Precipitate hardening is considered as an effective method to strengthen High-and medium-entropy alloys(HEAs and MEAs),especially the recently developed Co-free HEAs/MEAs,In this work,a systematic study on precipitati...Precipitate hardening is considered as an effective method to strengthen High-and medium-entropy alloys(HEAs and MEAs),especially the recently developed Co-free HEAs/MEAs,In this work,a systematic study on precipitation and mechanical behaviors of a Co-free HEAs with dilute amount of Al addition,Ni_(47-x)Fe_(30 C)r_(12)Mn_(8) Al_(x)Ti_(3)(x=2 at.%,5 at.% and 7 at.%),is presented.Results shown that the Ni_(45)Fe_(30)Cr_(12)Mn_(8) Al_(2) Ti_(3) has a face-centered cubic(FCC)+L1_(2)+η three-phased structure.With increasing Al content,the formation of η phase is inhibited,accompanying with an enhanced formation of B2 phase,and FCC+L1_(2)+B2 three-phased structure is thus observed in alloys with x=5 and 7.The constrained lattice mismatch between FCC matrix and L1_(2) precipitates is decreased with increasing Al content,leading to an enhanced precipitation behavior of L1_(2) phase.As a result of microstructural evolution,the mechanical properties of the aged HEAs changed:the Ni_(42)Fe_(30)Cr_(12)Mn_(8) Al_5 Ti_(3) alloy exhibits a better combination of a yield strength of 661 MPa and tensile ductility of 29.7% as compared to the 2 at.% Al alloyed HEA;and addition of Al beyond 5 at.% results in an increase of strength with a large expense of ductility.We believe that the present work is helpful for developing high-performance Co-free HEAs/MEAs strengthened by nanoprecipitates via composition optimizing.展开更多
The evolution of ferrite grain and cementite lamella during cold rolling in a granular carbide–pearlite steel has been investigated.Particular attention has been given to a quantitative characterization of changes in...The evolution of ferrite grain and cementite lamella during cold rolling in a granular carbide–pearlite steel has been investigated.Particular attention has been given to a quantitative characterization of changes in the ferrite grains.Electron backscattered diff raction and transmission electron microscopy observations show that the ultrafi ne ferrite(~388 nm)can be produced through low equivalent strain cold rolling without severe plastic deformation(SPD)and annealing.The average grain size of ferrite depends on the volume fraction,shape and distribution of granular carbides as well as interlamellar spacing of pearlite.A general explanation of granular carbides-assisted grain refi nement is that the embedded carbides between natural barrier will signifi cantly facilitate dislocation nucleation during cold rolling.Dislocation reaction occurs more drastically and quickly near these granular carbides.Such reactions promote the formation of high-angle grain boundaries.The formation of ultrafi ne ferrite grains and subgrains in steel after cold rolling toε=1.4 strain makes the strength and ductility increased simultaneously compared withε=0.6 cold-rolled steel.The results suggest a new material design strategy to obtain ultrafi ne-grained structure via the granular carbides assistance.展开更多
基金financially supported by the National Major Science and Technology Project of China (No. 2014ZX07214-002)the National Natural Science Foundation of China (No. 52001201)。
文摘Precipitate hardening is considered as an effective method to strengthen High-and medium-entropy alloys(HEAs and MEAs),especially the recently developed Co-free HEAs/MEAs,In this work,a systematic study on precipitation and mechanical behaviors of a Co-free HEAs with dilute amount of Al addition,Ni_(47-x)Fe_(30 C)r_(12)Mn_(8) Al_(x)Ti_(3)(x=2 at.%,5 at.% and 7 at.%),is presented.Results shown that the Ni_(45)Fe_(30)Cr_(12)Mn_(8) Al_(2) Ti_(3) has a face-centered cubic(FCC)+L1_(2)+η three-phased structure.With increasing Al content,the formation of η phase is inhibited,accompanying with an enhanced formation of B2 phase,and FCC+L1_(2)+B2 three-phased structure is thus observed in alloys with x=5 and 7.The constrained lattice mismatch between FCC matrix and L1_(2) precipitates is decreased with increasing Al content,leading to an enhanced precipitation behavior of L1_(2) phase.As a result of microstructural evolution,the mechanical properties of the aged HEAs changed:the Ni_(42)Fe_(30)Cr_(12)Mn_(8) Al_5 Ti_(3) alloy exhibits a better combination of a yield strength of 661 MPa and tensile ductility of 29.7% as compared to the 2 at.% Al alloyed HEA;and addition of Al beyond 5 at.% results in an increase of strength with a large expense of ductility.We believe that the present work is helpful for developing high-performance Co-free HEAs/MEAs strengthened by nanoprecipitates via composition optimizing.
基金supported by the Major Project for National Science and Technology of China(No.2014ZX07214-002)the BAOSTEEL-SJTU Joint Research Center for Future Steelfinancial support from the Startup Fund for Youngman Research at SJTU(No.SJTU.18X100040023)。
文摘The evolution of ferrite grain and cementite lamella during cold rolling in a granular carbide–pearlite steel has been investigated.Particular attention has been given to a quantitative characterization of changes in the ferrite grains.Electron backscattered diff raction and transmission electron microscopy observations show that the ultrafi ne ferrite(~388 nm)can be produced through low equivalent strain cold rolling without severe plastic deformation(SPD)and annealing.The average grain size of ferrite depends on the volume fraction,shape and distribution of granular carbides as well as interlamellar spacing of pearlite.A general explanation of granular carbides-assisted grain refi nement is that the embedded carbides between natural barrier will signifi cantly facilitate dislocation nucleation during cold rolling.Dislocation reaction occurs more drastically and quickly near these granular carbides.Such reactions promote the formation of high-angle grain boundaries.The formation of ultrafi ne ferrite grains and subgrains in steel after cold rolling toε=1.4 strain makes the strength and ductility increased simultaneously compared withε=0.6 cold-rolled steel.The results suggest a new material design strategy to obtain ultrafi ne-grained structure via the granular carbides assistance.
