The regulation of sintering temperature in spark plasma sintering enables the achievement of grain refinement,phase control,and performance enhancement in the preparation of AZ91D magnesium alloy.This study investigat...The regulation of sintering temperature in spark plasma sintering enables the achievement of grain refinement,phase control,and performance enhancement in the preparation of AZ91D magnesium alloy.This study investigates the influence of sintering temperature on microstructural evolution and mechanical properties of the AZ91D alloy.Microstructural analysis was conducted using scanning electron microscopy,electron backscatter diffraction,and X-ray diffraction.Microscopic structures and mechanical behaviors were examined through hardness and tensile tests.Elevated sintering temperatures resulted in reduced secondary phase content,leading to a decrease in mechanical performance.The alloy exhibited optimal mechanical properties at 320℃.The nanoparticle coarsening process and particle evolution during sintering were simulated using phase field methods.By optimizing the sintering temperature,precise control over microstructural and textural evolution can be achieved,facilitating the attainment of desired hardness levels and mechanical properties.展开更多
Ti-6Al-4V/Al7050 joints were fabricated by a method of insert molding and corresponding interfacial microstructure and mechanical properties were investigated. The interfacial thickness was sensitive to holding temper...Ti-6Al-4V/Al7050 joints were fabricated by a method of insert molding and corresponding interfacial microstructure and mechanical properties were investigated. The interfacial thickness was sensitive to holding temperature during the first stage, and a good metallurgical bonding interface with a thickness of about 90 μm can be obtained at 750°C. X-ray diffraction, transmission electron microscopy, and thermodynamic analyses showed that the interface mainly contained intermetallic compound TiAl_3 and Al matrix. The joints featured good mechanical properties, i.e., shear strength of 154 MPa, tensile strength of 215 MPa, and compressive strength of 283 MPa, which are superior to those of joints fabricated by other methods. Coherent boundaries between Al/TiAl_3 and TiAl_3/Ti were confirmed to contribute to outstanding interfacial mechanical properties and also explained constant fracture occurrence in the Al matrix. Follow-up studies should focus on improving mechanical properties of the Al matrix by deformation and heat treatment.展开更多
Iron-based metal matrix composites(IMMCs)have attracted significant research attention due to their high specific stiffness and strength,making them potentially suitable for various engineering applications.Microstruc...Iron-based metal matrix composites(IMMCs)have attracted significant research attention due to their high specific stiffness and strength,making them potentially suitable for various engineering applications.Microstructural design,including the selection of reinforcement and matrix phases,the reinforcement volume fraction,and the interface issues are essential factors determining the engineering performance of IMMCs.A variety of fabrication methods have been developed to manufacture IMMCs in recent years.This paper reviews the recent advances and development of IMMCs with particular focus on microstructure design,fabrication methods,and their engineering performance.The microstructure design issues of IMMC are firstly discussed,including the reinforcement and matrix phase selection criteria,interface geometry and characteristics,and the bonding mechanism.The fabrication methods,including liquid state,solid state,and gas-mixing processing are comprehensively reviewed and compared.The engineering performance of IMMCs in terms of elastic modulus,hardness and wear resistance,tensile and fracture behavior is reviewed.Finally,the current challenges of the IMMCs are highlighted,followed by the discussion and outlook of the future research directions of IMMCs.展开更多
The quantitative relationship between microstructure and properties of austenitic Fe-28Mn-xAl-1C（x=10 and 12 wt.%）low-density steels was evaluated using Rietveld method to refine X-ray diffraction（XRD）patterns.The...The quantitative relationship between microstructure and properties of austenitic Fe-28Mn-xAl-1C（x=10 and 12 wt.%）low-density steels was evaluated using Rietveld method to refine X-ray diffraction（XRD）patterns.The results showed that a typical three-phase austenitic steel was obtained in the forged Mn28Al10（i.e.Fe-28Mn-10Al-1C）steel,which included about 92.85 wt.% γ-Fe（Mn,Al,C）（austenite）,5.28 wt.%（Fe,Mn）_3AlC_（0.5）（κ-carbide）,and 1.87 wt.% α-Fe（Al,Mn）（ferrite）.For the forged Mn28Al12（i.e.Fe-28Mn-12Al-1C）steel,nevertheless,only about 76.64 wt.% austenite,9.63 wt.%κ-carbide,9.14 wt.%ferrite and 4.59 wt.