The relationship of the P and C grain boundary segregation and its effect on bake hardening behavior were investigated in ultra-low carbon bake hardening (ULC-BH)steel with and without P addition annealed at 810 ℃ fo...The relationship of the P and C grain boundary segregation and its effect on bake hardening behavior were investigated in ultra-low carbon bake hardening (ULC-BH)steel with and without P addition annealed at 810 ℃ for various time using electron probe micro-analyzer,electroh backscattered diffraction,and three-dimensional atomic probe techniques.Results revealed that P addition and annealing duration considerably affected the bake hardening behavior of experimental steel. The BH value of ULC-BH steel without P addition is lower than that with P addition within a short annealing time,and the difference in the BH value gradually decreases as the annealing duration is prolonged.P segregation is dominant in terms of a high P bulk content in steels with P addition at the expense of C segregation during annealing.By contrast,opposite effects are observed in low carbon bake hardening steel.The high residual solute C content in steel with P addition is due to P segregation at the grain boundary.Site competition is mainly responsible for the lower BH value in ULC-BH steel without P addition than that with P addition.As the annealing time is further extended,C segregation begins at grain boundary despite the delayed P segregation,leading to a gradual decrease in the solute concentration in the matrix of steels with P addition.C and P segregations reach the equilibrium as the annealing time increases to 60 min at 810 ℃ in the two steel samples.Theoretical calculations reveal that the residual solute C concentration in the matrix decreases to zero,and this finding is consistent with the change trend of the bake hardening value.Hence,the C segregation at grain boundary. adversely influences the bake hardening property of ULC-BH steel.展开更多
Modern engineering has long been in demand for high-performance additive manufactured materials for harsh working conditions.The idea of high entropy alloy(HEA),medium entropy alloy(MEA),and multi-principal-element al...Modern engineering has long been in demand for high-performance additive manufactured materials for harsh working conditions.The idea of high entropy alloy(HEA),medium entropy alloy(MEA),and multi-principal-element alloy(MPEA)provides a new way for alloy design.In this work,we develop a Co42 Cr20 Ni30 Ti4 Al4 quinary MEA which exhibits a superiority of mechanical properties over a wide tem-perature ranging from 77 to 873 K via selective laser melting(SLM)and post-heat treatment.The present MEA achieves an excellent ultimate tensile strength(UTS)of 1586 MPa with a total elongation(TE)of 22.7%at 298 K,a UTS of 1944 MPa with a TE of 22.6%at 77 K,and a UTS of 1147 MPa with a TE of 9.1%at 873 K.The excellent mechanical properties stem from the microstructures composed of partially refined grains and heterogeneously precipitated L12 phase due to the concurrence of recrystallization and precipitation.The grain boundary hardening,precipitation hardening,and dislocation hardening con-tribute to the high YS at 298 and 77 K.Interactions of nano-spaced stacking faults(SFs)including SFs networks,Lomer-Cottrell locks(L-C locks),and anti-phase boundaries(APBs)induced by the shearing of L12 phase are responsible for the high strain hardening rate and plasticity at 77 K.Our work provides a new insight for the incorporation of precipitation hardening and additive manufacturing technology,paving the avenue for the development of high-performance structural materials.展开更多
Quenching Oils are comprised mostly of mineral oil as major component, but mineral oil alone result in lower cooling performance. Therefore, various additives are formulated as required for each particular case. Cooli...Quenching Oils are comprised mostly of mineral oil as major component, but mineral oil alone result in lower cooling performance. Therefore, various additives are formulated as required for each particular case. Cooling curves of mineral oil as determined by JIS method can be divided into three stages, vapor film stage, boiling stage and convection stage. And there are many types of additives used for quenching oil, one effective to shorten vapor film stage and another to shift boiling stage toward lower temperature side. As rapid quenching required temperature range for particular steel varies pending on its shape of CCT curve"1, it is possible to provide higher quench hardening performance using quenching oil formulated of adequate additives.展开更多
