GH4169D合金电子束焊接接头显微组织和持久断裂特征

采用金相显微镜和扫描电镜分析了GH4169D合金电子束焊接接头的显微组织,利用显微硬度计测试了母材、热影响区和焊缝的显微硬度,采用体式显微镜和扫描电镜研究了焊接接头持久断裂特征。结果表明,GH4169D母材中的主要析出相为1~20μm长的片层状晶界η相、30~80 nm的颗粒状γ′相和少量的碳氮化物。热影响区中的主要析出相为10~20 nm的颗粒状γ′相,几乎没有晶界η相。焊缝中为枝晶组织,枝晶间存在含有共晶组织的白色析出相,析出相尺寸为2~6μm,枝晶杆中含有10 nm以下的细小颗粒状γ′相。母材的显微硬度低于热影响区和焊缝,不同区域的显微硬度主要受γ′相尺寸的影响。焊接接头的持久断裂过程包括蠕变裂纹扩展、快速扩展和瞬断3个阶段,蠕变裂纹扩展区中为沿晶断裂,快速扩展区中为沿晶和穿晶混合断裂,瞬断区为穿晶断裂。蠕变裂纹扩展起始于试样表面的热影响区,热影响区中晶界η相含量低和裂纹尖端晶界氧化是导致焊接接头持久性能低于母材的主要原因。

Microstructure and stress rupture characteristic of electron beam welded GH4169D alloy

The microstructure of electron beam welded GH4169 D alloy was analyzed by optical microscope(OM)and scanning electron microscope(SEM).Micro hardness of fusion zone,heat affected zone(HAZ)and base metal was examined by micro hardness tester.The stress rupture characteristic of electron beam welded GH4169 D alloy was researched by stereo microscope(SM)and SEM.Results show that The precipitated phases of GH4169 D alloy are composed of lamellarηphase with 1~20μm in length,granularγ′phase with 30~80 nm of size,and a small amount of carbonitride.The precipitated phases of heat affected zone are mainly composed of granularγ′phase with size of 10~20 nm and fewηphase on grain boundary.Dendritic structures form in fusion zone,Nb,Ti,and Al are extensively rejected into the interdendritic liquid and the eutectic constituents form with a size of 2~6μm.There are fine granularγ′phase with a size less than 10 nm in gamma dendrites.The microhardness of base metal is lower than that of heat affected zone and fusion zone.Microhardness of different zones depends on the particle size ofγ′phase.Stress rupture process is composed of creep crack growth,rapid crack growth and final fracture.Intergranular fracture occurs in creep crack growth zone,mixed intergranular and transgranular fracture occur in rapid crack growth zone and transgranular fracture occurs in final fracture zone.The creep crack imitates in the surface of HAZ of weld specimen.Because of low content of intergranularηphase and oxidation of grain boundary in crack tip,the stress rupture life and elongation are lower than those of GH4169 D base metal.