This research studied the mechanisms of Ca and Zn microalloying on the enhancement of ductility of extruded Mg-Gd sheet by combing electron backscattered diffraction and slip trace analysis.The ductility and microstru...This research studied the mechanisms of Ca and Zn microalloying on the enhancement of ductility of extruded Mg-Gd sheet by combing electron backscattered diffraction and slip trace analysis.The ductility and microstructure of extruded Mg-0.6Gd and Mg-0.6Gd-0.3Ca-0.2Zn(wt%)sheets were investigated.Basal slip was the main deformation mode under investigation.Ca and Zn microalloying increased the frequency of grain boundaries(GBs)with misorientation angles(θs)<35°,promoted slip transfer across GBs and restricted the basal slip localization.In addition,there were a higher number of GB cracks homogeneously distributed in the Mg-0.6Gd sheet than in the Mg-0.6Gd-0.3Ca-0.2Zn sheet,attributed to the increased cohesion of GBs.The enhancement of basal slip,the suppression of slip localization and the suppression of GB cracking were contributed to the increased ductility for Mg-0.6Gd-0.3Ca-0.2Zn sheet.展开更多
For TA15 titanium alloy, slip is the dominant plastic deformation mechanism because of relatively high Al content. In order to reveal the grain-scale stress field and geometrically necessary dislocation（GND） density...For TA15 titanium alloy, slip is the dominant plastic deformation mechanism because of relatively high Al content. In order to reveal the grain-scale stress field and geometrically necessary dislocation（GND） density distribution around the slip traces and phase boundaries where the slip lines are blocked due to Burgers orientation relationship（OR） missing. We experimentally investigated tensile deformation on TA15 titanium alloy up to 2.0% strain at room temperature. The slip traces were observed and identified using high resolution scanning electron microscopy（SEM） and electron backscatter diffraction（EBSD） measurements. The grain-scale stress fields around the slip traces and phase boundaries were calculated by the cross-correlationbased method. Based on strain gradient theories, the density of GND was calculated and analyzed. The results indicate that the grain-scale stress is significantly concentrated at phase/grain boundaries and slip traces. Although there is an obvious GND accumulation in the vicinity of phase and subgrain boundaries, no GND density accumulation appears near the slip traces.展开更多
This work investigated the effects of grain size(GS)on individual slip mode activities and the corresponding Hall-Petch coefficients in a rolled basal-textured pure Mg sheet under uniaxial tension using statistical sl...This work investigated the effects of grain size(GS)on individual slip mode activities and the corresponding Hall-Petch coefficients in a rolled basal-textured pure Mg sheet under uniaxial tension using statistical slip trace analysis and electron backscatter diffraction.The studied regions covered a total of 1150 grains,in which 136 sets of slip traces were identified and analyzed in detail.The basalslip always dominated the deformation,whose frequencies decreased(from 81.0%to 62.5%)with increasing GS(from 10 to 85μm).The prismaticslip activity increased from 10.8%(10μm)to 27.5%(85μm),while that for pyramidal II<c+a>slip was almost constant.Critical resolved shear stress(CRSS)ratios were estimated based on the identified slip activity statistics,and then the Hall-Petch coefficients(k)of individual slip modes were calculated.The k value for prismaticslip(194 MPa·μm^(1/2))was lower than that for pyramidal II<c+a>slip(309 MPa·μm^(1/2)),which implies that pyramidal II<c+a>slip was more GS sensitive.Twinning activity exhibited a positive correlation with GS,though it remained limited partly due to the unfavorable loading direction.The macroscopic Hall-Petch relationship was divided into two regions,i.e.,the k value(753 MPa·μm^(1/2))for the coarse-grain region(30-85μm)was significantly larger than that(118 MPa·μm^(1/2))of the fine-grain region(10-30μm),which could be attributed to the transition of predominant deformation mechanisms from slip to slip combined twinning with increasing GS.This work provides detailed and quantitative experimental data of the GS effects on individual slip activities of Mg and provides new insights into the Hall-Petch relationship for individual slip modes.展开更多
