The origin of unique parallel alignment of(0001) poles to transverse direction(TD) was investigated using Mg-3Al-0.4Mn(mass%)alloy sheets rolled with different process conditions. When rolling was performed with inter...The origin of unique parallel alignment of(0001) poles to transverse direction(TD) was investigated using Mg-3Al-0.4Mn(mass%)alloy sheets rolled with different process conditions. When rolling was performed with intermediate reheating, the alloy showed a sluggish static recrystallization(SRX) behavior during post-annealing, facilitating the nucleation and growth of statically recrystallized grains from extension twins. This resulted in the apparent texture component with the parallel alignment of the(0001) poles to the TD, and the sheet exhibited good ductility for both the rolling direction(RD) and TD. In contrast, continuous rolling without intermediate reheating led to the formation of severely deformed regions near double twins. SRX was promoted at such regions, forming a typical basal textural feature with weak RD-split of the(0001) poles. Although extension twins were formed after the continuous rolling, SRX was facilitated at the severely deformed regions with double twins, and the formation of the unique alignment of the(0001) poles to the TD was suppressed. The RD-split texture led to the large elongation to failure along the RD, while it along the TD decreased owing to the narrow distribution of the(0001)poles toward the TD, resulting in the in-plane anisotropy in ductility.展开更多
The age-hardening behavior and mechanical properties of the extruded Mg-2Gd-1.2Y-0.5Zn(at.%)alloy with Zr or Mn additions were investigated.The results show that Mn added alloy exhibits more remarkable age-hardening r...The age-hardening behavior and mechanical properties of the extruded Mg-2Gd-1.2Y-0.5Zn(at.%)alloy with Zr or Mn additions were investigated.The results show that Mn added alloy exhibits more remarkable age-hardening response than Zr added alloy,which is attributed to the fact that partitioning of Mn into the β'phases,β'precipitates and long period stacking ordered(LPSO)phases leads to the decrement in(G d+Y)concentrations in the second phases,facilitating the precipitation during aging treatment.Both peak-aged alloys show bimodal microstructure comprising the fine DRXed grains with nano-sized β phases pinned at DRXed grain boundaries as well as coarse worked grains with strong fiber texture.High strength and good thermal stability were obtained in both peak-aged Mn and Zr added alloys.While the peak-aged Mn added alloy shows higher strength and superior creep resistance due to its denser β'precipitates,thin LPSO phases and γ'precipitates and higher area fraction of worked grains with strong fiber texture.The 0.2% tensile proof stress and ultimate tensile strength of peak-aged Mn added alloy reach up to 454 MPa and 508 MPa,respectively,with elongation of 3.2%at room temperature.The minimum creep rate of the peak-aged Mn added alloy at 250℃/150 MPa is 2.4 × 10^-8 s^-1,which is superior than previously reported extruded Mg-Gd based alloys.展开更多
Strength and ductility synergy in an Mg-3mass%Al-Mn(AM30)alloy sheet was successfully improved via twin-roll casting and annealing at low-temperature.An AM30 alloy sheet produced by twin-roll casting,homogenization,ho...Strength and ductility synergy in an Mg-3mass%Al-Mn(AM30)alloy sheet was successfully improved via twin-roll casting and annealing at low-temperature.An AM30 alloy sheet produced by twin-roll casting,homogenization,hot-rolling,and subsequent annealing at 170℃ for 64 h exhibits a good 0.2%proof stress of 170 MPa and a large elongation to failure of 33.1%along the rolling direction.The sheet also shows in-plane isotropic tensile properties,and the 0.2%proof stress and elongation to failure along the transverse direction are 176 MPa and 35.5%,respectively.Though the sheet produced by direct-chill casting also shows moderate strengths if the annealing condition is same,the direct-chill casting leads to the deteriorated elongation to failure of 23.9%and 30.0%for the rolling and transverse directions,respectively.As well as such excellent tensile properties,a high room-temperature stretch formability with an Index Erichsen value of 8.3 mm could be obtained in the twin-roll cast sheet annealed at 170℃ for 64 h.The annealing at a higher temperature further improves the stretch formability;however,this results in the decrease of the tensile properties.Microstructure characterization reveals that the excellent combination of strengths,ductility,and stretch formability in the twin-roll cast sheet annealed at the low-temperature annealing is mainly attributed to the uniform recrystallized microstructure,fine grain size,and circular distribution of(0001)poles away from the normal direction of the sheet.展开更多
