Nano-lamellar Ti_(3)Al/TiAl(α2/γ)alloy with significantly improved nanohardness was prepared using dual-wire-fed electron beam-directed energy deposition(EB-DED)in this study.This investigation focused on the evolut...Nano-lamellar Ti_(3)Al/TiAl(α2/γ)alloy with significantly improved nanohardness was prepared using dual-wire-fed electron beam-directed energy deposition(EB-DED)in this study.This investigation focused on the evolution of the colony shape and lamellar thickness of the Ti-43Al lamellar alloy at different heights.Nanoindentation tests were employed to evaluate deformation resistance,and numerical simulations provided deeper insights into the deposition process.The results indicate that the colonies are mostly columnar,except for a few equiaxed colonies at the top.Rapid cooling significantly refines theα2 lamellae,resulting in an average spacing of 218 nm and thickness of 41 nm.Additionally,substantial microstrain and a nonequilibrium Al distribution lead to a significant generation ofγvariants,refining theγlamellae to 57 nm.Abundantγ/γ’andα2/γinterfaces,along with fineα2 phases,contribute to improved deformation resistance.Consequently,the nano-lamellar TiAl alloy exhibited a notable 32%increase in nanohardness(8.3 GPa)while maintaining a similar modulus(197 GPa)to conventionally prepared alloys.This study holds significant promise for advancing high-performance TiAl alloys through the dual-wire-fed EB-DED process.展开更多
Titanium aluminide(TiAl)alloys,known for their light weight and high specific strength,hold promising potential for aerospace applications.Recent studies have focused on improving their properties through composite st...Titanium aluminide(TiAl)alloys,known for their light weight and high specific strength,hold promising potential for aerospace applications.Recent studies have focused on improving their properties through composite strengthening.An in situ synthesized Ti_(5)Si_(3)-reinforced TiAl composite with excellent performance was successfully fabricated via a dual-wire electron beam-directed energy deposition(EB-DED)process.The microstructure of the as-deposited Ti_(5)Si_(3)/TiAl composite consisted of primary Ti_(5)Si_(3)rods,eutectic Ti_(5)Si_(3)needles,and lamellar TiAl+Ti_(3)Al structures.The phase transformation during the EB-DED process was L→Ti_(5)Si_(3)+L→Ti_(5)Si_(3)+(α+Ti_(5)Si_(3))Eutectic→Ti_(5)Si_(3)+(Ti3Al+TiAl)Eutectoid.The expanded Blackburn orientation relationships among the ternary phases emerged from the eutectic reaction of L→α+Ti_(5)Si_(3)with an undercooling exceeding 136°C and the subsequent eutectoid reaction with ordering transformation and were expressed as<1120>TisAl//<10I0>Ti_(5)Si_(3)//<110]Ti_(3)Al and{0001}TiзA//{0001}Ti_(5)Si_(3)//{111}TiAl.The Ti_(5)Si_(3)phase had a greater hardness than did the lamellar structures and enhanced the mechanical properties of the matrix.The compressive yield strengths at room temperature and 750°C were 1221±51 and 1034±34 MPa,respectively,whereas the tensile yield strength was 347.4±12.7 MPa at 950°C,surpassing those of other TiAl alloys.The calculated strength with different strengthening mechanisms was 1056.4 MPa,and the greatest improvement in strength was attributed to the decreased interlamellar spacing.This work provides critical insight into the design of TiAl composites with superior mechanical properties and aids in understanding the microstructural evolution of as-deposited Ti_(5)Si_(3)/TiAl composites.展开更多
基金supported by the National Key Research and Development Program of China(No.2022YFF0609000)the National Natural Science Foundation of China(Nos.51871075,52171034 and 52101037).
文摘Nano-lamellar Ti_(3)Al/TiAl(α2/γ)alloy with significantly improved nanohardness was prepared using dual-wire-fed electron beam-directed energy deposition(EB-DED)in this study.This investigation focused on the evolution of the colony shape and lamellar thickness of the Ti-43Al lamellar alloy at different heights.Nanoindentation tests were employed to evaluate deformation resistance,and numerical simulations provided deeper insights into the deposition process.The results indicate that the colonies are mostly columnar,except for a few equiaxed colonies at the top.Rapid cooling significantly refines theα2 lamellae,resulting in an average spacing of 218 nm and thickness of 41 nm.Additionally,substantial microstrain and a nonequilibrium Al distribution lead to a significant generation ofγvariants,refining theγlamellae to 57 nm.Abundantγ/γ’andα2/γinterfaces,along with fineα2 phases,contribute to improved deformation resistance.Consequently,the nano-lamellar TiAl alloy exhibited a notable 32%increase in nanohardness(8.3 GPa)while maintaining a similar modulus(197 GPa)to conventionally prepared alloys.This study holds significant promise for advancing high-performance TiAl alloys through the dual-wire-fed EB-DED process.
基金financially supported by the National Natural Science Foundation of China(No.52301050)the Young Elite Scientists Sponsorship Program by the China Association for Science and Technology(No.2022QNRC001)the China Postdoctoral Science Foundation(No.2023M741701).
文摘Titanium aluminide(TiAl)alloys,known for their light weight and high specific strength,hold promising potential for aerospace applications.Recent studies have focused on improving their properties through composite strengthening.An in situ synthesized Ti_(5)Si_(3)-reinforced TiAl composite with excellent performance was successfully fabricated via a dual-wire electron beam-directed energy deposition(EB-DED)process.The microstructure of the as-deposited Ti_(5)Si_(3)/TiAl composite consisted of primary Ti_(5)Si_(3)rods,eutectic Ti_(5)Si_(3)needles,and lamellar TiAl+Ti_(3)Al structures.The phase transformation during the EB-DED process was L→Ti_(5)Si_(3)+L→Ti_(5)Si_(3)+(α+Ti_(5)Si_(3))Eutectic→Ti_(5)Si_(3)+(Ti3Al+TiAl)Eutectoid.The expanded Blackburn orientation relationships among the ternary phases emerged from the eutectic reaction of L→α+Ti_(5)Si_(3)with an undercooling exceeding 136°C and the subsequent eutectoid reaction with ordering transformation and were expressed as<1120>TisAl//<10I0>Ti_(5)Si_(3)//<110]Ti_(3)Al and{0001}TiзA//{0001}Ti_(5)Si_(3)//{111}TiAl.The Ti_(5)Si_(3)phase had a greater hardness than did the lamellar structures and enhanced the mechanical properties of the matrix.The compressive yield strengths at room temperature and 750°C were 1221±51 and 1034±34 MPa,respectively,whereas the tensile yield strength was 347.4±12.7 MPa at 950°C,surpassing those of other TiAl alloys.The calculated strength with different strengthening mechanisms was 1056.4 MPa,and the greatest improvement in strength was attributed to the decreased interlamellar spacing.This work provides critical insight into the design of TiAl composites with superior mechanical properties and aids in understanding the microstructural evolution of as-deposited Ti_(5)Si_(3)/TiAl composites.