The present work reports characteristics of dislocation slip behavior in an equi-atomic HfNbTiZr refractory medium entropy alloy(RMEA)and its systematic comparison with pure niobium(Nb).Fully-recrystallized specimens ...The present work reports characteristics of dislocation slip behavior in an equi-atomic HfNbTiZr refractory medium entropy alloy(RMEA)and its systematic comparison with pure niobium(Nb).Fully-recrystallized specimens were fabricated by cold rolling and subsequent annealing,and uniaxial tensile deformation was applied at room temperature.Slip trace morphologies on the surfaces of the tensile-deformed ma-terials were quantitatively characterized,and the so-calledψand x relationships of the observed slip traces were evaluated by a newly developed method for polycrystalline specimens.Wavy slip traces were observed in most grains in the pure Nb.They consisted of low-indexed slip planes,such as{110},and{112},and high-indexed(or undetermined)slip planes.Some straight slip traces persisting on the low-indexed slip planes were also found in the pure Nb.In contrast,straight slip traces were dominant in the RMEA.The straight slip traces in the RMEA were not parallel to particular slip planes but mostly distributed along the maximum shear stress plane(MSSP),indicating that frequent cross slip in very short intervals occurred.Large deviations of slip planes from the MSSP in a few grains of the RMEA were attributed to the slip transfer from neighboring grains as a characteristic of polycrystalline materi-als.Frequent cross slip in short intervals,attributed to homogeneous slip resistance distribution for screw dislocations in the RMEA originating from the chemical heterogeneity on an atomic scale,was proposed as a novel mechanism responsible for the unique slip behavior and macroscopic deformation behavior.展开更多
This work is intended to further understand the controversial temperature dependencies of various slip modes in Mg alloys,and their effects on the mechanical properties at high temperature(HT).A systematical and stati...This work is intended to further understand the controversial temperature dependencies of various slip modes in Mg alloys,and their effects on the mechanical properties at high temperature(HT).A systematical and statistical investigation on the temperature-dependent macroscopic deformation behavior and the corresponding grain-scale slip activity was performed for both an extruded Mg-10Y(wt.%)sheet and a pure Mg sheet during tension at 25-300℃.The alloy’s strength increased by up to 44 MPa(14.0%)at HT compared to that at 25℃and this was accompanied by decreased pyramidal II(c+a)slip activity;both phenomena were opposite to that for pure Mg.The critical resolved shear stress(CRSS)ratios were estimated based on the~1700 sets of observed slip traces,and a positive temperature-dependent CRSS_(pyr II)/CRSS_(bas)was found in Mg-10Y.Compared to pure Mg,Mg-10Y exhibited pronounced strain hard-ening at HT due to enhanced slip-slip interactions,including multiple slip and cross slip,increased GND accumulation,and Y solute-dislocation interactions.The significant pyramidal II(c+a)slip activity(up to 30%frequency),its thermal hardening and pronounced strain hardening nature are proposed to be the key reasons for the observed anomalous strength increase in Mg-10Y.The grain-scale experimental evidence for(c+a)dislocation activity and its correlation to mechanical properties were revealed in this study and compared to recent atomic-scale simulations.展开更多
Deformation behavior of 1 Al containing Mg alloy has been investigated in the present study.After annealing,the Mg-1 Al alloy shows a typical basal texture.When compared to the pure Mg having a similar texture and gra...Deformation behavior of 1 Al containing Mg alloy has been investigated in the present study.After annealing,the Mg-1 Al alloy shows a typical basal texture.When compared to the pure Mg having a similar texture and grain size,the Mg-1 Al alloy shows much higher strength and larger elongation.Slip trace analyses of the tensile strained specimens show that non-basal slips such as pyramidal I and II slips can be easily activated at an early stage of deformation in the Mg-1 Al alloy and the grains in the Mg-1 Al alloy are seen to accommodate a larger degree of deformation than those in the pure Mg at a given strain.With increasing tensile strain,however,there is a strain localization along the initially formed slip lines of non-basal slips,forming surface steps without activating multiple slip lines.展开更多
This work investigates the effect of solid solution on ductility and on the activation of individual deformation mechanisms at moderate temperatures and at quasi-static strain rates in Mg-Zn and Mg-Al alloys. With tha...This work investigates the effect of solid solution on ductility and on the activation of individual deformation mechanisms at moderate temperatures and at quasi-static strain rates in Mg-Zn and Mg-Al alloys. With that aim, four solid solution Mg-Zn and Mg-Al binary alloy ingots containing 1 and 2 wt.% solute atoms were subjected to hot rolling and subsequent annealing to generate polycrystals with similar average grain size and basal-type texture for each composition. The activity of the different slip systems after tensile testing at 150°C and at 250°C was evaluated in pure Mg and in the alloys by EBSD-assisted slip trace analysis. In addition, segregation of Zn and Al atoms at grain boundaries during the thermo-mechanical processing was characterized by HAADF-STEM and EDX. It was found that while the addition of Al and Zn atoms to pure Mg does not lead to major changes in the mechanical strength at the investigated temperatures, it does enhance ductility significantly, especially at 250℃. Our results show that this increase in ductility cannot be attributed to a higher activation of non-basal systems in the alloys, as reported earlier, as the incidence of non-basal systems is indeed considerably higher in pure Mg. This work suggests, on the contrary, that the ductility increase may be attributed to the presence of a more homogenous basal activity in the alloys due to a lower degree of orientation clustering, to grain boundary solute segregation, and to a higher slip diffusivity at grain interiors.展开更多