% Fe_3Al（DO_3）could be obtained.Nanometerκ-carbide and DO_3 were mainly distributed in austenite grains and at the interface between austenite and ferrite,respectively.The forged Mn28Al10 steel had a better combination of strength,ductility and specific strength as compared with the forged Mn28Al12 steel.The ductility of the forged Mn28Al12 steel was far lower than that of the forged Mn28Al10 steel.The oxidation kinetics of Mn28Al10 steel oxidized at 1323 Kfor 5-25 h had two-stage linear rate laws,and the oxidation rate of the second stage was faster than that of the first stage.Although the oxidation kinetics of Mn28Al12 steel under this condition also had two-stage linear rate laws,the oxidation rate of the second stage was slower than that of the first stage.When the oxidation temperature increased to 1373K,the oxidation kinetics of the two steels at 5-25 hhad only onestage linear rate law,and the oxidation rates of the two steels were far faster than those at 1323K for5-25 h.The oxidation resistance of Mn28Al12 steel was much better than that of Mn28Al10 steel.Ferrite layer formed between the austenite matrix and the oxidation layer of the two Fe-Mn-Al-C steels oxidized at high temperature.展开更多
The AZ31 alloy ingot with diameter of 110 mm and length of 3500 mm was fabricated successfully. The compositions and microstructure morphologies of the ingot at different locations were performed, which indicated that...The AZ31 alloy ingot with diameter of 110 mm and length of 3500 mm was fabricated successfully. The compositions and microstructure morphologies of the ingot at different locations were performed, which indicated that the chemical composition distributed homogeneously through the whole alloy ingot and the average grain size increased from the surface to the center. The results of the EDS and element face-scanning illustrated that the eutectic compounds mainly consisted of fl-Mg17Al12 and a small amount of fl-Mgl7（AlZn）12. Furthermore, slight improvements of the strength and ductility were observed from the center to the surface along the axial direction of the alloy ingot, while both the strength and elongation to failure of the samples along the radial direction are higher than that along the axial direction. The fine grain strengthening was the main contributors to the strength of the as-casted AZ31 alloy.展开更多
The effects of various cooling paths on uniformity of through-thickness microstructure and mechanical properties of X80 pipeline steel of 22.0 mm in thickness were studied. The finite difference method was employed to...The effects of various cooling paths on uniformity of through-thickness microstructure and mechanical properties of X80 pipeline steel of 22.0 mm in thickness were studied. The finite difference method was employed to calculate the temperature field during cooling. It was confirmed by the experimental result and temperature field calculation that the optimizing process was achieved by the ultra-fast cooling with medium cooling capacity（cooling rate of ＊23 K/s）followed by ultimate cooling capacity（cooling rate of ＊50 K/s）. After optimization, the experimental steel displayed much uniform microstructure and the deviation of through-thickness hardness was controlled within 20 HV. In addition,the yield strength, tensile strength and elongation of the experimental steel were 621, 728 MPa and 21.5%, respectively,meeting the requirements of the API standard for X80 pipeline steels.展开更多
Novel headstand pyrocarbon cones （HPCs） with hollow structure were developed on the surfaces of pyrocarbon layers of the carbon/carbon （C/C） composites at 650-750 °C by the electromagnetic-field-assisted chem...Novel headstand pyrocarbon cones （HPCs） with hollow structure were developed on the surfaces of pyrocarbon layers of the carbon/carbon （C/C） composites at 650-750 °C by the electromagnetic-field-assisted chemical vapor deposition in the absence of catalysts. The fine microstructures of the HPCs were characterized by high-resolution transmission electron microscopy. The results show that the textural features of the HPCs directly transfer from turbostratic structure in roots to a well-ordered high texture in stems. And the degree of high texture ordering decreases gradually from the stem to the tail of the HPCs. The formation mechanism of the HPCs was inferred as the comprehensive effect of polarization induction on electromagnetic fields and particle-filler property under disruptive discharge.展开更多
A new high throughput heat-treatment method with a continuous temperature gradient between 600 and 700 ？C was utilized on the Ti-5553 alloy（Ti-5 Al-5 Mo-5 V-3 Cr, mass fraction, %）. The temperature gradient was ind...A new high throughput heat-treatment method with a continuous temperature gradient between 600 and 700 ？C was utilized on the Ti-5553 alloy（Ti-5 Al-5 Mo-5 V-3 Cr, mass fraction, %）. The temperature gradient was induced by the variation of the axial section of sample, which was heated by the direct current. The variation of continuous cooling rates on the treated sample was realized by using the end quenching method. The microstructural evolution and mechanical properties under different heat treatment conditions were evaluated. The results show that the pseudo-spinodal decomposition of the alloy occurs at（617±1） ？C, and the size of the precipitated α phase is around 300 nm. Moreover, the highest microhardness is obtained after the heat treatment at the pseudo-spinodal decomposition temperature for 4 h. These indicate that the high throughput method is efficient and fast to determine the phase transformation temperature and corresponding microstructural evolution of alloys.展开更多
