The high ductility of Mg-Li alloy has been mainly ascribed to a high activity of pyramidal<c+a>slip to accommodate plastic strain.In the present study,however,a quantitative analysis reveals that Li-addition can...The high ductility of Mg-Li alloy has been mainly ascribed to a high activity of pyramidal<c+a>slip to accommodate plastic strain.In the present study,however,a quantitative analysis reveals that Li-addition can only slightly stimulate the activation of pyramidal<c+a>slip under compression along the normal direction of a hot-rolled Mg-4.5 wt.%Li plate,with a relative activity of approximately 18%.Although the limited activity of pyramidal<c+a>slip alone cannot accommodate a large plastic strain,it effectively reduces the number of{10.11}−{10.12}double twins,which are believed to be favorable sites for crack initiation.The evidently reduced activity of double twins leads to a lower cracking tendency,and therefore improves ductility.展开更多
Due to their low symmetry in crystal structure,low elastic modulus(~45 GPa)and low yielding stress,magnesium(Mg)alloys exhibit strong inelastic behaviors during unloading.As more and more Mg alloys are developed,their...Due to their low symmetry in crystal structure,low elastic modulus(~45 GPa)and low yielding stress,magnesium(Mg)alloys exhibit strong inelastic behaviors during unloading.As more and more Mg alloys are developed,their unloading behaviors were less investigated,especially for rare-earth(RE)Mg alloys.In the current work,the unloading behaviors of the RE Mg alloy ZE10 sheet is carefully studied by both mechanical tests and crystal plasticity modeling.In terms of the stress-strain curves,the inelastic strain,the chord modulus,and the active deformation mechanisms,the substantial anisotropy and the loading path dependency of the unloading behaviors of ZE10 sheets are characterized.The inelastic strains are generally larger under compressive Loading-Un Loading(L-UL)than under tensile L-UL,along the transverse direction(TD)than along the rolling direction(RD)under tensile L-UL,and along RD than along TD under compressive L-UL.The basal slip,twinning and de-twinning are found to be responsible for the unloading behaviors of ZE10 sheets.展开更多
The mechanical properties of magnesium alloy AZ31 were investigated experimentally with visco-plastic self-consistent modeling. Tension,compression and plane strain compression(PSC) tests were performed along 3 direct...The mechanical properties of magnesium alloy AZ31 were investigated experimentally with visco-plastic self-consistent modeling. Tension,compression and plane strain compression(PSC) tests were performed along 3 directions of a hot rolled plate, and the material parameters input in the model were fitted with the uniaxial stress-strain curves. The critical resolved shear stress(CRSS) for tension twinning was modeled with a modified Voce hardening law first decreasing, and then increasing with strain, that could reproduce better the flow stress for twin-predominant deformation. Such CRSS evolution may better model twin nucleation, propagation and growth. Firstly simulations were carried out assuming latent hardening coefficients for slip by other slip systems equal to self-hardening. Then different heterogeneous latent hardening were used, whose values were based on dislocation dynamics simulations from the literature. This study shows that equal self and latent hardening can reproduce the stress strain curves and plastic anisotropy as well as heterogeneous mode on mode latent hardening.Discrepancies between simulations and experimental results from PSC are explained by an under-estimation of twinning for some PSC strain paths.展开更多
Chromium released during municipal solid waste incineration(MSWI)is toxic and carcinogenic.The removal of chromium from simulated MSWI flue gas by four sorbents(CaO,bamboo charcoal(BC),powdered activated carbon(PAC),a...Chromium released during municipal solid waste incineration(MSWI)is toxic and carcinogenic.The removal of chromium from simulated MSWI flue gas by four sorbents(CaO,bamboo charcoal(BC),powdered activated carbon(PAC),and Al_(2)O_(3))and the effects of four oxides(SiO_(2),Al_(2)O_(3),Fe_(2)O_(3),and CaO)on chromium speciation transformationwere investigated.The results showed that the removal rates of total Cr by the four sorbents were Al_(2)O_(3)<CaO<PAC<BC,while the removal rates of Cr(Ⅵ)by the four sorbents were Al_(2)O_(3)<PAC<BC<CaO.CaO had a strong oxidizing effect on Cr(Ⅲ),while BC and PAC had a better-reducing effect