A study of ternary Ni-rich Ti-Ni-Si shape memory alloys

• Main Authors: Wei-Min Wu, 吳偉民
• Other Authors: Shy-Fang Hsien
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/74917174357790828057

碩士 === 國立高雄應用科技大學 === 模具工程系碩士班 === 92 === In this study, the phase transformation behavior, shape memory characteristics, microstructures of the aged ternary Ni-rich Ni50Ti50-XSiX (X=1.2 at.%) alloys were investigated. Experimental results reveal that in the matrix, the effect of Ni+Si in combiation on shape memory characteristics of Ni-rich Ni50Ti50-XSiX (X=1, 2 at.%) SMAs are similar to Ni-rich TiNi binary SMAs. The solution-treated alloys undergoes the one stage B2«B19’ martensitic transformation. However, the 400°C aged specimens can exhibit the different transformation sequence, in which the Ms point can be deeply depressed by the coherent stress of Ti11Ni14 precipitates to induce R-phase. In the beginning of the aging 3 Hrs at 400°C, Ni50Ti49Si1 alloy has one stage B2«B19’ transformation sequence. In the further aging, two stage B2®R®B19’ transformation sequence can be found in the cooling run, but one stage B2®B19’ transformation sequence in the heating run. Meanwhile, Ni50Ti49Si1 alloy has the B2«R«B19’ transformation sequence in the aging time more than 10 Hrs at 300°C. Ni50Ti48Si2 alloy has the transformation sequence B2«R«B19’ during the aging at 400°C for 50 Hrs, but B2«B19’ in the further aging. The Ti11Ni14 precipitates can be observed and identified by TEM. These aged Ni-rich Ti-Ni-Si alloys exhibit good shape memory effects, in which the maximal recovery occurs at the peak of hardness. All of these characteristics are associated with Ti11Ni14 precipitates during the aging process. No stress plateau can be observed in the stress-strain curves when the experimental specimens deformed in parent phase. In the cyclic test, the 25th cyclic stress-strain curve showed the linear- superelasticity. The longer aged time at 400°C, the less strength and the more residual plastic strain will be. In DMA measurement, the transformation temperature and sequence of the aged Ni50Ti48Si2 alloy is the same as the results of DSC test, in which the damping capacity (Q-1max) in martensite is better than that in premartensite and B2 phase.