高温合金皮秒激光旋切制孔孔壁特征研究(英文)

Characteristic of Hole Wall Trepanning by Picosecond Laser in Superalloy

研究了脉宽为2.1 ps的超短激光采用旋切法在不同厚度Ni3Al基定向凝固高温合金试样上,加工气膜孔的孔壁形貌。实验表明,孔壁上出现了周期性的条纹结构,条纹间距约为15μm,是由激光在孔壁上形成的烧蚀通道组成。在加工1 mm厚的合金试样上的气膜孔时,孔壁光滑而且不存在再铸层,孔形整体几乎无锥度。当加工2 mm厚试样上的气膜孔时,孔入口附近的孔壁上出现了厚度在2μm到5μm之间的再铸层。通过不同厚度试样加工情况的对比,在旋切加工条件下,脉宽2.1 ps的激光不会引起热传递现象,2 mm厚试样上的气膜孔孔壁再铸层是由加工过程中等离子从深孔中排出距离过长,从而速度下降,沉积在入口孔壁上所形成。孔壁再铸层中所含的氧元素是由等离子体与辅助气中的氧气反应形成。在不同厚度试样上的气膜孔的入口处都出现了宽度约5μm的熔融区。在皮秒激光加工不引起热传递的情况下,通过激光束截面的能量分布情况与激光辐射区域温度变化的关系,计算出了熔融区的宽度值为4.7μm,与实际相符。

Picosecond laser trepanning drilling of the directional solidification Ni3Al-based superalloy of different thickness has been studied.The experiment demonstrates that there are periodic stripes in the hole wall,of which the interval is about 15 μm.The stripes is the path formed by the laser ablation.It is showed that when the film-hole is drilled in 1mm thick alloy,the hole wall almost has no taper and no recast layer exists,while the thickness of alloy is 2 mm,the hole wall near the entrance appears a recast layer,of which thickness ranges from 2 μm to 5 μm.By comparison,the recast layer is mainly caused by the plasma deposited in the hole wall when the laser pulse width is 2.1 ps,and the reason of recast layer containing oxygen is that plasma and the oxygen of compressed air react chemically and deposits on the hole wall.In the surface of entrance of different thickness alloy,there is molten area of 5μm wide around the entrance of hole.Considering that the thermal diffusion can be ignored when the laser pulse width is 2.1 ps,the molten area can be explained according to the corresponding relationship between the temperature distribution of irradiated area and energy distribution of cross section of laser beam,and the width of molten area of entrance was calculated,it is in line with the actual width.