on Cr(Ⅵ).SiO_(2)was better for the reduction of Na_(2)CrO_(4)and K_(2)CrO_(4)above 1000℃due to its strong acidity,and the addition of CaO significantly inhibited the reduction of Cr(Ⅵ).MgCrO_(4)decomposed above 700℃to form MgCr_(2)O_(4),and the reaction between MgCrO_(4)and oxides also existed in the form of a more stable trivalent spinel.Furthermore,when investigating the effect of oxides on the oxidation of Cr(Ⅲ)in CrC_(l3),it was discovered that CaO promoted the conversion of Cr(Ⅲ)to Cr(Ⅵ),while the presence of chlorine caused chromium to exist in the form of Cr(V),and increasing the content of CaO and extending the heating time facilitated the oxidation of Cr(Ⅲ).In addition,silicate,aluminate,and ferrite were generated after the addition of SiO_(2),Al_(2)O_(3),and Fe_(2)O_(3),which reduced the alkalinity of CaO and had an important role in inhibiting the oxidation of Cr(Ⅲ).The acidic oxides can not only promote the reduction of Cr(Ⅵ)but also have an inhibitory effect on the oxidation of Cr(Ⅲ)ascribed to alkali metals/alkaline earth metals,and the proportion of acidic oxides can be increased moderately to reduce the generation of harmful substances in the hazardous solid waste heat treatment.展开更多
Long period stacking ordered(LPSO) structures are an effective strengthening phase in Mg alloys.However,the coarse LPSO phases in as-cast alloys are very difficult to refine,and they dramatically reduce the strengthen...Long period stacking ordered(LPSO) structures are an effective strengthening phase in Mg alloys.However,the coarse LPSO phases in as-cast alloys are very difficult to refine,and they dramatically reduce the strengthening effect.In the present study,friction stir processing(FSP) was employed to refine the structure of an Mg-12.8 Y-4.7 Zn(wt%) alloy with a very high content of coarse LPSO phases.An optimized FSP regime refined the coarse LPSO phases into densely ultrafine blocks with an average width of ~200 nm and an average length of~1 μm.An ultrahigh yield strength of ~800 MPa was achieved under compression of the FSP region.Theoretical calculations indicated that the strengthening by the densely ultrafine LPSO phases was up to approximately 630 MPa.展开更多
Although the{10-12}twinning behavior of Mg alloys under uniaxial tension and compression has been extensively investigated,the simulations of{10-12}twinning behavior under biaxial tension have rarely been reported.In ...Although the{10-12}twinning behavior of Mg alloys under uniaxial tension and compression has been extensively investigated,the simulations of{10-12}twinning behavior under biaxial tension have rarely been reported.In this work,the EVPSC-TDT model is first employed to systematically investigate the deformation behavior of a Mg alloy AZ31 plate under biaxial tension in the RD-TD and ND-TD planes.The RD,TD and ND refer to the rolling direction,transverse direction,and normal direction of the hot rolled plate.The measured stress-strain curves and texture evolutions are well predicted and the con-tours of plastic work under biaxial tension are also constructed for comparison with experiments.The plastic response has been interpreted in terms of relative activities of various deformation modes.For bi-axial tension in the RD-TD plane,basal and pyramidal slips mainly contribute to the plastic deformation for stress ratios ofσRD:σTD=1:2 to 2:1.Prismatic slip becomes more active forσRD:σTD=1:4 and 4:1.Compression twinning could be activated and so cause texture reorientation at large strains,especially forσRD:σTD=1:1.The six-fold feature of{10-10}pole figure could still be observed forσRD:σTD=1:4 and 4:1 at large strain.For biaxial tension in the ND-TD plane,tensile twinning plays an important role forσND:σTD≥1:2,while prismatic slip contributes to plastic deformation for the other cases.With the in-crease of stress ratio fromσND:σTD≥1:1 to 1:0,the predicted twin volume fractions(VFs)at a specific strain along the ND,εND,almost linearly decrease,however,it is seen that the experimental ones at given strains along the ND do not follow such a trend with the measured twin VFs within the range of stress ratios,2:1≤σND:σTD≤6:1,clearly being overestimated,and the difference between experiments and simulations becomes most obvious at the relatively small strain ofεND=0.015.The possible reasons for the observed difference are discussed.展开更多
