The microstructure of high Nb-TiAl alloys was optimized by the addition of a small amount of Ta elements to further improve their properties.A series of Ti46Al1.5Cr8Nb-xTa(x=0.2,0.4,0.6,0.8,1.0,at.%)alloys were prepar...The microstructure of high Nb-TiAl alloys was optimized by the addition of a small amount of Ta elements to further improve their properties.A series of Ti46Al1.5Cr8Nb-xTa(x=0.2,0.4,0.6,0.8,1.0,at.%)alloys were prepared by vacuum arc melting.The microstructure,mechanical properties,and related influencing mechanisms were systematically investigated.The results indicate that the solidification microstructure of the Ti46Al1.5Cr8Nb-xTa alloys comprises theγ-TiAl phase,α_(2)-Ti_(3)Al phase,and B2 phase.As the Ta content increases from 0.2 at.%to 1.0 at.%,the content ofα_(2)phase and B2 phase increases,while theγphase content decreases.Among them,the B2 phase shows the most pronounced change,being significantly refined,with its content increasing from 12.49%to 21.91%.In addition,the average size of the lamellar colony decreases from 160.65 to 94.44μm.The addition of the Ta element shifts the solidification path toward lower aluminum concentrations,leading to changes in phase content.The tantalum-induced increase in the B2 phase and enhanced supercooling at the solidification front provide the basis for lamellar colony refinement.Compressive testing at room temperature reveals that the Ti46 Al1.5 Cr8 Nb0.4 Ta alloy exhibits optimal compressive properties,achieving a compressive strength of 2,434 MPa and a compressive strain of 33.1%.The improvement of its properties is attributed to a combination of lamellar colony refinement,solid solution strengthening resulting from the incorporation of Ta element,and a reduction in the c/a of theγphase.展开更多
Ti-5Al-5Mo-5Cr-2Zr-xNb with different Nb(abbreviated as Ti-5552-xNb,x=3,6,9,12,wt.%)contents were stretched at 923 K to study their superplastic behavior and mechanical properties below recrystallization temperature.T...Ti-5Al-5Mo-5Cr-2Zr-xNb with different Nb(abbreviated as Ti-5552-xNb,x=3,6,9,12,wt.%)contents were stretched at 923 K to study their superplastic behavior and mechanical properties below recrystallization temperature.The microstructure of as-cast Ti-5552-xNb alloy is consisted of a singleβphase,and theβgrain size increases slightly with the increase of Nb content.The thermal effect in the process of high temperature drawing leads to the precipitation ofαphase.The addition of Nb in Ti-5552 titanium alloys reduces theα/βphase transformation temperature,which causes a decrease in the volume fraction ofαphase.Reducing theαphase content reduces incompatibility,but too low a proportion ofαphase will lead to premature fracture,so tensile strength and plasticity firstly increase and then decrease.The results show that Ti-5552-9Nb titanium alloy shows the best tensile strength(307.2 MPa)and superplasticity(106%).The superplastic mechanism of Ti-5552-9Nb alloy is mainly caused by relative sliding ofβgrain boundaries and dislocation movement.展开更多
(Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4))_(100−x)Al_(x)(x=0,0.1,0.2,0.3,0.4 at.%)lightweight high-entropy alloys with different contents of Al were prepared via vacuum non-consumable arc melting method.Effects of adding varying...(Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4))_(100−x)Al_(x)(x=0,0.1,0.2,0.3,0.4 at.%)lightweight high-entropy alloys with different contents of Al were prepared via vacuum non-consumable arc melting method.Effects of adding varying Al contents on phase constitution,microstructure characteristics and mechanical properties of the lightweight alloys were studied.Results show that Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4)alloy is composed of body-centered cubic(BCC)phase and C15 Laves phase,while(Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4))_(100−x)Al_(x)lightweight high-entropy alloys by addition of Al are composed of BCC phase and C14 Laves phase.Addition of Al into Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4)lightweight high-entropy alloy can transform C15 Laves phase to C14 Laves phase.With further addition of Al,BCC phase of alloys is significantly refined,and the volume fraction of C14 Laves phase is raised obviously.Meanwhile,the dimension of BCC phase in the alloy by addition of 0.3 at.%Al is the most refined and that of Laves phase is also obviously refined.Adding Al to Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4)alloy can not only reduce the density of(Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4))_(100−x)Al_(x)alloy,but also improve strength of(Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4))_(100−x)Al_(x)alloy.As Al content increased from 0 to 0.4 at.%,the density of the alloy decreased from 6.22±0.875 to 5.79±0.679 g cm^(−3).Moreover,compressive strength of the alloy by 0.3 at.%Al addition is the highest to 1996.9 MPa,while fracture strain of the alloy is 16.82%.Strength improvement of alloys mainly results from microstructure refinement and precipitation of C14 Laves by Al addition into Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4)lightweight high-entropy alloy.展开更多
Ti-Zr-Nb refractory multi-principal element alloys(RMPEAs)have attracted increased attention due to their excellent mechanical properties.In this study,(TiZr)_(80-x)Nb_(20)Mo_(x)(x=0,5 and 10)alloys were designed,and ...Ti-Zr-Nb refractory multi-principal element alloys(RMPEAs)have attracted increased attention due to their excellent mechanical properties.In this study,(TiZr)_(80-x)Nb_(20)Mo_(x)(x=0,5 and 10)alloys were designed,and the intrinsic conflicts between strength and ductility were overcome via composition optimization and recrystallization.The causes of the superior strength-ductility synergy were investigated in terms of their deformation mechanism and dislocation behavior.The results show that the strength improvement can be attributed to the deformation mechanism transition caused by local chemical fluctuations and lattice distortion.Specifically,the slip band widths decrease after Mo addition,and the measured slip traces in the fracture samples are associated with high-order{112}and{123}slip planes.Furthermore,the grain refinement achieved via recrystallization promotes multi-slip system activation and shortens the slip-band spacing,which reduces the stress concentration and inhibits crack source formation,thereby allowing the alloy to ensure sufficient ductility.Consequently,the Ti_(35)Zr_(35)Nb_(20)Mo_(10)alloy annealed at 900℃ exhibits high yield strength and elongation.These findings provide a new strategy for designing high-strength RMPEAs and addressing room-temperature brittleness.展开更多
