As a universal casting Mg-RE alloy,Mg-6Gd-3Y-Zr(GW63K,wt.%)alloy exhibits superior strength-ductility synergy and holds significant potential for engineering applications.In this study,the GW63K alloy is produced usin...As a universal casting Mg-RE alloy,Mg-6Gd-3Y-Zr(GW63K,wt.%)alloy exhibits superior strength-ductility synergy and holds significant potential for engineering applications.In this study,the GW63K alloy is produced using the laser powder bed fusion(LPBF)additive manufacturing(AM)process for the first time.The printability,microstructure characteristics,and post-heat treatment conditions of the GW63K alloy are systematically investigated.The as-built GW63K samples demonstrate high relative densities exceeding 99.6%and exhibit no macroscopic and microscopic cracking across a wide range of process parameters,indicating excellent printability.An exceptional heterogeneous microstructure is observed in the as-built GW63K alloy,comprising coarse columnar grains,fine equiaxed grains with an average grain size of 21.72μm,uniformly distributed nano-sized Mg_(24)(Gd,Y)_(5)secondary phase,and numerous dislocations.Consequently,the as-built GW63K alloy displays enhanced tensile strengths and ductility compared to the as-cast alloy,with yield strength(YS),ultimate tensile strength(UTS)and elongation(EL)values of 218±4 MPa,284±5 MPa and 11.9±1.6%respectively.Additionally,due to the absence of coarse micron-sized secondary phase,a specific direct aging(T5)heat treatment regime at 200℃for 128 h is optimized for the as-built GW63K alloy to introduce dense and dispersedβ’aging precipitates.This T5 treatment surpasses the conventional solution plus aging(T6)heat treatment in enhancing mechanical properties.The LPBF-T5 GW63K alloy exhibits YS,UTS and EL values of 293±6 MPa,359±4 MPa and 2.9±0.7%,respectively.Notably,the YS of the LPBF-T5 alloy represents the highest value for the GW63K alloy,even surpassing that of the extrusion-T5 alloy.This study indicates that the GW63K alloy is a highly promising material for manufacturing near-net-shape high-strength Mg alloy components with intricate geometries using LPBF.展开更多
To study the influence of aging heat treatments on the microstructure of single crystal superalloys with high content of refractory elements and optimal the aging heat treatment regimes, a single crystal superalloy co...To study the influence of aging heat treatments on the microstructure of single crystal superalloys with high content of refractory elements and optimal the aging heat treatment regimes, a single crystal superalloy containing 22 wt% refractory elements was investigated.Results show that for the experimental alloy, even the homogenization-solution heat treatment for 25 h cannot homogenize the alloying elements completely. During primary aging heat treatment, γ＇ phase grows larger and turns to regular cubes. Higher aging temperature induces larger γ＇ cubes. For specimens with primary aging heat treated at 1120 ℃,γ＇ morphology does not change apparently during secondary aging heat treatment. For specimens with primary aging heat treatment at 1150 ℃,γ＇phase in interdendrite grows obviously comparing with that in dendrites. By analyzing the precipitating kinetics of γ＇phase, it is found that owning to the dendrite segregation and different aging heat treatment temperatures, γ＇ phase at different regions grows under the control of different factors at different aging heat treatment stages. The two controlling factors that are driving forces of phase transformation and element diffusion rate induce obviously different growth rates of γ＇ phase. As a result, the γ＇-precipitating behaviors are variable based on different solute concentrations and aging temperatures. For advanced single crystal superalloys that are supposed to be used at relatively high temperatures, the final γ＇ size after aging heat treatment is suggested to be close to the crossing point of diffusion controlling curve and driving force controlling curve corresponding to the serving temperature. And then,high-temperature properties can be improved.展开更多
The effect of aging on the mechanical properties and microstructures of a new ZG12Cr9 MolColNiVNbNB ferritic heat resistant steel was investigated in this work to satisfy the high steam parameters of the ultra-supercr...The effect of aging on the mechanical properties and microstructures of a new ZG12Cr9 MolColNiVNbNB ferritic heat resistant steel was investigated in this work to satisfy the high steam parameters of the ultra-supercritical power plant.The results show that the main precipitates during aging are Fe（Cr,Mo）23C6,V（Nb）C,and（Fe2Mo） Laves in the steel.The amounts of the precipitated phases increase during aging,and correspondingly,the morphologies of phases are similar to be round.Fe（Cr,Mo）23C6 appears along boundaries and grows with increasing temperature.In addition,it is revealed that the martensitic laths are coarsened and eventually happen to be polygonization.The hardness and strength decrease gradually,whereas the plasticity of the steel increases.What＇s more,the hardness of this steel after creep is similar to that of other 9%-12%Cr ferritic steels.Thus,ZG12Cr9 MolColNiVNbNB can be used in the project.展开更多