In this work,we investigated the mechanical properties and corresponding deformation mechanisms of an Al1Mg0.4Si alloy,which exhibited significantly higher strength and outstanding strain hardening capacity at 77 K co...In this work,we investigated the mechanical properties and corresponding deformation mechanisms of an Al1Mg0.4Si alloy,which exhibited significantly higher strength and outstanding strain hardening capacity at 77 K compared to its counterparts at 298 K.The deformation mechanisms responsible for the excellent strength-ductility synergy and extraordinary strain hardening capacity at cryogenic temperature were elucidated through a combined experimental and simulation study.The results reveal the presence of numerous slip traces and microbands throughout grain surfaces during deformation at 298 K,whereas at 77 K,vague grain surfaces dominate,indicating the simultaneous operation of multiple slip systems.Transmission electron microscopy(TEM)analysis using the two-beam diffraction technique demonstrates the presence of dislocations with several different Burgers vectors inside a grain at cryogenic temperature,confirming the activation of multiple slip systems.The accumulation of dislocations facilitated by these multiple slip systems,combined with the high dislocation density,contributes to strain hardening and remarkable uniform elongation at 77 K.A modified dislocation density-based crystal plasticity model,incorporating the effect of grain boundary hardening(GBH)and temperature,was developed to gain a better understanding of the underlying mechanisms governing alloy’s strength and plasticity.The GBH effect significantly enhances statistically stored dislocation(SSD)density and screw dislocation proportion,which promote homogeneous deformation and enhance strain hardening capacity at cryogenic temperature.These findings deepen the understanding of plastic deformation at cryogenic temperatures and pave the way for the development of ultrahigh-performance metallic materials for cryogenic applications.展开更多
基金support from National Natural Science Foundation of China(51871032,52071039 and 51671040)Natural Science Foundation of Jiangsu Province(BK20202010)“111”Project by the Ministry of Education(B16007).
文摘The high ductility of Mg-Li alloy has been mainly ascribed to a high activity of pyramidal<c+a>slip to accommodate plastic strain.In the present study,however,a quantitative analysis reveals that Li-addition can only slightly stimulate the activation of pyramidal<c+a>slip under compression along the normal direction of a hot-rolled Mg-4.5 wt.%Li plate,with a relative activity of approximately 18%.Although the limited activity of pyramidal<c+a>slip alone cannot accommodate a large plastic strain,it effectively reduces the number of{10.11}−{10.12}double twins,which are believed to be favorable sites for crack initiation.The evidently reduced activity of double twins leads to a lower cracking tendency,and therefore improves ductility.
基金the support of the National Natural Science Foundation of China(Nos.51775337,51675331,51975365)Major Projects of the Ministry of Education(No.311017)+5 种基金the Program of Introducing Talents of Discipline to Universities(Grant No.B06012)sponsored by the Shanghai Pujiang Program(18PJ1405000)the University of Sydney-Shanghai Jiao Tong University Partnership Collaboration Awardssupported by the Natural Sciences and Engineering Research Council of Canada(Nos.RGPIN-201606464)partly supported by the Materials Genome Initiative Center,Shanghai Jiao Tong UniversityThe University of Michigan and Shanghai Jiao Tong University(UM-SJTU)joint research project(AE604401)。
文摘Due to their low symmetry in crystal structure,low elastic modulus(~45 GPa)and low yielding stress,magnesium(Mg)alloys exhibit strong inelastic behaviors during unloading.As more and more Mg alloys are developed,their unloading behaviors were less investigated,especially for rare-earth(RE)Mg alloys.In the current work,the unloading behaviors of the RE Mg alloy ZE10 sheet is carefully studied by both mechanical tests and crystal plasticity modeling.In terms of the stress-strain curves,the inelastic strain,the chord modulus,and the active deformation mechanisms,the substantial anisotropy and the loading path dependency of the unloading behaviors of ZE10 sheets are characterized.The inelastic strains are generally larger under compressive Loading-Un Loading(L-UL)than under tensile L-UL,along the transverse direction(TD)than along the rolling direction(RD)under tensile L-UL,and along RD than along TD under compressive L-UL.The basal slip,twinning and de-twinning are found to be responsible for the unloading behaviors of ZE10 sheets.