The regulation of martensitic transformation and intrinsic brittleness are critical issues for the application of Ni-Mn-Ga shape memory alloys,and they are closely related to the alloy composition andγphase.In this s...The regulation of martensitic transformation and intrinsic brittleness are critical issues for the application of Ni-Mn-Ga shape memory alloys,and they are closely related to the alloy composition andγphase.In this study,single and dual-phase Ni_(55+x)Mn_(25)Ga_(20-x)(x=0,2,4 and 6)alloys were fabricated.The proportion of theγphase was elevated gradually,and the peak martensitic transformation temperature was enhanced from 350 to 460℃ with an increasing Ni/Ga ratio.The microstructures of theγphase were further regulated from continuous block to dispersed granular after annealing.The annealed dual-phase alloy with x=2 exhibited greater yield stress,compressive strength and toughness than the annealed single-phase alloy.It maintained plastic deformation without fracture,even at a strain of 30%.High strain energy and dislocation density were observed in the martensite of the dual-phase alloy,which can be attributed toγphases and the interface between martensite andγphases.Furthermore,[001]-oriented martensite variants were obtained during deformation in the dual-phase alloy.They were parallel to the loading direction and conducive to improving the compressive strength.This protocol provides in-depth insight into the influence of theγphase on the texture evolution and mechanical behavior of martensite during deformation.展开更多
Nb-Si-based in situ composites are receiving attention as a substitute for Ni-based alloys in aerospace,while poor toughness limits its application.In this work,the toughness of Nb_(4)FeSi-containing Nb-Si-based alloy...Nb-Si-based in situ composites are receiving attention as a substitute for Ni-based alloys in aerospace,while poor toughness limits its application.In this work,the toughness of Nb_(4)FeSi-containing Nb-Si-based alloys was improved by hot deformation.The different deformation behaviors of reinforcements from traditional alloys,including the eutectoid decomposition ofβ-Nb_(5)Si_(3),and the stacking faults(SFs)and reorientation-induced plasticity(RIP)effect of Nb_(4)FeSi,are revealed.During hot deformation,theβ-Nb_(5)Si_(3)phase undergoes the eutectoid decomposition to obtain theα-Nb_(5)Si_(3)and niobium-based solid solutions(Nbss)phases,whichα-Nb_(5)Si_(3)and Nbss satisfy the relationship{110}_(α)//{110}_(Nbss).The[110]SFs and lath-like reoriented variants are formed in the Nb_(4)FeSi phase,where the matrix and variants follow[001]_(m)//[111]v,(110)_(m)//(110)v.Furthermore,the interface between matrix and variant isΣ33c symmetrical tilt boundaries,manifested as(110)/60°.The fracture toughness of the deformed alloy reaches 18.31 MPa·m1/2 at 1300℃/0.005 s^(-1)/0.7,which is 49%higher than the initial alloy.展开更多
To develop high-hardness and high-strength lightweight high entropy alloys(LHEAs),a series of CoxAlNbTiVCr alloys were designed.The phase constitution,distribution,and crystal structure of the Laves phase in alloys ca...To develop high-hardness and high-strength lightweight high entropy alloys(LHEAs),a series of CoxAlNbTiVCr alloys were designed.The phase constitution,distribution,and crystal structure of the Laves phase in alloys can be altered by adjusting the composition of HEAs,which in turn influences their mechanical properties.Co_(x)AlNbTiVCr(x=0,0.5,1,1.5,and 2,atomic ratio percentage)LHEAs were designed and prepared to characterize the microstructure and tailor the mechanical properties.The introduction of Co changes the microstructure of LHEAs from a single B2 structure to a mixture dendrite structure,which consists of B2 phase,C14 and C15 Laves phase.Wherein the C14 and C15 Laves phases exhibit coupled growth.Several parameters including mixing enthalpy(ΔH_(mix)),valence electron concentration(VEC),atomic radius size(δ),mixing entropy(ΔS),and electronegativity difference(Δχ)are used to predict the formation of B2 and Laves phase in LHEAs.When the Co content increases from 0 to 1.5at.%,Laves phase volume fraction gradually increases,which leads to an enhancement in the compressive strength from 1,520.8 MPa to 1,844.4 MPa.Co_(1.5)AlNbTiVCr alloy exhibits the maximum Vickers hardness of 699.4 HV.The improvement of mechanical properties mainly originates from solid solution strengthening and second phase strengthening.展开更多
The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al all...The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al alloys were heat treated by the directional annealing technique and their mechanical properties were tested.The results show that columnar grains with a maximum size of 22.29 mm can be obtained at a hot zone temperature of 1,350℃ and a temperature gradient of 8 K·mm^(-1).During the directional annealing process,Ti43Al alloys are heated toαsingle-phase domain to start the phase transformation.Columnar grains with a microstructure of fully lamellar colonies are obtained at different hot zone temperatures and temperature gradients.The distribution of the orientation difference for theα2 phase was found to be more random,suggesting that the growth of the columnar crystals may be stochastic in nature.Tensile testing results show that the strength and elongation of directional annealed Ti43Al alloy at 1,400℃-8 K·mm^(-1) are 411.23 MPa and 2.29%,and the remaining directional annealed alloys show almost plasticity.展开更多
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