Mechanical properties of semi-solid casting are dependent on multiple processing parameters,and improper processing parameters will not only reduce mean data but also increase variations.The present study investigated...Mechanical properties of semi-solid casting are dependent on multiple processing parameters,and improper processing parameters will not only reduce mean data but also increase variations.The present study investigated the impact of parameters in slurry preparation and heat treatment on the yield strength and ductility of T6 heat-treated A356 Al-Si alloy using rapid slurry forming(RSF)semi-solid casting.The focus was primarily on the robustness of mechanical properties based on Taguchi design method.By analyzing signal-to-noise ratio and minimum value calculated from-3S,the optimum slurry preparation parameters and heat treatment parameters were determined to be no quench,enthalpy exchange material(EEM)temperature of 140℃,EEM-to-melt ratio of 6mass%,stirring time of 18 s,solution heat treated at 520℃ for 2 h,and ageing heat treated at 190℃ for 6 h.In a small batch validation,the-3S yield strength and-3S elongation reach 256.1 MPa and 5.03% respectively,showing a satisfactory robustness.The hardness and microstructure of heat-treated samples with the best and worst properties were characterized to gain insight into the underlying mechanisms affecting the mean value and variations of mechanical properties.展开更多
Gradient cemented carbides with the surface depleted in cubic phases were prepared following normal powder metallurgical pro-cedures.Gradient zone formation and the influence of nitrogen introduction methods on the mi...Gradient cemented carbides with the surface depleted in cubic phases were prepared following normal powder metallurgical pro-cedures.Gradient zone formation and the influence of nitrogen introduction methods on the microstructure and performance of the alloys were investigated.The results show that the simple one-step vacuum sintering technique is doable for producing gradient cemented carbides.Gradient structure formation is attributed to the gradient in nitrogen activity during sintering,but is independent from nitrogen introduced methods.A uniform carbon distribution is found throughout the materials.Moreover,the transverse rupture strength of the cemented carbides can be increased by a gradient layer.Different nitrogen carriers give the alloys distinguishing microstructure and mechanical properties,and a gradient alloy with ultrafine-TiC0.5N0.5 is found optimal.展开更多
Commercially pure zirconium was processed by the surface mechanical attrition treatment(SMAT),and the microstructure observation showed that a gradient structure was induced.Nanoindentation measurements were taken to ...Commercially pure zirconium was processed by the surface mechanical attrition treatment(SMAT),and the microstructure observation showed that a gradient structure was induced.Nanoindentation measurements were taken to obtain the load-displacement curves at different depths below the treated surface.Using dimensional analysis,the local yield stress,hardness,strain hardening exponent,and elastic modulus at the corresponding depths were derived.The results showed that the yield stress and hardness varied with depth,while the strain hardening exponent and elastic modulus were approximately invariable.The finite element method was used to simulate nanoindentation at different depths below the treated surface to verify the derivation of the local elastic-plastic constitutive relationship.Stressstrain curves were computed for the treated samples through the rule of mixtures,and they agreed well with the experimental results.The analysis showed that the surface and subsurface hardening layers as well as the transition layer shared a high load applied to the samples,even though their volume fraction was small.展开更多
Cu-15Ni-8Sn-0.3Nb alloy rods were prepared by means of powder metallurgy followed by hot extrusion.Element maps obtained by electron probe micro analyzer(EPMA)showed that Nb-rich phases were formed and distributed wit...Cu-15Ni-8Sn-0.3Nb alloy rods were prepared by means of powder metallurgy followed by hot extrusion.Element maps obtained by electron probe micro analyzer(EPMA)showed that Nb-rich phases were formed and distributed within grains and at grain boundaries of the Cu-15Ni-8Sn-0.3Nb alloy.Transmission electron microscope(TEM)results indicated that there was no obvious orientation relationship between these phases and the matrix.Spinodal decomposition and ordering transformation appeared at early stages of aging at400°C and caused significant strengthening.Cu-15Ni-8Sn-0.3Nb alloy exhibited both higher strength(ultimate tensile strength>1030MPa)and higher tensile ductility(elongation>9.1%)than Cu-15Ni-8Sn alloy after aging treatment.The improvement was caused by Nb-rich phases at grain boundaries which led o the refinement of grain size and postponed the growth of discontinuous precipitates during aging.展开更多
