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
在Gleeble-1500热模拟机上对Ti-5Al-5Mo-5V-1Cr-1Fe合金进行高温热压缩实验,研究该合金在变形温度为750~900℃、应变速率为0.001~1 s 1条件下的流变应力行为。利用光学显微镜分析合金在不同变形条件下的组织演化规律。结果表明：合金的...在Gleeble-1500热模拟机上对Ti-5Al-5Mo-5V-1Cr-1Fe合金进行高温热压缩实验,研究该合金在变形温度为750~900℃、应变速率为0.001~1 s 1条件下的流变应力行为。利用光学显微镜分析合金在不同变形条件下的组织演化规律。结果表明：合金的流变应力随着应变速率的增大和变形温度的降低而增大;流变应力随着应变的增加而增大,出现峰值后逐渐趋于平稳;变形过程中的流变应力可用Arrhenius双曲正弦本构关系来描述,平均变形激活能为454.2 kJ/mol;各种变形条件均可细化原始晶粒尺寸。随着温度的升高和应变速率的降低,合金的主要软化机制由动态回复逐渐变为动态再结晶;在（α＋β）相区变形（750~850℃）时,α相对β晶粒的动态再结晶的发生起到阻碍作用。展开更多
采用热模拟试验机对Ti-5Al-5Mo-5V-1Cr-1Fe合金进行等温压缩试验,获得变形温度为750~900℃和应变速率为0.001~1 s 1时的真应力真应变曲线,并运用修正后的试验数据建立真应变为0.7的热加工图。通过显微组织观察,分析合金的变形机理,确定...采用热模拟试验机对Ti-5Al-5Mo-5V-1Cr-1Fe合金进行等温压缩试验,获得变形温度为750~900℃和应变速率为0.001~1 s 1时的真应力真应变曲线,并运用修正后的试验数据建立真应变为0.7的热加工图。通过显微组织观察,分析合金的变形机理,确定热变形失稳区。研究结果表明：Ti-5Al-5Mo-5V-1Cr-1Fe合金加工温度范围较宽,当加工温度低于800℃且变形速率大于0.1 s 1时易发生绝热剪切,造成流变失稳;随着变形温度升高,功率耗散因子η有增大趋势,合金的流动软化机制由动态回复逐渐变为动态再结晶,显微组织也随之细化、均匀。展开更多
In this work,a near-beta Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy was fabricated by selective laser melting(SLM),and the microstructure evolution together with the mechanical properties was studied.The as-fabricated alloy...In this work,a near-beta Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy was fabricated by selective laser melting(SLM),and the microstructure evolution together with the mechanical properties was studied.The as-fabricated alloy showed columnarβgrains spreading over multiple layers and paralleling to the building direction.The distinct microstructure of as-fabricated alloy was composed of near-β(more than 98.1%)with a submicron cellular structure.Different SLM processing parameters such as hatch spacing could affect the microstructure of as-fabricated alloy,which could thus further significantly affect the mechanical properties of as-fabricated alloy.In addition,the as-fabricated alloy with the distinct microstructure exhibits yield strength of 818 MPa combined with elongation of more than 19%,which shows that SLM is a potential technology for manufacturing near-beta titanium components.展开更多
Hot compression behavior of Ti-5 Al-5 Mo-5 V-1 Cr-1 Fe alloy with an equiaxed（α＋β） starting microstructure was investigated by isothermal compression test and optical microscopy. Based on the true strain-stress d...Hot compression behavior of Ti-5 Al-5 Mo-5 V-1 Cr-1 Fe alloy with an equiaxed（α＋β） starting microstructure was investigated by isothermal compression test and optical microscopy. Based on the true strain-stress data with temperature correction, constitutive models with a high accuracy were developed and processing maps were established. Strain inhomogeneity at different locations in the compressed sample is reduced by raising temperature, leading to a uniform distribution of α phases. For the temperature range of 800-840 ℃ with a strain rate of 10 s^-1, the transformed volume fraction of α phase increases and the average grain size of α phase decreases slightly with increasing the temperature, indicating co-existence of dynamic recovery and dynamic recrystallization. Flow localization and faint β grain boundaries are observed at the strain rate of 10 s^-1 in the temperature range of 860-900 ℃. The processing map analysis shows that hot working of Ti-5 Al-5 Mo-5 V-1 Cr-1 Fe alloy should be conducted with the strain rate lower than 0.01 s^-1 to extend its workability.展开更多
