摘要
In this paper,the microstructure evolution and tensile behavior of wrought ATI 718 Plus superalloy during long-term thermal exposure(LTTE) were investigated.The γ’ phase evolves from spherical morphology to cuboidal morphology at 800℃,which is related to increasing γ’/γ misfit because of the increase of elastic energy.The amounts of η phase obviously increased and γ’ precipitate free zones(PFZs) were found in 800-LTTE samples due to the increase of η phase amount by consuming Al,Ti,and Nb.According to the formula of “MC+γ→M_(23)C_(6)+η”,η phase is also related to the decomposition of MC carbide,which involves the diffusion and segregation of Nb and Ti.In addition,some short rod-like and irregular Cr,Mo-rich σ phases were prone to precipitate near η phases after LTTE at 800℃ for 500 and 1000 h.σ phase has a crystallographic relationship with ηphase as(002)_(σ)//(10■0)_(η),[0■0]_(σ)//[01■0]_(η).The deteriorated tensile strength after LTTE is mainly attributed to that:(1) the evident coarsening of γ’ phase results in that the deformation mechanism transforms from stacking faults(SFs) shearing to Orowan looping,which is also convinced by calculated critical resolved shear stress(CRSS);(2) the noticeable increasing number of η phase contributes to stress concentration,resulting in micro-cracks formation;and (3) the apparently increasing number of η phase promotes the PFZs formation.
基金
supported by the National Natural Science Foundation of China (Grant Nos.52034004,51974201&52122409)。