Semi-solid metal processing is being developed in die casting applications to give several cost benefits. To efficiently apply this emerging technology, it is important to understand the evolution of microstructure in...Semi-solid metal processing is being developed in die casting applications to give several cost benefits. To efficiently apply this emerging technology, it is important to understand the evolution of microstructure in semi-solid slurries for the control of the theological behavior in semi-solid state. An experimental apparatus was developed which can capture the grain structure at different times at early stages to understand how the semi-solid structure evolves. In this technique, semi-solid slurry was produced by injecting fine gas bubbles into the melt through a graphite diffuser during solidification. Then, a copper quenching mold was used to draw some semi-solid slurry into a thin channel. The semi-solid slurry was then rapidly frozen in the channel giving the microstructure of the slurry at the desired time. Samples of semi-solid 356 aluminum alloy were taken at different gas injection times of 1, 5, 10, 15, 20, 30, 35, 40, and 45 s. Analysis of the microstructure suggests that the fragmentation by remelting mechanism should be responsible for the formation of globular structure in this rheocasting process.展开更多
In this study,the effect of micron-sized titanium and aluminum addition on the microstructural,mechanical and work-hardening behavior of pure Mg is investigated.Pure Mg reinforced with 10%Ti and 10%Ti-1%Al particulate...In this study,the effect of micron-sized titanium and aluminum addition on the microstructural,mechanical and work-hardening behavior of pure Mg is investigated.Pure Mg reinforced with 10%Ti and 10%Ti-1%Al particulates were synthesized through semi-powder metallurgy route followed by hot extrusion.Semi-powder metallurgy appears to be promising approach for the synthesis of Mg based composite,as it is free of ball milling.Tensile results indicate that the direct addition of micron-sized 10wt.%titanium particulates to pure Mg,caused an improvement in elastic modulus,0.2%yield strength,ultimate tensile strength,and failure strain(+72%;+41%;+29%;and+79%respectively).The addition of micron-sized 10wt.%titanium particles along with 1.0wt.%Al particles to pure Mg,resulted in an enhancement in elastic modulus,0.2%yield strength,ultimate tensile strength,and failure strain(+74%;+56%;+45%;and+241%respectively).Besides tensile test,Vickers hardness and work-hardening behavior of prepared composites were also examined.Impressive failure strain of Mg-10Ti-1Al composite can be attributed to the better compatibility of Ti particulates with Mg due to presence of alloying element Al.展开更多
To predict the amount of different phases in gray cast iron by a finite difference model （FDM） on the basis of cooling rate （R）, the volume fractions of total y phase, graphite, and cementite were calculated. The ...To predict the amount of different phases in gray cast iron by a finite difference model （FDM） on the basis of cooling rate （R）, the volume fractions of total y phase, graphite, and cementite were calculated. The results of phase composition were evaluated to find a proper correlation with cooling rate. More trials were carried out to find a good correlation between the hardness and phase composition. New proposed formulas show that the hardness of gray cast iron decreases as the amount of graphite phase increases, and increases as the amount of cementite inereases. The,qe fnrrnulas are develoned to correlate the nhase volume fraction to hardness. The results are compared with exverimental data and show reasonable agreement.展开更多
A numerical analysis was performed to study the influence of process parameters on the microstructure evolution of IN718 alloy in rotary forging using the finite element method （FEM）. For this purpose, a constitutiv...A numerical analysis was performed to study the influence of process parameters on the microstructure evolution of IN718 alloy in rotary forging using the finite element method （FEM）. For this purpose, a constitutive equation considering the effects of strain hardening and dynamic softening of IN718 alloy was built. The constitutive equation and microstructure models were implemented into the finite element code to investigate the microstructure evolution during rotary forging subject to large deformations. The simulations were carried out in the ratio of initial height to diameter range 0.2-0.8, the angle of the rocker 3°-7° and the relative feed per revolution range 0.01-0.1 r^-1. The research results revealed the deformation mechanism and the correlation of process parameters with the grain size evolution of IN718 alloy during rotary forging. These provide evidence for the selection of rotary forging parameters.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52074246,22008224,52275390,52205429,52201146)National Defense Basic Scientific Research Program of China(Nos.JCKY2020408B002,WDZC2022-12)+2 种基金Key Research and Development Program of Shanxi Province(202102050201011,2022ZDYF035)Science and Technology Major Project of Shanxi Province(20191102008,20191102007)Guiding Local Science and Technology Development Projects by the Central Government(YDZJSX2022A025,YDZJSX2021A027).
