原位钛基复合材料激光焊接过程中TiB晶须增强体的微观结构演变

Microstructural evolutions of in-situ TiB whisker reinforcement during laser welding TiB/Ti composites

摘要:

本研究采用Nd:YAG激光成功地对TiB晶须和La₂O₃颗粒混杂增强的原位钛基复合材料进行了焊接。利用金相观察、X-ray衍射、扫描电镜(SEM)和透射电镜(TEM)等测试方法,研究了激光焊接过程中TiB的演变行为,探讨了激光焊接头中的物相组成,TiB的分布及形貌特征,及TiB(或La₂O₃)和基体之间的界面关系。研究结果表明,TiB依然存在于焊接接头中,未发现有害物相的形成。在接头熔化区和靠近焊接热源的热影响区中,TiB尺寸显著细化,重新分布于b柱状晶晶界形成新颖的网络状结构。而在远离熔合线的热影响区中,由于受焊接热输入影响小,仅有少量TiB晶须通过B原子的强化扩散而改变了尺寸大小。而靠近母材的TiB未有变化,保持着和母材中TiB相似的形貌特征。进一步的TEM研究证明,增强体和基体之间的界面干净,仍保持良好的界面结合关系,未发现任何不良界面反应的发生,这也表明在激光焊接过程中,增强体和钛基体之间的界面结构是比较稳定的。

Abstract:

In this paper, in-situ synthesized titanium matrix composites (TMCs) reinforced with TiB whisker plus La₂O₃ particle were successfully fabricated by the laser beam welding (LBW) process with a Nd:YAG laser source. The evolution behavior of TiB was investigated during laser welding. Optical microscope (OM), X-ray diffractometry (XRD) analysis, scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) were used to analyze the phase, distribution and morphology characteristics of TiB whisker reinforcements in the laser weld seam, and the interface between TiB whiskers (or La₂O₃ particles) and titanium matrix was also discussed. Research results show that TiB is still retained in the welding joints, and no harmful substances are found. TiB is significantly refined and redistributed at b grain boundaries, a novel network structure forms in the fusion zone and the heat-affected zone near the fusion zone. Relatively, only some TiB whiskers in the heat-affected zone far away from the fusion zone change their sizes through intensi?ed diffusion of boron, and TiB near the base metal exhibits no changes and similar morphological features with that in the base metal. Further examination by TEM proves that interfaces between the reinforcements and the titanium matrix are very clean, and TiB maintains good bonding relationship with the matrix. There is no interfacial reaction which explains that interfacial microstructures between the reinforcements and the matrix are very stable during welding.