以轧制态、铸态、铸后均匀化三种状态的Inconel-718镍基合金薄板为对象, 进行钨极氩弧焊(TIG)接头部分熔化区(PMZ)的研究. 通过OM, SEM, EDS等手段观测不同焊接线能量下PMZ的微观组织. 通过EDS测得晶内奥氏体、偏析区、Laves相的合金元素含量后, 采用热力学软件Themo-Calc计算其理论固液相线温度, 比较当母材状态不同时焊接接头PMZ各相的液化及凝固温度, 分析液膜存在的温度范围大小. 结果表明, Inconel-718镍基合金TIG焊接接头PMZ存在微观组织遗传性, 铸态、铸后均匀化接头PMZ中仍然保持树枝晶的结构特征, 而轧制态接头PMZ中仍是等轴晶. 接头PMZ中皆析出链状Laves和颗粒状MC相, 母材中原有偏析区消失. 铸态母材固液相线间距最大, 铸后均匀化的次之, 轧制态的最小. 当母材状态、几何尺寸相同时, 随着焊接线能量的增加, PMZ宽度增大. 当焊接线能量相同时, 铸态PMZ宽度大于铸后均匀化和轧制态PMZ宽度.

Element segregation, such as Nb in Ni-based Inconel-718 superalloy, causes the precipitation of low melting point phase during solidification. The actual base metal can melt in a lower temperature and the structural continuity is damaged during welding thermo cycle curve. The liquid film easily generates between austenite grains and leads to stress concentration before solidifying into the low melting point phase. Microstructure evolution of Inconel-718 welding joint increases the hot crack sensitivity and changes mechanical property of the joint. The partially melted zone (PMZ) is close to the molten metal in the fusion zone, which is the most liquation crack sensitive region of welding joint heat affected zone (HAZ). Different microstructures exists among wrought, as-cast and homogenization Inconel-718 superalloy inducing weldability differences of these material. Especially, the solidus-liquidus curve differences of low melting point phase in PMZ notably affect the high temperature mechanical property of welding joint. The wrought, as-cast and homogenization Inconel-718 superalloy sheets were respectively welded by tungsten inert gas arc welding (TIG) with different heat inputs. The microstructure of PMZ was observed by OM and SEM. Alloy element content of intradendritic austenite, interdendritic segregated region and Laves phase was investigated by EDS. The theoretical solidus-liquidus temperature of these phases was calculated by Thermo-Calc software. The melting and solidification temperature of austenite and Laves in PMZ of different base metal was investigated to analyze the temperature range for the formulation of liquid film. The results show that the microstructure heredity phenomenon obviously exists in the PMZ of Inconel-718 welding joint. The equiaxed grains remain in the PMZ of wrought joint, and the dendritic structure is still kept in the PMZ of as-cast and homogenization joint. The slender Laves and particle MC phase precipitate along the boundary of the austenite in PMZ of welding joint. But the segregated region originally existed in base metal disperses. The calculating results show that the maximum solidus-liquidus temperature range is in as-cast base metal, secondary in homogenization, minimum in wrought. The width of PMZ is increased with the increasing heat input and PMZ of as-cast is larger than PMZ of wrought and homogenization Inconel-718 superalloy.