由于稀土(RE)元素在激光粉末床熔融(Laser powder bed fusion,LPBF)制备的WE43合金中具有超高的固溶度,因此本文省去固溶处理过程,直接对其进行T5时效处理,研究了T5时效处理对其微观组织、物相、缺陷以及拉伸性能的影响。结果表明:T5时...由于稀土(RE)元素在激光粉末床熔融(Laser powder bed fusion,LPBF)制备的WE43合金中具有超高的固溶度,因此本文省去固溶处理过程,直接对其进行T5时效处理,研究了T5时效处理对其微观组织、物相、缺陷以及拉伸性能的影响。结果表明:T5时效处理后,WE43合金中的椭圆形和鱼鳞纹组织消失,平均晶粒尺寸由2μm长大至8.5μm,稀土相由点状弥散分布在α-Mg晶体内转变为连续或较小间距的分布在晶界处,形状为碟状或片状、针状,整体分布均匀;T5时效处理后WE43合金的屈服强度、抗拉强度和伸长率相对于LPBF态分别下降了12.6%、10.7%和6.6%,其力学性能降低的原因可归因于以下3个方面:时效后合金的晶粒尺寸增大;时效后连续或较小间距分布于晶界处的脆性析出相破坏了晶界的连续性,以及微孔等缺陷依然存在;时效后稀土元素从α-Mg基体中析出,导致其在α-Mg基体中的固溶度降低;但稀土原子在α-Mg中的固溶度对LPBF制备的WE43合金塑性的影响程度相对较低。展开更多
Solution and aging treatment were conducted on the laser directed energy deposition(LDED)-prepared carbon nanotubes(CNTs)-reinforced WE43(CNTs/WE43)layers to optimize their microstructure and surface properties in thi...Solution and aging treatment were conducted on the laser directed energy deposition(LDED)-prepared carbon nanotubes(CNTs)-reinforced WE43(CNTs/WE43)layers to optimize their microstructure and surface properties in this study.The microstructure of the WE43 and CNTs/WE43 layers was systematically compared.The dissolution of divorced eutectics at the grain boundaries was retarded by CNTs during solution treatment.The spot segregation composed of Mg_(24)Y_(5),CNTs,and Zr cores in the solution treated CNTs/WE43 layer presented a slight decreasing in Y content.The grain growth of both types of layers underwent three stages:slow,rapid,and steady-state.The significant inhibitory effect of CNTs on the grain growth of the LDED WE43 matrix was more pronounced than the promoting effect of temperature,resulting in a 47%increase at 510℃ and a 35%increase at 540℃ in the grain growth exponent compared to the WE43 layers at 510℃.During the subsequent aging treatment at 225℃,the precipitation sequences from plate-shaped β″to plate-shaped and globular β′ were observed in both types of layers.CNTs can facilitate an increase in the nucleation rate of precipitates,but without accelerating precipitation hardening rate.The long and short diameters of the precipitates in peak-aged state were decreased by 48.5%and 43.1%by addition of CNTs,respectively.The wear resistance of both the WE43 and CNTs/WE43 layers can be significantly enhanced through solution and aging treatment.The enhancement in wear resistance for the CNTs/WE43 layers is considerably greater than that of the WE43 layers.展开更多
WE43MEO magnesium foils(thickness≤200μm)were successfully produced via hot rolling.The initially extruded material was heat treated at 450℃for 2 h to achieve a more homogenous microstructure.Afterwards the sheets w...WE43MEO magnesium foils(thickness≤200μm)were successfully produced via hot rolling.The initially extruded material was heat treated at 450℃for 2 h to achieve a more homogenous microstructure.Afterwards the sheets were hot rolled at 480℃in two to five rolling passes to achieve a uniform thickness of less than 200μm and finally heat treated(T5 and T6 heat treatment).After foil rolling and final heat treatment the microstructural und texture evolution as well as resulting mechanical properties were investigated.Therefore,the samples were quenched directly after foil rolling and the final heat treatment.The foil rolling led either to a deformation microstructure(two and three passes)or globular grains(four and five passes)depending on the number of rolling passes.As main recrystallisation mechanisms continuous dynamic recrystallisation(CDRX)and twinning induced dynamic recrystallisation(TDRX)were identified.The resulting textures revealed the activation of non-basal slip of<c+a>-dislocations during prior foil rolling.As a result of the rolling,the strength increased and the elongation decreased compared to the extruded and heat-treated state.Furthermore,it was found that a T6 temper increased corrosion resistance of the tested WE43MEO foils.展开更多
