水导激光加工K424高温合金热损伤机制研究

Research on thermal damage mechanism of K424 superalloy processed with water-jet guided laser

为研究水导激光技术加工K424高温合金的热损伤区规律,使用自主研发的水导激光加工系统对K424高温合金薄片进行打孔实验,采用旋切法进行钻孔,并在激光穿透材料后在孔壁继续旋转几圈去边缘毛刺。将切下的圆形工件进行镶嵌、打磨、抛光、腐蚀和清洗,使用Zeiss EVO 10扫描电镜观测工件上的热影响区情况与重铸层的厚度。实验结果发现,水导激光加工后工件边缘位置的晶粒无明显变化,不存在热影响区。重铸层的厚度在2μm以上,但是分布不均匀,有的位置甚至不存在重铸层。分析后得出结论为水导激光的激光功率过高或脉宽时间过长等相关参数会导致材料内部产生多余的热量,如果这些热量过高会造成加工位置附近形成热影响区,并产生过多的熔渣使重铸层的厚度增加。同时,加工过程中会由于水柱变向回流或者熔渣较大导致排水不畅等因素,都会造成水射流的不稳定,使工件切口处的重铸层的厚度变的不均匀。根据上述结论提出了解决水射流不稳定的加工方法。

In order to study the rule of thermal damage zone of K424 superalloy processed with water-jet guided laser technology,the thin sheet of K424 superalloy is drilled on a self-developed water-jet guided laser processing system with the method of rotary cutting.After the material is penetrated,the laser needs to rotate several times closed to the hole wall to remove the edge burr.The cut circular workpiece was inlaid,polished,etched and cleaned.The scanning electron microscope(SEM)was employed to analyze the situation of the heat affected zone and evaluate the thickness of the recast layer on the workpiece.The experimental result shows that the grains at the edge of the workpiece have no obvious change and therefore there is no heat affected zone.The thickness of the recast layer is more than 2μm but uneven,and the edge of the workpiece don′t have recast layer in some locations.It is indicated that relevant parameters such as high laser power or long laser pulse width time can lead to excess heat inside the workpiece.If there is too much heat,it will form the heat affected zone near the processing location,and generate excess slag which increase the thickness of the recast layer.Meanwhile,the instability of water jet will be caused by factors such as water column reflux or poor drainage caused by excessive slag in the process.Thus,the thickness of the recast layer becomes uneven.According to the above conclusions,a machining method to solve the instability of water jet is put forward.