To study the effects of La on the microstructure and mechanical properties of refractory high entropy alloys,NbMoTiVSi0.2 alloys with different La contents were prepared.Phase constitution,microstructure evolution,com...To study the effects of La on the microstructure and mechanical properties of refractory high entropy alloys,NbMoTiVSi0.2 alloys with different La contents were prepared.Phase constitution,microstructure evolution,compressive properties and related mechanisms were systematically studied.Results show that the alloys with La addition are composed of BCC solid solution,eutectic structure,MSi2 disilicide phase and La-containing precipitates.Eutectic structure and most of La precipitates are formed at the grain boundaries.Disilicide phase is formed in the grains.La can change the grain morphologies from dendritic structure to near-equiaxed structure,and the average grain size decreases from 180 to 20μm with the increase of La content from 0 to 0.5 at.%.Compressive testing shows that the ultimate strength and the yield strength increase with the increase of La content,which is resulted from the grain boundary strengthening.However,they cannot be greatly improved because of the formation of MSi2 disilicide phase with low strength.The ductility decreases with the increase of La content,which is due to the La precipitates and brittle MSi2 disilicide phase.展开更多
In order to elucidate the microstructure evolution and silicide precipitation behavior during high-temperature deformation,TiB reinforced titanium matrix composites were subjected to isothermal hot compression at 950...In order to elucidate the microstructure evolution and silicide precipitation behavior during high-temperature deformation,TiB reinforced titanium matrix composites were subjected to isothermal hot compression at 950℃,strain rate of 0.05 s^(−1) and employing different strains of 0.04,0.40,0.70 and 1.00.The results show that with the increase of strain,a decrease in the content,dynamic recrystallization of theαphase and the vertical distribution of TiB along the compression axis lead to stress stability.Meantime,continuous dynamic recrystallization reduces the orientation difference of the primaryαphase,which weakens the texture strength of the matrix.The recrystallization mechanisms are strain-induced grain boundary migration and particle stimulated nucleation by TiB.The silicide of Ti_(6)Si_(3) is mainly distributed at the interface of TiB andαphase.The precipitation of silicide is affected by element diffusion,and TiB whisker accelerates the precipitation behavior of silicide by hindering the movement of dislocations and providing nucleation particles.展开更多
In order to improve mechanical properties and optimize composition of TiAl-Nb alloys, Ti46 Al5 Nb0.1 B alloys with different contents of Fe(0, 0.3, 0.5, 0.7, 0.9, and 1.1 at.%) were prepared by melting. Macro/microstr...In order to improve mechanical properties and optimize composition of TiAl-Nb alloys, Ti46 Al5 Nb0.1 B alloys with different contents of Fe(0, 0.3, 0.5, 0.7, 0.9, and 1.1 at.%) were prepared by melting. Macro/microstructure and compression properties of the alloys were systematically investigated. Results show that Fe element can decrease the grain size, aggravate the Al-segregation and also form the Fe-rich B2 phase in the interdendritic area. Compressive testing results indicate that the Ti46 Al5 Nb0.1 B0.3 Fe alloy shows the highest ultimate compressive strength and fracture strain, which are 1869.5 MPa and 33.53%, respectively. The improved ultimate compression strength is ascribed to the grain refinement and solid solution strengthening of Fe, and the improved fracture strain is due to the reduced lattice tetragonality of γ phase and grain refinement of the alloys. However, excessive Fe addition decreases compressive strength and fracture strain, which is caused by the severe Al-segregation.展开更多
In the present research, microstructure refinement of a high-Nb TiAl alloy （Ti-48Al-8Nb-0.15B） was realized by means of the electromagnetic continuous casting （EMCC） technique. The microstructure of an ingot obtai...In the present research, microstructure refinement of a high-Nb TiAl alloy （Ti-48Al-8Nb-0.15B） was realized by means of the electromagnetic continuous casting （EMCC） technique. The microstructure of an ingot obtained by EMCC was analyzed using scanning electron microscopy （SEM）. As compared with the raw as-cast alloy, the obtained EMCC alloy presented a much finer microstructure with lamellar colonies with a mean size of about 50-70 μm because the electromagnetic stirring broke initial dendrites and enhanced the heterogeneous nucleation. As the grains were refined, the properties of the TiAl alloy were improved significantly. This implies that the EMCC technique could offer the possibility of application for high-Nb TiAl alloys with a refined microstructure and excellent properties to be used as a structural material.展开更多
Ti43Al and Ti47Al alloys with different contents of zirconium were prepared by non-consumable vacuum arc melting furnace.The microstructure and mechanical properties were investigated.The results showed that Zr had no...Ti43Al and Ti47Al alloys with different contents of zirconium were prepared by non-consumable vacuum arc melting furnace.The microstructure and mechanical properties were investigated.The results showed that Zr had no obvious effect on microstructure morphology of Ti43Al,while that of Ti47Al was modified from dendrites into equiaxed grains.The addition of Zr could refine the grains.Zr promoted the formation ofγphase significantly and the solubility values of Zr inγphase were 12.0%and 5.0%(molar fraction)in Ti43Al and Ti47Al,respectively.Zr-richγphase mainly formed throughβ→γin Ti43Al-xZr(molar fraction,%)andβ→α→γin Ti47Al-xZr(molar fraction,%).Fine-grain strengthening and solution strengthening were beneficial to improving the compressive strength while severe micro-segregation was detrimental to compressive properties.Large solubility of Zr was bad for ductility of alloys as well.The maximum compressive strengths of Ti43Al-xZr and Ti47Al-xZr were 1684.82 MPa(x=5.0%)and 2158.03 MPa(x=0.5%),respectively.The compressive strain fluctuated slightly in Ti43Al-xZr and reached the maximum value of 35.24%(x=0.5%)in Ti47Al-xZr.Both alloys showed brittle fracture.展开更多