文摘The regulation of sintering temperature in spark plasma sintering enables the achievement of grain refinement,phase control,and performance enhancement in the preparation of AZ91D magnesium alloy.This study investigates the influence of sintering temperature on microstructural evolution and mechanical properties of the AZ91D alloy.Microstructural analysis was conducted using scanning electron microscopy,electron backscatter diffraction,and X-ray diffraction.Microscopic structures and mechanical behaviors were examined through hardness and tensile tests.Elevated sintering temperatures resulted in reduced secondary phase content,leading to a decrease in mechanical performance.The alloy exhibited optimal mechanical properties at 320℃.The nanoparticle coarsening process and particle evolution during sintering were simulated using phase field methods.By optimizing the sintering temperature,precise control over microstructural and textural evolution can be achieved,facilitating the attainment of desired hardness levels and mechanical properties.
基金financially supported by the National Natural Science Foundation of China (Nos.51671017 and 51471024)Fundamental Research Funds for the Central Universities (No.FRFBR-15-078A)
文摘Ti-6Al-4V/Al7050 joints were fabricated by a method of insert molding and corresponding interfacial microstructure and mechanical properties were investigated. The interfacial thickness was sensitive to holding temperature during the first stage, and a good metallurgical bonding interface with a thickness of about 90 μm can be obtained at 750°C. X-ray diffraction, transmission electron microscopy, and thermodynamic analyses showed that the interface mainly contained intermetallic compound TiAl_3 and Al matrix. The joints featured good mechanical properties, i.e., shear strength of 154 MPa, tensile strength of 215 MPa, and compressive strength of 283 MPa, which are superior to those of joints fabricated by other methods. Coherent boundaries between Al/TiAl_3 and TiAl_3/Ti were confirmed to contribute to outstanding interfacial mechanical properties and also explained constant fracture occurrence in the Al matrix. Follow-up studies should focus on improving mechanical properties of the Al matrix by deformation and heat treatment.
基金funding support from the National Natural Science Foundation of China(No.52101046)Shuangjie Chu appreciates the funding support from the National Key Research and Development Program of China(No.2022YFB3705600).
文摘Iron-based metal matrix composites(IMMCs)have attracted significant research attention due to their high specific stiffness and strength,making them potentially suitable for various engineering applications.Microstructural design,including the selection of reinforcement and matrix phases,the reinforcement volume fraction,and the interface issues are essential factors determining the engineering performance of IMMCs.A variety of fabrication methods have been developed to manufacture IMMCs in recent years.This paper reviews the recent advances and development of IMMCs with particular focus on microstructure design,fabrication methods,and their engineering performance.The microstructure design issues of IMMC are firstly discussed,including the reinforcement and matrix phase selection criteria,interface geometry and characteristics,and the bonding mechanism.The fabrication methods,including liquid state,solid state,and gas-mixing processing are comprehensively reviewed and compared.The engineering performance of IMMCs in terms of elastic modulus,hardness and wear resistance,tensile and fracture behavior is reviewed.Finally,the current challenges of the IMMCs are highlighted,followed by the discussion and outlook of the future research directions of IMMCs.