基金National Natural Science Foundation of China (51871032, 52071039 and 51671040)the 111 Project (B16007) of the Ministry of Education。
文摘The mechanical properties of magnesium alloy AZ31 were investigated experimentally with visco-plastic self-consistent modeling. Tension,compression and plane strain compression(PSC) tests were performed along 3 directions of a hot rolled plate, and the material parameters input in the model were fitted with the uniaxial stress-strain curves. The critical resolved shear stress(CRSS) for tension twinning was modeled with a modified Voce hardening law first decreasing, and then increasing with strain, that could reproduce better the flow stress for twin-predominant deformation. Such CRSS evolution may better model twin nucleation, propagation and growth. Firstly simulations were carried out assuming latent hardening coefficients for slip by other slip systems equal to self-hardening. Then different heterogeneous latent hardening were used, whose values were based on dislocation dynamics simulations from the literature. This study shows that equal self and latent hardening can reproduce the stress strain curves and plastic anisotropy as well as heterogeneous mode on mode latent hardening.Discrepancies between simulations and experimental results from PSC are explained by an under-estimation of twinning for some PSC strain paths.
基金supported by the National R&D Program Project of China(No.2019YFC1907000)the Key Research and Development Program of Hubei Province(No.2020BCA076)+1 种基金the Natural Sciences Foundation of China(No.52176127)Natural Science Foundation of Hubei Province(No.2022CFB045)。
文摘Chromium released during municipal solid waste incineration(MSWI)is toxic and carcinogenic.The removal of chromium from simulated MSWI flue gas by four sorbents(CaO,bamboo charcoal(BC),powdered activated carbon(PAC),and Al_(2)O_(3))and the effects of four oxides(SiO_(2),Al_(2)O_(3),Fe_(2)O_(3),and CaO)on chromium speciation transformationwere investigated.The results showed that the removal rates of total Cr by the four sorbents were Al_(2)O_(3)<CaO<PAC<BC,while the removal rates of Cr(Ⅵ)by the four sorbents were Al_(2)O_(3)<PAC<BC<CaO.CaO had a strong oxidizing effect on Cr(Ⅲ),while BC and PAC had a better-reducing effect on Cr(Ⅵ).SiO_(2)was better for the reduction of Na_(2)CrO_(4)and K_(2)CrO_(4)above 1000℃due to its strong acidity,and the addition of CaO significantly inhibited the reduction of Cr(Ⅵ).MgCrO_(4)decomposed above 700℃to form MgCr_(2)O_(4),and the reaction between MgCrO_(4)and oxides also existed in the form of a more stable trivalent spinel.Furthermore,when investigating the effect of oxides on the oxidation of Cr(Ⅲ)in CrC_(l3),it was discovered that CaO promoted the conversion of Cr(Ⅲ)to Cr(Ⅵ),while the presence of chlorine caused chromium to exist in the form of Cr(V),and increasing the content of CaO and extending the heating time facilitated the oxidation of Cr(Ⅲ).In addition,silicate,aluminate,and ferrite were generated after the addition of SiO_(2),Al_(2)O_(3),and Fe_(2)O_(3),which reduced the alkalinity of CaO and had an important role in inhibiting the oxidation of Cr(Ⅲ).The acidic oxides can not only promote the reduction of Cr(Ⅵ)but also have an inhibitory effect on the oxidation of Cr(Ⅲ)ascribed to alkali metals/alkaline earth metals,and the proportion of acidic oxides can be increased moderately to reduce the generation of harmful substances in the hazardous solid waste heat treatment.
基金financially supported by the National Natural Science Foundation of China(Nos.52071039,51871032 and 51901068)the Natural Science Foundation of Jiangsu Province(No.BK20202010)。
文摘Long period stacking ordered(LPSO) structures are an effective strengthening phase in Mg alloys.However,the coarse LPSO phases in as-cast alloys are very difficult to refine,and they dramatically reduce the strengthening effect.In the present study,friction stir processing(FSP) was employed to refine the structure of an Mg-12.8 Y-4.7 Zn(wt%) alloy with a very high content of coarse LPSO phases.An optimized FSP regime refined the coarse LPSO phases into densely ultrafine blocks with an average width of ~200 nm and an average length of~1 μm.An ultrahigh yield strength of ~800 MPa was achieved under compression of the FSP region.Theoretical calculations indicated that the strengthening by the densely ultrafine LPSO phases was up to approximately 630 MPa.
