纳米Al2O3对Ni基合金激光抛光表面光洁度的影响

为提高激光抛光表面光洁度,采用1 070nm,200W光纤激光器(SPI激光器SP-200C-A-A6-A-C)进行激光抛光实验。首先在电镀纯Ni样品上进行实验,采用相同的参数对Ni/Al_2O_3(4.4%,体积百分比)纳米复合材料进行激光抛光。在其他参数相同的情况下,通过改变激光能量密度进行实验,最后通过形貌和微观结构表征研究Al_2O_3纳米颗粒对Ni抛光性能的影响,再利用光学和热物理性质对激光熔化进行了数值模拟。结果表明,在最佳激光抛光工艺条件下,Ni/Al_2O_3的表面粗糙度由323nm降低到72nm,纯Ni的表面粗糙度由254nm降低到107nm。在纳米颗粒的帮助下,标准化表面粗糙度降低了近2倍。激光加工区截面的微观结构研究表明,通过添加Al_2O_3纳米粒子,激光熔化区(MZ)深度从1.8μm增加到3.2μm,而热影响区(HAZ)的大小从8.4μm显著减小到2.9μm。激光抛光中通过纳米粒子调节熔池动力学,克服了激光抛光的基本限制。随着纳米粒子对热物理性质的改变,热毛细流动的开始发生了改变,从而为毛细区提供了更宽的处理窗口。纳米颗粒的增黏作用提高了毛细区的平滑效率。数值模拟进一步证明了纳米颗粒抑制了热传递,增强了表面层内的热积累,从而降低了MZ深度。纳米粒子限制了晶粒的生长,提高了晶粒生长温度,使热影响区缩小。

Effect of Nano-Al2O3 on Laser Polishing Surface Finish of Ni-based Alloy

To improve the surface finish of laser polishing. Laser polishing experiments were carried out with 1070 nm, 200W fiber laser (SPI laser SP-200C-A-A6-A-C). Firstly, experiments were carried out on electroplated pure Ni samples. Laser polishing of Ni/Al2O3(4.4 vol.) nanocomposites was carried out with the same parameters. With the same other parameters, experiments were carried out by changing the laser energy density. Finally, the effect of Al2O3 nanoparticles on the polishing performance of Ni was studied by morphology and microstructure characterization. Laser melting was simulated by using optical and thermophysical properties. The results show that under the optimum laser polishing conditions, the surface roughness of Ni/Al2O3decreases from 323 nm to 72 nm, and that of pure Ni decreases from 254 nm to 107 nm. With the help of nanoparticles, the standardized surface roughness has been reduced by nearly two times. Microstructure study of cross section of laser processing zone shows that by adding Al2O3nanoparticles, the depth of laser melting zone (MZ) increases from 1.8 to 3.2 microns, while the size of heat affected zone (HAZ) decreases significantly from 8.4 microns to 2.9 microns. In laser polishing, the basic limitation of laser polishing is overcome by adjusting the dynamics of molten pool via nanoparticles. With the change of thermophysical properties of nanoparticles, the thermal capillary flow begins to change, which provides a wider processing window for the capillary region. The viscosifying effect of nanoparticles improves the smoothing efficiency of capillary zone. The numerical simulation further proves that nanoparticles inhibit heat transfer and enhance heat accumulation in the surface layer, thus reduce the depth of MZ. Nanoparticles restrict the growth of grains, increase the growth temperature of grains, and narrow the heat affected zone.