The static recrystallization and associated texture evolution were investigated in an extruded Mg-Zn-Gd alloy with bimodal microstructure based on a quasi-in-situ electron back-scatter diffraction(EBSD)method.The typi...The static recrystallization and associated texture evolution were investigated in an extruded Mg-Zn-Gd alloy with bimodal microstructure based on a quasi-in-situ electron back-scatter diffraction(EBSD)method.The typical rare earth(RE)texture formed during annealing,evolving from the bimodal microstructure with[1010]basal fiber texture that consisted of fine recrystallized(RXed)grains and coarse unrecrystallized(un RXed)grains elongated along the extrusion direction.In both RXed and un RXed regions,the RXed nucleation produced randomized orientations without preferred selection and the RXed grains with RE texture orientation had more intensive growth ability than those with basal fiber orientation,thereby leading to the preferred selection of RE texture orientation during grain growth.The relationships between stored strain energy,solute drag,grain growth and texture evolution are discussed in detail.This study provided direct evidence of the RE texture evolution in an extruded Mg-RE alloy,which assists in understanding the formation mechanisms for RE texture during extrusion and better developing wrought Mg alloys with improved formability.展开更多
The homogenized Mg-8.2 Gd-3.8 Y-1.0 Zn-0.4 Zr(wt.%)alloy full of plate-shaped long period stacking ordered(LPSO)phases was hot extruded in the atmosphere and cooled by the forced-air,then the effect of forced-air cool...The homogenized Mg-8.2 Gd-3.8 Y-1.0 Zn-0.4 Zr(wt.%)alloy full of plate-shaped long period stacking ordered(LPSO)phases was hot extruded in the atmosphere and cooled by the forced-air,then the effect of forced-air cooling on the microstructure and age-hardening response of the alloy was investigated in this work.The results show that in comparison with the extruded sample cooling in the atmosphere,the forced-air cooling restricts dynamic recrystallization(DRX)and brings about finer dynamic recrystallized(DRXed)grain size,stronger basal texture and higher dislocation density.Furthermore,the forced-air cooling promotes the dynamic precipitation in the DRXed regions and facilitates formation of plate-shaped LPSO phases andγ’phases with smaller interspacing in the unrecrystallized(un DRXed)regions,then slightly restricts the precipitation ofβphases during aging.After peak-ageing treatment,the extruded sample with forced-air cooling shows superior tensile properties with a tensile yield strength of 439 MPa,an ultimate tensile strength of 493 MPa,and elongation to failure of 18.6%.展开更多
The creep strength enhanced martensitic steels are key material for the main power generating units in ultra-supercritical plants.Studies on the evaluation of their creep rupture life show there is an overestimation o...The creep strength enhanced martensitic steels are key material for the main power generating units in ultra-supercritical plants.Studies on the evaluation of their creep rupture life show there is an overestimation of rupture life after long-term creep,which is known as premature failure.However,the microstructural origin of the premature failure remains unclear.Here in this study,we have carefully investigated the microstructural transformations and their influences on creep rupture behavior,showing that the evolution of martensite and M_(23)C_(6) carbides as well as Laves phase are responsible for the premature failure.By using multi-step TTP-LMP method,we confirmed a three-stage creep rupture behavior under different stress regions.Further quantitative analysis showed that the coarsening of M_(23)C_(6) carbides and recovery of martensite exert equal and dominant effects on the premature failure in the medium stress region,while precipitation and coarsening of Laves phase are responsible for the premature failure in the low stress region.展开更多
