DD8单晶镍基高温合金热机械疲劳后的微观结构

MICROSTRUCTURES OF DD8 SINGLE CRYSTAL NICKEL BASE SUPERALLOY AFTER THERMOMECHANICAL FATIGUE

透射电镜(TEM)观察表明,DD8单晶镍基高温合金经过热机械疲劳(TMF)后,在同位相(IP)和反位相(OP)加载的条件下,合金内部的位错组态和γ′沉淀相的形貌有很大的区别,在IP加载条件下,垂直应力轴的,γ/γ′相界面上存在着密集的六角形位错网,平行应力轴的相界面上存在的是四边形的位错网,而且在小机械应变幅下,γ′相出现明显的筏化现象,并且随着应变幅的增加,γ′沉淀相的筏化现象也越来越不明显,在OP加载条件下,在γ/γ′相界面上则没有位错网被观察到,γ′被层错剪切,并且没有明显的筏化出现。

The microstructures of DD8 single crystal nickel base superalloy were observed by TEM before and after thermo-mechanical fatigue. It is found that both dislocation configurations and gamma' precipitate morphologies under in phase(IP) testing are obvious different from that under out of phase(OP) testing. Under IP testing, dense hexagonal dislocation networks exist on the gamma/gamma' interfaces normal to the stress axis, and rectangular dislocation networks exist on the gamma/gamma' interfaces parallel to the stress axis. With decreasing mechanical strain amplitude rafting of the gamma precipitates is more pronounced. Under OP testing, no dislocation network is found on the gamma/gamma' interfaces, gamma precipitates are sheared by superlattice stacking faults, and not rafted obviously.