Meeting the damage tolerance requirements for engineering-grade titanium alloys pose a significant challenge in achieving high fracture toughness in direct energy deposition(DED)titanium alloys.This work primarily inv...Meeting the damage tolerance requirements for engineering-grade titanium alloys pose a significant challenge in achieving high fracture toughness in direct energy deposition(DED)titanium alloys.This work primarily investigated the relationship between the microstructure and the fracture toughness of DED new Ti-6Al-4V-1Mo alloy.Two types of microstructures were designed via two process strategies:high-line energy density(HE)and low-line energy density(LE).Relative to LE samples,HE samples possess larger-sized microstructural characteristics(coarser grain boundaryα(α_(GB)),largerαcolonies,and coarserαlaths).Lessα/βphase boundaries were formed by coarserαlaths in the HE samples,increasing the movement of dislocations,resulting in tensile strength decreasing from 1007.1 MPa(LE)to 930.8 MPa(HE)and elongation increasing from 10.8%(LE)to 15.7%(HE).Also,HE samples exhibited an excellent fracture toughness of 114.0 MPa m^(1/2),significantly higher than that of LE samples(76.8 MPa m^(1/2)).An analysis of crack propagation paths was conducted to investigate the factors contributing to toughening.The primary factor enhancing toughness is the frequent obstruction of cracks by coarseαGB and largeαcolonies in HE samples.Particularly,the pretty large-angle deflections induced by the superposition effect of coarseαGB and largeαcolonies play a vital of significant role.These factors induced the long and tortuous high-energy pathways,which resulted in ultimately improved fracture toughness.The discovered microstructural toughening mechanisms can serve as a reference for future studies involving titanium alloys,offering insights on how to enhance fracture toughness by achieving similar characteristics.展开更多
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.
文摘在Gleeble-1500热模拟机上对Ti-5Al-5Mo-5V-1Cr-1Fe合金进行高温热压缩实验,研究该合金在变形温度为750~900℃、应变速率为0.001~1 s 1条件下的流变应力行为。利用光学显微镜分析合金在不同变形条件下的组织演化规律。结果表明：合金的流变应力随着应变速率的增大和变形温度的降低而增大;流变应力随着应变的增加而增大,出现峰值后逐渐趋于平稳;变形过程中的流变应力可用Arrhenius双曲正弦本构关系来描述,平均变形激活能为454.2 kJ/mol;各种变形条件均可细化原始晶粒尺寸。随着温度的升高和应变速率的降低,合金的主要软化机制由动态回复逐渐变为动态再结晶;在（α＋β）相区变形（750~850℃）时,α相对β晶粒的动态再结晶的发生起到阻碍作用。
文摘采用热模拟试验机对Ti-5Al-5Mo-5V-1Cr-1Fe合金进行等温压缩试验,获得变形温度为750~900℃和应变速率为0.001~1 s 1时的真应力真应变曲线,并运用修正后的试验数据建立真应变为0.7的热加工图。通过显微组织观察,分析合金的变形机理,确定热变形失稳区。研究结果表明：Ti-5Al-5Mo-5V-1Cr-1Fe合金加工温度范围较宽,当加工温度低于800℃且变形速率大于0.1 s 1时易发生绝热剪切,造成流变失稳;随着变形温度升高,功率耗散因子η有增大趋势,合金的流动软化机制由动态回复逐渐变为动态再结晶,显微组织也随之细化、均匀。
基金Project(2019B010943001)supported by Key-area Research and Development Program of Guangdong Province,ChinaProject(2020)supported by the Fund of State Key Laboratory of Powder Metallurgy,Central South University,China。
文摘In this work,a near-beta Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy was fabricated by selective laser melting(SLM),and the microstructure evolution together with the mechanical properties was studied.The as-fabricated alloy showed columnarβgrains spreading over multiple layers and paralleling to the building direction.The distinct microstructure of as-fabricated alloy was composed of near-β(more than 98.1%)with a submicron cellular structure.Different SLM processing parameters such as hatch spacing could affect the microstructure of as-fabricated alloy,which could thus further significantly affect the mechanical properties of as-fabricated alloy.In addition,the as-fabricated alloy with the distinct microstructure exhibits yield strength of 818 MPa combined with elongation of more than 19%,which shows that SLM is a potential technology for manufacturing near-beta titanium components.