The strength-ductility trade-off has been the most challenging problem for structural metals for centuries.Nanoprecipitation strengthening is an ideal approach to enhance the strength without significantly sacrificing...The strength-ductility trade-off has been the most challenging problem for structural metals for centuries.Nanoprecipitation strengthening is an ideal approach to enhance the strength without significantly sacrificing the ductility.Stable nanoprecipitates have been successfully acquired by nanostructural design,but the number density of nanoprecipitates cannot be further increased.Researchers attempted to enhance number density by introducing highly potent nucleation sites(e.g.,dislocations).However,there remains controversy over the influence of dislocations on the nucleation and growth of coherent nanoprecipitates with minimized nucleation barrier.Here,Cu-rich nanoprecipitates in an HSLA steel,as a typical type of coherent nanoprecipitates,are investigated.By combining analytical calculation and experiments,we show that dislocations are harmful for the formation of large numbered Cu-rich nanoprecipitates in a certain density range.Insufficient dislocations deprive solute atoms which decrease homogenous precipitation that cannot be compensated by the increase in heterogeneous precipitation.Under such circumstance,Cu-rich nanoprecipitates have smaller number density but larger size and higher fraction of incoherent structures due to rapid Ostwald ripening.As a result,by controlling dislocation density,the yield strength is increased by 24%without obvious loss in ductility as compared with traditional solution-quench-age process.Our work would help to optimize composition and processing routes that fully exploit the nanoprecipitation strengthening effect.展开更多
Background JUNO(The Jiangmen Underground Neutrino Observatory)is a multipurpose neutrino experiment,and it has very strict requirements for the detector.According to the MC simulation for JUNO experiment requirements,...Background JUNO(The Jiangmen Underground Neutrino Observatory)is a multipurpose neutrino experiment,and it has very strict requirements for the detector.According to the MC simulation for JUNO experiment requirements,the Rn concentration in the water of the veto detector should be less than 0.2Bq/m^(3).In order to measure such low Rn concentration,two kinds of high-sensitivity Rn measurement systems have been developed.Method Based on the water system of JUNO prototype,two kinds of high-sensitivity Rn detectors have been developed,namely the Si-PIN Rn detector and the LS Rn detector.The Si-PIN Rn detector uses a Si-PIN photodiode to detect theαfrom ^(214)Po decay and the LS Rn detector detects the coincident signals ofβfrom ^(214)Bi decay andβfrom ^(214)Po decay.Result The background measurement of Si-PIN Rn detector and LS Rn detector is performed to estimate the sensitivity.The sensitivity of Si-PIN Rn detector is around 9.0mBq/m^(3) and the sensitivity of LS Rn detector is around 64.0Bq/m^(3).Conclusion Both of the Si-PIN Rn detector and the LS Rn detector are working well with the JUNO prototype at present,and both of them can be developed as an online Rn concentration monitoring device for JUNO veto detector.展开更多
基金supported by JSPS KAKENHI Grant Numbers JP22H00259,JP22K18900,JP21H01669The Light Metal Educational Foundation,Inc.,Japan+1 种基金National Natural Science Foundation of China (51971075,52220105003)National Key Research & Development Program of China (2021YFB3703300,2022YFE0110600)。
文摘The origin of unique parallel alignment of(0001) poles to transverse direction(TD) was investigated using Mg-3Al-0.4Mn(mass%)alloy sheets rolled with different process conditions. When rolling was performed with intermediate reheating, the alloy showed a sluggish static recrystallization(SRX) behavior during post-annealing, facilitating the nucleation and growth of statically recrystallized grains from extension twins. This resulted in the apparent texture component with the parallel alignment of the(0001) poles to the TD, and the sheet exhibited good ductility for both the rolling direction(RD) and TD. In contrast, continuous rolling without intermediate reheating led to the formation of severely deformed regions near double twins. SRX was promoted at such regions, forming a typical basal textural feature with weak RD-split of the(0001) poles. Although extension twins were formed after the continuous rolling, SRX was facilitated at the severely deformed regions with double twins, and the formation of the unique alignment of the(0001) poles to the TD was suppressed. The RD-split texture led to the large elongation to failure along the RD, while it along the TD decreased owing to the narrow distribution of the(0001)poles toward the TD, resulting in the in-plane anisotropy in ductility.
基金This work was supported by National Natural Science Foundation for Young Scientists of China,Grant No.51801042 and 51704088Fundamental Research Funds for the Central Universities,National Natural Science Foundation,Grant No.51775150JSPS KAKENHI Grant-in-Aid for Young Scientists,Grant No.JP 16K18266,and JST,Advanced Low Carbon Technology Research and Development Program(ALCA),Grant No.12102886.
