The effect of strain rate on ultimate strength and fractograph was investigated for tungsten alloy with four different technologies. As the strain rate rises, the ultimate strength increases and morphology of fracture...The effect of strain rate on ultimate strength and fractograph was investigated for tungsten alloy with four different technologies. As the strain rate rises, the ultimate strength increases and morphology of fracture surface gradually transits from detachment of interface between W pellets and matrices to cleavage of W pellets. Meanwhile, low strength tungsten alloy has higher sensitivity to strain rate.展开更多
SEM microfractography of near-threshold fatigue crack propagation were carried out in the dual-phase steels of 3 martensite morphologies and 6 volume fractions of martensite (V_m). All of them are featured by cyclic c...SEM microfractography of near-threshold fatigue crack propagation were carried out in the dual-phase steels of 3 martensite morphologies and 6 volume fractions of martensite (V_m). All of them are featured by cyclic cleavage characteristics in near-threshold region,i.e.,main- ly controlled by mode Ⅱ stress.In the higher ΔK regions,the fracture surfaces are character- ized by mixed modes including cyclic cleavage facets,two types of secondary cracks and striations,etc..The roughness-induced crack closure of fracture surface is attributed primarily to extreme high fatigue crack growth threshold values.展开更多
Crack initiation and propagation have been investigated under tensile and shear loading in ceramically and carbon bonded refractories.A wedge splitting test procedure and a modified shear test have been applied.Test r...Crack initiation and propagation have been investigated under tensile and shear loading in ceramically and carbon bonded refractories.A wedge splitting test procedure and a modified shear test have been applied.Test results have been used for material characterization especially with respect to brittleness.Furthermore a microscopic fractographic test procedure was developed and applied on fractured test specimens.In order to explain brittleness dependence on structure properties correlation of fractographic and fracture mechanical results has been evaluated.Frequently brittleness reduction is achieved by a lower amount of transgranular crack propagation associated with a strength decrease while maintaining specific fracture energy unchanged.Deviations from pure linear fracture mechanics increase with decreasing brittleness and contribute to specific fracture energy.Shear specimens may show two generations of cracks,a first one initiated by tensile loads （stable propagation） and a second one by shear loads （unstable propagation）.展开更多
The effect of mineral oil on the mechanical properties and fractographs of Fe3(Al,Cr,Zr) in termetallic alloy has been investigated. The results show that the tensile ductility of the Fe3(Al,Cr,Zr) alloy tested in oil...The effect of mineral oil on the mechanical properties and fractographs of Fe3(Al,Cr,Zr) in termetallic alloy has been investigated. The results show that the tensile ductility of the Fe3(Al,Cr,Zr) alloy tested in oil is comparable with the results obtained in oxygen and is in sensitive to strain rate. The fracture mode of the Fe3(Al,Cr,Zr) alloy treated at 700℃/1.5 h and tested in oil, is cleavage and with dimples in some areas.展开更多
A new type of hybrid SiC foam-SiC particles-Al composites used as an electronic packaging substrate material were fabricated by squeeze casting technique. The mechanical properties and the fracture mechanism of the hy...A new type of hybrid SiC foam-SiC particles-Al composites used as an electronic packaging substrate material were fabricated by squeeze casting technique. The mechanical properties and the fracture mechanism of the hybrid composites were investigated. The influence of SiC particles and foam hybrid reinforcement on the behavior of the composites was studied. The results show that the interface bonding in the hybrid composites is good for the composites with the unique double interpenetrating structure. The compressive strength of the hybrid composite reinforced by the SiC with the volume fraction of 59.9% is 680 MPa,which is higher than that of any other composites with the same volume fraction of SiC particles reinforcement.展开更多
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
The mechanical properties, microstructures, and fractographs of TA15 sheets vacuum-annealed under different patterns were investigated. The results indicate that vacuum annealing significantly improves the mechanical ...The mechanical properties, microstructures, and fractographs of TA15 sheets vacuum-annealed under different patterns were investigated. The results indicate that vacuum annealing significantly improves the mechanical properties of the sheets in comparison with those after ambient annealing. With increasing the annealing temperature, the phase boundaries and secondary a-phase increase, whereas the volume fraction of primary a-phase decreases, resulting in increased strength and decreased elongation A relatively fine secondary a-phase is obtained after double annealing. The desirable mechanical properties （i.e., ultimate tensile strength, yield strength, and elongation are 1070 MPa, 958 MPa, and 15%, respectively） are obtained through double annealing （（950 ℃/2 h, AC）＋（600 ℃/2 h, AC））. The fractographs obtained after tensile tests show that the deepest and largest dimples are formed in the specimen annealed at 850 ℃, which indicates that the best plasticity is obtained at this annealing temperature.展开更多
文摘The effect of strain rate on ultimate strength and fractograph was investigated for tungsten alloy with four different technologies. As the strain rate rises, the ultimate strength increases and morphology of fracture surface gradually transits from detachment of interface between W pellets and matrices to cleavage of W pellets. Meanwhile, low strength tungsten alloy has higher sensitivity to strain rate.
