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 hot deformation behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with equiaxed microstructure was characterized in the temperature range of 900～1060 ℃ and strain rate range of 10-3～10 s-1.The experimental results i...The hot deformation behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with equiaxed microstructure was characterized in the temperature range of 900～1060 ℃ and strain rate range of 10-3～10 s-1.The experimental results indicate that the plastic deformation behavior of the titanium alloys is rather sensitive to temperature and strain rate.In the α+β phase temperature region,all of the stress-strain curves exhibit different degrees of the flow softening after a peak stress.In the β phase temperature region,the titanium alloy shows a stress softening at high strain rates and a steady flow stress at low strain rates.On the basis of the peak stress data,the constitutive equations were constructed in the α+β phase temperature region and β phase temperature region,respectively.Activation energy parameters were calculated to be 344.923 kJ·mol-1 in the β phase temperature region and 628.3 kJ·mol-1 in the α+β phase temperature region.Microstructure of the compressed specimens in water-quenched conditions was found to be quite dependent on the conditions of deformation.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This work is financially supported by the National Key Natural Science Foundation of China ( No 5131903ZT1)
文摘The hot deformation behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with equiaxed microstructure was characterized in the temperature range of 900～1060 ℃ and strain rate range of 10-3～10 s-1.The experimental results indicate that the plastic deformation behavior of the titanium alloys is rather sensitive to temperature and strain rate.In the α+β phase temperature region,all of the stress-strain curves exhibit different degrees of the flow softening after a peak stress.In the β phase temperature region,the titanium alloy shows a stress softening at high strain rates and a steady flow stress at low strain rates.On the basis of the peak stress data,the constitutive equations were constructed in the α+β phase temperature region and β phase temperature region,respectively.Activation energy parameters were calculated to be 344.923 kJ·mol-1 in the β phase temperature region and 628.3 kJ·mol-1 in the α+β phase temperature region.Microstructure of the compressed specimens in water-quenched conditions was found to be quite dependent on the conditions of deformation.
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.