文摘The age-hardening behavior and mechanical properties of the extruded Mg-2Gd-1.2Y-0.5Zn(at.%)alloy with Zr or Mn additions were investigated.The results show that Mn added alloy exhibits more remarkable age-hardening response than Zr added alloy,which is attributed to the fact that partitioning of Mn into the β'phases,β'precipitates and long period stacking ordered(LPSO)phases leads to the decrement in(G d+Y)concentrations in the second phases,facilitating the precipitation during aging treatment.Both peak-aged alloys show bimodal microstructure comprising the fine DRXed grains with nano-sized β phases pinned at DRXed grain boundaries as well as coarse worked grains with strong fiber texture.High strength and good thermal stability were obtained in both peak-aged Mn and Zr added alloys.While the peak-aged Mn added alloy shows higher strength and superior creep resistance due to its denser β'precipitates,thin LPSO phases and γ'precipitates and higher area fraction of worked grains with strong fiber texture.The 0.2% tensile proof stress and ultimate tensile strength of peak-aged Mn added alloy reach up to 454 MPa and 508 MPa,respectively,with elongation of 3.2%at room temperature.The minimum creep rate of the peak-aged Mn added alloy at 250℃/150 MPa is 2.4 × 10^-8 s^-1,which is superior than previously reported extruded Mg-Gd based alloys.
基金supported by JSPS KAKENHI Grant Numbers JP19K15321,JP18H03837The Amada Foundation(AF2019037-C2)+2 种基金Advanced Low Carbon Technology Research and Development Program(ALCA),12102886National Natural Science Foundation,Grant Number 51971075Nagaoka University of Technology(NUT)Presidential Research Grant.
文摘Strength and ductility synergy in an Mg-3mass%Al-Mn(AM30)alloy sheet was successfully improved via twin-roll casting and annealing at low-temperature.An AM30 alloy sheet produced by twin-roll casting,homogenization,hot-rolling,and subsequent annealing at 170℃ for 64 h exhibits a good 0.2%proof stress of 170 MPa and a large elongation to failure of 33.1%along the rolling direction.The sheet also shows in-plane isotropic tensile properties,and the 0.2%proof stress and elongation to failure along the transverse direction are 176 MPa and 35.5%,respectively.Though the sheet produced by direct-chill casting also shows moderate strengths if the annealing condition is same,the direct-chill casting leads to the deteriorated elongation to failure of 23.9%and 30.0%for the rolling and transverse directions,respectively.As well as such excellent tensile properties,a high room-temperature stretch formability with an Index Erichsen value of 8.3 mm could be obtained in the twin-roll cast sheet annealed at 170℃ for 64 h.The annealing at a higher temperature further improves the stretch formability;however,this results in the decrease of the tensile properties.Microstructure characterization reveals that the excellent combination of strengths,ductility,and stretch formability in the twin-roll cast sheet annealed at the low-temperature annealing is mainly attributed to the uniform recrystallized microstructure,fine grain size,and circular distribution of(0001)poles away from the normal direction of the sheet.
基金the financial supports from the National Natural Science Foundation of China(NSFC,No.52005340 and 51601193)State Key Program of National Natural Science of China(No.51531002)+3 种基金National Key Research and Development Program of China(No.2016YFB0301104)National Basic Research Program of China(973 Program,No.2013CB632202)Guangdong Basic and Applied Basic Research Foundation(No.2019A1515110541)Shenzhen Bureau of Industry and Information Technology(No.ZDYBH201900000008)。
文摘The static recrystallization and associated texture evolution were investigated in an extruded Mg-Zn-Gd alloy with bimodal microstructure based on a quasi-in-situ electron back-scatter diffraction(EBSD)method.The typical rare earth(RE)texture formed during annealing,evolving from the bimodal microstructure with[1010]basal fiber texture that consisted of fine recrystallized(RXed)grains and coarse unrecrystallized(un RXed)grains elongated along the extrusion direction.In both RXed and un RXed regions,the RXed nucleation produced randomized orientations without preferred selection and the RXed grains with RE texture orientation had more intensive growth ability than those with basal fiber orientation,thereby leading to the preferred selection of RE texture orientation during grain growth.The relationships between stored strain energy,solute drag,grain growth and texture evolution are discussed in detail.This study provided direct evidence of the RE texture evolution in an extruded Mg-RE alloy,which assists in understanding the formation mechanisms for RE texture during extrusion and better developing wrought Mg alloys with improved formability.
