Deformation kinking as an uncommon plastic deformation mechanism has been reported in several materials while the relevant microstructure evolution and grain refinement behavior at a large strain remain unclear so far...Deformation kinking as an uncommon plastic deformation mechanism has been reported in several materials while the relevant microstructure evolution and grain refinement behavior at a large strain remain unclear so far.In this study,the issue was systematically investigated by utilizing cold forging to impose severe plastic deformation(SPD)on Ti-11 V metastableβ-Ti alloys.It is found that the formation of kink bands experiences dislocation gliding,pre-kinking and the ripening of pre-kinks in sequences.The kink bands are subsequently thickened through the coalescence of multiple kink bands in a manner of high accommodation.Ordinary dislocation slip is developed as a dominant deformation mechanism when deformation kinking is exhausted.The resulting grain refinement involves transverse breakdown and longitudinal splitting of dislocation walls and cells,which fragment kink bands into smallβ-blocks.Further refinement of theβ-blocks is still governed by dislocation activities,and finally nanograins with a diameter of~15 nm are produced at a large strain of 1.2.Alternatively,it is revealed that nanocrystallization is highly localized inside kink bands while the outer microstructure maintains original coarse structures.Such localized refinement characterization is ascribed to the intrinsic soft nature of kink bands,shown as low hardness in nanoindentation testing.The intrinsic softening of kink bands is uncovered to originate from the inner degraded dislocation density evidenced by both experimental measurement and theoretical calculation.These findings enrich fundamental understanding of deformation kinking,and shed some light on exploring the deformation accommodation mechanisms for metal materials at large strains.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51871176,51722104,51922017,51972009)the National Key Research and Development Program of China(Nos.2017YFA0700701,2017YFB0702301)+2 种基金the 111 Project 2.0 of China(No.PB2018008)Natural Science Basic Research Plan in Shaanxi Province of China(No.2018JM5098)the Fundamental Research Funds for the Central Universities(No.xtr022019004)。
文摘Deformation kinking as an uncommon plastic deformation mechanism has been reported in several materials while the relevant microstructure evolution and grain refinement behavior at a large strain remain unclear so far.In this study,the issue was systematically investigated by utilizing cold forging to impose severe plastic deformation(SPD)on Ti-11 V metastableβ-Ti alloys.It is found that the formation of kink bands experiences dislocation gliding,pre-kinking and the ripening of pre-kinks in sequences.The kink bands are subsequently thickened through the coalescence of multiple kink bands in a manner of high accommodation.Ordinary dislocation slip is developed as a dominant deformation mechanism when deformation kinking is exhausted.The resulting grain refinement involves transverse breakdown and longitudinal splitting of dislocation walls and cells,which fragment kink bands into smallβ-blocks.Further refinement of theβ-blocks is still governed by dislocation activities,and finally nanograins with a diameter of~15 nm are produced at a large strain of 1.2.Alternatively,it is revealed that nanocrystallization is highly localized inside kink bands while the outer microstructure maintains original coarse structures.Such localized refinement characterization is ascribed to the intrinsic soft nature of kink bands,shown as low hardness in nanoindentation testing.The intrinsic softening of kink bands is uncovered to originate from the inner degraded dislocation density evidenced by both experimental measurement and theoretical calculation.These findings enrich fundamental understanding of deformation kinking,and shed some light on exploring the deformation accommodation mechanisms for metal materials at large strains.