Developing high-strength and ductile metallic parts with designable shapes is an unfading research topic for material science and engineering.As a revolutionary technology,additive manufacturing(AM)pro-vides a new pat...Developing high-strength and ductile metallic parts with designable shapes is an unfading research topic for material science and engineering.As a revolutionary technology,additive manufacturing(AM)pro-vides a new pathway for producing complex-shaped metallic parts with the possibility of in situ tailoring their microstructure.However,AM is not always ideally applicable for all metals and alloys.Eutectic high entropy alloys(EHEAs)contain both the advantages of the eutectic alloys and high entropy alloys(HEAs),and EHEAs show significant potential in AM due to their excellent mechanical properties and good fluid-ity.Herein,heterogeneous and ultra-fine eutectic lamellar microstructure with directional growth along the deposition direction(DD)was obtained by adjusting the process parameters of AM to improve the strength and ductility of EHEAs.Compared with the as-cast sample,the simultaneous increment in both strength and ductility is achieved by AM.Combination of strength and ductility of the AM sample ten-sile along the DD direction(yield strength σ_(y)=1115 MPa,ultimate tensile strength σ_(UTS)=1417 MPa,ultimate tensile strain ε_(U)=23%)in this work was superior to most of the additive manufactured al-loys and comparable to the thermomechanical-treated EHEAs with the best mechanical properties.The high strength and good ductility of the AM were mainly attributed to the ultra-fine lamellar nature and fully constrained soft and hard lamellar microstructure,which produces an obvious hetero-deformation induced(HDI)strengthening and high crack buffering effect during the deformation.This work provides a new possibility to achieve high strength and ductile complex-shaped metallic parts via designing direc-tional lamellar eutectic structures by AM.展开更多
As a potent grain refiner for steel casting,TiN is now widely used to refineγ-austenite in steel additive manufacturing(AM).However,the refining mechanism of TiN during AM remains unclear despite intensive research i...As a potent grain refiner for steel casting,TiN is now widely used to refineγ-austenite in steel additive manufacturing(AM).However,the refining mechanism of TiN during AM remains unclear despite intensive research in recent years.This work aims to boost our understanding on the mechanism of TiN in refining theγ-austenite in AM-fabricated 316 stainless steel and its corresponding effect on the mechanical behaviour.Experimental results show that addition of 1 wt.%TiN nanoparticles led to complete columnarto-equiaxed transition and significant refinement of the austenite grains to∼2μm in the 316 steel.Thermodynamic and kinetic simulations confirmed that,despite the rapid AM solidification,δ-ferrite is the primary solid phase during AM of the 316 steel andγ-austenite forms through subsequent peritectic reaction or direct transformation from theδ-ferrite.This implies that the TiN nanoparticles actually refined theδ-ferrite through promoting its heterogenous nucleation,which in turn refined theγ-austenite.This assumption is verified by the high grain refining efficiency of TiN nanoparticles in an AM-fabricated Fe-4 wt.%Siδ-ferrite alloy,in whichδ-ferrite forms directly from the melt and is retained at room temperature.The grain refinement is attributed to the good atomic matching betweenδ-ferrite and TiN.Grain refinement in the 316 steel through 1 wt.%TiN inoculation not only eliminated the property anisotropy but also led to a high strain-hardening rate upon plastic deformation and thereby a superior strengthductility synergy with yield strength of 561 MPa,tensile strength of 860 MPa and elongation of 48%.展开更多
Additively manufactured(AM)metals exhibit highly complex microstructures,particularly in terms of grain morphology which typically features heterogeneous grain size distribution,irregular and anisotropic grain shapes,...Additively manufactured(AM)metals exhibit highly complex microstructures,particularly in terms of grain morphology which typically features heterogeneous grain size distribution,irregular and anisotropic grain shapes,and the so-called columnar grains.The conventional morphological descriptors based on grain shape idealization are generally inadequate for representing complex and anisotropic grain mor-phology of AM microstructures.The primary aspect of microstructural grain morphology is the state of grain boundary spacing or grain size whose effect on the mechanical response is known to be cru-cial.In this paper,we formally introduce the notion of axial grain size from which we derive mean axial grain size,effective grain size,and grain size anisotropy as robust morphological descriptors ca-pable of effectively representing highly complex grain morphologies.We instantiated a discrete sample of polycrystalline