The complex non-equilibrium solidification effects of the laser powder bed fusion(LPBF)combined with the high solubility of rare-earth(RE)elements,provide a new advanced powder metallurgy process for Mg RE alloys with...The complex non-equilibrium solidification effects of the laser powder bed fusion(LPBF)combined with the high solubility of rare-earth(RE)elements,provide a new advanced powder metallurgy process for Mg RE alloys with outstanding mechanical performances.However,its creep mechanism has not been revealed yet.The present study systematically investigates and evaluates the high-temperature creep mechanism of LPBFed WE43 alloy under varying temperatures and applied stress conditions.In addition,it thoroughly elucidates the interactions and evolution mechanisms between precipitates and disloca-tions during the creep process.Subject to residual stresses and thermal cycling,theβphase is formed in the form of“precipitation chains”(PCs)within the grains.The metastable phasesβ″,β′,andβ_(1) in-situ precipitate between the PCs.The creep resistance of the(LPBFed)WE43 alloy is governed by the evolution of precipitates and their interactions with dislocations during the creep.Under creep condi-tions at 200℃,a large number of<c+a>anddislocations undergo climb and cross-slip behaviors within the grains.During the climb and cross-slip of dislocations,the Orowan strengthening effect ofβ″,the cutting mechanisms ofβ′andβ_(1) phases relative to dislocations,and the dislocation barriers formed by theβphase arrays collectively impart excellent creep resistance to the WE43 alloy.As creep time progresses,dislocations accumulate within the grains,and theβandβ_(1) phases promote the forma-tion of subgrain boundaries,further triggering discontinuous dynamic recrystallization behaviors during the creep process.Furthermore,influenced by the directional diffusion of elements,precipitates dynami-cally form around the grain boundaries of recrystallized grains,thereby enhancing the resistance to grain boundary sliding.When the creep temperature increases to 250℃ or 300℃,a large number of<c+a>dislocations,accompanied by the dissolution of metastable phases and elemental re-diffusion,transform during the creep process into stacking faults(SFs).SFs not only exhibit high thermal stability but also act as effective dislocation barriers at high temperatures through lattice mismatch mechanisms.However,under high-temperature conditions,thermal activation leads to the dissolution of unstable metastable phases,promoting rapid coarsening and transformation of precipitates into various morphologies ofβphases,thereby causing a catastrophic decline in creep performance.At the same time,high tempera-tures further exacerbate elemental diffusion,resulting in precipitate-free zones near grain boundaries,thereby inducing crack initiation.Therefore,the creep resistance of as-deposited alloys decreases signif-icantly at higher temperatures.Building on this,the future development trends of LPBFed WE43 alloys are envisioned,where homogenizing heterostructures or introducing high aspect ratio precipitates and high-density SFs prior to creep can be regarded as a promising approach for enhancing creep resistance in LPBFed WE43 alloys.展开更多
WE43 is a high-strength magnesium alloy containing rare-earth elements such as Y,Gd and Nd.Nevertheless,how to further obtain the balance of strength and ductility,as well as the manufacture of complex structures is s...WE43 is a high-strength magnesium alloy containing rare-earth elements such as Y,Gd and Nd.Nevertheless,how to further obtain the balance of strength and ductility,as well as the manufacture of complex structures is still a dilemma for its engineering application.In this study,WE43 alloy samples withfine microstructures,high densification and excellent mechanical properties were successfully prepared by laser powder bed fusion(LPBF)additive manufacturing.The optimal process window was established,and the formation mechanisms of three types of porosity defects were revealed,namely lack-of-fusion pores,meltfluctuation-induced pores,and keyhole-induced pores.With the combined process of laser power of 200 W and scanning speed of 600 mm/s,samples with a high density of 99.89%were obtained.Furthermore,periodic heterogeneous microstructure was prepared along the build direction,i.e.,fine grains(∼4.1μm)at melt pool boundaries and coarse grain(∼23.6μm)inside melt pool.This was mainly due to the preferential precipitation of Zr and Mg_(3)(Gd,Nd)nano-precipitates at the melt pool boundaries providing nucleation sites for the grains.This special feature could provide an extra hetero-deformation induced(HDI)strengthening and retard fracture.The optimal tensile yield strength,ultimate tensile strength and elongation at break were 276±1 MPa,292±1 MPa and 6.1±0.2%,respectively.The obtained tensile properties were superior to those of other magnesium alloys and those fabricated by other processes.The solid solution strengthening(∼24.5%),grain boundary strengthening(∼14.4%)and HDI strengthening(∼32.2%)were the main sources of high yield strength.This work provides a guidance on studying the pore defect suppression and strengthening mechanisms of WE43 alloy and other magnesium alloys produced by LPBF.展开更多