基金funded by the National Natural Science Foundation of China (Grant No.51674004)Education Department of Anhui Province of China (Grant Nos.KJ2016A104 and KJ2017A805)
文摘The quantitative relationship between microstructure and properties of austenitic Fe-28Mn-xAl-1C（x=10 and 12 wt.%）low-density steels was evaluated using Rietveld method to refine X-ray diffraction（XRD）patterns.The results showed that a typical three-phase austenitic steel was obtained in the forged Mn28Al10（i.e.Fe-28Mn-10Al-1C）steel,which included about 92.85 wt.% γ-Fe（Mn,Al,C）（austenite）,5.28 wt.%（Fe,Mn）_3AlC_（0.5）（κ-carbide）,and 1.87 wt.% α-Fe（Al,Mn）（ferrite）.For the forged Mn28Al12（i.e.Fe-28Mn-12Al-1C）steel,nevertheless,only about 76.64 wt.% austenite,9.63 wt.%κ-carbide,9.14 wt.%ferrite and 4.59 wt.% Fe_3Al（DO_3）could be obtained.Nanometerκ-carbide and DO_3 were mainly distributed in austenite grains and at the interface between austenite and ferrite,respectively.The forged Mn28Al10 steel had a better combination of strength,ductility and specific strength as compared with the forged Mn28Al12 steel.The ductility of the forged Mn28Al12 steel was far lower than that of the forged Mn28Al10 steel.The oxidation kinetics of Mn28Al10 steel oxidized at 1323 Kfor 5-25 h had two-stage linear rate laws,and the oxidation rate of the second stage was faster than that of the first stage.Although the oxidation kinetics of Mn28Al12 steel under this condition also had two-stage linear rate laws,the oxidation rate of the second stage was slower than that of the first stage.When the oxidation temperature increased to 1373K,the oxidation kinetics of the two steels at 5-25 hhad only onestage linear rate law,and the oxidation rates of the two steels were far faster than those at 1323K for5-25 h.The oxidation resistance of Mn28Al12 steel was much better than that of Mn28Al10 steel.Ferrite layer formed between the austenite matrix and the oxidation layer of the two Fe-Mn-Al-C steels oxidized at high temperature.
基金Project(2010A090200078)supported by the Special Foundation Project of Industry,University and Research Institute Collaboration of Guangdong Provincial Government and the Ministry of Education,ChinaProject(2010B090500010)supported by the Special Commissioners’ Workstation Construction Project of Guangdong Provincial Government,China
文摘The AZ31 alloy ingot with diameter of 110 mm and length of 3500 mm was fabricated successfully. The compositions and microstructure morphologies of the ingot at different locations were performed, which indicated that the chemical composition distributed homogeneously through the whole alloy ingot and the average grain size increased from the surface to the center. The results of the EDS and element face-scanning illustrated that the eutectic compounds mainly consisted of fl-Mg17Al12 and a small amount of fl-Mgl7（AlZn）12. Furthermore, slight improvements of the strength and ductility were observed from the center to the surface along the axial direction of the alloy ingot, while both the strength and elongation to failure of the samples along the radial direction are higher than that along the axial direction. The fine grain strengthening was the main contributors to the strength of the as-casted AZ31 alloy.
基金supported by the National Natural Science Foundation of China(No.51234002)the Fundamental Research Funds for the Central Universities(N130407001)
文摘The effects of various cooling paths on uniformity of through-thickness microstructure and mechanical properties of X80 pipeline steel of 22.0 mm in thickness were studied. The finite difference method was employed to calculate the temperature field during cooling. It was confirmed by the experimental result and temperature field calculation that the optimizing process was achieved by the ultra-fast cooling with medium cooling capacity（cooling rate of ＊23 K/s）followed by ultimate cooling capacity（cooling rate of ＊50 K/s）. After optimization, the experimental steel displayed much uniform microstructure and the deviation of through-thickness hardness was controlled within 20 HV. In addition,the yield strength, tensile strength and elongation of the experimental steel were 621, 728 MPa and 21.5%, respectively,meeting the requirements of the API standard for X80 pipeline steels.
基金Project (2011CB605801) supported by the National Basic Research Program of ChinaProject (2011M500127) supported by the China Postdoctoral Science Foundation+1 种基金Projects (50802115, 51102089) supported by the National Natural Science Foundation of ChinaProject supported by the Postdoctoral Fund of the Central South University, China
文摘Novel headstand pyrocarbon cones （HPCs） with hollow structure were developed on the surfaces of pyrocarbon layers of the carbon/carbon （C/C） composites at 650-750 °C by the electromagnetic-field-assisted chemical vapor deposition in the absence of catalysts. The fine microstructures of the HPCs were characterized by high-resolution transmission electron microscopy. The results show that the textural features of the HPCs directly transfer from turbostratic structure in roots to a well-ordered high texture in stems. And the degree of high texture ordering decreases gradually from the stem to the tail of the HPCs. The formation mechanism of the HPCs was inferred as the comprehensive effect of polarization induction on electromagnetic fields and particle-filler property under disruptive discharge.