Alloying additions of 0 at%-1.1 at% Fe were added into Ti43A1Nb0.1B alloys for increasing the roomtemperature strength and ductility,and the microstructure and mechanical properties were systematically studied.The res...Alloying additions of 0 at%-1.1 at% Fe were added into Ti43A1Nb0.1B alloys for increasing the roomtemperature strength and ductility,and the microstructure and mechanical properties were systematically studied.The results show that the lattice tetragonality(c/a) of γ phase and the average width of columnar grains of alloys decrease with Fe content increasing.Fe addition brings about the formation of Fe-rich B2 phase both in the dendrites and in interdendritic regions,and its content increases with Fe contents increasing.Furthermore,Fe addition aggravates the Al segregations in the interdendritic regions.The alloy with 0.7 at% Fe exhibits higher combined mechanical properties with the ultimate compression strength and fracture strain of 1958.4 MPa and 29.8%,respectively.The grain refinement strengthening and solid-solution strengthening of Fe are responsible for the improvement in the strength and the strain.However,excessive Fe addition results in the decrease in the strength and strain,which is attributed to the severe A1 segregations in the interdendritic regions that cause the premature fracture during compression.展开更多
In order to improve mechanical properties of TiAlNb alloys,different contents of silicon were added into Ti48Al6Nb alloy.The Ti48Al6NbxSi (x=0,0.1,0.2,0.3,0.4 and 0.5,at.%) alloys were prepared by vacuum arc melting.T...In order to improve mechanical properties of TiAlNb alloys,different contents of silicon were added into Ti48Al6Nb alloy.The Ti48Al6NbxSi (x=0,0.1,0.2,0.3,0.4 and 0.5,at.%) alloys were prepared by vacuum arc melting.The phase constitution,microstructure evolution and mechanical properties of the alloys were studied.Results show that the Ti48Al6NbxSi alloys consist of γ-TiAl phase,α2-Ti3Al phase and B2 phase,and Ti5Si3 silicide phase is formed when the addition of silicon is higher than 0.3at.%.The addition of silicon leads to the decrease in γ phase and increase in α2 phase.The formation of silicide decreases the amount of Nb dissolved in the TiAl matrix,and therefore decreases B2 phase.Compressive tests show that the ultimate strength of the alloys increases from 2,063 MPa to 2,281 MPa with an increase in silicon from 0 to 0.5at.%,while the fracture strain decreases from 34.7% to 30.8%.The increase of compressive strength and decrease of fracture strain can be attributed to the decrease of B2 phase and the formation of Ti5Si3 phase by the addition of silicon.The strengthening mechanism is changed from solid solution strengthening when the addition of silicon is less than 0.3at.% to combination of solid solution strengthening and secondary phase strengthening when the addition of silicon is higher than 0.3at.%.展开更多
This study examines the microstructure,mechanical properties(with a focus on room-temperature toughness),and oxidation resistance of Ho-doped NbDSi based in-situ composites.The base alloy consists of the coarse primar...This study examines the microstructure,mechanical properties(with a focus on room-temperature toughness),and oxidation resistance of Ho-doped NbDSi based in-situ composites.The base alloy consists of the coarse primary Nb_(5)Si_(3)phase and the Nb_(5)Si_(3)+Nbss(Nb solid solution)eutectic cells.Ho doping influences the solidification path.When the Ho doping is higher than0.2 at%,the alloys transform into eutectic alloys.Ho can be solid-solved in trace amounts in the Nbss phase.However,most of Ho forms a stable Ho oxide phase,which alleviates oxygen contamination problem to some extent.Moreover,the interface separation between Ho oxide and other phases reduces the plastic deformation constraint.Thus,with 0.4 at%Ho doping,the K_(Q)value is18.03 MPa·m^(1/2),which is 31.1%higher than that of the base alloy.The strength of the Ho-doped alloys does not deteriorate with an increase in toughness.However,the large network-like Ho_(2)O_(3)in the 0.8Ho alloy causes a decrease in toughness and strength.In addition,the Ho oxide phase effectively blocks the inward oxygen intrusion.With 0.8 at%Ho doping,the oxidation mass gain per unit area is 10.16 mg·cm^(2),which is 39.7%lower than that of the base alloy.展开更多
基金the financial support by the Major Science and Technology Achievement Transformation Project in Heilongjiang Province(No.ZC2023SH0075)the National Natural Science Foundation of China(Nos.52425401,U2441255,52474377,and 52371015)+1 种基金the Young Elite Scientists Sponsorship·Program by CAST(No.2021QNRC001)the Henan Provincial Key Research and Development&Promotion Special Program(No.251111231400)。
文摘The microstructure of high Nb-TiAl alloys was optimized by the addition of a small amount of Ta elements to further improve their properties.A series of Ti46Al1.5Cr8Nb-xTa(x=0.2,0.4,0.6,0.8,1.0,at.%)alloys were prepared by vacuum arc melting.The microstructure,mechanical properties,and related influencing mechanisms were systematically investigated.The results indicate that the solidification microstructure of the Ti46Al1.5Cr8Nb-xTa alloys comprises theγ-TiAl phase,α_(2)-Ti_(3)Al phase,and B2 phase.As the Ta content increases from 0.2 at.%to 1.0 at.%,the content ofα_(2)phase and B2 phase increases,while theγphase content decreases.Among them,the B2 phase shows the most pronounced change,being significantly refined,with its content increasing from 12.49%to 21.91%.In addition,the average size of the lamellar colony decreases from 160.65 to 94.44μm.The addition of the Ta element shifts the solidification path toward lower aluminum concentrations,leading to changes in phase content.The tantalum-induced increase in the B2 phase and enhanced supercooling at the solidification front provide the basis for lamellar colony refinement.Compressive testing at room temperature reveals that the Ti46 Al1.5 Cr8 Nb0.4 Ta alloy exhibits optimal compressive properties,achieving a compressive strength of 2,434 MPa and a compressive strain of 33.1%.The improvement of its properties is attributed to a combination of lamellar colony refinement,solid solution strengthening resulting from the incorporation of Ta element,and a reduction in the c/a of theγphase.