aggregate as a representative volume element(RVE)featuring random crystallographic orientation and misorientation distributions.However,the instantiated RVE incorporates the typical mor-phological features of AM microstructures including distinctive grain size heterogeneity and anisotropic grain size owing to its pronounced columnar grain morphology.We ensured that any anisotropy ob-served in the macroscopic mechanical response of the instantiated sample primarily originates from its underlying anisotropic grain size.The RVE was then employed for mesoscale full-field crystal plasticity simulations corresponding to uniaxial tensile deformation along various axes via a spectral solver and a physics-based crystal plasticity constitutive model which was developed,calibrated,and validated in ear-lier studies.Through the numerical analyses,we isolated the contribution of anisotropic grain size to the anisotropy in the mechanical response of polycrystalline aggregates,particularly those with the charac-teristic complex grain morphology of AM metals.This contribution can be described by an inverse square relation.展开更多
The present work has investigated the effect of trace elements Cd and Sn on the microstructure and mechanical properties of Al-Si-Cu-Mg cast alloy. With the increase of Cd addition the strength of alloy rises at first...The present work has investigated the effect of trace elements Cd and Sn on the microstructure and mechanical properties of Al-Si-Cu-Mg cast alloy. With the increase of Cd addition the strength of alloy rises at first and then drops. The optimal amount of Cd and Sn addition for Al-Si-Cu-Mg alloy is about 0.27% and 0.1% respectively. Due to the formation of some coarse Cd-rich phases and pure Cd particles the mechanical properties of alloy decrease when Cd amount exceeds 0.27%. When more than 0.1% Sn added, some Sn atoms form low-melting eutectic compound at grain boundary, and then cause over-burning in alloy when solution treated, which may deteriorate properties of alloy, especially ductility of alloy. On the other hand, the addition of Cd and Sn remarkably increases the peak hardness and reduces the time to reach aging peak in Al-Si-Cu-Mg alloy. The action of Cd /Sn in quaternary Al-Si-Cu-Mg alloy is effectively the same as that occur in binary Al-Cu alloy that the enhanced hardening associated with Cd / Sn addition is due to the promotion of the 6’ phase.展开更多
在分析多轴疲劳几种常用非比例度定义的基础上,提出了一种非比例度定义方法,进而以American Society of Mechanical Engineers(ASME)规范案例中非比例加载多轴疲劳设计准则采用的应变参量作为基本损伤参量,发展了一种新的多轴疲劳寿命...在分析多轴疲劳几种常用非比例度定义的基础上,提出了一种非比例度定义方法,进而以American Society of Mechanical Engineers(ASME)规范案例中非比例加载多轴疲劳设计准则采用的应变参量作为基本损伤参量,发展了一种新的多轴疲劳寿命预测模型.结果表明:1所提出的非比例度定义可以描述任意已知轮廓的、非周期的、变幅的非比例加载路径;2与两种常用的多轴非比例加载疲劳寿命模型的预测结果对比可知,新的寿命预测模型对14种比例和非比例加载路径下304不锈钢材料的寿命预测与试验吻合更好,预测结果基本位于2倍分散带以内.展开更多
基金the National Natural Science Foundation of China (Nos.51874114 and 51501052)the Youth Talent Support Program of Hebei Province (No.BJ2017056).
文摘The relationship of the P and C grain boundary segregation and its effect on bake hardening behavior were investigated in ultra-low carbon bake hardening (ULC-BH)steel with and without P addition annealed at 810 ℃ for various time using electron probe micro-analyzer,electroh backscattered diffraction,and three-dimensional atomic probe techniques.Results revealed that P addition and annealing duration considerably affected the bake hardening behavior of experimental steel. The BH value of ULC-BH steel without P addition is lower than that with P addition within a short annealing time,and the difference in the BH value gradually decreases as the annealing duration is prolonged.P segregation is dominant in terms of a high P bulk content in steels with P addition at the expense of C segregation during annealing.By contrast,opposite effects are observed in low carbon bake hardening steel.The high residual solute C content in steel with P addition is due to P segregation at the grain boundary.Site competition is mainly responsible for the lower BH value in ULC-BH steel without P addition than that with P addition.As the annealing time is further extended,C segregation begins at grain boundary despite the delayed P segregation,leading to a gradual decrease in the solute concentration in the matrix of steels with P addition.C and P segregations reach the equilibrium as the annealing time increases to 60 min at 810 ℃ in the two steel samples.Theoretical calculations reveal that the residual solute C concentration in the matrix decreases to zero,and this finding is consistent with the change trend of the bake hardening value.Hence,the C segregation at grain boundary. adversely influences the bake hardening property of ULC-BH steel.
基金supported by the National Natural Science Foundation of China(No.52020105013).