Nature-inspired designs have increasingly influenced biomedical engineering by providing superior biomechanical performance and structural stability.In this study,the diabolical ironclad beetle elytra structure was ap...Nature-inspired designs have increasingly influenced biomedical engineering by providing superior biomechanical performance and structural stability.In this study,the diabolical ironclad beetle elytra structure was applied to stent strut designs and thoroughly evaluated through various computational simulations to assess their potential to enhance the mechanical performance of WE43 magnesium alloy stents.Connected elliptical structures with a vertical-to-horizontal length ratio of 1:1.8 were incorporated in varying numbers and then compared to conventional laser-cut stents using 3-point bending,crush,crimping,and expansion tests,internal carotid artery insertion simulations,and computational fluid dynamics analyses.The results demonstrated that the biomimetic stents exhibited significantly improved stress distribution and reduced applied stress while maintaining hemodynamic stability.Computational fluid dynamics simulations further confirmed that the biomimetic could reduce wall shear stress and improve blood flow,thereby potentially minimizing the risk of restenosis and thrombosis.These findings suggest that diabolical ironclad beetle-inspired stent structures may offer enhanced biomechanical performance and clinical safety in magnesium-based endovascular interventions.展开更多
文摘由于稀土(RE)元素在激光粉末床熔融(Laser powder bed fusion,LPBF)制备的WE43合金中具有超高的固溶度,因此本文省去固溶处理过程,直接对其进行T5时效处理,研究了T5时效处理对其微观组织、物相、缺陷以及拉伸性能的影响。结果表明:T5时效处理后,WE43合金中的椭圆形和鱼鳞纹组织消失,平均晶粒尺寸由2μm长大至8.5μm,稀土相由点状弥散分布在α-Mg晶体内转变为连续或较小间距的分布在晶界处,形状为碟状或片状、针状,整体分布均匀;T5时效处理后WE43合金的屈服强度、抗拉强度和伸长率相对于LPBF态分别下降了12.6%、10.7%和6.6%,其力学性能降低的原因可归因于以下3个方面:时效后合金的晶粒尺寸增大;时效后连续或较小间距分布于晶界处的脆性析出相破坏了晶界的连续性,以及微孔等缺陷依然存在;时效后稀土元素从α-Mg基体中析出,导致其在α-Mg基体中的固溶度降低;但稀土原子在α-Mg中的固溶度对LPBF制备的WE43合金塑性的影响程度相对较低。
基金supported by the National Natural Science Foundation of China(52005264).
文摘Solution and aging treatment were conducted on the laser directed energy deposition(LDED)-prepared carbon nanotubes(CNTs)-reinforced WE43(CNTs/WE43)layers to optimize their microstructure and surface properties in this study.The microstructure of the WE43 and CNTs/WE43 layers was systematically compared.The dissolution of divorced eutectics at the grain boundaries was retarded by CNTs during solution treatment.The spot segregation composed of Mg_(24)Y_(5),CNTs,and Zr cores in the solution treated CNTs/WE43 layer presented a slight decreasing in Y content.The grain growth of both types of layers underwent three stages:slow,rapid,and steady-state.The significant inhibitory effect of CNTs on the grain growth of the LDED WE43 matrix was more pronounced than the promoting effect of temperature,resulting in a 47%increase at 510℃ and a 35%increase at 540℃ in the grain growth exponent compared to the WE43 layers at 510℃.During the subsequent aging treatment at 225℃,the precipitation sequences from plate-shaped β″to plate-shaped and globular β′ were observed in both types of layers.CNTs can facilitate an increase in the nucleation rate of precipitates,but without accelerating precipitation hardening rate.The long and short diameters of the precipitates in peak-aged state were decreased by 48.5%and 43.1%by addition of CNTs,respectively.The wear resistance of both the WE43 and CNTs/WE43 layers can be significantly enhanced through solution and aging treatment.The enhancement in wear resistance for the CNTs/WE43 layers is considerably greater than that of the WE43 layers.
