phase NiTiPdSc matrix with a few scandium oxide particles at isolated places. TEM and X-ray diffraction studies confirmed matrix phase of the alloys to be of orthorhombic B19 structure. TEM observations showed that NiTiPdSc alloy had relatively larger martensite plates with a smaller twin ratio compared to that of NiTiPd alloy. Also, APB (anti-phase boundary) like regions with twinless martensites was observed in both the alloys, area fraction of APB-like regions being more in NiTiPdSc alloy. Thermal analysis showed that transformation temperatures (TTs) of NiTiPd alloy decreased significantly with addition of Sc. The martensite finish temperature (Mf) of 181 °C for NiTiPd alloy lowered to 139 °C upon 1.0 at.% Sc addition. The transformation hysteresis of Ni24.7Ti49.3Pd25.0Sc1.0 (at.%) alloy was measured to be 7 °C, significantly lower than that of 15 °C for Ni24.5Ti50.0Pd25.0Sc0.5 alloy, reported in literature. Alloy purity, lower volume fraction of second phase and presence of twinless/small twin ratio martensite in microstructure is believed to be the reasons for such low transformation hysteresis. The transformation behaviour of the alloys upon stress-free thermal cycling was found stable, variation in TTs being within 1–2 °C. |
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| Keywords: | A. Intermetallics, miscellaneous B. Shape-memory effects B. Phase transformation D. Microstructure F. Electron microscopy |
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