The hot deformation behavior of Ti-3.0Al-3.7Cr-2.0Fe-0.1B (TACFB) titanium alloy was investigated using a Gleeble-1500D thermal simulator in the temperature range of 800-950 °C, at constant strain rate from 0.01 ...The hot deformation behavior of Ti-3.0Al-3.7Cr-2.0Fe-0.1B (TACFB) titanium alloy was investigated using a Gleeble-1500D thermal simulator in the temperature range of 800-950 °C, at constant strain rate from 0.01 s-1 to 10 s-1 and with height reduction of 70%. Flow stress and microstructure evolution during hot compression of TACFB alloy were investigated. The processing map of TACFB alloy was obtained. The results indicate that the hot deformation behavior of TACFB alloy is sensitive to the deformation temperature and strain rate. The peak flow stress decreases with increasing the test temperature and decreasing the strain rate. The constitutive relationship of TACFB alloy was obtained on the base of Arrhenius equations. When the strain rates are higher than 1.0 s-1, the dynamic recrystallization occurs, and the higher the strain rates are, the more the recrystallization is.展开更多
Laser powder bed fusion(LPBF)is an advanced manufacturing technology;however,inappropriate LPBF process parameters may cause printing defects in materials.In the present work,the LPBF process of Ti-6.5Al-3.5Mo-1.5Zr-0...Laser powder bed fusion(LPBF)is an advanced manufacturing technology;however,inappropriate LPBF process parameters may cause printing defects in materials.In the present work,the LPBF process of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy was investigated by a two-step optimization approach.Subsequently,heat transfer and liquid flow behaviors during LPBF were simulated by a well-tested phenomenological model,and the defect formation mechanisms in the as-fabricated alloy were discussed.The optimized process parameters for LPBF were detected as laser power changed from 195 W to 210 W,with scanning speed of 1250 mm/s.The LPBF process was divided into a laser irradiation stage,a spreading flow stage,and a solidification stage.The morphologies and defects of deposited tracks were affected by liquid flow behavior caused by rapid cooling rates.The findings of this research can provide valuable support for printing defect-free metal components.展开更多
The characteristics of hot deformation of an α＋β titanium alloy Ti-6.5Al-3.5Mo-1.5Zr-0.3Si with acicular microstructure were studied using isothermal hot compressive tests in a strain rate range of 0.01-10 s^-1 at ...The characteristics of hot deformation of an α＋β titanium alloy Ti-6.5Al-3.5Mo-1.5Zr-0.3Si with acicular microstructure were studied using isothermal hot compressive tests in a strain rate range of 0.01-10 s^-1 at 860-1 100 ℃. The true stress-tree strain curves of alloy hot-compressed in the α＋β region exhibit a peak stress followed by continuous flow softening; whereas in the β region, the flow stress attains a steady-state regime. At a strain rate of 10 s^-1 and in a wide temperature range, the alloy exhibits plastic flow instability. According to the kinetic rate equation, the apparent activation energies are estimated to be about 633 kJ/mol in the α＋β region and 281 kJ/mol in the β region, respectively. The processing maps show a domain of the globularization process of a colony structure and α dynamic recrystallization in the temperature range of 860-960 ℃ with a peak efficiency of about 60%, and a domain of β dynamic recrystallization in the β region with a peak efficiency of 80%.展开更多
A method is proposed for prediction of the unstable deformation in hot forging process using both the determined thermomechnical parameter windows of the unstable deformation zones and finite element simulation. Takin...A method is proposed for prediction of the unstable deformation in hot forging process using both the determined thermomechnical parameter windows of the unstable deformation zones and finite element simulation. Taking Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy as the testing material, the thermomechnical parameter windows of the unstable deformation zones for the Ti-alloy are integrated into a commercial finite element simulation software platform. The distribution and variation of the unstable deformation zones of the alloy in hot compression process are simulated and predicted using the tailor-made finite element codes in the finite element platform. The simulation results tally with the physical experiments and the proposed method for simulation and prediction of the unstable deformation is thus verified and its efficiency is validated.展开更多