Laser powder bed fusion(LPBF)of Mg alloys mainly focuses on the traditional commercial casting Mg alloys such as AZ91D,ZK60 and WE43,which usually display relatively low tensile strengths.Herein we developed a novel h...Laser powder bed fusion(LPBF)of Mg alloys mainly focuses on the traditional commercial casting Mg alloys such as AZ91D,ZK60 and WE43,which usually display relatively low tensile strengths.Herein we developed a novel high-strength Mg-12 Gd-2 Y-1 Zn-0.5 Mn(wt.%,GWZ1221M)alloy for the LPBF additive manufacturing process,and the evolution of microstructure and mechanical properties from the as-built state to LPBF-T4 and LPBF-T6 states was systematically investigated.The as-built GWZ1221M alloy exhibited fine equiaxed grains with an average grain size of only 4.3±2.2μm,while the as-cast alloy displayed typical coarse dendrite grains(178.2±73.6μm).Thus,the as-built alloy showed significantly higher tensile strengths than the as-cast counterpart,and its yield strength(YS),ultimate tensile strength(UTS)and elongation(EL)were 315±8 MPa,340±7 MPa and 2.7±0.5%respectively.Solution treatment transformed hard and brittleβ-(Mg,Zn)_(3)(Gd,Y)phase into basal X phase and lamellar long period stacking ordered(LPSO)with better plastic deformability,leading to the improvement of EL.Then peak-aging heat treatment introduced numerous nano-sized prismaticβprecipitates inside grains,resulting in the enhancement of YS.Finally,the LPBF-T6 alloy achieved appreciably high strength with YS,UTS and EL of 320±3 MPa,395±4 MPa and 2.1±0.4%respectively.Both as-built and LPBF-T6 GWZ1221M alloys showed remarkably higher tensile strengths than the as-cast counterparts and as-built commercial Mg alloys,highlighting the great potential of high-strength as-built Mg-Gd based alloys for structural applications.展开更多
The accurate simulation of boundary layer transition process plays a very important role in the prediction of turbine blade temperature field. Based on the Abu-Ghannam and Shaw （AGS） and c-Re h transition models, a ...The accurate simulation of boundary layer transition process plays a very important role in the prediction of turbine blade temperature field. Based on the Abu-Ghannam and Shaw （AGS） and c-Re h transition models, a 3D conjugate heat transfer solver is developed, where the fluid domain is discretized by multi-block structured grids, and the solid domain is discretized by unstructured grids. At the unmatched fluid/solid interface, the shape function interpolation method is adopted to ensure the conservation of the interfacial heat flux. Then the shear stress transport （SST） model, SST ＆ AGS model and SST ＆ c-Re h model are used to investigate the flow and heat transfer characteristics of Mark II turbine vane. The results indicate that compared with the full turbulence model （SST model）, the transition models could improve the prediction accuracy of temperature and heat transfer coefficient at the laminar zone near the blade leading edge. Compared with the AGS transition model, the c-Re h model could predict the transition onset location induced by shock/boundary layer interaction more accurately, and the prediction accuracy of temperature field could be greatly improved.展开更多
Fatigue lives for the smooth and notched specimens of 8090 Al-Li alloy jn the different ageing conditions have been studied. For the smooth samples of 8090 alloy the artificial ageing results in an increase in fatigue...Fatigue lives for the smooth and notched specimens of 8090 Al-Li alloy jn the different ageing conditions have been studied. For the smooth samples of 8090 alloy the artificial ageing results in an increase in fatigue life in comparison with natural ageing. On the contrary, the notched specimens of 8090 alloy in the naturally aged condition show higher fatigue life than in the peak-aged. The exposure to either the peak-aged or naturally aged leads to superior fatigue properties of Al-Li alloy to the traditional high strength aluminum alloys of 7075 and 2024, especially in the latter aged condition. In all ageing conditions, i,e. naturally, under-, peak- and over-aged, the peak-aged 8090 alloy displays the highest fatigue life and the over-aged material has a minimum value at the same stress amplitude. The difference in fatigue life is mainly attributable to the size and distribution of strengthening precipitates as well as the wide of precipitate free zones (PFZ's) along grain boundaries.展开更多
基金supported by the National Key Research and Development Program of China (No.2021YFB3701000)the National Natural Science Foundation of China (Nos. U21A2047, 52201129, 51821001,U2037601)+1 种基金the support by the China Postdoctoral Science Foundation (No. 2023M742219)the Postdoctoral Fellowship Program (Grade B) of CPSF(No. GZB20240419)
