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用光学显微镜、示差扫描热分析仪、X射线衍射仪及拉伸试验研究了Ti-49.8Ni-1.0Co(at%)形状记忆合金组织、相变和力学性能。结果表明,400℃和600℃退火态合金的组织分别呈纤维状和等轴状,且冷却和加热时分别发生ARM两阶段和AM一阶段相变。400℃退火态合金的马氏体相变热滞大于600℃退火态。退火时间ta对该合金相变类型影响不大,但随ta延长,合金的相变温度升高。室温下,400℃和600℃退火态合金呈形状记忆效应(SME)+超弹性(SE),600℃退火态合金的应力诱发马氏体临界应力和塑性高于400℃退火态。随ta延长合金的应力诱发马氏体应力降低。当试验温度Td≤20℃时合金呈SME+SE,当Td≥30℃时呈SE。随Td升高,合金的应力-应变滞回面积减小,SE特性增强。
The microstructure, phase transformation and mechanical properties of Ti-49.8Ni-1.0Co (at%) shape memory alloy were investigated by optical microscope, differential scanning calorimeter, X-ray diffraction and tensile test. The results show that the microstructures of annealed alloys at 400 ℃ and 600 ℃ are fibrous and equiaxed, respectively, and the phases ARM and AM first phase occur during cooling and heating, respectively. The martensitic transformation temperature hysteresis of annealed alloy at 400 ℃ is larger than that at 600 ℃. The annealing time ta has little effect on the type of phase transformation of the alloy, but with the extension of ta, the phase transition temperature of the alloy increases. At room temperature, the shape-memory effect (SME) + superelasticity (SE) of the as-annealed alloys at 400 ℃ and 600 ℃, the stress-induced martensitic critical stress at 600 ℃ and the plasticity higher than 400 ℃. The stress-induced martensitic stress decreases with the elongation of the alloy. When the test temperature Td ≤ 20 ℃ when the alloy was SME + SE, when Td ≥ 30 ℃ was SE. With the increase of Td, the stress-strain hysteresis area of the alloy decreases and the SE characteristic increases.