文摘WE43MEO magnesium foils(thickness≤200μm)were successfully produced via hot rolling.The initially extruded material was heat treated at 450℃for 2 h to achieve a more homogenous microstructure.Afterwards the sheets were hot rolled at 480℃in two to five rolling passes to achieve a uniform thickness of less than 200μm and finally heat treated(T5 and T6 heat treatment).After foil rolling and final heat treatment the microstructural und texture evolution as well as resulting mechanical properties were investigated.Therefore,the samples were quenched directly after foil rolling and the final heat treatment.The foil rolling led either to a deformation microstructure(two and three passes)or globular grains(four and five passes)depending on the number of rolling passes.As main recrystallisation mechanisms continuous dynamic recrystallisation(CDRX)and twinning induced dynamic recrystallisation(TDRX)were identified.The resulting textures revealed the activation of non-basal slip of<c+a>-dislocations during prior foil rolling.As a result of the rolling,the strength increased and the elongation decreased compared to the extruded and heat-treated state.Furthermore,it was found that a T6 temper increased corrosion resistance of the tested WE43MEO foils.
基金financially supported by the National Natu-ral Science Foundation of China(Nos.52201105 and 52475324)the National Key Research and Development Program of China(Nos.2023YFB3408003 and 2023YFB3308001)+4 种基金the Graduate Sci-entific Research and Innovation Foundation of Chongqing(No.CYB23018)the Innovation Support Program for Overseas Re-turnees in Chongqing(No.cx2023061)the Research Project from Chongqing Key Laboratory of High-performance Structural Additive Manufacturing(No.02090011044158)the Chengdu Key Research and Development Support Program(No.2023-YF11-00077-HZ)the Fundamental Research Foundation for the Central Universities in China(Nos.2024IAIS-QN012 and 2023CDJKYJH049)。
文摘The complex non-equilibrium solidification effects of the laser powder bed fusion(LPBF)combined with the high solubility of rare-earth(RE)elements,provide a new advanced powder metallurgy process for Mg RE alloys with outstanding mechanical performances.However,its creep mechanism has not been revealed yet.The present study systematically investigates and evaluates the high-temperature creep mechanism of LPBFed WE43 alloy under varying temperatures and applied stress conditions.In addition,it thoroughly elucidates the interactions and evolution mechanisms between precipitates and disloca-tions during the creep process.Subject to residual stresses and thermal cycling,theβphase is formed in the form of“precipitation chains”(PCs)within the grains.The metastable phasesβ″,β′,andβ_(1) in-situ precipitate between the PCs.The creep resistance of the(LPBFed)WE43 alloy is governed by the evolution of precipitates and their interactions with dislocations during the creep.Under creep condi-tions at 200℃,a large number of<c+a>anddislocations undergo climb and cross-slip behaviors within the grains.During the climb and cross-slip of dislocations,the Orowan strengthening effect ofβ″,the cutting mechanisms ofβ′andβ_(1) phases relative to dislocations,and the dislocation barriers formed by theβphase arrays collectively impart excellent creep resistance to the WE43 alloy.As creep time progresses,dislocations accumulate within the grains,and theβandβ_(1) phases promote the forma-tion of subgrain boundaries,further triggering discontinuous dynamic recrystallization behaviors during the creep process.Furthermore,influenced by the directional diffusion of elements,precipitates dynami-cally form around the grain boundaries of recrystallized grains,thereby enhancing the resistance to grain boundary sliding.When the creep temperature increases to 250℃ or 300℃,a large number of<c+a>dislocations,accompanied by the dissolution of metastable phases and elemental re-diffusion,transform during the creep process into stacking faults(SFs).SFs not only exhibit high thermal stability but also act as effective dislocation barriers at high temperatures through lattice mismatch mechanisms.However,under high-temperature conditions,thermal activation leads to the dissolution of unstable metastable phases,promoting rapid coarsening and transformation of precipitates into various morphologies ofβphases,thereby causing a catastrophic decline in creep performance.At the same time,high tempera-tures further exacerbate elemental diffusion,resulting in precipitate-free zones near grain boundaries,thereby inducing crack initiation.Therefore,the creep resistance of as-deposited alloys decreases signif-icantly at higher temperatures.Building on this,the future development trends of LPBFed WE43 alloys are envisioned,where homogenizing heterostructures or introducing high aspect ratio precipitates and high-density SFs prior to creep can be regarded as a promising approach for enhancing creep resistance in LPBFed WE43 alloys.
