Ti-6Al-4Zr-2Sn-6Mo alloy is one of the most recent titanium alloys processed using powder bed fusion-laser beam(PBF-LB)technology.This alloy has the potential to replace Ti-6Al-4V in automotive and aerospace applicati...Ti-6Al-4Zr-2Sn-6Mo alloy is one of the most recent titanium alloys processed using powder bed fusion-laser beam(PBF-LB)technology.This alloy has the potential to replace Ti-6Al-4V in automotive and aerospace applications,given its superior mechanical properties,which are approximately 10%higher in terms of ultimate tensile strength(UTS)and yield strength after appropriate heat treatment.In as-built conditions,the alloy is characterized by the presence of soft orthorhombicα″martensite,necessitating a postprocessing heat treatment to decompose this phase and enhance the mechanical properties of the alloy.Usually,PBFed Ti6246 components undergo an annealing process that transforms theα″martensite into anα-βlamellar microstructure.The primary objective of this research was to develop a solution treatment and aging(STA)heat treatment tailored to the unique microstructure produced by the additive manufacturing process to achieve an ultrafine bilamellar microstructure reinforced by precipitation hardening.This study investigated the effects of various solution temperatures in theα-βfield(ranging from 800 to 875℃),cooling media(air and water),and aging time to determine the optimal heat treatment parameters for achieving the desired bilamellar microstructure.For each heat treatment condition,differentα-βmicrostructures were found,varying in terms of theα/βratio and the size of the primaryα-phase lamellae.Particular attention was given to how these factors were influenced by increases in solution temperature and how microhardness correlated with the percentage of the metastableβphase present after quenching.Tensile tests were performed on samples subjected to the most promising heat treatment parameters.A comparison with literature data revealed that the optimized STA treatment enhanced hardness and UTS by13%and 23%,respectively,compared with those of the annealed alloy.Fracture surface analyses were conducted to investigate fracture mechanisms.展开更多
Dual-phase heterogeneous structures confer eutectic high-entropy alloy(EHEA)with excellent strength-ductility synergy under quasi-static tensile loading.However,it is questionable whether the EHEAs pos-sess equally go...Dual-phase heterogeneous structures confer eutectic high-entropy alloy(EHEA)with excellent strength-ductility synergy under quasi-static tensile loading.However,it is questionable whether the EHEAs pos-sess equally good impact toughness because the phase interfaces are vulnerable to crack initiation.This work aimed to study the Charpy impact toughness and fracture behavior of AlCoCrFeNi_(2.1) EHEA.The results indicate that while maintaining high tensile strength and ductility,the AlCoCrFeNi_(2.1) EHEA also shows a satisfactory impact toughness of 25.86 J/cm^(2),superior to most other dual-phase alloys like TC4 titanium alloy or DP steel.Fractography analysis reveals characteristic regions of the fracture surface,which suggests energy absorption mechanisms primarily through ductile dimples,flat cleavage facets,secondary cracks,and microvoids,corresponding to a ductile-brittle mixed fracture mode.Detailed obser-vations of the deformed microstructure through TEM and EBSD demonstrate that FCC(L1_(2))and BCC(B2)phases underwent concurrent tearing along their phase boundaries,indicating a crucial influence of phase boundaries over crack initiation and propagation.The FCC(L1_(2))phase bore almost all plastic deformation of the sample through dislocation slip,whereas the BCC(B2)phase underwent a rapid shearing but almost no dislocation slip.Crack initiation under impact loading typically starts at the FCC(L1_(2))/BCC(B2)inter-face before propagating through the BCC(B2)phase.Additionally,this work further examines the effect of sample size and notch shape on the impact toughness of AlCoCrFeNi_(2.1) EHEA.A comparative analysis of the mechanical behavior under static and impact loading was also conducted,highlighting differences and connections in stress distribution and fracture surface morphology.The study offers valuable insights into the mechanical response and fracture behavior of AlCoCrFeNi_(2.1) EHEA under impact loading,provid-ing crucial information for its potential industrial applications.展开更多
