To explore the formation mechanism of anisotropy in Ti-6Al-4V alloy fabricated by selective laser melting(SLM),the compressive mechanical properties,microhardness,microstructure,and crystallographic orientation of the...To explore the formation mechanism of anisotropy in Ti-6Al-4V alloy fabricated by selective laser melting(SLM),the compressive mechanical properties,microhardness,microstructure,and crystallographic orientation of the alloy across different planes were investigated.The anisotropy of SLM-fabricated Ti-6Al-4V alloys was analyzed,and the electron backscatter diffraction technique was used to investigate the influence of different grain types and orientations on the stress-strain distribution at various scales.Results reveal that in room-temperature compression tests at a strain rate of 10^(-3) s^(-1),both the compressive yield strength and microhardness vary along the deposition direction,indicating a certain degree of mechanical property anisotropy.The alloy exhibits a columnar microstructure;along the deposition direction,the grains appear equiaxed,and they have internal hexagonal close-packed(hcp)α/α'martensitic structure.α'phase has a preferential orientation approximately along the<0001>direction.Anisotropy arises from the high aspect ratio of columnar grains,along with the weak texture of the microstructure and low symmetry of the hcp crystal structure.展开更多
The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy,which is developed for laser directed energy deposition technique,was investigated before and after cyclic heat treatment(CHT).Changes in microstru...The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy,which is developed for laser directed energy deposition technique,was investigated before and after cyclic heat treatment(CHT).Changes in microstructure,fracture surfaces,and crack growth paths were analyzed before and after CHT.Results indicate that in the stable crack growth region,the growth rates for the as-deposited and cyclic heat-treated specimens follow the relationships da/dN=1.8651×10^(−8)(ΔK)^(3.2271)and da/dN=1.4112×10^(−8)(ΔK)^(3.1125),respectively.Compared with that at the as-deposited state,the microstructure after CHT is transformed from a uniform basket-weave microstructure to a dual-phase microstructure consisting of near-sphericalαandβ-transformed matrix phases.The cyclic process also disrupts the continuity of the grain boundaryα(αGB)at the primaryβ-phase grain boundary.The coarsening of primaryαand the disruption ofαGB continuity are the primary factors to release stress concentration and promote crack deflection,thereby decreasing the fatigue crack growth rate.Additionally,the increased occurrence of crack branching,secondary cracking,and crack bridging in cyclic heat-treated specimens further reduces the crack driving force and slows the fatigue crack growth rate.展开更多
Three-beam wire-feed laser cladding,which generates a uniform energy distribution with a wire vertically fed into the molten pool,is a promising additive manufacturing technology.In this study,an experimental investig...Three-beam wire-feed laser cladding,which generates a uniform energy distribution with a wire vertically fed into the molten pool,is a promising additive manufacturing technology.In this study,an experimental investigation and a statistical analysis of Ti-6Al-4V wire cladding using three-beam laser coaxial wire-feed cladding technology coupled with a 2 kW continuous fiber laser were carried out.The influences of the main parameters,including the laser power,wire feeding speed,and laser scanning speed,on the cladding geometry and process were investigated.The prediction models correlating the process parameters and clad geometry were developed via the response surface methodology(RSM).The models were checked using analysis of variance(ANOVA).Through optimization,the optimal parameters were achieved for the required clad with a width-to-height ratio of 5:1.A high-speed camera was used to investigate the cladding process under various process parameters.The laser power positively affected the widths of the molten pool and cladding layer.The molten pool and clad heights decreased with increases in laser power and scanning speed.Fine acicular martensite grains in the colony and basket-weave distributions were predominant in the cross-section of the cladding layer.The macrostructure investigation showed that the widths of columnar prior-βgrains decreased with the increase in laser scanning speed.展开更多
基金National Natural Science Foundation of China(51504138,51674118,52271177)Hunan Provincial Natural Science Foundation of China(2023JJ50181)Supported by State Key Laboratory of Materials Processing and Die&Mould Technology,Huazhong University of Science and Technology(P2024-022)。
文摘To explore the formation mechanism of anisotropy in Ti-6Al-4V alloy fabricated by selective laser melting(SLM),the compressive mechanical properties,microhardness,microstructure,and crystallographic orientation of the alloy across different planes were investigated.The anisotropy of SLM-fabricated Ti-6Al-4V alloys was analyzed,and the electron backscatter diffraction technique was used to investigate the influence of different grain types and orientations on the stress-strain distribution at various scales.Results reveal that in room-temperature compression tests at a strain rate of 10^(-3) s^(-1),both the compressive yield strength and microhardness vary along the deposition direction,indicating a certain degree of mechanical property anisotropy.The alloy exhibits a columnar microstructure;along the deposition direction,the grains appear equiaxed,and they have internal hexagonal close-packed(hcp)α/α'martensitic structure.α'phase has a preferential orientation approximately along the<0001>direction.Anisotropy arises from the high aspect ratio of columnar grains,along with the weak texture of the microstructure and low symmetry of the hcp crystal structure.
基金National Key Research and Development Program of China(2024YFB4610803)。
文摘The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy,which is developed for laser directed energy deposition technique,was investigated before and after cyclic heat treatment(CHT).Changes in microstructure,fracture surfaces,and crack growth paths were analyzed before and after CHT.Results indicate that in the stable crack growth region,the growth rates for the as-deposited and cyclic heat-treated specimens follow the relationships da/dN=1.8651×10^(−8)(ΔK)^(3.2271)and da/dN=1.4112×10^(−8)(ΔK)^(3.1125),respectively.Compared with that at the as-deposited state,the microstructure after CHT is transformed from a uniform basket-weave microstructure to a dual-phase microstructure consisting of near-sphericalαandβ-transformed matrix phases.The cyclic process also disrupts the continuity of the grain boundaryα(αGB)at the primaryβ-phase grain boundary.The coarsening of primaryαand the disruption ofαGB continuity are the primary factors to release stress concentration and promote crack deflection,thereby decreasing the fatigue crack growth rate.Additionally,the increased occurrence of crack branching,secondary cracking,and crack bridging in cyclic heat-treated specimens further reduces the crack driving force and slows the fatigue crack growth rate.
基金Supported by the National Natural Science Foundation of China(Grant Nos.62173239,61903268)Suzhou Vocational Institute of Industrial Technology Foundation(Grant Nos.2024kyqd003,2021kyqd005 and 2022kypy09).
文摘Three-beam wire-feed laser cladding,which generates a uniform energy distribution with a wire vertically fed into the molten pool,is a promising additive manufacturing technology.In this study,an experimental investigation and a statistical analysis of Ti-6Al-4V wire cladding using three-beam laser coaxial wire-feed cladding technology coupled with a 2 kW continuous fiber laser were carried out.The influences of the main parameters,including the laser power,wire feeding speed,and laser scanning speed,on the cladding geometry and process were investigated.The prediction models correlating the process parameters and clad geometry were developed via the response surface methodology(RSM).The models were checked using analysis of variance(ANOVA).Through optimization,the optimal parameters were achieved for the required clad with a width-to-height ratio of 5:1.A high-speed camera was used to investigate the cladding process under various process parameters.The laser power positively affected the widths of the molten pool and cladding layer.The molten pool and clad heights decreased with increases in laser power and scanning speed.Fine acicular martensite grains in the colony and basket-weave distributions were predominant in the cross-section of the cladding layer.The macrostructure investigation showed that the widths of columnar prior-βgrains decreased with the increase in laser scanning speed.
