To determine the liquid-solid phase equilibria of the Nb-Si-Ti ternary system, Nb-Si-Ti alloys of different compositions are prepared. By means of scanning electron microscopy （SEM）, X-ray diffraction （XRD） and el...To determine the liquid-solid phase equilibria of the Nb-Si-Ti ternary system, Nb-Si-Ti alloys of different compositions are prepared. By means of scanning electron microscopy （SEM）, X-ray diffraction （XRD） and electron probe microanalysis （EPMA）, the phases in the alloys, such as Si-based solutions, Ti（Nb）Si, Ti（Nb）Si2, Nb（Ti）Si2, Ti（Nb）5Si4, Nb（Ti）5Si3, Ti（Nb）5Si3, Nb（Ti）3Si and Nb-based solutions are identified, and the phase evolution is analyzed. As a result, the microstmctural and microchemical evidence provides a clear definition of the Nb-Si-Ti liquidus surface projection and indicates that the ternary phase diagram has seven transition reactions.展开更多
Effects of pressure on lattice parameters, electronic, thermodynamic and mechanical properties of the fully ordered Ti_(2)AlNb orthorhombic phase were studied using first-principles calculations based on density funct...Effects of pressure on lattice parameters, electronic, thermodynamic and mechanical properties of the fully ordered Ti_(2)AlNb orthorhombic phase were studied using first-principles calculations based on density functional theory(DFT). The bonding nature for ordering orthorhombic Ti_(2)AlNb was revealed quantitatively through the electronic structure analyzing. The external pressures play limited roles in the elastic anisotropy of the alloy due to the outstanding dynamical and mechanical stabilities under pressure. However, the shear modulus of O phase manifests anisotropic, where {010} shear planes are the easiest planes to cleave among the principal planes under all pressures.The heat capacities, volume expansions and thermal expansion coefficients were calculated using the quasi-harmonic approximation model based on the phonon dispersion curves. Meanwhile, the bulk modulus, Young’s modulus,shear modulus and the hardness are promptly enhanced under pressure. The predicted results give hints to design Ti_(2)AlNb-based alloy as high-pressure applications.展开更多
Abstract The α ＋ β→β phase transformation kinetics of Ti-1300 alloy during continuous heating at different heating rates were investigated using dilatometric method. Results show that the curves of the α ＋ β...Abstract The α ＋ β→β phase transformation kinetics of Ti-1300 alloy during continuous heating at different heating rates were investigated using dilatometric method. Results show that the curves of the α ＋ β→β phase transformation exhibit a typical S-shaped pattern, which indicates that the α ＋ β→β phase transformation is a nucleation-growth-controlled process. The overall activation energy of the α ＋ β→β transformation of the alloy is 797 kJ·mol^-1. The nucleation and growth mechanism of the α ＋ β→β transformation was also investigated using the non-isothermal Avrami exponent. The Avrami exponent during α ＋ β→β transformation process significantly changes with transformed volume fraction increasing, which indicates that the α ＋ β→β transformation mechanism in the Ti-1300 alloy varies at different sections.展开更多
The effects of temperature and Ti content on the deformation mechanisms of pure Zr and Zr-Ti alloys were investigated by transmission electron microscopy.The results indicate the existence of a relation between deform...The effects of temperature and Ti content on the deformation mechanisms of pure Zr and Zr-Ti alloys were investigated by transmission electron microscopy.The results indicate the existence of a relation between deformation-induced phase transformation from a hexagonal close-packed structure to a facecentered cubic structure and{10■1}deformation twinning.That is,when one is suppressed,the other will be promoted.The phase transformation was suppressed while the{10■1}compressive twinning was promoted with increasing the rolling temperature and/or Ti content.This can be attributed to the activation of basal<a>dislocations at high temperature and the increased stacking fault energy with Ti content.展开更多
Precipitation response of a recently developed β-type Ti-25Nb-2Mo-4Sn alloy （wt%） during aging was investigated in detail. Experimental results indicate that the metastable co or equilibrium α phase can form alter...Precipitation response of a recently developed β-type Ti-25Nb-2Mo-4Sn alloy （wt%） during aging was investigated in detail. Experimental results indicate that the metastable co or equilibrium α phase can form alternatively even under the same aging condition, depending on the condition prior to the aging, i.e., solution treatment or severe cold rolling. This provides, for the first time, the direct evidence for the competition between ω and α in aged β-type Ti alloys. This peculiar aging response is found to be closely related to high-density dislocations and grain boundaries which suppress the formation of ω but favor the precipitation of fine α phase.展开更多
