Behavior of Helium Bubble in Laser Weldment of Helium Ion Implanted Stainless Steel

采用氦离子注入和激光焊接的方法，研究了掺氦SUS316L奥氏体不锈钢焊件中氦气泡的形成。氦离子注入是用8 MeV注入装置进行的，样品(热(A))在6 MeV掺杂2.45×10^；lt；19；原子/m^2，然后在5 MeV掺杂lx10^；lt；19&gt；19&gt；用蒙特卡罗模拟和高斯分布方法计算了2.6 MeV下的氦浓度分布。当激光功率较低且满足快速冷却条件时，焊缝金属体积变小，焊缝金属中氦的平均浓度增加，在热影响区与焊缝金属的结合区附近主要形成直径大于2微米的较大氦气泡。在高功率激光作用下，虽然焊件的氦气含量降低，但在焊合区形成了较大的氦气泡，导致了焊趾裂纹的发生；通过透射电子显微镜观察到，焊缝金属的枝晶细胞边界处有细小的氦泡；在交叉堆焊补焊时，在第一道和第二道焊道的交叉处也观察到了氦泡。

The formation of helium bubble in helium-doped SUS316L austenitic stainless steel weldments was investigated, by procedures in which the stainless steel was helium ion-implanted and then welded by YAG laser apparatus.1. Helium ion implanting to the sample was carried out using 8MeV implantation apparatus.The samples (Heat (A)) were doped 2.45x 10^<19> atoms/m^2 at 6MeV and then lx 10^<19> atoms/m^2 at 5MeV, and the samples (Heat (B)) were doped to 9.0x10^<18> atoms/m^2 at 2.0MeV, 9.5x 10^<18> atoms /m^2 at 2.3MeV and 1.Ox 10^<19> atoms/m^2 at 2.6MeV.The helium concentration distribution was calculated using Monte Carlo Simulation and Gauss distribution method.2. When laser power is low and rapid cooling conditions are satisfied, the volume of weld metal becomes small, and a mean helium concentration in the weld metal is increased.Very large helium bubbles more than 2 mum in diameter were present mainly near the bond region between the heat affected zone and the weld metal.3. At high laser power, large helium bubbles are formed at the bond region, which lead to the occurrence of toe cracks, although the helium level of the weldment is decreased.Fine helium bubbles were observed at the dendrite cell boundaries in the weld metal by transmission electron microscopy.Helium bubbles were also observed at the crossing region between the first bead and the second bead in the cross bead repair welding.