基金supported by the National Natural Science Foundation of China(Nos.52275333,52375335 and U22A202494)the Stabilization Support Project of AVIC Manufacturing Technology Institute(No.KZ571801)+1 种基金the Knowledge Innovation Special Project of Wuhan(No.2022010801010302)the Fundamental Research Funds for the Central Universities(No.YCJJ20230359).
文摘WE43 is a high-strength magnesium alloy containing rare-earth elements such as Y,Gd and Nd.Nevertheless,how to further obtain the balance of strength and ductility,as well as the manufacture of complex structures is still a dilemma for its engineering application.In this study,WE43 alloy samples withfine microstructures,high densification and excellent mechanical properties were successfully prepared by laser powder bed fusion(LPBF)additive manufacturing.The optimal process window was established,and the formation mechanisms of three types of porosity defects were revealed,namely lack-of-fusion pores,meltfluctuation-induced pores,and keyhole-induced pores.With the combined process of laser power of 200 W and scanning speed of 600 mm/s,samples with a high density of 99.89%were obtained.Furthermore,periodic heterogeneous microstructure was prepared along the build direction,i.e.,fine grains(∼4.1μm)at melt pool boundaries and coarse grain(∼23.6μm)inside melt pool.This was mainly due to the preferential precipitation of Zr and Mg_(3)(Gd,Nd)nano-precipitates at the melt pool boundaries providing nucleation sites for the grains.This special feature could provide an extra hetero-deformation induced(HDI)strengthening and retard fracture.The optimal tensile yield strength,ultimate tensile strength and elongation at break were 276±1 MPa,292±1 MPa and 6.1±0.2%,respectively.The obtained tensile properties were superior to those of other magnesium alloys and those fabricated by other processes.The solid solution strengthening(∼24.5%),grain boundary strengthening(∼14.4%)and HDI strengthening(∼32.2%)were the main sources of high yield strength.This work provides a guidance on studying the pore defect suppression and strengthening mechanisms of WE43 alloy and other magnesium alloys produced by LPBF.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(RS-2024-00449812,2022R1I1A3064173)the Korea government(MSIT)(No.RS-2024-00335915).
文摘Nature-inspired designs have increasingly influenced biomedical engineering by providing superior biomechanical performance and structural stability.In this study,the diabolical ironclad beetle elytra structure was applied to stent strut designs and thoroughly evaluated through various computational simulations to assess their potential to enhance the mechanical performance of WE43 magnesium alloy stents.Connected elliptical structures with a vertical-to-horizontal length ratio of 1:1.8 were incorporated in varying numbers and then compared to conventional laser-cut stents using 3-point bending,crush,crimping,and expansion tests,internal carotid artery insertion simulations,and computational fluid dynamics analyses.The results demonstrated that the biomimetic stents exhibited significantly improved stress distribution and reduced applied stress while maintaining hemodynamic stability.Computational fluid dynamics simulations further confirmed that the biomimetic could reduce wall shear stress and improve blood flow,thereby potentially minimizing the risk of restenosis and thrombosis.These findings suggest that diabolical ironclad beetle-inspired stent structures may offer enhanced biomechanical performance and clinical safety in magnesium-based endovascular interventions.