基金the financial support by the Major Science and Technology Achievement Transformation Project in Heilongjiang Province(ZC2023SH0075)the National Natural Science Foundation of China(52425401,U2441255,52474377,and 52371015)+1 种基金the Young Elite Scientists Sponsorship Program by·CAST(2021QNRC001)the Henan Provincial Key Research and Development&Promotion Special Program(251111231400)。
文摘Ti-5Al-5Mo-5Cr-2Zr-xNb with different Nb(abbreviated as Ti-5552-xNb,x=3,6,9,12,wt.%)contents were stretched at 923 K to study their superplastic behavior and mechanical properties below recrystallization temperature.The microstructure of as-cast Ti-5552-xNb alloy is consisted of a singleβphase,and theβgrain size increases slightly with the increase of Nb content.The thermal effect in the process of high temperature drawing leads to the precipitation ofαphase.The addition of Nb in Ti-5552 titanium alloys reduces theα/βphase transformation temperature,which causes a decrease in the volume fraction ofαphase.Reducing theαphase content reduces incompatibility,but too low a proportion ofαphase will lead to premature fracture,so tensile strength and plasticity firstly increase and then decrease.The results show that Ti-5552-9Nb titanium alloy shows the best tensile strength(307.2 MPa)and superplasticity(106%).The superplastic mechanism of Ti-5552-9Nb alloy is mainly caused by relative sliding ofβgrain boundaries and dislocation movement.
基金supported by National Natural Science Foundation of China(Grant No.52001114)Program for Science and Technology Innovation Talents in Universities of Henan Province(No.23HASTIT022 and 2021GGJS064)Scientific Research Fund of State Key Laboratory of Materials Processing and Die and Mould Technology(Grant No.P2023-005).
文摘(Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4))_(100−x)Al_(x)(x=0,0.1,0.2,0.3,0.4 at.%)lightweight high-entropy alloys with different contents of Al were prepared via vacuum non-consumable arc melting method.Effects of adding varying Al contents on phase constitution,microstructure characteristics and mechanical properties of the lightweight alloys were studied.Results show that Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4)alloy is composed of body-centered cubic(BCC)phase and C15 Laves phase,while(Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4))_(100−x)Al_(x)lightweight high-entropy alloys by addition of Al are composed of BCC phase and C14 Laves phase.Addition of Al into Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4)lightweight high-entropy alloy can transform C15 Laves phase to C14 Laves phase.With further addition of Al,BCC phase of alloys is significantly refined,and the volume fraction of C14 Laves phase is raised obviously.Meanwhile,the dimension of BCC phase in the alloy by addition of 0.3 at.%Al is the most refined and that of Laves phase is also obviously refined.Adding Al to Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4)alloy can not only reduce the density of(Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4))_(100−x)Al_(x)alloy,but also improve strength of(Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4))_(100−x)Al_(x)alloy.As Al content increased from 0 to 0.4 at.%,the density of the alloy decreased from 6.22±0.875 to 5.79±0.679 g cm^(−3).Moreover,compressive strength of the alloy by 0.3 at.%Al addition is the highest to 1996.9 MPa,while fracture strain of the alloy is 16.82%.Strength improvement of alloys mainly results from microstructure refinement and precipitation of C14 Laves by Al addition into Ti_(8)Zr_(6)Nb_(4)V_(5)Cr_(4)lightweight high-entropy alloy.
基金supported by the National Key Research and Development Program of China(No.2022YFF0609000)the National Natural Science Foundation of China(Nos.52171034 and 52101037)the Postdoctoral Fellowship Program of CPSF(No.GZB20230944).
