Fatigue-creep Interaction Behvior Of Incoloy 825 Nickel-based Superalloy

Incoloy 825 nickel-based superalloy,with outstanding mechanical performances,oxidation and corrosion resistances,is widely used in the aerospace,gas turbine and nuclear power industries.As the material used for the high temperature components,Incoloy 825nickel-based superalloy is often subjected to various harsh working conditions.The fatigue-creep interaction is one of main failure modes during the operation of components.In this investigation,the fatigue-creep interaction behavior of Incoloy 825 nickel-based superalloy was studied under the strain controlled loading mode with introducing the tensile,compressive,and tensile-compressive strain hold time at 650°C.The cyclic stress response behavior,fatigue-creep life behavior and cyclic stress-strain behavior of the alloy were clarified,and the corresponding strain fatigue parameters were given.The dislocation substructures and fracture surface morphologies after the fatigue-creep deformation for the alloy were observed and analyzed with the transmission electron microscope(TEM)and scanning electron microscope(SEM),respectively,in order to provide a reliable theoretical basis for the anti-fatigue-creep failure design of Incoloy 825 nickel-based superalloy engineering components.The results of fatigue-creep interaction tests show that the Incoloy 825 nickel-based superalloy exhibits the cyclic hardening behavior or cyclic hardening behavior followed by either cyclic softening behavior or cyclic stability during the cyclic deformation with the tensile strain hold time,while the alloy exhibits the cyclic hardening behavior or the cyclic hardening behavior followed by cyclic stability during the cyclic deformation with the compressive and tensile-compressive strain hold time.When the total strain amplitude is the same,the lives of the alloy are the longest for the cycling deformation with introducing the compressive strain hold time,the longer for the cycling deformation with introducing the tensile strain hold time,and the shortest for the cycling deformation with introducing the tensile-compressive strain hold time.Under three cyclic waveforms with introducing the strain hold time,the relationship between both plastic and elastic strain amplitudes with reversals to failure for the alloy shows a single slope linear behavior,which can be described by the Coffin-Manson and Basquin equations,respectively.The observation and analysis results on the microstructures as well as the crack initiation and propagation modes of the alloy after the fatigue-creep deformation under different loading conditions reveal that the deformation mechanism of the alloy is mainly the planar slip.In the alloy subjected to the cyclic deformation,such dislocation substructures as the dislocation array,dislocation entanglement and dislocation wall can be observed.In addition,the cracks initiate and propagate in the transgranular mode during the fatigue-creep loading.