Laser powder bed fusion(LPBF)has been extensively investigated owing to its high geometry formation accuracy and excellent mechanical properties.However,the LPBFed Haynes 230 parts typically display poor tensile and w...Laser powder bed fusion(LPBF)has been extensively investigated owing to its high geometry formation accuracy and excellent mechanical properties.However,the LPBFed Haynes 230 parts typically display poor tensile and wear properties due to internal porosity.In this work,the ultrasonic impact treatment(UIT)was applied as a post-treatment to the LPBFed Haynes 230 alloy,porosity and microstructure mod-ulation were performed to improve the strength properties and wear resistance.The pore closure and mi-crostructure were studied by numerical simulations and experiments,and the mechanisms of increasing densification and strength were discussed.Results show that UIT can effectively close pores and reduce porosity,the internal porosity of the ultrasonic impacted layer for one,two,and three times decreases by 63.6%,70.9%,and 81.8%,respectively.Pore closure is attributed to the residual compressive stress and shear stress introduced by UIT.Besides,the UIT weakened texture strength and refined grains,especially promoting the formation of fine grains.Meanwhile,it also promotes the formation of a high disloca-tion density and improves the phase structure distribution.Furthermore,the ultimate tensile and yield strengths of the optimal impact process increased by 9.6%and 34.6%,respectively.The improvement in strength was attributed to dislocation,grain boundary,and promoting densification strengthening.The average friction coefficient reduces by 4.9%-14.6%by refining the surface grains and increasing dislo-cation density.This work has verified the feasibility of improving the mechanical properties and pore closure of the LPBFed Haynes 230 alloy by UIT.展开更多
Nickel-based superalloys(Haynes 230)fabricated by laser powder bed fusion suffer from high cracking suscepti-bility,leading to a decrease in mechanical performance.In this study,the cracking mechanism of Haynes 230 wa...Nickel-based superalloys(Haynes 230)fabricated by laser powder bed fusion suffer from high cracking suscepti-bility,leading to a decrease in mechanical performance.In this study,the cracking mechanism of Haynes 230 was investigated based on microstructural and thermodynamic calculations.It was found that C and carbide-forming elements(such as Mo and Cr)were segregated at the grain boundaries,which increased the solidification range and impeded liquid film backfalling by forming nano-carbides.Additionally,the coalescence of high-angle grain boundaries(>15°)requires a higher undercoolingΔT_(b)than that of low-angle grain boundaries(2-15°),which increases the susceptibility to hot cracking.Through gradually reducing laser energy input,the grain size is sig-nificantly decreased from 27.86μm(47.40 J/mm^(3))to 14.66μm(31.81 J/mm^(3)).Moreover,the calculated cooling rate|dT∕dt|and temperature gradient|dT∕ds|gradually increase with decreasing energy input,which reduces the duration of dendrite merging and shortens the length of the liquid film.Compared with cracked samples,the optimized sample showed superior mechanical properties,including high yield strength(678 MPa),ultimate tensile strength(943 MPa),and elongation to failure(19.2%),which increased by 16.1%,9.7%,and 77.7%,respectively.展开更多
基金supported by the National Key Research and Development Program of China(No.2022YFB4600800)the Fundamental Research Funds for the Central Universities(No.2042024kf0015).
文摘Laser powder bed fusion(LPBF)has been extensively investigated owing to its high geometry formation accuracy and excellent mechanical properties.However,the LPBFed Haynes 230 parts typically display poor tensile and wear properties due to internal porosity.In this work,the ultrasonic impact treatment(UIT)was applied as a post-treatment to the LPBFed Haynes 230 alloy,porosity and microstructure mod-ulation were performed to improve the strength properties and wear resistance.The pore closure and mi-crostructure were studied by numerical simulations and experiments,and the mechanisms of increasing densification and strength were discussed.Results show that UIT can effectively close pores and reduce porosity,the internal porosity of the ultrasonic impacted layer for one,two,and three times decreases by 63.6%,70.9%,and 81.8%,respectively.Pore closure is attributed to the residual compressive stress and shear stress introduced by UIT.Besides,the UIT weakened texture strength and refined grains,especially promoting the formation of fine grains.Meanwhile,it also promotes the formation of a high disloca-tion density and improves the phase structure distribution.Furthermore,the ultimate tensile and yield strengths of the optimal impact process increased by 9.6%and 34.6%,respectively.The improvement in strength was attributed to dislocation,grain boundary,and promoting densification strengthening.The average friction coefficient reduces by 4.9%-14.6%by refining the surface grains and increasing dislo-cation density.This work has verified the feasibility of improving the mechanical properties and pore closure of the LPBFed Haynes 230 alloy by UIT.
基金supported by the National Key R&D Program of China(Grant No.2022YFB3707405)National Natural Science Foun-dation of China(Grant Nos.U22A20113,52371135,52201156)+2 种基金Hei-longjiang Provincial Natural Science Foundation of China(Grant No.TD2020E001)Young Elite Scientists Sponsorship Program by CAST(Grant No.2023QNRC001)Heilongjiang Touyan Team Program.
文摘Nickel-based superalloys(Haynes 230)fabricated by laser powder bed fusion suffer from high cracking suscepti-bility,leading to a decrease in mechanical performance.In this study,the cracking mechanism of Haynes 230 was investigated based on microstructural and thermodynamic calculations.It was found that C and carbide-forming elements(such as Mo and Cr)were segregated at the grain boundaries,which increased the solidification range and impeded liquid film backfalling by forming nano-carbides.Additionally,the coalescence of high-angle grain boundaries(>15°)requires a higher undercoolingΔT_(b)than that of low-angle grain boundaries(2-15°),which increases the susceptibility to hot cracking.Through gradually reducing laser energy input,the grain size is sig-nificantly decreased from 27.86μm(47.40 J/mm^(3))to 14.66μm(31.81 J/mm^(3)).Moreover,the calculated cooling rate|dT∕dt|and temperature gradient|dT∕ds|gradually increase with decreasing energy input,which reduces the duration of dendrite merging and shortens the length of the liquid film.Compared with cracked samples,the optimized sample showed superior mechanical properties,including high yield strength(678 MPa),ultimate tensile strength(943 MPa),and elongation to failure(19.2%),which increased by 16.1%,9.7%,and 77.7%,respectively.