文摘Modern engineering has long been in demand for high-performance additive manufactured materials for harsh working conditions.The idea of high entropy alloy(HEA),medium entropy alloy(MEA),and multi-principal-element alloy(MPEA)provides a new way for alloy design.In this work,we develop a Co42 Cr20 Ni30 Ti4 Al4 quinary MEA which exhibits a superiority of mechanical properties over a wide tem-perature ranging from 77 to 873 K via selective laser melting(SLM)and post-heat treatment.The present MEA achieves an excellent ultimate tensile strength(UTS)of 1586 MPa with a total elongation(TE)of 22.7%at 298 K,a UTS of 1944 MPa with a TE of 22.6%at 77 K,and a UTS of 1147 MPa with a TE of 9.1%at 873 K.The excellent mechanical properties stem from the microstructures composed of partially refined grains and heterogeneously precipitated L12 phase due to the concurrence of recrystallization and precipitation.The grain boundary hardening,precipitation hardening,and dislocation hardening con-tribute to the high YS at 298 and 77 K.Interactions of nano-spaced stacking faults(SFs)including SFs networks,Lomer-Cottrell locks(L-C locks),and anti-phase boundaries(APBs)induced by the shearing of L12 phase are responsible for the high strain hardening rate and plasticity at 77 K.Our work provides a new insight for the incorporation of precipitation hardening and additive manufacturing technology,paving the avenue for the development of high-performance structural materials.
文摘Quenching Oils are comprised mostly of mineral oil as major component, but mineral oil alone result in lower cooling performance. Therefore, various additives are formulated as required for each particular case. Cooling curves of mineral oil as determined by JIS method can be divided into three stages, vapor film stage, boiling stage and convection stage. And there are many types of additives used for quenching oil, one effective to shorten vapor film stage and another to shift boiling stage toward lower temperature side. As rapid quenching required temperature range for particular steel varies pending on its shape of CCT curve"1, it is possible to provide higher quench hardening performance using quenching oil formulated of adequate additives.
基金supported by the National Key Re-search and Development Program of China(No.2024YFC2816500)the National Natural Science Foundation of China(Nos.U2341261 and 52471121)the Fundamental Research Funds for the Cen-tral Universities(No.DUT24RC(3)107).
文摘Developing high-strength and ductile metallic parts with designable shapes is an unfading research topic for material science and engineering.As a revolutionary technology,additive manufacturing(AM)pro-vides a new pathway for producing complex-shaped metallic parts with the possibility of in situ tailoring their microstructure.However,AM is not always ideally applicable for all metals and alloys.Eutectic high entropy alloys(EHEAs)contain both the advantages of the eutectic alloys and high entropy alloys(HEAs),and EHEAs show significant potential in AM due to their excellent mechanical properties and good fluid-ity.Herein,heterogeneous and ultra-fine eutectic lamellar microstructure with directional growth along the deposition direction(DD)was obtained by adjusting the process parameters of AM to improve the strength and ductility of EHEAs.Compared with the as-cast sample,the simultaneous increment in both strength and ductility is achieved by AM.Combination of strength and ductility of the AM sample ten-sile along the DD direction(yield strength σ_(y)=1115 MPa,ultimate tensile strength σ_(UTS)=1417 MPa,ultimate tensile strain ε_(U)=23%)in this work was superior to most of the additive manufactured al-loys and comparable to the thermomechanical-treated EHEAs with the best mechanical properties.The high strength and good ductility of the AM were mainly attributed to the ultra-fine lamellar nature and fully constrained soft and hard lamellar microstructure,which produces an obvious hetero-deformation induced(HDI)strengthening and high crack buffering effect during the deformation.This work provides a new possibility to achieve high strength and ductile complex-shaped metallic parts via designing direc-tional lamellar eutectic structures by AM.
基金University of Queensland are very grateful to Australia Research Council(ARC)Discovery Project(DP210103162)program for funding support.Greta Lindwall acknowledges support from Vinnova,Formas and Energimyndigheten via LIGHTer Academy.
