几何缺陷对Ti-7.5Nb-4Mo-2.5Sn形状记忆合金超弹性能的影响

Effect of geometric defects on superelasticity of Ti-7.5Nb-4Mo-2.5Sn shape memory alloy

对Ti-7.5Nb-4Mo-2.5Sn形状记忆合金试样以及带有几何缺陷(中心圆孔和单边半圆缺口)合金试样的力学性能及超弹性能进行测试,并采用ARAMIS三维变形分析测试系统对单轴加载-卸载过程中试样的全场应变场分布进行实时观察,研究几何缺陷对合金应变场分布、应力诱发马氏体相变和超弹性能的影响。结果表明:在拉伸加载过程中,带几何缺陷的试样在缺陷周围产生了应力集中,导致合金试样在局部具有较高的应变速率和应变量;应力诱发马氏体相变主要受应力场分布的影响,而且主要发生在局部变形带中。因此,与完整试样相比,带几何缺陷的试样表现出较高的诱发马氏体相变的临界应力和较低的超弹性。

The mechanical properties and superelasticity of the Ti-6.5Nb-4Mo-2.5Sn alloy and the samples with a central circular hole and a unilateral semicircular notch, respectively, were evaluated. The full field strain distributions of the samples were monitored during the uni-axis loading-unloading tensile tests by using ARAMIS three-dimensional optical deformation measurement system. The effects of the geometric defects on the strain field, the stress-induced martensite phase transformation and superelasticity were investigated. The results indicate that the samples with geometric defects have the stress concentration closing to the defects on loading, resulting in relatively high strain rate and strain in local zone of alloy. The stress-induced martensite phase transformation is mainly influenced by the strain distributions, and the martensite phase transformation occurs in a localized area. Thus, the samples with the geometry defects exhibit a high critical stress for inducing the martensite transformation and a low superelasticity in comparison with the perfect sample.