文摘Ti-Zr-Nb refractory multi-principal element alloys(RMPEAs)have attracted increased attention due to their excellent mechanical properties.In this study,(TiZr)_(80-x)Nb_(20)Mo_(x)(x=0,5 and 10)alloys were designed,and the intrinsic conflicts between strength and ductility were overcome via composition optimization and recrystallization.The causes of the superior strength-ductility synergy were investigated in terms of their deformation mechanism and dislocation behavior.The results show that the strength improvement can be attributed to the deformation mechanism transition caused by local chemical fluctuations and lattice distortion.Specifically,the slip band widths decrease after Mo addition,and the measured slip traces in the fracture samples are associated with high-order{112}and{123}slip planes.Furthermore,the grain refinement achieved via recrystallization promotes multi-slip system activation and shortens the slip-band spacing,which reduces the stress concentration and inhibits crack source formation,thereby allowing the alloy to ensure sufficient ductility.Consequently,the Ti_(35)Zr_(35)Nb_(20)Mo_(10)alloy annealed at 900℃ exhibits high yield strength and elongation.These findings provide a new strategy for designing high-strength RMPEAs and addressing room-temperature brittleness.
基金supported by the Natural Science Foundation of Heilongjiang Province,China(No.LH2021E051)the National Natural Science Foundation of China(No.52204386)Outstanding Youth Science Fund of Heilongjiang,China(No.JQ2023E003).
文摘The regulation of martensitic transformation and intrinsic brittleness are critical issues for the application of Ni-Mn-Ga shape memory alloys,and they are closely related to the alloy composition andγphase.In this study,single and dual-phase Ni_(55+x)Mn_(25)Ga_(20-x)(x=0,2,4 and 6)alloys were fabricated.The proportion of theγphase was elevated gradually,and the peak martensitic transformation temperature was enhanced from 350 to 460℃ with an increasing Ni/Ga ratio.The microstructures of theγphase were further regulated from continuous block to dispersed granular after annealing.The annealed dual-phase alloy with x=2 exhibited greater yield stress,compressive strength and toughness than the annealed single-phase alloy.It maintained plastic deformation without fracture,even at a strain of 30%.High strain energy and dislocation density were observed in the martensite of the dual-phase alloy,which can be attributed toγphases and the interface between martensite andγphases.Furthermore,[001]-oriented martensite variants were obtained during deformation in the dual-phase alloy.They were parallel to the loading direction and conducive to improving the compressive strength.This protocol provides in-depth insight into the influence of theγphase on the texture evolution and mechanical behavior of martensite during deformation.
基金supported by the National Natural Science Foundation of China(Nos.52425401 and 52374384)the Foundation of National Key Laboratory for Precision Hot Processing of Metals(No.JCKYS2021603C001)the Fundamental Research Funds for the Central Universities(No.2023FRFK06014).
文摘Nb-Si-based in situ composites are receiving attention as a substitute for Ni-based alloys in aerospace,while poor toughness limits its application.In this work,the toughness of Nb_(4)FeSi-containing Nb-Si-based alloys was improved by hot deformation.The different deformation behaviors of reinforcements from traditional alloys,including the eutectoid decomposition ofβ-Nb_(5)Si_(3),and the stacking faults(SFs)and reorientation-induced plasticity(RIP)effect of Nb_(4)FeSi,are revealed.During hot deformation,theβ-Nb_(5)Si_(3)phase undergoes the eutectoid decomposition to obtain theα-Nb_(5)Si_(3)and niobium-based solid solutions(Nbss)phases,whichα-Nb_(5)Si_(3)and Nbss satisfy the relationship{110}_(α)//{110}_(Nbss).The[110]SFs and lath-like reoriented variants are formed in the Nb_(4)FeSi phase,where the matrix and variants follow[001]_(m)//[111]v,(110)_(m)//(110)v.Furthermore,the interface between matrix and variant isΣ33c symmetrical tilt boundaries,manifested as(110)/60°.The fracture toughness of the deformed alloy reaches 18.31 MPa·m1/2 at 1300℃/0.005 s^(-1)/0.7,which is 49%higher than the initial alloy.
基金supported by the National Outstanding Youth Science Fund Project of National Natural Science Foundation of China(No.51825401)the China Postdoctoral Science Foundation(No.2023TQ0099).
文摘To develop high-hardness and high-strength lightweight high entropy alloys(LHEAs),a series of CoxAlNbTiVCr alloys were designed.The phase constitution,distribution,and crystal structure of the Laves phase in alloys can be altered by adjusting the composition of HEAs,which in turn influences their mechanical properties.Co_(x)AlNbTiVCr(x=0,0.5,1,1.5,and 2,atomic ratio percentage)LHEAs were designed and prepared to characterize the microstructure and tailor the mechanical properties.The introduction of Co changes the microstructure of LHEAs from a single B2 structure to a mixture dendrite structure,which consists of B2 phase,C14 and C15 Laves phase.Wherein the C14 and C15 Laves phases exhibit coupled growth.Several parameters including mixing enthalpy(ΔH_(mix)),valence electron concentration(VEC),atomic radius size(δ),mixing entropy(ΔS),and electronegativity difference(Δχ)are used to predict the formation of B2 and Laves phase in LHEAs.When the Co content increases from 0 to 1.5at.%,Laves phase volume fraction gradually increases,which leads to an enhancement in the compressive strength from 1,520.8 MPa to 1,844.4 MPa.Co_(1.5)AlNbTiVCr alloy exhibits the maximum Vickers hardness of 699.4 HV.The improvement of mechanical properties mainly originates from solid solution strengthening and second phase strengthening.
基金supported by the National Natural Science Foundation of China(Grant Nos.52074229,52371035)the Key R&D Plan of Sichuan Province(Grant No.SC2022A1C01J)the State Key Lab of Advanced Metals and Materials(Grant No.2020-ZD05).
