利用TEM和拉伸实验研究了时效工艺对Ti-50.8Ni-0.3Cr(原子分数, %)形状记忆合金(SMA)显微组织和超弹性的影响. 随时效时间($t_{\rm ag}$)延长, 300 ℃时效态Ti-50.8Ni-0.3Cr SMA的Ti3Ni4析出相呈细小颗粒状, 400 ℃时效态合金的析出相由颗粒状逐渐变为针状, 500 ℃时效态合金的析出相由针状逐渐变为粗片状. 时效温度对析出相形态的影响比tag显著. 随tag延长, 300和400 ℃时效态合金的抗拉强度(σb)先增大后趋于稳定, σb(500 ℃)先减小后趋于稳定, 且σb(400 ℃)>σb(300 ℃)>σb(500℃). 300和400 ℃时效态合金的超弹性优于500 ℃时效态合金. 随tag延长, 该合金的应力诱发马氏体相变临界应力逐渐减小, 300 ℃时效态合金的超弹性能耗(ΔW)降低, 400 ℃时效态合金的ΔW升高, 500 ℃时效态合金的ΔW先升高后降低.
The low temperature superelastic alloys are of wide range of applications, such as to make the energy storage devices, the earthquake protective devices and the abrasion parts, etc. The shape memory alloy (SMA) Ti-50.8Ni-0.3Cr (atomic fraction, \%) is a good low temperature superelastic alloy with low martensitic transformation temperature and high critical stress for inducing martensitic transformation. So far, the effects of the annealing and aging processes on the transformation behaviors of Ti-50.8Ni-0.3Cr SMA, and the characteristics of the shape memory effect, the superelasticity and the stress-strain cycle for annealed Ti-50.8Ni-0.3Cr SMA have been studied, systematically, while the microstructure and deformation characteristics of aged Ti-50.8Ni-0.3Cr SMA were not studied yet. In this paper, the influences of aging processes on the microstructure and superelasticity in Ti-50.8Ni-0.3Cr SMA were investigated using TEM and tensile test. With increasing aging time (tag), the morphology of Ti3Ni4 precipitate shows fine particle-shape in 300 ℃ aged Ti-50.8Ni-0.3Cr SMA, the morphology of Ti3Ni4 precipitate changes from the fine particle-shape to the needle-shape in 400 ℃ aged alloy, and the morphology of Ti3Ni4 precipitate changes from the needle-shape to the plate-shape in 500 ℃ aged alloy. The effect of aging temperature on the precipitate morphology is more outstanding than that of aging time. With increasing tag, the tensile strengths (σb) in 300 and 400 ℃ aged alloys are increase first and then tend to stable, while σb (500 ℃) is decrease first and then tend to stable, and σb(400 ℃)>σb(300 ℃)>σb(500 ℃). The superelasticities of 300 and 400 ℃ aged alloys are better than that of 500 ℃ aged alloy. With increasing tag, the critical stress for inducing martensitic transformation of Ti-50.8Ni-0.3Cr SMA is decrease, the superelasticity energy dissipation (ΔW) of 300 ℃ aged alloy is decrease, the $\Delta W$ of 400 ℃ aged alloy is increase, and the ΔW of 500 ℃ aged alloy is increase first and then decrease.
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