钛合金微沟槽的纳秒激光烧蚀工艺研究

Research on nanosecond laser ablation process of titanium alloy micro-groove

为减小激光烧蚀钛合金过程产生的热影响区及避免钛合金表面微裂纹萌生,分析了纳秒紫外激光的扫描速度、重复频率、光斑重叠率、扫描次数对Ti6Al4V钛合金微沟槽几何尺寸、热影响区和微裂纹的影响规律。研究结果表明:在脉冲能量为0.4 mJ、扫描速度为100 mm/s、重复频率为50 kHz时,钛合金微沟槽的深度和其火山口的高度最大,沟槽边缘火山口的高度和宽度与扫描次数、重复频率呈正相关,而与扫描速度呈负相关;当激光的光斑重叠率小于0.8时,烧蚀界面的热影响区较小;当微沟槽的槽间距较窄时,烧蚀边缘残余拉应力的集中引起裂纹的萌生;当槽间距较宽、扫描速度较低和扫描次数较高时,在较窄槽宽的沟槽内,由能量过度集中引起的热应力导致微裂纹萌生。

In order to reduce the heat-affected zone during laser ablation of titanium alloy and avoid the development of microcracks on the surface of titanium alloy, the effects of scanning speed, repetition frequency, spot overlap rate and scanning times of nanosecond UV laser on the geometry of microgrooves, heat-affected zone and microcracks of Ti6Al4V titanium alloy were analyzed. The research indicates that the depth of the titanium alloy microgrooves and the height of the crater are the largest when the pulse energy is 0.4 mJ, scanning speed is 100 mm/s and the repetition frequency is 50 kHz. The height and width of the crater at the edge of the groove are positively correlated with the scanning times and repetition frequency but are negatively correlated with the scanning speed. When the spot overlap rate of the laser is less than 0.8, the heat-affected zone of the ablation interface is smaller. When the groove spacing of the microgrooves is narrow, the concentration of residual tensile stress at the ablation edge causes the initiation of cracks. When the groove spacing is wider, the scanning speed is lower, and the scanning times are higher, the thermal stress caused by the excessive concentration of energy in the groove with a narrow groove width leads to the initiation of microcracks.