基金Project(2014CB644002)supported by the National Basic Research and Development Project of ChinaProject(2015CX004)supported by the Innovation-driven Plan in Central South University,China
文摘A new high throughput heat-treatment method with a continuous temperature gradient between 600 and 700 ？C was utilized on the Ti-5553 alloy（Ti-5 Al-5 Mo-5 V-3 Cr, mass fraction, %）. The temperature gradient was induced by the variation of the axial section of sample, which was heated by the direct current. The variation of continuous cooling rates on the treated sample was realized by using the end quenching method. The microstructural evolution and mechanical properties under different heat treatment conditions were evaluated. The results show that the pseudo-spinodal decomposition of the alloy occurs at（617±1） ？C, and the size of the precipitated α phase is around 300 nm. Moreover, the highest microhardness is obtained after the heat treatment at the pseudo-spinodal decomposition temperature for 4 h. These indicate that the high throughput method is efficient and fast to determine the phase transformation temperature and corresponding microstructural evolution of alloys.
文摘Mechanical properties of semi-solid casting are dependent on multiple processing parameters,and improper processing parameters will not only reduce mean data but also increase variations.The present study investigated the impact of parameters in slurry preparation and heat treatment on the yield strength and ductility of T6 heat-treated A356 Al-Si alloy using rapid slurry forming(RSF)semi-solid casting.The focus was primarily on the robustness of mechanical properties based on Taguchi design method.By analyzing signal-to-noise ratio and minimum value calculated from-3S,the optimum slurry preparation parameters and heat treatment parameters were determined to be no quench,enthalpy exchange material(EEM)temperature of 140℃,EEM-to-melt ratio of 6mass%,stirring time of 18 s,solution heat treated at 520℃ for 2 h,and ageing heat treated at 190℃ for 6 h.In a small batch validation,the-3S yield strength and-3S elongation reach 256.1 MPa and 5.03% respectively,showing a satisfactory robustness.The hardness and microstructure of heat-treated samples with the best and worst properties were characterized to gain insight into the underlying mechanisms affecting the mean value and variations of mechanical properties.
基金supported by the Science and Technology Projects of Sichuan Province,China,(No.2008GZ0179)
文摘Gradient cemented carbides with the surface depleted in cubic phases were prepared following normal powder metallurgical pro-cedures.Gradient zone formation and the influence of nitrogen introduction methods on the microstructure and performance of the alloys were investigated.The results show that the simple one-step vacuum sintering technique is doable for producing gradient cemented carbides.Gradient structure formation is attributed to the gradient in nitrogen activity during sintering,but is independent from nitrogen introduced methods.A uniform carbon distribution is found throughout the materials.Moreover,the transverse rupture strength of the cemented carbides can be increased by a gradient layer.Different nitrogen carriers give the alloys distinguishing microstructure and mechanical properties,and a gradient alloy with ultrafine-TiC0.5N0.5 is found optimal.
基金financially supported by the National Natural Science Foundation of China (Nos. 51674187 and 51671153)the Science and Technology Department of Shaanxi Province(No.2017GY-115)the Education Department of Shaanxi Province(No. 16JK1466)
文摘Commercially pure zirconium was processed by the surface mechanical attrition treatment(SMAT),and the microstructure observation showed that a gradient structure was induced.Nanoindentation measurements were taken to obtain the load-displacement curves at different depths below the treated surface.Using dimensional analysis,the local yield stress,hardness,strain hardening exponent,and elastic modulus at the corresponding depths were derived.The results showed that the yield stress and hardness varied with depth,while the strain hardening exponent and elastic modulus were approximately invariable.The finite element method was used to simulate nanoindentation at different depths below the treated surface to verify the derivation of the local elastic-plastic constitutive relationship.Stressstrain curves were computed for the treated samples through the rule of mixtures,and they agreed well with the experimental results.The analysis showed that the surface and subsurface hardening layers as well as the transition layer shared a high load applied to the samples,even though their volume fraction was small.
基金Project (2016YFB0301400) supported by the National Key Research and Development Program of ChinaProject (9140A12040515QT48167) supported by the Pre-research Fund of the General Armaments Department of ChinaProject (CSU20151024) supported by the Innovation-driven Plan of Central South University,China
文摘Cu-15Ni-8Sn-0.3Nb alloy rods were prepared by means of powder metallurgy followed by hot extrusion.Element maps obtained by electron probe micro analyzer(EPMA)showed that Nb-rich phases were formed and distributed within grains and at grain boundaries of the Cu-15Ni-8Sn-0.3Nb alloy.Transmission electron microscope(TEM)results indicated that there was no obvious orientation relationship between these phases and the matrix.Spinodal decomposition and ordering transformation appeared at early stages of aging at400°C and caused significant strengthening.Cu-15Ni-8Sn-0.3Nb alloy exhibited both higher strength(ultimate tensile strength>1030MPa)and higher tensile ductility(elongation>9.1%)than Cu-15Ni-8Sn alloy after aging treatment.The improvement was caused by Nb-rich phases at grain boundaries which led o the refinement of grain size and postponed the growth of discontinuous precipitates during aging.
