A solid state phase transformation of Ti-6Al-4V was studied using high speed in situ x-ray diffraction measurements made during rapid cooling of a cold metal transfer arc weld bead deposited onto a water cooled substrate. Analysis of body centered cubic (BCC) and hexagonal close packed (HCP) lattices revealed an abrupt, nonlinear shift in the lattice parameters of both phases just after the HCP phase had nucleated. Postmortem transmission electron microscopy confirmed that V diffusion was mostly suppressed during cooling. Together, these results indicate that at this cooling rate of approximately 104 K/s, which is representative of cooling rates of many additive manufacturing and welding processes, kinematic coherency of the BCC–HCP interfaces gives rise to the anomalous lattice expansion and contraction behaviors of both phases during the initial nucleation and growth stages of (mostly) martensitic transformation from BCC to HCP; the role of diffusion in such lattice anomalies is shown to be minimal.

中文翻译：

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运动学约束和扩散在 Ti-6Al-4V 非平衡固态相变中的作用

Ti-6Al-4V 的固态相变使用高速原位 X 射线衍射测量进行了研究，该测量是在快速冷却沉积在水冷基板上的冷金属过渡电弧焊珠的过程中进行的。对体心立方 (BCC) 和密排六方 (HCP) 晶格的分析表明，在 HCP 相刚刚成核后，两相的晶格参数发生了突然的非线性变化。尸检透射电子显微镜证实，V 扩散在冷却过程中大部分受到抑制。总之，这些结果表明，在大约 104 K/s 的冷却速率下，这代表了许多增材制造和焊接工艺的冷却速率，BCC-HCP 界面的运动相干性导致在从 BCC 到 HCP 的（大部分）马氏体转变的初始成核和生长阶段期间两相的异常晶格膨胀和收缩行为；扩散在这种晶格异常中的作用被证明是最小的。