The effects of heat treatments on the phase transformation behavior of Ti49Ni49.5Fe1V0.5and Ti48Ni48.5Fe1V2.5 alloys were investigated. The results indicate that the alloys subjected to different heat treatments have ...The effects of heat treatments on the phase transformation behavior of Ti49Ni49.5Fe1V0.5and Ti48Ni48.5Fe1V2.5 alloys were investigated. The results indicate that the alloys subjected to different heat treatments have B2 structure at room temperature. All the specimens exhibit a twostage B2 → R → B19r martensitic transformation on cooling, but a B19’ → B2 one-stage reverse martensitic transformation on heating except aged A1 alloy, which undergoes an abnormal two-stage transformation upon heating. The phase transformation temperatures are affected by heat treatments and V content, which can be attributed to the variation of the second-phase particles content in the matrix.展开更多
TEM examination proves that the second phase particle within the as-forged Ti-55alloy consists of either bright or dark 'matrix' (nano-Nd3Sn) and some small dark blocks (SnO) dispersed in the 'matrix'...TEM examination proves that the second phase particle within the as-forged Ti-55alloy consists of either bright or dark 'matrix' (nano-Nd3Sn) and some small dark blocks (SnO) dispersed in the 'matrix'. The HREM observation shows that the nanoNd3Sn phase is roughly spherical and about 3-15nm in diameter, and the grain boundaries with atout 1nm width are 'gas-like' structure.展开更多
High resolution electron microscopy studies of rure earth-rich phase particles in a melt-quenched Ti-5Al-4Sn-2Zr-1MO-0.25Si-1Nd alloy indicate that the α-Ti matrix crystallizes prior to the rare earth-rich phase part...High resolution electron microscopy studies of rure earth-rich phase particles in a melt-quenched Ti-5Al-4Sn-2Zr-1MO-0.25Si-1Nd alloy indicate that the α-Ti matrix crystallizes prior to the rare earth-rich phase particles. According to a new nucleation model, the heteropeneous nucleation of the rare earth-rich phase particles at the matrix interface is easier than the homogeneous nucleation off the interface matrix, which is consistent with the results of the HREM obseroations.展开更多
The energetic, electronic structure and elastic property of β-type Ti1-xXx (X=Nb and Mo, x=0.041 7, 0.062 5, 0.125 0, 0.187 5, 0.250 0, 0.312 5 and 0.375) binary alloys were calculated by the method of supercell and ...The energetic, electronic structure and elastic property of β-type Ti1-xXx (X=Nb and Mo, x=0.041 7, 0.062 5, 0.125 0, 0.187 5, 0.250 0, 0.312 5 and 0.375) binary alloys were calculated by the method of supercell and augmented plane waves plus local orbitals within generalized gradient approximation. The elastic moduli of the polycrystals for these Ti1-xXx alloys were calculated from the elastic constants of the single crystal by the Voigt-Reuss-Hill averaging method. Based on the calculated results, the influence of X content on the phase stability and elastic property of β-type Ti1-xXx alloys was investigated. The results show that the phase stability, tetragonal shear constant C′, bulk modulus, elastic modulus and shear modulus of β-type Ti1-xXx alloys increase with an increase of X content monotonously. When the valence electron number of β-type Ti1-xXx alloys is around 4.10, i.e. the content of Nb is 9.87% (molar fraction) in the Ti-Nb alloy and Mo is 4.77% (molar fraction) in Ti-Mo alloy, the tetragonal shear constant is nearly zero. The Ti1-xXx alloys achieve low phase stability and low elastic modulus when the tetragonal shear constant reaches nearly zero. In addition, the phase stability of β-type Ti1-xXx alloys was discussed together with the calculated electronic structure.展开更多
The morphologies of the Nd-rich phase particles in the Ti-5Al-4Sn-2Zn -1Mo-0.25Si-1Nd alloy after high temperature deformation are investigaied by optical microscope and transmission electron microscope. It is found t...The morphologies of the Nd-rich phase particles in the Ti-5Al-4Sn-2Zn -1Mo-0.25Si-1Nd alloy after high temperature deformation are investigaied by optical microscope and transmission electron microscope. It is found that the Nd-rich phase particles are 1.0～14 μm in diameter and uniformly distributed in ihe matrix, and the majority of the particles are elliptical. Under high temperature deformaiton, high stress concentration occurs on the particles, the particles near to sphericity are obtained.展开更多
