This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process.An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a co...This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process.An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a controlled manner and subsequently electropulsed to investigate the changes in microstructure and defect configuration.AISI 1020 steel was chosen as it has a simple microstructure(plain ferritic)and composition with low alloying conditions.It is an appropriate material to study the effect of trans-mitting electric pulses on the microstructural defect evolution.A combination of electron-backscattered diffraction and transmission electron microscopy proved to be an effective tool in characterizing the post-electropulsing effects critically.By application of electropulsing,a reduction in the surface residual stress layer was noticed.Also,reductions in misorientation and dislocation density together with the disentan-glement of dislocations within the cold-worked layer were observed after electropulsing.Additionally,the annihilation of shot-peening-induced deformation bands beyond the residual layer depth was observed.These effects have been rationalised by taking into account the various possibilities of athermal effects of electropulsing.展开更多
The annealing tests heated by pulsed current(PC)or furnace for AZ31B magnesium sheets were carried out,and the effects of PC on the microstructure and dislocation density of the alloy were analyzed.The results show th...The annealing tests heated by pulsed current(PC)or furnace for AZ31B magnesium sheets were carried out,and the effects of PC on the microstructure and dislocation density of the alloy were analyzed.The results show that PC strengthens the migration of boundaries,and then the twin grains,most of which distribute in the coarse grains,“spheroidize”to equiaxed grains,thus separating the coarse grains and refining the microstructure.This process homogenizes the initial microstructure and eliminate the typically lamellar twin grains.Moreover,PC also strengthens the dislocation annihilation.When the specimens were annealed by PC at 300℃for 4 min,the dislocation density was even lower than that annealed by furnaces at 400℃for 3 h before deformation.Furthermore,dislocation annihilation is enhanced with the increase of peak current density and the decrease of pulsed frequency.展开更多
Creep behavior of Fe-15Cr-25Ni alloys with different grain boundary features has been in- vestigated at 850 and 950℃ and in stress range of 14.7～78.5 MPa.The single phase alloy exhibits typical recovery creep charac...Creep behavior of Fe-15Cr-25Ni alloys with different grain boundary features has been in- vestigated at 850 and 950℃ and in stress range of 14.7～78.5 MPa.The single phase alloy exhibits typical recovery creep characteristics,and for the alloy in which M_(23)C_6 carbides densely precipitate at grain boundaries,the creep rate dramatically decreases and creep behav- ior is also significantly different from the single phase alloy.When the carbides precipitate at grain boundaries,the dislocation density are higher and the size of subgrains near grain boundaries are smaller than those of single phase alloy.The creep mechanisms for two grain boundary features have been discussed.展开更多
基金supported by the National Research Foundation of Singapore,Rolls-Royce Singapore Pte.Ltd.,and Nanyang Technological University through grants#002123-00009 and #002124-00009.
文摘This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process.An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a controlled manner and subsequently electropulsed to investigate the changes in microstructure and defect configuration.AISI 1020 steel was chosen as it has a simple microstructure(plain ferritic)and composition with low alloying conditions.It is an appropriate material to study the effect of trans-mitting electric pulses on the microstructural defect evolution.A combination of electron-backscattered diffraction and transmission electron microscopy proved to be an effective tool in characterizing the post-electropulsing effects critically.By application of electropulsing,a reduction in the surface residual stress layer was noticed.Also,reductions in misorientation and dislocation density together with the disentan-glement of dislocations within the cold-worked layer were observed after electropulsing.Additionally,the annihilation of shot-peening-induced deformation bands beyond the residual layer depth was observed.These effects have been rationalised by taking into account the various possibilities of athermal effects of electropulsing.
基金Project(51635005)supported by the National Natural Science Foundation of China
文摘The annealing tests heated by pulsed current(PC)or furnace for AZ31B magnesium sheets were carried out,and the effects of PC on the microstructure and dislocation density of the alloy were analyzed.The results show that PC strengthens the migration of boundaries,and then the twin grains,most of which distribute in the coarse grains,“spheroidize”to equiaxed grains,thus separating the coarse grains and refining the microstructure.This process homogenizes the initial microstructure and eliminate the typically lamellar twin grains.Moreover,PC also strengthens the dislocation annihilation.When the specimens were annealed by PC at 300℃for 4 min,the dislocation density was even lower than that annealed by furnaces at 400℃for 3 h before deformation.Furthermore,dislocation annihilation is enhanced with the increase of peak current density and the decrease of pulsed frequency.
文摘Creep behavior of Fe-15Cr-25Ni alloys with different grain boundary features has been in- vestigated at 850 and 950℃ and in stress range of 14.7～78.5 MPa.The single phase alloy exhibits typical recovery creep characteristics,and for the alloy in which M_(23)C_6 carbides densely precipitate at grain boundaries,the creep rate dramatically decreases and creep behav- ior is also significantly different from the single phase alloy.When the carbides precipitate at grain boundaries,the dislocation density are higher and the size of subgrains near grain boundaries are smaller than those of single phase alloy.The creep mechanisms for two grain boundary features have been discussed.