Although tension-compression(T-C)asymmetry in yield strength was rarely documented in coarse-grained face centered cubic(FCC)metals as critical resolved shear stress(CRSS)for dislocation slip differs little between te...Although tension-compression(T-C)asymmetry in yield strength was rarely documented in coarse-grained face centered cubic(FCC)metals as critical resolved shear stress(CRSS)for dislocation slip differs little between tension and compression,the T-C asymmetry in strength,i.e.,higher strength when loaded in compression than in tension,was reported in some FCC high entropy alloys(HEAs)due to twinning and phase transitions activated at high strain regimes in compression.In this paper,we demonstrate a reversed and atypical tension-compression asymmetry(tensile strength markedly exceeds compressive strength)in a non-equiatomic FCC Ni_(2)CoFeV_(0.5)Mo_(0.2) medium entropy alloy(MEA)under dynamic loading,wherein dislocation slip governs dynamic deformation without twins or phase transitions.The asymme-try can be primarily interpreted as higher CRSS and more hard slip modes(lower average Schmid factor)activated in grains under dynamic tension than compression.Besides,larger strain rate sensitivity in dy-namic tension overwhelmingly contributes to the higher flow stress,thanks to the occurrence of more immobile Lomer-locks,narrower spacing of planar slip bands and higher dislocation density.This finding may provide some insights into designing MEAs/HEAs with desired properties under extreme conditions such as blast,impact and crash.展开更多
基金financial supports from the National Key Research and Development Program of China(2016YFB0101700 and 2016YFB0301104)the National Natural Science Foundation of China(U1764253,U2037601,51971044 and 52001037)+2 种基金the National Defense Basic Scientific Research program of China,the Qinghai Science and Technology Program(2018GX-A1)the Chongqing Science and Technology Commission(cstc2017zdcy-zdzx X0006)Chongqing Scientific&Technological Talents Program(KJXX2017002)。
文摘This research studied the mechanisms of Ca and Zn microalloying on the enhancement of ductility of extruded Mg-Gd sheet by combing electron backscattered diffraction and slip trace analysis.The ductility and microstructure of extruded Mg-0.6Gd and Mg-0.6Gd-0.3Ca-0.2Zn(wt%)sheets were investigated.Basal slip was the main deformation mode under investigation.Ca and Zn microalloying increased the frequency of grain boundaries(GBs)with misorientation angles(θs)<35°,promoted slip transfer across GBs and restricted the basal slip localization.In addition,there were a higher number of GB cracks homogeneously distributed in the Mg-0.6Gd sheet than in the Mg-0.6Gd-0.3Ca-0.2Zn sheet,attributed to the increased cohesion of GBs.The enhancement of basal slip,the suppression of slip localization and the suppression of GB cracking were contributed to the increased ductility for Mg-0.6Gd-0.3Ca-0.2Zn sheet.
基金Funded by National Natural Science Foundation of China(No.51401226)
文摘For TA15 titanium alloy, slip is the dominant plastic deformation mechanism because of relatively high Al content. In order to reveal the grain-scale stress field and geometrically necessary dislocation（GND） density distribution around the slip traces and phase boundaries where the slip lines are blocked due to Burgers orientation relationship（OR） missing. We experimentally investigated tensile deformation on TA15 titanium alloy up to 2.0% strain at room temperature. The slip traces were observed and identified using high resolution scanning electron microscopy（SEM） and electron backscatter diffraction（EBSD） measurements. The grain-scale stress fields around the slip traces and phase boundaries were calculated by the cross-correlationbased method. Based on strain gradient theories, the density of GND was calculated and analyzed. The results indicate that the grain-scale stress is significantly concentrated at phase/grain boundaries and slip traces. Although there is an obvious GND accumulation in the vicinity of phase and subgrain boundaries, no GND density accumulation appears near the slip traces.
基金supported by the National Natural Science Foundation of China(No.52171125)the Sichuan Science and Technology Program(No.2024NSFSC0193).