基金Project(BS2013CL034)supported by the Promotive Research Fund for Excellent Young and Middle-aged Scientists of Shandong Province,ChinaProject(51401115)supported by the National Natural Science Foundation of ChinaProject(GN2013001)supported by Independent Innovation Foundation of Shandong University,China
文摘Hot compression behavior of Ti-5 Al-5 Mo-5 V-1 Cr-1 Fe alloy with an equiaxed（α＋β） starting microstructure was investigated by isothermal compression test and optical microscopy. Based on the true strain-stress data with temperature correction, constitutive models with a high accuracy were developed and processing maps were established. Strain inhomogeneity at different locations in the compressed sample is reduced by raising temperature, leading to a uniform distribution of α phases. For the temperature range of 800-840 ℃ with a strain rate of 10 s^-1, the transformed volume fraction of α phase increases and the average grain size of α phase decreases slightly with increasing the temperature, indicating co-existence of dynamic recovery and dynamic recrystallization. Flow localization and faint β grain boundaries are observed at the strain rate of 10 s^-1 in the temperature range of 860-900 ℃. The processing map analysis shows that hot working of Ti-5 Al-5 Mo-5 V-1 Cr-1 Fe alloy should be conducted with the strain rate lower than 0.01 s^-1 to extend its workability.
基金This work was supported by the Key Research and Development Projects of Shaanxi Province(2023-YBGY-359)the China CEEC University Joint Education Project(2021108)+1 种基金the Science and Technology Plan of Xi'an City(21ZCZZHXJS-QCY6-0001,21CXLHTJSGG-QCY8-0003)the Open Fund of Key Laboratory of Plasma Dynamics of Air Force Engineering University(6142202210203).
文摘Meeting the damage tolerance requirements for engineering-grade titanium alloys pose a significant challenge in achieving high fracture toughness in direct energy deposition(DED)titanium alloys.This work primarily investigated the relationship between the microstructure and the fracture toughness of DED new Ti-6Al-4V-1Mo alloy.Two types of microstructures were designed via two process strategies:high-line energy density(HE)and low-line energy density(LE).Relative to LE samples,HE samples possess larger-sized microstructural characteristics(coarser grain boundaryα(α_(GB)),largerαcolonies,and coarserαlaths).Lessα/βphase boundaries were formed by coarserαlaths in the HE samples,increasing the movement of dislocations,resulting in tensile strength decreasing from 1007.1 MPa(LE)to 930.8 MPa(HE)and elongation increasing from 10.8%(LE)to 15.7%(HE).Also,HE samples exhibited an excellent fracture toughness of 114.0 MPa m^(1/2),significantly higher than that of LE samples(76.8 MPa m^(1/2)).An analysis of crack propagation paths was conducted to investigate the factors contributing to toughening.The primary factor enhancing toughness is the frequent obstruction of cracks by coarseαGB and largeαcolonies in HE samples.Particularly,the pretty large-angle deflections induced by the superposition effect of coarseαGB and largeαcolonies play a vital of significant role.These factors induced the long and tortuous high-energy pathways,which resulted in ultimately improved fracture toughness.The discovered microstructural toughening mechanisms can serve as a reference for future studies involving titanium alloys,offering insights on how to enhance fracture toughness by achieving similar characteristics.
