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

采用氦离子注入和YAG激光焊接工艺，研究了掺氦SUS 316L奥氏体不锈钢焊接件中氦气泡的形成.采用8 MeV的氦离子注入装置对样品进行了氦离子注入，在6 MeV时，样品（Heat（A））的掺杂量为2.45 × 10^<19>atoms/m^2，<19>在5 MeV时，样品（Heat（B））的掺杂量为1 × 10 ^ atoms/m^2，在2.0MeV时，样品（Heat（A））的掺杂量为9.0 × 10 ^atoms<18>/m^2，在2.3MeV时，样品（Heat（B））的掺杂量为9.5 × 10 ^<18>atoms/m^2，在2.6MeV时，样品（Heat（B））的掺杂量为1.0 × 10^<19>atoms/m^2.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，主要在热影响区与焊缝金属的结合区附近出现直径大于2 μ m的大氦泡.在高激光功率下，虽然焊缝中氦含量降低，但在熔合区仍会形成较大的氦泡，导致焊趾裂纹的产生;透射电镜观察到焊缝金属中枝晶胞界处存在细小的氦泡;在交叉焊道补焊中，第一焊道与第二焊道之间的交叉区域也存在氦泡。

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.