激光焊接TB9钛合金接头的显微组织演变和不均匀析出

Microstructural Evolution and Heterogeneous Precipitation of Laser Welded TB9 Alloy Joints

摘要:

研究了激光焊接和焊后热处理过程中TB9钛合金激光焊接接头的显微组织演变规律。研究结果表明，在激光焊接过程中，随着激光功率的增大，焊缝区β相的平均晶粒尺寸增大。在焊后时效处理过程中，随着温度的升高，α相的尺寸增大，数量减少；随着时效时间的延长，α相的尺寸增大，同时，α相的形态由针状变为椭球状。焊后热处理后，焊接接头的焊缝区、热影响区（HAZ）和母材中均观察到无析出区（PFZs）存在，这主要是α相的不均匀析出和长大造成的。PFZs存在于焊缝区的枝晶臂之间，HAZ的晶界附近，以及母材的小角度晶界（LAGBs）和晶界附近。焊缝区PFZs产生的主要原因是Cr元素在枝晶臂间富集。在HAZ和母材中，PFZs的形成则是由于晶界和LAGBs附近的空位耗竭。

Abstract:

The microstructural evolution during the laser welding and subsequent post-weld heat treatment processes of laser welded TB9 joints was investigated. Results show that, during the laser welding process, the average size of β grains in the fusion zone increases with the increase in laser power. During the aging treatment, the size of the α phase increases with the increase in temperature. Concurrently, the quantity of the α phase decreases. The size of the α phase also increases with the prolongation of holding time. Meanwhile, the morphology of α phase transforms from a needle-like structure to an elliptical one. After the heat treatments, the precipitation-free zones (PFZs) are observed in the fusion zone, heat-affected zone (HAZ), and base metal of the welded joint. The formation of PFZs is due to the inhomogeneous precipitation and growth of α phase. PFZs exist between the dendrite arms in the fusion zone, near the grain boundaries in HAZ, and near the low angle grain boundaries (LAGBs) and grain boundaries of the base metal. In the fusion zone, the formation of PFZs is due to the enrichment of element Cr between dendrite arms. In HAZ and base metal, the formation of PFZs is attributed to vacancy depletion around grain boundaries as well as LAGBs.