基金Y.C.Xin was financially supported by the National Natural Sci-ence Foundation of China(Nos.52071039 and 51871032)the Natural Science Foundation of Jiangsu Province(No.BK20202010)P.D.Wu was financially supported by the Natural Sciences and En-gineering Research Council of Canada(No.RGPIN-2016-06464).
文摘Although the{10-12}twinning behavior of Mg alloys under uniaxial tension and compression has been extensively investigated,the simulations of{10-12}twinning behavior under biaxial tension have rarely been reported.In this work,the EVPSC-TDT model is first employed to systematically investigate the deformation behavior of a Mg alloy AZ31 plate under biaxial tension in the RD-TD and ND-TD planes.The RD,TD and ND refer to the rolling direction,transverse direction,and normal direction of the hot rolled plate.The measured stress-strain curves and texture evolutions are well predicted and the con-tours of plastic work under biaxial tension are also constructed for comparison with experiments.The plastic response has been interpreted in terms of relative activities of various deformation modes.For bi-axial tension in the RD-TD plane,basal and pyramidal slips mainly contribute to the plastic deformation for stress ratios ofσRD:σTD=1:2 to 2:1.Prismatic slip becomes more active forσRD:σTD=1:4 and 4:1.Compression twinning could be activated and so cause texture reorientation at large strains,especially forσRD:σTD=1:1.The six-fold feature of{10-10}pole figure could still be observed forσRD:σTD=1:4 and 4:1 at large strain.For biaxial tension in the ND-TD plane,tensile twinning plays an important role forσND:σTD≥1:2,while prismatic slip contributes to plastic deformation for the other cases.With the in-crease of stress ratio fromσND:σTD≥1:1 to 1:0,the predicted twin volume fractions(VFs)at a specific strain along the ND,εND,almost linearly decrease,however,it is seen that the experimental ones at given strains along the ND do not follow such a trend with the measured twin VFs within the range of stress ratios,2:1≤σND:σTD≤6:1,clearly being overestimated,and the difference between experiments and simulations becomes most obvious at the relatively small strain ofεND=0.015.The possible reasons for the observed difference are discussed.
基金supported by the National Natural Science Foundation of China(Nos.92263201,51927801,52001160,and 52205378)the National Key Research&Development Plan(Nos.2020YFA0405900 and 2019YFA0708801)Natural Science Foundation of Jiangsu Province(No.BK20202010).
文摘In this work,we investigated the mechanical properties and corresponding deformation mechanisms of an Al1Mg0.4Si alloy,which exhibited significantly higher strength and outstanding strain hardening capacity at 77 K compared to its counterparts at 298 K.The deformation mechanisms responsible for the excellent strength-ductility synergy and extraordinary strain hardening capacity at cryogenic temperature were elucidated through a combined experimental and simulation study.The results reveal the presence of numerous slip traces and microbands throughout grain surfaces during deformation at 298 K,whereas at 77 K,vague grain surfaces dominate,indicating the simultaneous operation of multiple slip systems.Transmission electron microscopy(TEM)analysis using the two-beam diffraction technique demonstrates the presence of dislocations with several different Burgers vectors inside a grain at cryogenic temperature,confirming the activation of multiple slip systems.The accumulation of dislocations facilitated by these multiple slip systems,combined with the high dislocation density,contributes to strain hardening and remarkable uniform elongation at 77 K.A modified dislocation density-based crystal plasticity model,incorporating the effect of grain boundary hardening(GBH)and temperature,was developed to gain a better understanding of the underlying mechanisms governing alloy’s strength and plasticity.The GBH effect significantly enhances statistically stored dislocation(SSD)density and screw dislocation proportion,which promote homogeneous deformation and enhance strain hardening capacity at cryogenic temperature.These findings deepen the understanding of plastic deformation at cryogenic temperatures and pave the way for the development of ultrahigh-performance metallic materials for cryogenic applications.
