真空电子束焊接气孔缺陷诱发及平衡机制分析

Study on inducement and equilibrium mechanism of pore defects in vacuum electron beam welding

针对真空电子束焊接试验焊缝出现的气孔缺陷,从受力平衡的角度分析了气孔的诱发机制及热力学平衡机理,提出了熔池中气孔的最小半径生存条件.结果表明,由气泡动力学的观点,加热面气化核心是诱发气泡的重要因素.不满足最小半径生存条件的气泡不具备热力学平衡条件,因此是无法生存的,最终不能发展成为气孔.对于产生于焊缝中部壁面的气泡的大小主要取决于气泡内的气体密度、表面张力以及气泡中气相成分的过热度.其中,过热度不但是气泡稳定性的推动力,也是决定气泡大小的主要因素.

Pore defects are the major problem in vacuum electron beam welding.The inducement mechanism and thermodynamic equilibrium mechanism were analyzed from the perspective of force balance condition,and the minimum radius survival conditions for pores in molten pool were proposed.The results showed that the gasification nucleus is an important factor induced bubbles in molten pool from the perspective of bubble dynamics.The bubbles,which don't meet the minimum radius survival condition,do not satisfy the thermodynamic equilibrium condition and therefore can't develop into the pores.The size of the bubbles generated on the wall of middle part of weld depends largely on the gas density in bubble,surface tension of bubble,and overheating of gas-phase components in bubble.The overheating is not only a driving force for bubble stability,but also a main factor determining the bubble size.