Influence Of Misorientation On Creep Behavior Of A Single Crystal Nickel-based Superalloy

In the paper, the influences of misorientation and temperature on microstructure and creep properties of [001] orientation single crystal nickel-based superalloy were investigated by means of creep property measurment and SEM observation. And the deformation mechanisms and microstructure evolution of the alloy during creep were discussed by means of TEM observation and dislocation configuration analysis.The results show that, during higher applied stress and strain, the main slip system (111)[0?11] and secondary slip system (11?1)[011] are successively activated in turn to increase the strain of the alloy. When tha main slip system operates until continuing slip is unfavoured, the secondary system operates and cuts the main slip bands, thereafter, the main slip system again and cuts the secondary slip bands until the cracks is initiated at the slipping traces intersecting region, and propagated along the {111} slipping planes, which is thought to be the mian deformed mechanisms during higher applied stress and strain. During creep at 760℃/810MPa conditions, theγ′phase in the alloy is transformed into the unintegrated rafted structure, and the creep feature of the alloy displays an obvious dependence of the misorientation. Thereinto, the alloy with 12°and 6°misorientations possesses a lower strain rate and longer creep lifetime, and the one with 7°misorientation possesses a higher strain rate and shorter creep lifetime. No obvious dependance of misorientation is detected in the alloy during creep at 980℃/300MPa and 1070℃/160MPa conditions. The deformed mechanisms of the alloy during creep at 760℃/810MPa is <110> super-dislocation shearing into theγ′phase, and the <110> super-dislocation which shears into theγ′phase may be decomposed to form the configuration of (1/3)<112> super-Shockleys partial dislocation + stacking fault. During creep at 980℃/300MPa and 1070℃/160MPa conditions, theγ′phase in the alloy is transformed into the integrated rafted structure, and the deformation mechanisms of the alloy during creep are (1/2)<110> dislocation shearing into theγphase and <110> super dislocation shearing into theγ′phase, respectively, thereinto, in the former, a few <110> super-dislocation which shears into theγ′phase is decomposed to form the configuration of (1/2)<110> super partial dislocation + stacking fault.In the later stage of creep at 760℃/810MPa conditions, the two systems of the main/secondary slipping are alternately operated, which promotes the micro-cracks initiated at the region of the intersected each other, and propagated along the (111) slipping planes to occur the cleavage fracture. In the later stage of creep at high temperature, the cracks are initiated at theγ′/γphases interfaces, and propagated along the interfaces, which is thought to be the fracture mechanism of the alloy during creep.