Surface deformation, applied in-process by machine hammer peening (MHP), has the potential to refine the coarse columnar β-grain structures normally found in high deposition rate Wire-Arc Additive Manufacturing (WAAM) processes with Ti alloys like Ti-6Al-4V. Effective refinement, as well as a reduction in texture strength, has been achieved in relatively thick sections and to a depth that is greater than that expected from the surface deformation induced by MHP. By application of MHP to each deposition track, the average β-grain size could be reduced from cm’s to less than 0.5 mm. Systematic experiments have been performed to investigate the origin of this interesting effect, which included ‘stop-action’ trials and separation of the strain and temperature gradients induced by the two process steps. The maximum depth of the plastic deformation from MHP required to generate new β-grain orientations was determined by electron backscatter diffraction local average misorientation analysis to be < 0.5 mm, which was less than the melt pool depth in the WAAM process. Nevertheless, new β-grain orientations were observed to form within the peened layer ahead of the approaching heat source as the peak temperature rose above the β transus, which then grew into the less deformed core of the wall as the temperature rose. This allowed the new grain orientations to penetrate deeper than the melt pool depth and survive to act as substrates for epitaxial growth at the fusion boundary during solidification, resulting in significant grain refinement.

表面变形，通过机锤击（MHP）过程中的应用，具有细化粗大的柱状的电势β -grain结构通常在高沉积速率线弧添加剂制造（WAAM）发现的Ti合金等的Ti-6Al-流程4V。在相对较厚的部分中实现了有效的细化以及纹理强度的降低，并且其深度大于由MHP引起的表面变形所预期的深度。通过将MHP应用于每个沉积轨迹，平均β-晶粒尺寸可以从厘米减小到小于0.5毫米。已经进行了系统的实验来研究这种有趣作用的起源，其中包括“停止作用”试验以及由两个工艺步骤引起的应变和温度梯度的分离。通过电子反向散射衍射局部平均取向错误分析确定，产生新的β晶粒取向所需的MHP塑性变形的最大深度小于0.5 mm，小于WAAM工艺中的熔池深度。然而，随着峰值温度升至β以上，观察到在热源附近的喷丸层内会形成新的β-晶粒取向。Transus，然后随着温度的升高而成长为壁变形较小的核心。这使得新的晶粒取向可以比熔池深度更深地渗透，并且可以在凝固过程中继续充当熔融边界外延生长的基质，从而显着改善晶粒。