文摘This work investigated the effects of grain size(GS)on individual slip mode activities and the corresponding Hall-Petch coefficients in a rolled basal-textured pure Mg sheet under uniaxial tension using statistical slip trace analysis and electron backscatter diffraction.The studied regions covered a total of 1150 grains,in which 136 sets of slip traces were identified and analyzed in detail.The basalslip always dominated the deformation,whose frequencies decreased(from 81.0%to 62.5%)with increasing GS(from 10 to 85μm).The prismaticslip activity increased from 10.8%(10μm)to 27.5%(85μm),while that for pyramidal II<c+a>slip was almost constant.Critical resolved shear stress(CRSS)ratios were estimated based on the identified slip activity statistics,and then the Hall-Petch coefficients(k)of individual slip modes were calculated.The k value for prismaticslip(194 MPa·μm^(1/2))was lower than that for pyramidal II<c+a>slip(309 MPa·μm^(1/2)),which implies that pyramidal II<c+a>slip was more GS sensitive.Twinning activity exhibited a positive correlation with GS,though it remained limited partly due to the unfavorable loading direction.The macroscopic Hall-Petch relationship was divided into two regions,i.e.,the k value(753 MPa·μm^(1/2))for the coarse-grain region(30-85μm)was significantly larger than that(118 MPa·μm^(1/2))of the fine-grain region(10-30μm),which could be attributed to the transition of predominant deformation mechanisms from slip to slip combined twinning with increasing GS.This work provides detailed and quantitative experimental data of the GS effects on individual slip activities of Mg and provides new insights into the Hall-Petch relationship for individual slip modes.
基金supported by the Elements Strategy Initiative for Structural Materials(ESISM,No.JPMXP0112101000)the JSP EIG CONCERT-Japan(No.JPMJSC21C6)+5 种基金the Grant-in-Aid for Scientific Research on Innovative Area“High Entropy Alloys”(Nos.JP18H05455 and JP18H05451)the Grant-in-Aid for Scientific Re-search(A)(Nos.JP20H00306 and JP23H00234)the Grant-in-Aid for Research Activity Start-up(No.JP21K20487)the Grant-in-Aid for Early-Career Scientists(No.JP22K14501)the Grant-in-Aid for JSPS Research Fellow(No.JP18J20766)supported by China Scholarship Council(CSC),China.
文摘The present work reports characteristics of dislocation slip behavior in an equi-atomic HfNbTiZr refractory medium entropy alloy(RMEA)and its systematic comparison with pure niobium(Nb).Fully-recrystallized specimens were fabricated by cold rolling and subsequent annealing,and uniaxial tensile deformation was applied at room temperature.Slip trace morphologies on the surfaces of the tensile-deformed ma-terials were quantitatively characterized,and the so-calledψand x relationships of the observed slip traces were evaluated by a newly developed method for polycrystalline specimens.Wavy slip traces were observed in most grains in the pure Nb.They consisted of low-indexed slip planes,such as{110},and{112},and high-indexed(or undetermined)slip planes.Some straight slip traces persisting on the low-indexed slip planes were also found in the pure Nb.In contrast,straight slip traces were dominant in the RMEA.The straight slip traces in the RMEA were not parallel to particular slip planes but mostly distributed along the maximum shear stress plane(MSSP),indicating that frequent cross slip in very short intervals occurred.Large deviations of slip planes from the MSSP in a few grains of the RMEA were attributed to the slip transfer from neighboring grains as a characteristic of polycrystalline materi-als.Frequent cross slip in short intervals,attributed to homogeneous slip resistance distribution for screw dislocations in the RMEA originating from the chemical heterogeneity on an atomic scale,was proposed as a novel mechanism responsible for the unique slip behavior and macroscopic deformation behavior.
基金supported by the National Natural Science Foundation of China(No.52171125)the Sichuan Science and Technology Program(No.2024NSFSC0193)。
文摘This work is intended to further understand the controversial temperature dependencies of various slip modes in Mg alloys,and their effects on the mechanical properties at high temperature(HT).A systematical and statistical investigation on the temperature-dependent macroscopic deformation behavior and the corresponding grain-scale slip activity was performed for both an extruded Mg-10Y(wt.%)sheet and a pure Mg sheet during tension at 25-300℃.The alloy’s strength increased by up to 44 MPa(14.0%)at HT compared to that at 25℃and this was accompanied by decreased pyramidal II(c+a)slip activity;both phenomena were opposite to that for pure Mg.The critical resolved shear stress(CRSS)ratios were estimated based on the~1700 sets of observed slip traces,and a positive temperature-dependent CRSS_(pyr II)/CRSS_(bas)was found in Mg-10Y.Compared to pure Mg,Mg-10Y exhibited pronounced strain hard-ening at HT due to enhanced slip-slip interactions,including multiple slip and cross slip,increased GND accumulation,and Y solute-dislocation interactions.The significant pyramidal II(c+a)slip activity(up to 30%frequency),its thermal hardening and pronounced strain hardening nature are proposed to be the key reasons for the observed anomalous strength increase in Mg-10Y.The grain-scale experimental evidence for(c+a)dislocation activity and its correlation to mechanical properties were revealed in this study and compared to recent atomic-scale simulations.
