The complex thermal histories present during additive manufacturing (AM) of metals result in the generation of residual stresses, which may result in distortion and early failure of the fabricated component. The amount of residual stress built up or relieved during deposition depends on the stress relaxation behavior of the deposited material as well as the substrate onto which the component is built, over the typical timescale for depositing a few layers in AM (seconds to minutes), which corresponds to the timescale over which the material is subjected to both stress and elevated temperature. This work presents a method for investigating stress relaxation behavior and mechanisms in conventionally processed and additively manufactured Ti-6Al-4V (CP Ti-6Al-4V and AM Ti-6Al-4V) through compression tests at 600 °C and 700 °C with in situ neutron diffraction. The results show that with an applied plastic deformation, 60–80% of the initial stress in Ti-6Al-4V was relieved in ten minutes and the stress stabilized at a negligibly low level. With the same applied strain, the stress relaxation rate at 700 °C was 2–4 times higher than that at 600 °C, and the peak stress at 600 °C was twice as high as that at 700 °C. It was determined that neither stress partitioning nor phase transformation were active in Ti-6Al-4V at the temperatures studied. Thus, it was hypothesized that the stress relaxation was primarily due to dislocation glide and climb. The presently reported relaxation behavior can be used in the development and validation of thermomechanical models used to predict and mitigate residual stresses and distortion in AM, or to predict distortion in Ti-6Al-4V used in structural applications at elevated temperatures.

在金属的增材制造（AM）期间存在的复杂热历史会导致残余应力的产生，而残余应力可能会导致变形和所制造部件的早期失效。在沉积过程中累积或释放的残余应力的大小取决于在AM上沉积几层的典型时间范围内（几秒至几分钟）沉积材料以及组件所构建在其上的基材的应力松弛行为，这对应于材料承受应力和高温的时间范围。这项工作提出了一种方法，用于通过在600°C和700°C的压缩试验下，以常规方式加工和添加制造的Ti-6Al-4V（CP Ti-6Al-4V和AM Ti-6Al-4V）来研究应力松弛行为和机理。原位中子衍射。结果表明，在施加塑性变形后，Ti-6Al-4V的初始应力在60分钟内释放了60-80％，应力稳定在很小的水平。在相同的施加应变下，700°C时的应力松弛率是600°C时的2-4倍，并且600°C时的峰值应力是700°C时的两倍。确定在所研究的温度下，应力分配和相变在Ti-6Al-4V中均不起作用。因此，假设应力松弛主要是由于位错滑行和爬升引起的。目前报道的松弛行为可用于开发和验证用于预测和减轻AM中残余应力和变形的热力学模型，