文摘SEM microfractography of near-threshold fatigue crack propagation were carried out in the dual-phase steels of 3 martensite morphologies and 6 volume fractions of martensite (V_m). All of them are featured by cyclic cleavage characteristics in near-threshold region,i.e.,main- ly controlled by mode Ⅱ stress.In the higher ΔK regions,the fracture surfaces are character- ized by mixed modes including cyclic cleavage facets,two types of secondary cracks and striations,etc..The roughness-induced crack closure of fracture surface is attributed primarily to extreme high fatigue crack growth threshold values.
文摘Crack initiation and propagation have been investigated under tensile and shear loading in ceramically and carbon bonded refractories.A wedge splitting test procedure and a modified shear test have been applied.Test results have been used for material characterization especially with respect to brittleness.Furthermore a microscopic fractographic test procedure was developed and applied on fractured test specimens.In order to explain brittleness dependence on structure properties correlation of fractographic and fracture mechanical results has been evaluated.Frequently brittleness reduction is achieved by a lower amount of transgranular crack propagation associated with a strength decrease while maintaining specific fracture energy unchanged.Deviations from pure linear fracture mechanics increase with decreasing brittleness and contribute to specific fracture energy.Shear specimens may show two generations of cracks,a first one initiated by tensile loads （stable propagation） and a second one by shear loads （unstable propagation）.
文摘The effect of mineral oil on the mechanical properties and fractographs of Fe3(Al,Cr,Zr) in termetallic alloy has been investigated. The results show that the tensile ductility of the Fe3(Al,Cr,Zr) alloy tested in oil is comparable with the results obtained in oxygen and is in sensitive to strain rate. The fracture mode of the Fe3(Al,Cr,Zr) alloy treated at 700℃/1.5 h and tested in oil, is cleavage and with dimples in some areas.
基金Project(50765005) supported by the National Natural Science Foundation of ChinaProject(01306016) supported by the Science Research Foundation of East China Jiaotong University, China
文摘A new type of hybrid SiC foam-SiC particles-Al composites used as an electronic packaging substrate material were fabricated by squeeze casting technique. The mechanical properties and the fracture mechanism of the hybrid composites were investigated. The influence of SiC particles and foam hybrid reinforcement on the behavior of the composites was studied. The results show that the interface bonding in the hybrid composites is good for the composites with the unique double interpenetrating structure. The compressive strength of the hybrid composite reinforced by the SiC with the volume fraction of 59.9% is 680 MPa,which is higher than that of any other composites with the same volume fraction of SiC particles reinforcement.
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.
基金Project supported by Beijing Laboratory of Metallic Materials and Processing for Modern Transportation
文摘The mechanical properties, microstructures, and fractographs of TA15 sheets vacuum-annealed under different patterns were investigated. The results indicate that vacuum annealing significantly improves the mechanical properties of the sheets in comparison with those after ambient annealing. With increasing the annealing temperature, the phase boundaries and secondary a-phase increase, whereas the volume fraction of primary a-phase decreases, resulting in increased strength and decreased elongation A relatively fine secondary a-phase is obtained after double annealing. The desirable mechanical properties （i.e., ultimate tensile strength, yield strength, and elongation are 1070 MPa, 958 MPa, and 15%, respectively） are obtained through double annealing （（950 ℃/2 h, AC）＋（600 ℃/2 h, AC））. The fractographs obtained after tensile tests show that the deepest and largest dimples are formed in the specimen annealed at 850 ℃, which indicates that the best plasticity is obtained at this annealing temperature.
