During direct energy deposition (DED), changes in the powder feeding behavior significantly affect the deposition process. In this study, a high-speed photography method was developed to observe the dynamic evolution of the powder stream for various powder feeding durations, and the synchronous evolution of the inner channel characteristics of the nozzle were also measured. Combined with powder stream simulations, the contribution of the evolution of each channel characteristic on the powder divergence was discussed. The results show that as the powder feeding duration increased, the inner channel characteristics of the nozzle changed dynamically, which led to the powder stream divergence. For a powder feeding duration of 60 h, the nominal powder spot size increased by 41.4% at the plane 15 mm below the nozzle exit. As the powder feeding time increased, the inner wall roughness, inner channel diameter, and the exit size of the nozzle also increased owing to the scouring erosion from the high-speed powder particles. Subsequently, changes in the inner wall roughness and inner channel diameter of the nozzle tended to be smaller owing to the formation of a work hardening layer. It was also demonstrated that the changes in the inner wall roughness of the nozzle had a negligible effect on the powder stream divergence, an increase in the inner channel diameter of the nozzle extended the maximum divergence range of the particle trajectory at the nozzle exit, and the expansion of the nozzle exit size reduced the constraint causing the allowed trajectory range of the ejected powder particles to increase. The deposited height gradually decreased as the powder feeding duration increased, resulting in a 38.7% decrease after 60 h.

在直接能量沉积（DED）期间，粉末进料行为的变化会显着影响沉积过程。在这项研究中，开发了一种高速摄影方法来观察在各种供粉持续时间内粉末流的动态演变，并且还测量了喷嘴内部通道特性的同步演变。结合粉末流模拟，讨论了每个通道特性的演变对粉末发散的贡献。结果表明，随着送粉时间的延长，喷嘴的内部通道特性动态变化，从而导致了粉流的发散。对于60 h的粉末进料时间，在喷嘴出口下方15 mm的平面上，标称粉末斑点尺寸增加了41.4％。随着粉末进料时间的增加，由于高速粉末颗粒的冲刷侵蚀，内壁粗糙度，内部通道直径和喷嘴的出口尺寸也增加了。随后，由于加工硬化层的形成，喷嘴的内壁粗糙度和内部通道直径的变化趋于减小。还证明了喷嘴内壁粗糙度的变化对粉末流的发散的影响可以忽略不计，喷嘴内通道直径的增加扩展了喷嘴出口处颗粒轨迹的最大发散范围，并且喷嘴出口尺寸的扩大减小了约束，从而导致所喷射粉末颗粒的允许轨迹范围增大。