文摘Deformation behavior of 1 Al containing Mg alloy has been investigated in the present study.After annealing,the Mg-1 Al alloy shows a typical basal texture.When compared to the pure Mg having a similar texture and grain size,the Mg-1 Al alloy shows much higher strength and larger elongation.Slip trace analyses of the tensile strained specimens show that non-basal slips such as pyramidal I and II slips can be easily activated at an early stage of deformation in the Mg-1 Al alloy and the grains in the Mg-1 Al alloy are seen to accommodate a larger degree of deformation than those in the pure Mg at a given strain.With increasing tensile strain,however,there is a strain localization along the initially formed slip lines of non-basal slips,forming surface steps without activating multiple slip lines.
基金funding from the Madrid region under programme S2018/NMT4381-MAT4.0-CM projectFunding from projects PID2019111285RB-I00 and PID2020-118626RB-I00 awarded by the Spanish Ministry of Science, Innovation and Universitiesfinancial support from the China Scholarship Council (Grant no 201706050154)
文摘This work investigates the effect of solid solution on ductility and on the activation of individual deformation mechanisms at moderate temperatures and at quasi-static strain rates in Mg-Zn and Mg-Al alloys. With that aim, four solid solution Mg-Zn and Mg-Al binary alloy ingots containing 1 and 2 wt.% solute atoms were subjected to hot rolling and subsequent annealing to generate polycrystals with similar average grain size and basal-type texture for each composition. The activity of the different slip systems after tensile testing at 150°C and at 250°C was evaluated in pure Mg and in the alloys by EBSD-assisted slip trace analysis. In addition, segregation of Zn and Al atoms at grain boundaries during the thermo-mechanical processing was characterized by HAADF-STEM and EDX. It was found that while the addition of Al and Zn atoms to pure Mg does not lead to major changes in the mechanical strength at the investigated temperatures, it does enhance ductility significantly, especially at 250℃. Our results show that this increase in ductility cannot be attributed to a higher activation of non-basal systems in the alloys, as reported earlier, as the incidence of non-basal systems is indeed considerably higher in pure Mg. This work suggests, on the contrary, that the ductility increase may be attributed to the presence of a more homogenous basal activity in the alloys due to a lower degree of orientation clustering, to grain boundary solute segregation, and to a higher slip diffusivity at grain interiors.
基金the National Key R&D Program of China(No.2017YFA0204403)the National Natural Science Foundation of China(Nos.51971112 and51225102)+2 种基金the Fundamental Research Funds for the Central Universities(No.30919011405)X.Chen would like to acknowledge the finan-cial support from the National Natural Science Foundation of China(Nos.52001165 and 51931003)the Natural Science Foundation of Jiangsu Province,China(No.BK20200475),and the Fundamen-tal Research Funds for the Central Universities(No.30921011215).
文摘Although tension-compression(T-C)asymmetry in yield strength was rarely documented in coarse-grained face centered cubic(FCC)metals as critical resolved shear stress(CRSS)for dislocation slip differs little between tension and compression,the T-C asymmetry in strength,i.e.,higher strength when loaded in compression than in tension,was reported in some FCC high entropy alloys(HEAs)due to twinning and phase transitions activated at high strain regimes in compression.In this paper,we demonstrate a reversed and atypical tension-compression asymmetry(tensile strength markedly exceeds compressive strength)in a non-equiatomic FCC Ni_(2)CoFeV_(0.5)Mo_(0.2) medium entropy alloy(MEA)under dynamic loading,wherein dislocation slip governs dynamic deformation without twins or phase transitions.The asymme-try can be primarily interpreted as higher CRSS and more hard slip modes(lower average Schmid factor)activated in grains under dynamic tension than compression.Besides,larger strain rate sensitivity in dy-namic tension overwhelmingly contributes to the higher flow stress,thanks to the occurrence of more immobile Lomer-locks,narrower spacing of planar slip bands and higher dislocation density.This finding may provide some insights into designing MEAs/HEAs with desired properties under extreme conditions such as blast,impact and crash.
