锆合金焊缝在酸性环境中的应力腐蚀损伤机制研究

Stress Corrosion Deterioration Mechanism of Zirconium Alloy Welding in Acidic Environment

采用超景深光学显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)、显微硬度计对锆合金702焊缝的显微组织与力学性能进行观察和分析;对锆合金焊缝的铆钉连接工况及塑性变形进行模拟,分析其对锆合金焊缝在5 mol·L^(-1)的醋酸溶液中腐蚀损伤的影响,研究了氢对锆合金焊缝在5 mol·L^(-1)的醋酸溶液中腐蚀损伤的影响。结果表明:焊缝金属为等轴晶状组织,焊缝和热影响区没有发生硬化和脆化现象,焊接过程中发生了铁离子污染,在酸性腐蚀介质中产生了均匀腐蚀,为应力腐蚀裂纹的产生提供了加速条件。铆钉的使用使连接处不仅有塑性变形,而且还产生了应力,较大的塑性变形容易使表面氧化膜破裂,加快了锆合金在酸性腐蚀介质中的溶解。服役环境中存在的大量氢气进一步促进了较大应力的产生和微观缺陷的扩展,在应力和酸性介质的工作条件下产生了沿晶扩展的应力腐蚀裂纹,导致锆合金焊缝损伤失效。

The microstructures and mechanical properties of zirconium alloy 702 welding were observed and analyzed by ultra-depth optical microscope （OM）, scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS） and microhardness test. The condition of rivet connection and plastic deformation of zirconium alloy welding were simulated, and the impact on the corrosion and damage of zirconium alloy welding in 5 mol.L-1 acetic acid were analyzed. The effect of hydrogen on the corrosion and damage of zirconium alloy welding was also studied. The results showed that the equiaxial as-cast microstructures existed in the welding metal. There was no hardening and embrittlement phenomenon in welds and heat affected zone. Iron contamination occurred during welding, and produced a uniform corrosion in acidic corrosive media, providing a stimulative condition for stress corrosion cracking. Rivets used for connection produced plastic deformation as well as stress. Large plastic deformation could easily break the surface oxide film, which accelerated the dissolution of zirconium alloy in acidic medium. Large amount of hydrogen presented in the service environment promoted the generation of large stress and the expansion of microscopic defects. Stress corrosion cracking in a way of intergranular extensible occurred in the conditions of stress and acidic medium, resulting in destruction of the zirconium alloy welding.