文摘The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al alloys were heat treated by the directional annealing technique and their mechanical properties were tested.The results show that columnar grains with a maximum size of 22.29 mm can be obtained at a hot zone temperature of 1,350℃ and a temperature gradient of 8 K·mm^(-1).During the directional annealing process,Ti43Al alloys are heated toαsingle-phase domain to start the phase transformation.Columnar grains with a microstructure of fully lamellar colonies are obtained at different hot zone temperatures and temperature gradients.The distribution of the orientation difference for theα2 phase was found to be more random,suggesting that the growth of the columnar crystals may be stochastic in nature.Tensile testing results show that the strength and elongation of directional annealed Ti43Al alloy at 1,400℃-8 K·mm^(-1) are 411.23 MPa and 2.29%,and the remaining directional annealed alloys show almost plasticity.
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support from the National Natural Science Foundation of China (No. 51825401)the Foundation of National Key Laboratory for Precision Hot Processing of Metals, China (No. JCKYS2021603C001)the Natural Science Foundation of Heilongjiang Province, China (No. LH2020E032)。
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(51825401 and 52001114)the State Key Laboratory of Materials Processing and Die&Mould Technology(P2020-023)the Guangdong Introducing Innovative and Entrepreneurial Teams,China(2016ZT06G025).
文摘To study the effects of La on the microstructure and mechanical properties of refractory high entropy alloys,NbMoTiVSi0.2 alloys with different La contents were prepared.Phase constitution,microstructure evolution,compressive properties and related mechanisms were systematically studied.Results show that the alloys with La addition are composed of BCC solid solution,eutectic structure,MSi2 disilicide phase and La-containing precipitates.Eutectic structure and most of La precipitates are formed at the grain boundaries.Disilicide phase is formed in the grains.La can change the grain morphologies from dendritic structure to near-equiaxed structure,and the average grain size decreases from 180 to 20μm with the increase of La content from 0 to 0.5 at.%.Compressive testing shows that the ultimate strength and the yield strength increase with the increase of La content,which is resulted from the grain boundary strengthening.However,they cannot be greatly improved because of the formation of MSi2 disilicide phase with low strength.The ductility decreases with the increase of La content,which is due to the La precipitates and brittle MSi2 disilicide phase.
基金financial supports from the National Natural Science Foundation of China (No. 51871184)the Natural Science Foundation of Shandong Province, China (No. ZR2019MEM037)+1 种基金the Zhoucun School-City Integration Development Plan, China (No. 2020ZCXCZH03)the School-city Integration Development Project of Zibo, China (No. 2019ZBXC022)。
文摘In order to elucidate the microstructure evolution and silicide precipitation behavior during high-temperature deformation,TiB reinforced titanium matrix composites were subjected to isothermal hot compression at 950℃,strain rate of 0.05 s^(−1) and employing different strains of 0.04,0.40,0.70 and 1.00.The results show that with the increase of strain,a decrease in the content,dynamic recrystallization of theαphase and the vertical distribution of TiB along the compression axis lead to stress stability.Meantime,continuous dynamic recrystallization reduces the orientation difference of the primaryαphase,which weakens the texture strength of the matrix.The recrystallization mechanisms are strain-induced grain boundary migration and particle stimulated nucleation by TiB.The silicide of Ti_(6)Si_(3) is mainly distributed at the interface of TiB andαphase.The precipitation of silicide is affected by element diffusion,and TiB whisker accelerates the precipitation behavior of silicide by hindering the movement of dislocations and providing nucleation particles.
基金Project(2017YFA0403802)supported by the National Key Research and Development Program of ChinaProject(51825401)supported by the National Natural Science Foundation of ChinaProject(2019TQ0076)supported by the China Postdoctoral Science Foundation。
文摘In order to improve mechanical properties and optimize composition of TiAl-Nb alloys, Ti46 Al5 Nb0.1 B alloys with different contents of Fe(0, 0.3, 0.5, 0.7, 0.9, and 1.1 at.%) were prepared by melting. Macro/microstructure and compression properties of the alloys were systematically investigated. Results show that Fe element can decrease the grain size, aggravate the Al-segregation and also form the Fe-rich B2 phase in the interdendritic area. Compressive testing results indicate that the Ti46 Al5 Nb0.1 B0.3 Fe alloy shows the highest ultimate compressive strength and fracture strain, which are 1869.5 MPa and 33.53%, respectively. The improved ultimate compression strength is ascribed to the grain refinement and solid solution strengthening of Fe, and the improved fracture strain is due to the reduced lattice tetragonality of γ phase and grain refinement of the alloys. However, excessive Fe addition decreases compressive strength and fracture strain, which is caused by the severe Al-segregation.
基金financially supported by the National Science Foundation of China(Grant No.51171053 and No.51471062)
文摘In the present research, microstructure refinement of a high-Nb TiAl alloy （Ti-48Al-8Nb-0.15B） was realized by means of the electromagnetic continuous casting （EMCC） technique. The microstructure of an ingot obtained by EMCC was analyzed using scanning electron microscopy （SEM）. As compared with the raw as-cast alloy, the obtained EMCC alloy presented a much finer microstructure with lamellar colonies with a mean size of about 50-70 μm because the electromagnetic stirring broke initial dendrites and enhanced the heterogeneous nucleation. As the grains were refined, the properties of the TiAl alloy were improved significantly. This implies that the EMCC technique could offer the possibility of application for high-Nb TiAl alloys with a refined microstructure and excellent properties to be used as a structural material.