基金financed by the European Union-Next Generation EU(National Sustainable Mobility Center CN00000023,Italian Ministry of University and Research Decree n.1033-17/06/2022,Spoke 11-Innovative Materials&Lightweighting)。
文摘Ti-6Al-4Zr-2Sn-6Mo alloy is one of the most recent titanium alloys processed using powder bed fusion-laser beam(PBF-LB)technology.This alloy has the potential to replace Ti-6Al-4V in automotive and aerospace applications,given its superior mechanical properties,which are approximately 10%higher in terms of ultimate tensile strength(UTS)and yield strength after appropriate heat treatment.In as-built conditions,the alloy is characterized by the presence of soft orthorhombicα″martensite,necessitating a postprocessing heat treatment to decompose this phase and enhance the mechanical properties of the alloy.Usually,PBFed Ti6246 components undergo an annealing process that transforms theα″martensite into anα-βlamellar microstructure.The primary objective of this research was to develop a solution treatment and aging(STA)heat treatment tailored to the unique microstructure produced by the additive manufacturing process to achieve an ultrafine bilamellar microstructure reinforced by precipitation hardening.This study investigated the effects of various solution temperatures in theα-βfield(ranging from 800 to 875℃),cooling media(air and water),and aging time to determine the optimal heat treatment parameters for achieving the desired bilamellar microstructure.For each heat treatment condition,differentα-βmicrostructures were found,varying in terms of theα/βratio and the size of the primaryα-phase lamellae.Particular attention was given to how these factors were influenced by increases in solution temperature and how microhardness correlated with the percentage of the metastableβphase present after quenching.Tensile tests were performed on samples subjected to the most promising heat treatment parameters.A comparison with literature data revealed that the optimized STA treatment enhanced hardness and UTS by13%and 23%,respectively,compared with those of the annealed alloy.Fracture surface analyses were conducted to investigate fracture mechanisms.
基金financially supported by the Natural Science Spe-cial(Special Post)Research Foundation of Guizhou University(No.2023-46)the Youth Science and Technology Talent Development Program of Guizhou(No.QKJ[2024]24)the National Natural Science Foundation of China(Nos.52274260,52074096,and 52164017).
文摘Dual-phase heterogeneous structures confer eutectic high-entropy alloy(EHEA)with excellent strength-ductility synergy under quasi-static tensile loading.However,it is questionable whether the EHEAs pos-sess equally good impact toughness because the phase interfaces are vulnerable to crack initiation.This work aimed to study the Charpy impact toughness and fracture behavior of AlCoCrFeNi_(2.1) EHEA.The results indicate that while maintaining high tensile strength and ductility,the AlCoCrFeNi_(2.1) EHEA also shows a satisfactory impact toughness of 25.86 J/cm^(2),superior to most other dual-phase alloys like TC4 titanium alloy or DP steel.Fractography analysis reveals characteristic regions of the fracture surface,which suggests energy absorption mechanisms primarily through ductile dimples,flat cleavage facets,secondary cracks,and microvoids,corresponding to a ductile-brittle mixed fracture mode.Detailed obser-vations of the deformed microstructure through TEM and EBSD demonstrate that FCC(L1_(2))and BCC(B2)phases underwent concurrent tearing along their phase boundaries,indicating a crucial influence of phase boundaries over crack initiation and propagation.The FCC(L1_(2))phase bore almost all plastic deformation of the sample through dislocation slip,whereas the BCC(B2)phase underwent a rapid shearing but almost no dislocation slip.Crack initiation under impact loading typically starts at the FCC(L1_(2))/BCC(B2)inter-face before propagating through the BCC(B2)phase.Additionally,this work further examines the effect of sample size and notch shape on the impact toughness of AlCoCrFeNi_(2.1) EHEA.A comparative analysis of the mechanical behavior under static and impact loading was also conducted,highlighting differences and connections in stress distribution and fracture surface morphology.The study offers valuable insights into the mechanical response and fracture behavior of AlCoCrFeNi_(2.1) EHEA under impact loading,provid-ing crucial information for its potential industrial applications.