基金financially supported by the National Natural Science Foundation for Young Scientists of China(Nos.51801042 and 51704088)the National Natural Science Foundation(Nos.51971075 and 51775150)+2 种基金the Fundamental Research Funds for the Central Universitiesthe JST Advanced Low Carbon Technology Researchthe Development Program(ALCA)(No.12102886)。
文摘The homogenized Mg-8.2 Gd-3.8 Y-1.0 Zn-0.4 Zr(wt.%)alloy full of plate-shaped long period stacking ordered(LPSO)phases was hot extruded in the atmosphere and cooled by the forced-air,then the effect of forced-air cooling on the microstructure and age-hardening response of the alloy was investigated in this work.The results show that in comparison with the extruded sample cooling in the atmosphere,the forced-air cooling restricts dynamic recrystallization(DRX)and brings about finer dynamic recrystallized(DRXed)grain size,stronger basal texture and higher dislocation density.Furthermore,the forced-air cooling promotes the dynamic precipitation in the DRXed regions and facilitates formation of plate-shaped LPSO phases andγ’phases with smaller interspacing in the unrecrystallized(un DRXed)regions,then slightly restricts the precipitation ofβphases during aging.After peak-ageing treatment,the extruded sample with forced-air cooling shows superior tensile properties with a tensile yield strength of 439 MPa,an ultimate tensile strength of 493 MPa,and elongation to failure of 18.6%.
基金supported by the National Natural Science Foundation of China[grant numbers 51571117,91860104]。
文摘The creep strength enhanced martensitic steels are key material for the main power generating units in ultra-supercritical plants.Studies on the evaluation of their creep rupture life show there is an overestimation of rupture life after long-term creep,which is known as premature failure.However,the microstructural origin of the premature failure remains unclear.Here in this study,we have carefully investigated the microstructural transformations and their influences on creep rupture behavior,showing that the evolution of martensite and M_(23)C_(6) carbides as well as Laves phase are responsible for the premature failure.By using multi-step TTP-LMP method,we confirmed a three-stage creep rupture behavior under different stress regions.Further quantitative analysis showed that the coarsening of M_(23)C_(6) carbides and recovery of martensite exert equal and dominant effects on the premature failure in the medium stress region,while precipitation and coarsening of Laves phase are responsible for the premature failure in the low stress region.
基金the National Natural Science Foundation of China(nos.51571117,51731006,92163215 and 52174364)。
文摘The strength-ductility trade-off has been the most challenging problem for structural metals for centuries.Nanoprecipitation strengthening is an ideal approach to enhance the strength without significantly sacrificing the ductility.Stable nanoprecipitates have been successfully acquired by nanostructural design,but the number density of nanoprecipitates cannot be further increased.Researchers attempted to enhance number density by introducing highly potent nucleation sites(e.g.,dislocations).However,there remains controversy over the influence of dislocations on the nucleation and growth of coherent nanoprecipitates with minimized nucleation barrier.Here,Cu-rich nanoprecipitates in an HSLA steel,as a typical type of coherent nanoprecipitates,are investigated.By combining analytical calculation and experiments,we show that dislocations are harmful for the formation of large numbered Cu-rich nanoprecipitates in a certain density range.Insufficient dislocations deprive solute atoms which decrease homogenous precipitation that cannot be compensated by the increase in heterogeneous precipitation.Under such circumstance,Cu-rich nanoprecipitates have smaller number density but larger size and higher fraction of incoherent structures due to rapid Ostwald ripening.As a result,by controlling dislocation density,the yield strength is increased by 24%without obvious loss in ductility as compared with traditional solution-quench-age process.Our work would help to optimize composition and processing routes that fully exploit the nanoprecipitation strengthening effect.
基金This work is supported by Xie Jialin Foundation of Institute of High Energy Physics(IHEP,Y7546150U2).
文摘Background JUNO(The Jiangmen Underground Neutrino Observatory)is a multipurpose neutrino experiment,and it has very strict requirements for the detector.According to the MC simulation for JUNO experiment requirements,the Rn concentration in the water of the veto detector should be less than 0.2Bq/m^(3).In order to measure such low Rn concentration,two kinds of high-sensitivity Rn measurement systems have been developed.Method Based on the water system of JUNO prototype,two kinds of high-sensitivity Rn detectors have been developed,namely the Si-PIN Rn detector and the LS Rn detector.The Si-PIN Rn detector uses a Si-PIN photodiode to detect theαfrom ^(214)Po decay and the LS Rn detector detects the coincident signals ofβfrom ^(214)Bi decay andβfrom ^(214)Po decay.Result The background measurement of Si-PIN Rn detector and LS Rn detector is performed to estimate the sensitivity.The sensitivity of Si-PIN Rn detector is around 9.0mBq/m^(3) and the sensitivity of LS Rn detector is around 64.0Bq/m^(3).Conclusion Both of the Si-PIN Rn detector and the LS Rn detector are working well with the JUNO prototype at present,and both of them can be developed as an online Rn concentration monitoring device for JUNO veto detector.