基金Project(51741404)supported by the National Natural Science Foundation of ChinaProject(2017YFA0403802)supported by National Key Research and Development Program of China
文摘Ti43Al and Ti47Al alloys with different contents of zirconium were prepared by non-consumable vacuum arc melting furnace.The microstructure and mechanical properties were investigated.The results showed that Zr had no obvious effect on microstructure morphology of Ti43Al,while that of Ti47Al was modified from dendrites into equiaxed grains.The addition of Zr could refine the grains.Zr promoted the formation ofγphase significantly and the solubility values of Zr inγphase were 12.0%and 5.0%(molar fraction)in Ti43Al and Ti47Al,respectively.Zr-richγphase mainly formed throughβ→γin Ti43Al-xZr(molar fraction,%)andβ→α→γin Ti47Al-xZr(molar fraction,%).Fine-grain strengthening and solution strengthening were beneficial to improving the compressive strength while severe micro-segregation was detrimental to compressive properties.Large solubility of Zr was bad for ductility of alloys as well.The maximum compressive strengths of Ti43Al-xZr and Ti47Al-xZr were 1684.82 MPa(x=5.0%)and 2158.03 MPa(x=0.5%),respectively.The compressive strain fluctuated slightly in Ti43Al-xZr and reached the maximum value of 35.24%(x=0.5%)in Ti47Al-xZr.Both alloys showed brittle fracture.
基金financially supported by the National Key Research and Development Program of China(No.2017YFA0403802)the National Natural Science Foundation of China(Nos.51741404 and 51274076)
文摘Alloying additions of 0 at%-1.1 at% Fe were added into Ti43A1Nb0.1B alloys for increasing the roomtemperature strength and ductility,and the microstructure and mechanical properties were systematically studied.The results show that the lattice tetragonality(c/a) of γ phase and the average width of columnar grains of alloys decrease with Fe content increasing.Fe addition brings about the formation of Fe-rich B2 phase both in the dendrites and in interdendritic regions,and its content increases with Fe contents increasing.Furthermore,Fe addition aggravates the Al segregations in the interdendritic regions.The alloy with 0.7 at% Fe exhibits higher combined mechanical properties with the ultimate compression strength and fracture strain of 1958.4 MPa and 29.8%,respectively.The grain refinement strengthening and solid-solution strengthening of Fe are responsible for the improvement in the strength and the strain.However,excessive Fe addition results in the decrease in the strength and strain,which is attributed to the severe A1 segregations in the interdendritic regions that cause the premature fracture during compression.
基金the National Natural Science Foundation of China(Grant Nos.51825401,51971121,52001114)the Scientific Research Fund of State Key Laboratory of Materials Processing and Die&Mould Technology(Grant No.P2020-023)Henan Provincial Department of Science and Technology Research Project(Grant No.182102110096)。
文摘In order to improve mechanical properties of TiAlNb alloys,different contents of silicon were added into Ti48Al6Nb alloy.The Ti48Al6NbxSi (x=0,0.1,0.2,0.3,0.4 and 0.5,at.%) alloys were prepared by vacuum arc melting.The phase constitution,microstructure evolution and mechanical properties of the alloys were studied.Results show that the Ti48Al6NbxSi alloys consist of γ-TiAl phase,α2-Ti3Al phase and B2 phase,and Ti5Si3 silicide phase is formed when the addition of silicon is higher than 0.3at.%.The addition of silicon leads to the decrease in γ phase and increase in α2 phase.The formation of silicide decreases the amount of Nb dissolved in the TiAl matrix,and therefore decreases B2 phase.Compressive tests show that the ultimate strength of the alloys increases from 2,063 MPa to 2,281 MPa with an increase in silicon from 0 to 0.5at.%,while the fracture strain decreases from 34.7% to 30.8%.The increase of compressive strength and decrease of fracture strain can be attributed to the decrease of B2 phase and the formation of Ti5Si3 phase by the addition of silicon.The strengthening mechanism is changed from solid solution strengthening when the addition of silicon is less than 0.3at.% to combination of solid solution strengthening and secondary phase strengthening when the addition of silicon is higher than 0.3at.%.
基金supported by the National Natural Science Foundation of China(Nos.51825401 and 52374384)the Fundamental Research Funds for the Central Universities(No.2023FRFK06014).
文摘This study examines the microstructure,mechanical properties(with a focus on room-temperature toughness),and oxidation resistance of Ho-doped NbDSi based in-situ composites.The base alloy consists of the coarse primary Nb_(5)Si_(3)phase and the Nb_(5)Si_(3)+Nbss(Nb solid solution)eutectic cells.Ho doping influences the solidification path.When the Ho doping is higher than0.2 at%,the alloys transform into eutectic alloys.Ho can be solid-solved in trace amounts in the Nbss phase.However,most of Ho forms a stable Ho oxide phase,which alleviates oxygen contamination problem to some extent.Moreover,the interface separation between Ho oxide and other phases reduces the plastic deformation constraint.Thus,with 0.4 at%Ho doping,the K_(Q)value is18.03 MPa·m^(1/2),which is 31.1%higher than that of the base alloy.The strength of the Ho-doped alloys does not deteriorate with an increase in toughness.However,the large network-like Ho_(2)O_(3)in the 0.8Ho alloy causes a decrease in toughness and strength.In addition,the Ho oxide phase effectively blocks the inward oxygen intrusion.With 0.8 at%Ho doping,the oxidation mass gain per unit area is 10.16 mg·cm^(2),which is 39.7%lower than that of the base alloy.
