GH4169D合金电子束焊接接头显微组织和持久断裂特征

Microstructure and stress rupture characteristic of electron beam welded GH4169D alloy

摘要:

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、30~80nm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10~20nm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,析出相尺寸约为2~6μm,枝晶杆中含有10nm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、快速扩展和瞬断三个阶段,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持久性能的主要原因。

Abstract:

The microstructure of electron beam welded GH4169D alloy was analyzed by optical microscope (OM) and scanning electron microscope (SEM). Micro hardness of fusion zone, heat affected zone (HAZ) and base metal were examined by micro hardness tester. The stress rupture characteristic of electron beam welded GH4169D alloy was researched by stereo microscope (SM) and SEM. The precipitated phases of GH4169D alloy are composed of lamellar η phase about 1~20μm in length, granular γ′ phase in size of 30~80nm, and a small amount of carbonitride. The precipitated phases of heat affected zone are mainly composed of granular γ′ phase in size of 10~20nm and few of η phase on grain boundary. Dendritic structures are formed in fusion zone, Nb, Ti, and Al are extensively rejected into the interdendritic liquid and the eutectic constituents are form in size of 2~6μm. There are fine granular γ′ phase in size of 10nm in gamma dendrites. The micro hardness of base metal is lower than that of heat affected zone and fusion zone. Micro hardness of different zone is depend on the particle size of γ′ phase. Stress rupture process is composed of creep crack growth, rapidly crack growth and final fracture. Intergranular fracture is occurred in creep crack growth zone, mixed of intergranular and transgranular fracture is occurred in rapidly crack growth zone and transgranular fracture is occurred in final fracture zone. The creep crack imitated in the surface of HAZ of weld specimen. Because of low content of intergranular η phase and oxidation of grain boundary in crack tip, the stress rupture life and elongation are lower than those of GH4169D base metal.