As to multifunctional titanium alloys with high strength and low elastic modulus, thermal training is crucial to tune their thermal expansion from positive to negative, resulting in a novel linear expansion which is stable in a wide temperature range. Aided by the high-order Hooke’s law of elastic solids, a reversible atomic rearrangement mechanism was proposed to explain the novel findings which are unexpected from typical shape memory alloys. To confirm this continuous mechanism, a Ti-Nb based alloy, which possesses a nanoscale spongy microstructure consisting of the interpenetrated Nb-rich and Nb-lean domains produced by spinodal decomposition, was used to trace the crystal structure change by in-situ high energy synchrotron X-ray diffraction analyses. By increasing exposure time, the overlapped diffraction peaks can be separated accurately. The calculated results demonstrate that, in the nanoscale Nb-lean domains, the crystal structure parameters vary linearly with changing temperature along the atomic pathway of the bcc-hcp transition. This linear relationship in a wide temperature range is unusual for first-order martensitic shape memory alloys but is common for Invar alloys with high-order spin transitions. Furthermore, the alloy exhibits smooth DSC curves free of transformation-induced heat peaks observed in shape memory alloys, which is consistent with the proposed mechanism that the reversible transition is of high-order.

对于具有高强度和低弹性模量的多功能钛合金，热训练对于将其热膨胀从正值调整为负值至关重要，因此需要一种在宽温度范围内稳定的新型线性膨胀。借助于弹性固体的高阶胡克定律，提出了一种可逆的原子重排机制来解释新颖的发现，这是典型的形状记忆合金所无法预料的。为了证实这种连续的机理，使用了一种Ti-Nb基合金，该合金具有纳米级海绵状微结构，该结构由旋节线分解产生的互穿的富Nb和富Nb畴相互渗透，通过原位高能来追踪晶体结构的变化。同步加速器X射线衍射分析。通过增加曝光时间，可以准确地分离出重叠的衍射峰。计算结果表明，在纳米Nb贫域中，晶体结构参数随bcc-hcp跃迁原子途径的温度变化而线性变化。一阶马氏体形状记忆合金在宽温度范围内的这种线性关系是不寻常的，但对于具有高阶自旋转变的殷钢合金则很常见。此外，该合金显示出平滑的DSC曲线，没有在形状记忆合金中观察到的由相变引起的热峰，这与所提出的可逆相变具有高阶机制是一致的。一阶马氏体形状记忆合金在宽温度范围内的这种线性关系是不寻常的，但对于具有高阶自旋转变的殷钢合金则很常见。此外，该合金显示出平滑的DSC曲线，没有在形状记忆合金中观察到的由相变引起的热峰，这与所提出的可逆相变具有高阶机制是一致的。一阶马氏体形状记忆合金在宽温度范围内的这种线性关系是不寻常的，但对于具有高阶自旋转变的殷钢合金则很常见。此外，该合金显示出平滑的DSC曲线，没有在形状记忆合金中观察到的由相变引起的热峰，这与所提出的可逆相变是高阶机理相一致。