激光3D打印TC4钛合金工件的根部出现了裂纹。通过分析裂纹的微观特征以及工件的残余应力,分析了裂纹产生的主要原因。结果表明: 以高速、微层、微区连续熔凝为特征的激光3D打印, 其热输入量较小, 打印层对已成型层的退火作用小, 导致激光3D打印TC4钛合金工件外表面出现严重的拉应力, 最大值达到了640 MPa；同时3D打印过程中存在的飞溅、咬边和熔道不连续等缺陷, 会影响下一层铺粉厚度和密度的均匀性, 导致微观缺陷的产生, 或使得打印工件的性能在微观上不均匀; 微观分析显示, 裂纹起源和终止于微缺陷处, 在扩展过程中有向微缺陷处发展的特征; 预热温度不够、严重的残余拉应力、微观缺陷或性能不均匀的共同作用, 是导致激光3D打印TC4钛合金工件根部出现裂纹的主要原因。

The TC4 titanium alloy parts produced by laser 3D printing, cracked from the initial printing layer. The main causes of cracks were investigated by analyzing the microscopic characteristics of the cracks and the residual stress of the parts. The results show that the heat input of laser 3D printing with characteristics of high speed, micro-bedded and micro-zone continuous melting was small, and the annealing effect of the printing layer on the forming layer was feeble, which resulted in a very high residual tensile stress on surface of the printed parts and the maximum stress value even reached 640 MPa. Meanwhile, the defects such as splash, undercut and molten bead discontinuity formed during 3D printing, would affect the uniformity of thickness and density of the next layer powders, which led to the generation of micro defects and the mechanical heterogeneity of the printing parts. The micro analysis shows that the cracks originated from and terminated at the micro-defects and the cracks would develop toward the micro-defects. So, the low preheating temperature, high residual tensile stress, more micro-defects and the mechanical heterogeneity played the key roles for the root cracks in the TC4 titanium alloy parts produced by laser 3D printing.