使用示差扫描量热仪(DSC)和拉伸实验研究了Cr掺杂对550℃退火态Ti-50.8Ni(原子分数, %)形状记忆合金相变和循环形变特性的影响. 结果表明, Ti-50.8Ni合金冷却/加热时发生B2→R→M/M→B2型可逆相变, 掺杂0.3%Cr后所得Ti-50.8Ni-0.3Cr合金的相变类型为B2→R→M/M→R→B2, 相变温度大幅度降低. 室温下, Ti-50.8Ni和Ti-50.8Ni-0.3Cr合金的相组成均为母相B2, 前者呈现形状记忆效应, 后者呈现超弹性. 随循环变形次数n的增加, Ti-50.8Ni合金的特性由形状记忆效应演变为线性超弹性, 合金的应力诱发马氏体临界应力和积累残余应变迅速增加; Ti-50.8Ni-0.3Cr合金的特性由非完全超弹性演变为完全超弹性, 超弹性应力-应变曲线形态比较稳定. 随$n$增加, Ti-50.8Ni合金的超弹性残余应变εr减小, 超弹性应变恢复率ηs增加; Ti-50.8Ni-0.3Cr合金的εr和ηs则分别稳定在较低和较高水平, 超弹性稳定.
The effect of Cr addition on the transformation and the cyclic deformation characteristics in 550℃ annealed Ti-50.8Ni shape memory alloy (SMA) were investigated by differential scanning calorimetry (DSC) and tensile test. The B2→R→M/M→B2 type reversiable transformation occurred in Ti-50.8Ni alloy upon cooling/heating. After the addition of 0.3%Cr in Ti-50.8Ni alloy, the transformation type for Ti-50.8Ni-0.3Cr alloy was B2→R→M/M→R→B2, and the transformation temperatures decreased significantly. At room temperature, the phase composition was parent phase B2 for both Ti-50.8Ni and Ti-50.8Ni-0.3Cr alloys, while the former showed shape memory effect; the latter showed superelasticity. With increasing cyclic deformation number n, Ti-50.8Ni alloy evolved from shape memory effect to linear superelasticity, and its stress inducing martensitic critical stress and the accumulation residual strain increased rapidly; while Ti-50.8Ni-0.3Cr alloy evolved from incomplete superelastic to complete superelastic, and the stress-strain curve shape was stable. With increasing n, the superelastic residual strain εr decreased and the superelastic strain recovery ratio ηs of Ti-50.8Ni alloy increased, while the εr and ηs in Ti-50.8Ni-0.3Cr alloy kept at lower and higher values, respectively. The superelastic of Ti-50.8-0.3Cr alloy was stable.
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