Isothermal β heat treatments of Ti-6.5 Al-3.5 Mo-1.5 Zr-0.3 Si alloy were performed at the temperature of1040-1240 ℃ to examine the influence of heating conditions on grain growth of the alloy. The results show that...Isothermal β heat treatments of Ti-6.5 Al-3.5 Mo-1.5 Zr-0.3 Si alloy were performed at the temperature of1040-1240 ℃ to examine the influence of heating conditions on grain growth of the alloy. The results show that the grain size increases with heating temperature and holding time increasing. Rapid β grain growth of the alloy takes place at the temperature of over 1140 ℃. The grain growth kinetics for the alloy follows the classical isothermal grain growth law.The growth time exponent(n) of 0.5651 and activation energy(Q) of 129.6 kJ mol-1 are determined. Finally, in order to determine the grain size under different heating conditions,the grain growth model of the alloy was established.展开更多
Laser powder bed fusion(LPBF)yields unique advantages during the fabrication of titanium alloys.In the present work,Ti-6.5 Al-3.5 Mo-1.5 Zr-0.3 Si alloy specimens with excellent mechanical performances were fabricated...Laser powder bed fusion(LPBF)yields unique advantages during the fabrication of titanium alloys.In the present work,Ti-6.5 Al-3.5 Mo-1.5 Zr-0.3 Si alloy specimens with excellent mechanical performances were fabricated by LPBF.The as-built specimens displayed relatively high strength and ductility under modest volume energy densities(VEDs),whereas they manifested high strength with low ductility under high VEDs.To investigate the key reason of this phenomenon,the specimens were designed with two VEDs ranges of 60 J/mm^(3) and 85 J/mm^(3).Special attention was paid to the influences of residual stress and micro-deformation on microstructures and mechanical properties for the first time.The results indicated that the residual stresses and relative density of the 60 J/mm^(3) range specimens were higher than that of the 85 J/mm3 range specimens.Dislocation multiplication and dislocation movement promoted by the residual stress were hindered by the initialα’phase grain boundary(prior-α’GB),leading to the formation ofα’metastable structures.The mean tensile strength and elongation of the 60 J/mm^(3) range specimens were 1248.1 MPa and 12.3%,respectively,whereas the corresponding values for the 85 J/mm^(3) range specimens were 1405.3 MPa,5.0%,respectively.During deformation,the strength and ductility of the specimens were first improved by lamellar structures generated from prior-α’phases,and then effectively enhanced by the interaction between the{10–12}twins and dislocations.However,pores significantly reduced the ductility;hence,high VED specimens with large twins and numerous large pores increased the strength and reduce the ductility.展开更多
基金Project (2010DFA52280) supported by International Science and Technology CooperationProject (20100470260) supported by China Postdoctoral Science Foundation
文摘The hot deformation behavior of Ti-3.0Al-3.7Cr-2.0Fe-0.1B (TACFB) titanium alloy was investigated using a Gleeble-1500D thermal simulator in the temperature range of 800-950 °C, at constant strain rate from 0.01 s-1 to 10 s-1 and with height reduction of 70%. Flow stress and microstructure evolution during hot compression of TACFB alloy were investigated. The processing map of TACFB alloy was obtained. The results indicate that the hot deformation behavior of TACFB alloy is sensitive to the deformation temperature and strain rate. The peak flow stress decreases with increasing the test temperature and decreasing the strain rate. The constitutive relationship of TACFB alloy was obtained on the base of Arrhenius equations. When the strain rates are higher than 1.0 s-1, the dynamic recrystallization occurs, and the higher the strain rates are, the more the recrystallization is.
基金Supported by Development of a Verification Platform for Product Design,Process and Information Exchange Standards in Additive Manufacturing (Grant No.2019-00899-1-1)Ministry of Science and Technology of the People’s Republic of China (Grant No.2017YFB1103000)+1 种基金National Natural Science Foundation of China (Grant No.51375242)Natural Science Foundation of Jiangsu Province (Grant No.BK20180483)。
文摘Laser powder bed fusion(LPBF)is an advanced manufacturing technology;however,inappropriate LPBF process parameters may cause printing defects in materials.In the present work,the LPBF process of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy was investigated by a two-step optimization approach.Subsequently,heat transfer and liquid flow behaviors during LPBF were simulated by a well-tested phenomenological model,and the defect formation mechanisms in the as-fabricated alloy were discussed.The optimized process parameters for LPBF were detected as laser power changed from 195 W to 210 W,with scanning speed of 1250 mm/s.The LPBF process was divided into a laser irradiation stage,a spreading flow stage,and a solidification stage.The morphologies and defects of deposited tracks were affected by liquid flow behavior caused by rapid cooling rates.The findings of this research can provide valuable support for printing defect-free metal components.