文摘As a universal casting Mg-RE alloy,Mg-6Gd-3Y-Zr(GW63K,wt.%)alloy exhibits superior strength-ductility synergy and holds significant potential for engineering applications.In this study,the GW63K alloy is produced using the laser powder bed fusion(LPBF)additive manufacturing(AM)process for the first time.The printability,microstructure characteristics,and post-heat treatment conditions of the GW63K alloy are systematically investigated.The as-built GW63K samples demonstrate high relative densities exceeding 99.6%and exhibit no macroscopic and microscopic cracking across a wide range of process parameters,indicating excellent printability.An exceptional heterogeneous microstructure is observed in the as-built GW63K alloy,comprising coarse columnar grains,fine equiaxed grains with an average grain size of 21.72μm,uniformly distributed nano-sized Mg_(24)(Gd,Y)_(5)secondary phase,and numerous dislocations.Consequently,the as-built GW63K alloy displays enhanced tensile strengths and ductility compared to the as-cast alloy,with yield strength(YS),ultimate tensile strength(UTS)and elongation(EL)values of 218±4 MPa,284±5 MPa and 11.9±1.6%respectively.Additionally,due to the absence of coarse micron-sized secondary phase,a specific direct aging(T5)heat treatment regime at 200℃for 128 h is optimized for the as-built GW63K alloy to introduce dense and dispersedβ’aging precipitates.This T5 treatment surpasses the conventional solution plus aging(T6)heat treatment in enhancing mechanical properties.The LPBF-T5 GW63K alloy exhibits YS,UTS and EL values of 293±6 MPa,359±4 MPa and 2.9±0.7%,respectively.Notably,the YS of the LPBF-T5 alloy represents the highest value for the GW63K alloy,even surpassing that of the extrusion-T5 alloy.This study indicates that the GW63K alloy is a highly promising material for manufacturing near-net-shape high-strength Mg alloy components with intricate geometries using LPBF.
基金financially supported by the Foundation of Beijing Institute of Aeronautical Materials (No.KJSJ150109)
文摘To study the influence of aging heat treatments on the microstructure of single crystal superalloys with high content of refractory elements and optimal the aging heat treatment regimes, a single crystal superalloy containing 22 wt% refractory elements was investigated.Results show that for the experimental alloy, even the homogenization-solution heat treatment for 25 h cannot homogenize the alloying elements completely. During primary aging heat treatment, γ＇ phase grows larger and turns to regular cubes. Higher aging temperature induces larger γ＇ cubes. For specimens with primary aging heat treated at 1120 ℃,γ＇ morphology does not change apparently during secondary aging heat treatment. For specimens with primary aging heat treatment at 1150 ℃,γ＇phase in interdendrite grows obviously comparing with that in dendrites. By analyzing the precipitating kinetics of γ＇phase, it is found that owning to the dendrite segregation and different aging heat treatment temperatures, γ＇ phase at different regions grows under the control of different factors at different aging heat treatment stages. The two controlling factors that are driving forces of phase transformation and element diffusion rate induce obviously different growth rates of γ＇ phase. As a result, the γ＇-precipitating behaviors are variable based on different solute concentrations and aging temperatures. For advanced single crystal superalloys that are supposed to be used at relatively high temperatures, the final γ＇ size after aging heat treatment is suggested to be close to the crossing point of diffusion controlling curve and driving force controlling curve corresponding to the serving temperature. And then,high-temperature properties can be improved.
基金supported by the Science and Technology Program of Sichuan Province,China(No.2013GZX0146)
文摘The effect of aging on the mechanical properties and microstructures of a new ZG12Cr9 MolColNiVNbNB ferritic heat resistant steel was investigated in this work to satisfy the high steam parameters of the ultra-supercritical power plant.The results show that the main precipitates during aging are Fe（Cr,Mo）23C6,V（Nb）C,and（Fe2Mo） Laves in the steel.The amounts of the precipitated phases increase during aging,and correspondingly,the morphologies of phases are similar to be round.Fe（Cr,Mo）23C6 appears along boundaries and grows with increasing temperature.In addition,it is revealed that the martensitic laths are coarsened and eventually happen to be polygonization.The hardness and strength decrease gradually,whereas the plasticity of the steel increases.What＇s more,the hardness of this steel after creep is similar to that of other 9%-12%Cr ferritic steels.Thus,ZG12Cr9 MolColNiVNbNB can be used in the project.
