Coarsening Kinetics Of Cubic ?' Precipitates During Thermal Exposure And Stress Rupture Mechanical Behavior Of DD5 Single Crystal Superalloy

In this dissertation,the coarsening kinetics study of cubic ?'precipitates during thermal exposure has been conducted on the second generation DD5 single crystal superalloy by means of scanning eletrcon microscope(SEM)and electron probe micro-analyzer(EPMA).As well as high-temperature stress rupture behavior and the corresponding microstructural deformation mechanisms and fracture analysis of DD5 single crystal superalloy have been studied by way of scanning electron microscope(SEM)and transmission electron microscope(TEM).In this experiment,there is no topologically close-packed(TCP)phase precipitated in the DD5 alloy during thermal exposure,which demonstrates that the DD5 alloy shows good structure stability.It is found that the cubic ?' precipitates growth during thermal exposure allows to the classici LSW theory and the calculation of the activation energy Q of coarsening kinetics of cubic ?' precipitates,which quantificationally confirms the controlling factors of growth of cubic ?' precipitates in this DD5 alloy is that the oppositely coupled diffusion between?' phase forming elements and y phase forming elements.The big difference in the stress rupture properties under the conditions of 900?/445MPa and 1100?/100MPa of DD5 alloy indicates the different deformation mechanism and fracture process occurred at the two conditions,respectively.The fromer dominant deformation mechanism is the dislocation slipping in the matrix channels and the crack propagation along the ?/? interface due to the coupling interaction of vacancies and ?/? interface dislocations.The latter dominant deformation mechanism is the ?/?' interface dislocations sliping and climbing and the crack propagation cross the ?-?' phases.The event of script-shape M23C6 caribde cracked in the early stage of deformation limits the stress rupture lifetimes at 900?/445MPa,while the occurrence of topological inversion of ?-?' microstructure leads to the short elongation under 1100?/100MPa.DD5 alloy with[001],[011]and[111]orientations exhibits the strong stress rupture behaviour anisotropy both under the conditions of 900?/445MPa and 1100?/100MPa.The main reason is the orientation dependence of Schmid factor(SF)of{111}<110>or{111}<112>slip systems and the number of activated slip systems,as well as the difference in the regular degree of ?/?' interface dislocations networks and the extent of hindering to matrix dislocation cutting into the ?' phase between the three main orientations.In addition,the fracture process of the three main orientations under 900?/445MPa and 1100?/100MPa is thought to be plasticity deformation type microvoid acccumulation fracture and cavanics and plasticity deformation coupling type microvoid accumulation fracture,respectively.