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
A common challenge in direct energy deposition(DED)is eliminating the anisotropy in mechanical performance associated with microstructure and the formation of coarse columnar grains.In this work,a heterogeneous nuclea...A common challenge in direct energy deposition(DED)is eliminating the anisotropy in mechanical performance associated with microstructure and the formation of coarse columnar grains.In this work,a heterogeneous nucleation mechanism was introduced into the melt pool,and,from this mechanism,an almost fully equiaxed grain morphology was obtained in the DED of Ti-6 Al-3 Mo.Three types of grain morphologies in DED Ti-6 Al-3 Mo,including full columnar grains,near-equiaxed grains and almost fully equiaxed grains were obtained from premixed and satellite powder blends from Ti,6 wt.%Al and 3 wt.%Mo,respectively.Combined with the analysis of the interactions between powder particles and the melt pool in DED,the formation mechanism of the equiaxed grains caused by the incomplete melting of high melting point Mo particles was revealed.As the prior-βgrains transformed from coarse columnar grains to fine-equiaxed grains,the strong<100>fiber texture along the deposition direction was weakened,while the size of theα-laths in the prior-βgrains slightly decreased,and the selection ofα-variants was weakened.Due to the transformation of the prior-βgrains from coarse columnar grains to fine-equiaxed grains,the tensile strength of the deposited samples increased from 982 MPa to 1082 MPa,while the yield strength increased from 840 MPa to 922 MPa,and the elongation of the as-deposited alloy also increased from 9.0%to 9.8%,which confirmed that the presence of fine-equiaxed grains is beneficial to the strength and plasticity of the DED alloy.This work further demonstrates the role that satelliting powders can play in terms of enhancing the columnar to equiaxed transition(CET)behavior associated with DED.展开更多
A method for Cu(Ⅱ)-catalyzed dehydrogenative amidation of azoarene using air as the terminal oxidant was developed. Various amides, such as arylamides, alkylamides, lactams, and imides, are all effective amidation re...A method for Cu(Ⅱ)-catalyzed dehydrogenative amidation of azoarene using air as the terminal oxidant was developed. Various amides, such as arylamides, alkylamides, lactams, and imides, are all effective amidation reagents and provide the desired products in moderate to excellent yields. Notably, good yields can also be obtained on a gram-scale with this amidation reaction.In this protocol of azoarene amidation, the catalyst(Cu(OAc)_2) and oxidant(air) are inexpensive and readily available, and the process is highly efficient and atom economical.展开更多
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.
基金financially supported by the National Key Research and Development Program of China(No.2016YFB1100103)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2020JM-239)+2 种基金the National Natural Science Foundation of China(No.51475380)the Fundamental Research Funds for the Central Universities CHD(No.300102319208)the National Training Program of Innovation and Entrepreneurship for Undergraduates(No.S202010710142)。
文摘A common challenge in direct energy deposition(DED)is eliminating the anisotropy in mechanical performance associated with microstructure and the formation of coarse columnar grains.In this work,a heterogeneous nucleation mechanism was introduced into the melt pool,and,from this mechanism,an almost fully equiaxed grain morphology was obtained in the DED of Ti-6 Al-3 Mo.Three types of grain morphologies in DED Ti-6 Al-3 Mo,including full columnar grains,near-equiaxed grains and almost fully equiaxed grains were obtained from premixed and satellite powder blends from Ti,6 wt.%Al and 3 wt.%Mo,respectively.Combined with the analysis of the interactions between powder particles and the melt pool in DED,the formation mechanism of the equiaxed grains caused by the incomplete melting of high melting point Mo particles was revealed.As the prior-βgrains transformed from coarse columnar grains to fine-equiaxed grains,the strong<100>fiber texture along the deposition direction was weakened,while the size of theα-laths in the prior-βgrains slightly decreased,and the selection ofα-variants was weakened.Due to the transformation of the prior-βgrains from coarse columnar grains to fine-equiaxed grains,the tensile strength of the deposited samples increased from 982 MPa to 1082 MPa,while the yield strength increased from 840 MPa to 922 MPa,and the elongation of the as-deposited alloy also increased from 9.0%to 9.8%,which confirmed that the presence of fine-equiaxed grains is beneficial to the strength and plasticity of the DED alloy.This work further demonstrates the role that satelliting powders can play in terms of enhancing the columnar to equiaxed transition(CET)behavior associated with DED.
基金supported by the National Natural Science Foundation of China (21102005)Program for Innovative Research Team of Science and Technology in the University of Henan Province (18IRTSTHN004)
文摘A method for Cu(Ⅱ)-catalyzed dehydrogenative amidation of azoarene using air as the terminal oxidant was developed. Various amides, such as arylamides, alkylamides, lactams, and imides, are all effective amidation reagents and provide the desired products in moderate to excellent yields. Notably, good yields can also be obtained on a gram-scale with this amidation reaction.In this protocol of azoarene amidation, the catalyst(Cu(OAc)_2) and oxidant(air) are inexpensive and readily available, and the process is highly efficient and atom economical.