文摘As a potent grain refiner for steel casting,TiN is now widely used to refineγ-austenite in steel additive manufacturing(AM).However,the refining mechanism of TiN during AM remains unclear despite intensive research in recent years.This work aims to boost our understanding on the mechanism of TiN in refining theγ-austenite in AM-fabricated 316 stainless steel and its corresponding effect on the mechanical behaviour.Experimental results show that addition of 1 wt.%TiN nanoparticles led to complete columnarto-equiaxed transition and significant refinement of the austenite grains to∼2μm in the 316 steel.Thermodynamic and kinetic simulations confirmed that,despite the rapid AM solidification,δ-ferrite is the primary solid phase during AM of the 316 steel andγ-austenite forms through subsequent peritectic reaction or direct transformation from theδ-ferrite.This implies that the TiN nanoparticles actually refined theδ-ferrite through promoting its heterogenous nucleation,which in turn refined theγ-austenite.This assumption is verified by the high grain refining efficiency of TiN nanoparticles in an AM-fabricated Fe-4 wt.%Siδ-ferrite alloy,in whichδ-ferrite forms directly from the melt and is retained at room temperature.The grain refinement is attributed to the good atomic matching betweenδ-ferrite and TiN.Grain refinement in the 316 steel through 1 wt.%TiN inoculation not only eliminated the property anisotropy but also led to a high strain-hardening rate upon plastic deformation and thereby a superior strengthductility synergy with yield strength of 561 MPa,tensile strength of 860 MPa and elongation of 48%.
基金support of the German Federal Ministry of Education and Research within the NanoMatFutur project“MatAM-Design of additively manufactured highperformance alloys for automotive applications”(Project ID:03XP0264).
文摘Additively manufactured(AM)metals exhibit highly complex microstructures,particularly in terms of grain morphology which typically features heterogeneous grain size distribution,irregular and anisotropic grain shapes,and the so-called columnar grains.The conventional morphological descriptors based on grain shape idealization are generally inadequate for representing complex and anisotropic grain mor-phology of AM microstructures.The primary aspect of microstructural grain morphology is the state of grain boundary spacing or grain size whose effect on the mechanical response is known to be cru-cial.In this paper,we formally introduce the notion of axial grain size from which we derive mean axial grain size,effective grain size,and grain size anisotropy as robust morphological descriptors ca-pable of effectively representing highly complex grain morphologies.We instantiated a discrete sample of polycrystalline aggregate as a representative volume element(RVE)featuring random crystallographic orientation and misorientation distributions.However,the instantiated RVE incorporates the typical mor-phological features of AM microstructures including distinctive grain size heterogeneity and anisotropic grain size owing to its pronounced columnar grain morphology.We ensured that any anisotropy ob-served in the macroscopic mechanical response of the instantiated sample primarily originates from its underlying anisotropic grain size.The RVE was then employed for mesoscale full-field crystal plasticity simulations corresponding to uniaxial tensile deformation along various axes via a spectral solver and a physics-based crystal plasticity constitutive model which was developed,calibrated,and validated in ear-lier studies.Through the numerical analyses,we isolated the contribution of anisotropic grain size to the anisotropy in the mechanical response of polycrystalline aggregates,particularly those with the charac-teristic complex grain morphology of AM metals.This contribution can be described by an inverse square relation.
基金This project is supported by the National Natural Science Foundation of China.(No.50275098)
文摘The present work has investigated the effect of trace elements Cd and Sn on the microstructure and mechanical properties of Al-Si-Cu-Mg cast alloy. With the increase of Cd addition the strength of alloy rises at first and then drops. The optimal amount of Cd and Sn addition for Al-Si-Cu-Mg alloy is about 0.27% and 0.1% respectively. Due to the formation of some coarse Cd-rich phases and pure Cd particles the mechanical properties of alloy decrease when Cd amount exceeds 0.27%. When more than 0.1% Sn added, some Sn atoms form low-melting eutectic compound at grain boundary, and then cause over-burning in alloy when solution treated, which may deteriorate properties of alloy, especially ductility of alloy. On the other hand, the addition of Cd and Sn remarkably increases the peak hardness and reduces the time to reach aging peak in Al-Si-Cu-Mg alloy. The action of Cd /Sn in quaternary Al-Si-Cu-Mg alloy is effectively the same as that occur in binary Al-Cu alloy that the enhanced hardening associated with Cd / Sn addition is due to the promotion of the 6’ phase.
文摘在分析多轴疲劳几种常用非比例度定义的基础上,提出了一种非比例度定义方法,进而以American Society of Mechanical Engineers(ASME)规范案例中非比例加载多轴疲劳设计准则采用的应变参量作为基本损伤参量,发展了一种新的多轴疲劳寿命预测模型.结果表明:1所提出的非比例度定义可以描述任意已知轮廓的、非周期的、变幅的非比例加载路径;2与两种常用的多轴非比例加载疲劳寿命模型的预测结果对比可知,新的寿命预测模型对14种比例和非比例加载路径下304不锈钢材料的寿命预测与试验吻合更好,预测结果基本位于2倍分散带以内.