基金funded by the Thai Research Fund (Contract No.MRG5280215)the Royal Golden Jubilee Ph.D. Program (Grant No.PHD/0134/2551)
文摘Semi-solid metal processing is being developed in die casting applications to give several cost benefits. To efficiently apply this emerging technology, it is important to understand the evolution of microstructure in semi-solid slurries for the control of the theological behavior in semi-solid state. An experimental apparatus was developed which can capture the grain structure at different times at early stages to understand how the semi-solid structure evolves. In this technique, semi-solid slurry was produced by injecting fine gas bubbles into the melt through a graphite diffuser during solidification. Then, a copper quenching mold was used to draw some semi-solid slurry into a thin channel. The semi-solid slurry was then rapidly frozen in the channel giving the microstructure of the slurry at the desired time. Samples of semi-solid 356 aluminum alloy were taken at different gas injection times of 1, 5, 10, 15, 20, 30, 35, 40, and 45 s. Analysis of the microstructure suggests that the fragmentation by remelting mechanism should be responsible for the formation of globular structure in this rheocasting process.
基金The present work was supported by the National Natural Science Funds of China(No.50725413)the Ministry of Science and Technology of China(MOST)(No.2010DFR50010 and 2011FU125Z07)Chongqing Science and Technology Commission(CSTC2013JCYJC60001).
文摘In this study,the effect of micron-sized titanium and aluminum addition on the microstructural,mechanical and work-hardening behavior of pure Mg is investigated.Pure Mg reinforced with 10%Ti and 10%Ti-1%Al particulates were synthesized through semi-powder metallurgy route followed by hot extrusion.Semi-powder metallurgy appears to be promising approach for the synthesis of Mg based composite,as it is free of ball milling.Tensile results indicate that the direct addition of micron-sized 10wt.%titanium particulates to pure Mg,caused an improvement in elastic modulus,0.2%yield strength,ultimate tensile strength,and failure strain(+72%;+41%;+29%;and+79%respectively).The addition of micron-sized 10wt.%titanium particles along with 1.0wt.%Al particles to pure Mg,resulted in an enhancement in elastic modulus,0.2%yield strength,ultimate tensile strength,and failure strain(+74%;+56%;+45%;and+241%respectively).Besides tensile test,Vickers hardness and work-hardening behavior of prepared composites were also examined.Impressive failure strain of Mg-10Ti-1Al composite can be attributed to the better compatibility of Ti particulates with Mg due to presence of alloying element Al.
基金financially supported by Razi Metallurgical Research Center(RMRC) for the advanced manufacturing and data acquisition system
文摘To predict the amount of different phases in gray cast iron by a finite difference model （FDM） on the basis of cooling rate （R）, the volume fractions of total y phase, graphite, and cementite were calculated. The results of phase composition were evaluated to find a proper correlation with cooling rate. More trials were carried out to find a good correlation between the hardness and phase composition. New proposed formulas show that the hardness of gray cast iron decreases as the amount of graphite phase increases, and increases as the amount of cementite inereases. The,qe fnrrnulas are develoned to correlate the nhase volume fraction to hardness. The results are compared with exverimental data and show reasonable agreement.
基金the National Basic Research Program(973) of China (No. 2006CB705400).
文摘A numerical analysis was performed to study the influence of process parameters on the microstructure evolution of IN718 alloy in rotary forging using the finite element method （FEM）. For this purpose, a constitutive equation considering the effects of strain hardening and dynamic softening of IN718 alloy was built. The constitutive equation and microstructure models were implemented into the finite element code to investigate the microstructure evolution during rotary forging subject to large deformations. The simulations were carried out in the ratio of initial height to diameter range 0.2-0.8, the angle of the rocker 3°-7° and the relative feed per revolution range 0.01-0.1 r^-1. The research results revealed the deformation mechanism and the correlation of process parameters with the grain size evolution of IN718 alloy during rotary forging. These provide evidence for the selection of rotary forging parameters.