基金supported by the National Key Research and Development Program of China(No.2021YFB3701000)the National Natural Science Foundation of China(Nos.51971130,52201129,U21A2047,51821001,U2037601)。
文摘Laser powder bed fusion(LPBF)of Mg alloys mainly focuses on the traditional commercial casting Mg alloys such as AZ91D,ZK60 and WE43,which usually display relatively low tensile strengths.Herein we developed a novel high-strength Mg-12 Gd-2 Y-1 Zn-0.5 Mn(wt.%,GWZ1221M)alloy for the LPBF additive manufacturing process,and the evolution of microstructure and mechanical properties from the as-built state to LPBF-T4 and LPBF-T6 states was systematically investigated.The as-built GWZ1221M alloy exhibited fine equiaxed grains with an average grain size of only 4.3±2.2μm,while the as-cast alloy displayed typical coarse dendrite grains(178.2±73.6μm).Thus,the as-built alloy showed significantly higher tensile strengths than the as-cast counterpart,and its yield strength(YS),ultimate tensile strength(UTS)and elongation(EL)were 315±8 MPa,340±7 MPa and 2.7±0.5%respectively.Solution treatment transformed hard and brittleβ-(Mg,Zn)_(3)(Gd,Y)phase into basal X phase and lamellar long period stacking ordered(LPSO)with better plastic deformability,leading to the improvement of EL.Then peak-aging heat treatment introduced numerous nano-sized prismaticβprecipitates inside grains,resulting in the enhancement of YS.Finally,the LPBF-T6 alloy achieved appreciably high strength with YS,UTS and EL of 320±3 MPa,395±4 MPa and 2.1±0.4%respectively.Both as-built and LPBF-T6 GWZ1221M alloys showed remarkably higher tensile strengths than the as-cast counterparts and as-built commercial Mg alloys,highlighting the great potential of high-strength as-built Mg-Gd based alloys for structural applications.
基金National Natural Science Foundation of China(Grant No.91130013)Innovation Foundation of BUAA for PhD Graduates(YWF-12-RBYJ-010)Specialized Research Fund for the Doctoral Program of Higher Education(20101102110011)for funding this work
文摘The accurate simulation of boundary layer transition process plays a very important role in the prediction of turbine blade temperature field. Based on the Abu-Ghannam and Shaw （AGS） and c-Re h transition models, a 3D conjugate heat transfer solver is developed, where the fluid domain is discretized by multi-block structured grids, and the solid domain is discretized by unstructured grids. At the unmatched fluid/solid interface, the shape function interpolation method is adopted to ensure the conservation of the interfacial heat flux. Then the shear stress transport （SST） model, SST ＆ AGS model and SST ＆ c-Re h model are used to investigate the flow and heat transfer characteristics of Mark II turbine vane. The results indicate that compared with the full turbulence model （SST model）, the transition models could improve the prediction accuracy of temperature and heat transfer coefficient at the laminar zone near the blade leading edge. Compared with the AGS transition model, the c-Re h model could predict the transition onset location induced by shock/boundary layer interaction more accurately, and the prediction accuracy of temperature field could be greatly improved.
文摘Fatigue lives for the smooth and notched specimens of 8090 Al-Li alloy jn the different ageing conditions have been studied. For the smooth samples of 8090 alloy the artificial ageing results in an increase in fatigue life in comparison with natural ageing. On the contrary, the notched specimens of 8090 alloy in the naturally aged condition show higher fatigue life than in the peak-aged. The exposure to either the peak-aged or naturally aged leads to superior fatigue properties of Al-Li alloy to the traditional high strength aluminum alloys of 7075 and 2024, especially in the latter aged condition. In all ageing conditions, i,e. naturally, under-, peak- and over-aged, the peak-aged 8090 alloy displays the highest fatigue life and the over-aged material has a minimum value at the same stress amplitude. The difference in fatigue life is mainly attributable to the size and distribution of strengthening precipitates as well as the wide of precipitate free zones (PFZ's) along grain boundaries.