The high temperature oxidation behaviors of Ti Cr alloys containing 18% ～ 35% Cr with Laves phase TiCr 2 were investigated at 650 ～ 780?℃ for exposure up to 104?h. The results reveal that chromium content has criti...The high temperature oxidation behaviors of Ti Cr alloys containing 18% ～ 35% Cr with Laves phase TiCr 2 were investigated at 650 ～ 780?℃ for exposure up to 104?h. The results reveal that chromium content has critical significance to the oxidation resistance of the alloys. The scaling rates of the alloys with less than 21% Cr are higher than those measured for pure titanium, but for the alloys with more than 26% Cr their scaling rate is lowered by 1～2 times, under the same oxidizing conditions. Both an external and an internal oxidation layers were observed. The oxidation resistance enhancement by chromium alloying is contributed to the formation of a continuous and compact chromic oxide interleaf in the scale. Oxidation temperature significantly affects the scaling rates of Ti Cr alloys, and the mass gain is doubled with a temperature change from 650?℃ to 700?℃ or from 700?℃ to 780?℃, for the same exposure duration. TiCr 2 shows no negative influence on the high temperature oxidation resistance of the alloys.展开更多
The effects of applied tensile strain on the coherent α_2→O-phase transformation in Ti-Al-Nb alloys are explored bycomputer simulation using a phase-field method. The focus is on the influence of the applied strain ...The effects of applied tensile strain on the coherent α_2→O-phase transformation in Ti-Al-Nb alloys are explored bycomputer simulation using a phase-field method. The focus is on the influence of the applied strain direction onthe microstructure and volume fraction of the O-phase precipitates. It is found that altering applied strain directioncan modify microstructure of Ti-25Al-10～12Nb (at. pct) alloy during α_2→O-phase transformation effectively andfull laminate microstructure in the Ti-25Al-10Nb (at. pct) alloy can be realized by an applied strain only along thedirection 30°away from the α_2 phase <1010> in magnitude equivalent to the stress-free transformation strain. Thesimulation also shows that not only the magnitude of applied strain but also the applied strain direction influencesthe O-phase volume fraction and the effect of strain direction on the volume fraction is up to 25%.展开更多
A quantitative phase field method of multi-component diffusion-controlled phase transformations coupled with the Kim-Kim-Suzuki model was applied to study the effect of initial particle size distribution （PSD） in 3D...A quantitative phase field method of multi-component diffusion-controlled phase transformations coupled with the Kim-Kim-Suzuki model was applied to study the effect of initial particle size distribution （PSD） in 3D and space distribution in 2D on dissolution of α particles in Ti-6Al-4V alloy below β transus temperature in real time and length scale. The thermodynamic and mobility data were obtained from Thermo-Calc and DICTRA softwares, respectively. The results show that the volume fractions of α particles decay with time as： f =feq ＋ （f0 -feq） exp（-Ktn） for four cases of PSD. The sequence of dissolution kinetics from fast to slow is： uniform PSD, normal PSD, lognormal PSD and bimodal PSD. The space distribution is found to be a major factor affecting the dissolution kinetics and the microstructures. When the distance of the particles is less than critical value, the dissolution rates reduce with the decrease in distance. The Al and V concentration fields around the particles appear more obvious soft impingement.展开更多
The site occupations of the alloying elements of O phase in Ti 2AlNb based intermetallics are clarified. The ordering behaviours of the O phase in Ti y Al z Nb( y ≥ 25%, mole fraction) orthorhombic alloys are also in...The site occupations of the alloying elements of O phase in Ti 2AlNb based intermetallics are clarified. The ordering behaviours of the O phase in Ti y Al z Nb( y ≥ 25%, mole fraction) orthorhombic alloys are also investigated with a Bragg Williams model. In the temperature range where the O phases exist, the order parameters change with the alloy composition and temperature continuously, and the first order transition character is very "展开更多
