In-Situ SEM Study on Deformation and Failure Mechanism of TC4 Titanium Alloy by Laser Additive Manufacturing

SEM原位加载研究激光增材制造TC4合金变形破坏机制

School of Aeronautics, Northwestern Polytechnical University, Xi'an 710072, China

Received: 20 January 2020

Abstract

The in-situ tensile test of the field emission scanning electron microscope was used to study the deformation mechanism of the TC4 titanium alloy manufactured by laser additive manufacturing along the L direction (grain growth direction) and T direction (perpendicular to the grain growth direction). The test results show that during the tensile process, as deposited specimen mainly cracks along the interfaces of α and β which is 45 ° to the tensile direction. With the increase of load, the cracking increases. The surface of the sample fluctuates until breaks. There is no obvious change in the prior β grain boundary in L direction. The microcracks along grain boundaries were observed in T direction, which is consistent with the result that the plasticity in the T direction is less than that in L direction. After heat treatment, due to the increase of α lath width compared with the as-deposition, slip bands were observed in α phase. However, a large number of slip bands appear on the equiaxed α phase of the forged specimen.

摘要

利用扫描电镜的原位拉伸台研究了激光增材制造TC4钛合金沿晶粒生长方向（L）和垂直于晶粒生长方向（T）拉伸过程中的变形机理。结果表明沉积态拉伸过程中显微组织主要沿与拉伸方向呈约45°的α，β两相界面开裂；随着流动应力的增加，微裂纹数量增多，试样表面在载荷作用下出现起伏错动，直至破坏。L方向原始β晶界上没有明显的变化，T方向观察到沿晶界开裂的微裂纹，这与T方向的塑性比L方向差的结果相一致。热处理后由于α板条变宽，α相内出现滑移带，锻造态则是在等轴α相上出现了大量的滑移带。