基金Project(50901063) supported by the National Natural Science Foundation of ChinaProject(2007DS0414, 2007BS05006) supported by the Science and Technology Program of Shangdong Province, ChinaProject supported by the Open Research Fund from State Key Laboratory of Rolling and Automation, Northeastern University, China
文摘The characteristics of hot deformation of an α＋β titanium alloy Ti-6.5Al-3.5Mo-1.5Zr-0.3Si with acicular microstructure were studied using isothermal hot compressive tests in a strain rate range of 0.01-10 s^-1 at 860-1 100 ℃. The true stress-tree strain curves of alloy hot-compressed in the α＋β region exhibit a peak stress followed by continuous flow softening; whereas in the β region, the flow stress attains a steady-state regime. At a strain rate of 10 s^-1 and in a wide temperature range, the alloy exhibits plastic flow instability. According to the kinetic rate equation, the apparent activation energies are estimated to be about 633 kJ/mol in the α＋β region and 281 kJ/mol in the β region, respectively. The processing maps show a domain of the globularization process of a colony structure and α dynamic recrystallization in the temperature range of 860-960 ℃ with a peak efficiency of about 60%, and a domain of β dynamic recrystallization in the β region with a peak efficiency of 80%.
基金Project (51005112) supported by the National Natural Science Foundation of ChinaProject (GF200901008) supported by the Open Fund of National Defense Key Disciplines Laboratory of Light Alloy Processing Science and Technology,China
文摘A method is proposed for prediction of the unstable deformation in hot forging process using both the determined thermomechnical parameter windows of the unstable deformation zones and finite element simulation. Taking Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy as the testing material, the thermomechnical parameter windows of the unstable deformation zones for the Ti-alloy are integrated into a commercial finite element simulation software platform. The distribution and variation of the unstable deformation zones of the alloy in hot compression process are simulated and predicted using the tailor-made finite element codes in the finite element platform. The simulation results tally with the physical experiments and the proposed method for simulation and prediction of the unstable deformation is thus verified and its efficiency is validated.
基金financially supported by the National Natural Science Foundation of China (No. 51261020)the Aeronautical Science Foundation of China(No. 2014ZE56015)the Educational Committee of Jiangxi Province of China(No. GJJ14505)
文摘Isothermal β heat treatments of Ti-6.5 Al-3.5 Mo-1.5 Zr-0.3 Si alloy were performed at the temperature of1040-1240 ℃ to examine the influence of heating conditions on grain growth of the alloy. The results show that the grain size increases with heating temperature and holding time increasing. Rapid β grain growth of the alloy takes place at the temperature of over 1140 ℃. The grain growth kinetics for the alloy follows the classical isothermal grain growth law.The growth time exponent(n) of 0.5651 and activation energy(Q) of 129.6 kJ mol-1 are determined. Finally, in order to determine the grain size under different heating conditions,the grain growth model of the alloy was established.
基金The National Key R&D Program of China(Nos.2017YFB1103000,2016YFB1100504)The National Natural Science Foundation of China(Nos.51375242)The Natural Science Foundation of Jiangsu Province(No.BK20190463)。
文摘Laser powder bed fusion(LPBF)yields unique advantages during the fabrication of titanium alloys.In the present work,Ti-6.5 Al-3.5 Mo-1.5 Zr-0.3 Si alloy specimens with excellent mechanical performances were fabricated by LPBF.The as-built specimens displayed relatively high strength and ductility under modest volume energy densities(VEDs),whereas they manifested high strength with low ductility under high VEDs.To investigate the key reason of this phenomenon,the specimens were designed with two VEDs ranges of 60 J/mm^(3) and 85 J/mm^(3).Special attention was paid to the influences of residual stress and micro-deformation on microstructures and mechanical properties for the first time.The results indicated that the residual stresses and relative density of the 60 J/mm^(3) range specimens were higher than that of the 85 J/mm3 range specimens.Dislocation multiplication and dislocation movement promoted by the residual stress were hindered by the initialα’phase grain boundary(prior-α’GB),leading to the formation ofα’metastable structures.The mean tensile strength and elongation of the 60 J/mm^(3) range specimens were 1248.1 MPa and 12.3%,respectively,whereas the corresponding values for the 85 J/mm^(3) range specimens were 1405.3 MPa,5.0%,respectively.During deformation,the strength and ductility of the specimens were first improved by lamellar structures generated from prior-α’phases,and then effectively enhanced by the interaction between the{10–12}twins and dislocations.However,pores significantly reduced the ductility;hence,high VED specimens with large twins and numerous large pores increased the strength and reduce the ductility.
