TC4激光立体成形中基材热影响区组织性能优化研究

激光立体成形技术是一项基于同步送粉激光熔覆的先进制造技术。激光立体成形和修复过程中沉积层、热影响区以及基体材料组织、性能的差异将对最终零件的性能,尤其是疲劳性能产生重要影响。为改善基体、热影响区(HAZ)的组织、性能差异,针对TC4合金,提出在激光沉积前对基材表面进行多次激光重熔扫描预处理,从而优化基材热影响区组织性能。基于此,通过研究不同工艺条件下,多次激光重熔处理对热影响区组织性能的影响。结果表明:首先,多次激光重熔将引起的基材热影响区总体冷却速率下降,从而有效的消除热影响区的急冷组织;其次,重熔处理产生的多次热循环对基材热影响区的时效处理对于热影响区的组织、性能(硬度)也有一定的影响。通过在多层沉积前对基材进行适当的激光多次重熔扫描处理有效改善了沉积区、热影响区以及基材性能的大幅波动,实现了均匀渐变。

The Optimization of Microstructures and Properties in Heat Affect Zone of the Base in Laser Solid Formed TC4

Laser solid forming (LSF) is an advanced fabrication technique based on laser deposition with powder feed. However, the microstructure and properties difference among the deposition zone, the heat affect zone (HAZ) and the base in laser solid forming or laser repair has bad affects on the final properties of component especially the fatigue performance. In this study, it was suggested that several times laser remelting on the surface of Ti-6Al-4V base before laser deposition may optimize the mechanical properties of heat affect zone. So, the effects of laser remelting on the microstructure and prosperities of heat affect zone with different process parameters were investigated. It was found that the decrease of the total cooling rate was caused due to several laser remelting and eliminate the quenching microstructure in HAZ; In addition, the ageing treatment process of the thermal cycle caused by several time laser remelting also have important effects on microstructure and properities (hardness) of HAZ in TC4 base. Finally, the strong fluctuation of the hardness among the deposition zone, HAZ and base zone was improved by the proper laser remelting process before multilayer deposition, and the gradual change of the hardness was achieved.