Ti 48 Al 52 foils were examined by high resolution electron microscopy and electron microscopy. It was found that a Ti 2Al phase does exist in the sample tested, which is different from Ti 2AlN or Ti 2AlC phase. There...Ti 48 Al 52 foils were examined by high resolution electron microscopy and electron microscopy. It was found that a Ti 2Al phase does exist in the sample tested, which is different from Ti 2AlN or Ti 2AlC phase. There is some further research to be carried out. Firstly, the precise crystal structure of Ti 2Al is to be determined, especially the atom arrangement of the (0001) plane. Secondly, the structure of interface between Ti 2Al and Ti 3Al should be obtained so as to interpret their relation when they grow from the TiAl matrix in more detail.展开更多
Al-Ti-C master alloy was prepared by SHS (Self-propagating High temperature Synthesis)-melting technique. Effect of yttrium addition level on the microstructures of the master alloy was studied by XRD, SEM and EDS. Th...Al-Ti-C master alloy was prepared by SHS (Self-propagating High temperature Synthesis)-melting technique. Effect of yttrium addition level on the microstructures of the master alloy was studied by XRD, SEM and EDS. The experimental results show that the addition of 1.0% Y is beneficial to the formation of TiC particles; Al-Ti-C-1.0Y consists of rod-like and blocky TiAl3, TiC, Al3Y and α-Al matrix. Y is found around TiC particles in Al-Ti-C-0.5Y master alloy while blocky (AlTiY) phase appears in Al-Ti-C-1.0Y master alloy. Al3Y with dendritic morphology and small blocky Al2Y except for TiC are found in Al-Ti-C-2-0Y master alloy.展开更多
By means of optical microscope , scanning electron microscope （SEM） and transmission electron microscope （TEM）, the process of densification, the characterization of phase transformation and the microstructure for...By means of optical microscope , scanning electron microscope （SEM） and transmission electron microscope （TEM）, the process of densification, the characterization of phase transformation and the microstructure for spark plasma sintering （SPS） nano hard phase Ti（C,N）-based cermet were investigated. It is found that the spark plasma sintering （SPS） enables the nano hard phase Ti（C,N）-based cermet to densify rapidly, however, the full densification of the sintered samples can not be obtained. The rate of phase transformation is significantly quick. When being sintered at 1 200 ℃ for 8 min, Mo2C is completely dissolved, and TiN dissolves into TiC entirely and disappears. Above 1 200 ℃, Ti（C,N） begins to decompose and the atoms of C and N separate from Ti（C,N） resulting in the generation of N2 and the graphite. Due to the denitrification and the graphitization, the density and the hardness of sintered samples are rather low. The distribution of grain size of the sample sintered at 1 350 ℃ covers a wide range of 90500 nm, and most of the grain size are about 200 nm. The hard phase is not of typical core-rim structure. Oxides on the surface of particles can not be fully removed and present in sample as titanium oxide TiO2. Graphite exists in band-like shape.展开更多
The thermal stability of the rare earth rich phase particles in α, α+β and β phase regions of Ti 5Al 4Sn 2Zr 1Mo 0 25Si 1Nd(Ti 55) high temperature titanium alloy heat treated was studied. Under ...The thermal stability of the rare earth rich phase particles in α, α+β and β phase regions of Ti 5Al 4Sn 2Zr 1Mo 0 25Si 1Nd(Ti 55) high temperature titanium alloy heat treated was studied. Under conditions of 600～980 ℃/1～100 h and 1050～1500 ℃/1～10 h, the average particle size ranges from 3 34 to 4 20 μm, the circularity shape factor from 0 619 to 0 759, and the volume fraction from 1 4% to 1 8%. The results show that nearly no change is found for the size, shape, and volume fraction of the particles in the alloy, and the rare earth rich phase particles exhibit thermal stability.展开更多
基金National High-tech Research and Development Pro-gram(2006AA03Z102)Aeronautical Science Foundation of China(2006ZF51069)
文摘To determine the liquid-solid phase equilibria of the Nb-Si-Ti ternary system, Nb-Si-Ti alloys of different compositions are prepared. By means of scanning electron microscopy （SEM）, X-ray diffraction （XRD） and electron probe microanalysis （EPMA）, the phases in the alloys, such as Si-based solutions, Ti（Nb）Si, Ti（Nb）Si2, Nb（Ti）Si2, Ti（Nb）5Si4, Nb（Ti）5Si3, Ti（Nb）5Si3, Nb（Ti）3Si and Nb-based solutions are identified, and the phase evolution is analyzed. As a result, the microstmctural and microchemical evidence provides a clear definition of the Nb-Si-Ti liquidus surface projection and indicates that the ternary phase diagram has seven transition reactions.
基金financially supported by the National Natural Science Foundation of China (Nos.50971043 and 51171046)the Research Fund for the Doctoral Program of Higher Education of China (No.20133514110006)+1 种基金the Natural Science Foundation of Fujian Province,China (No.2014J01176)the Program for New Century Excellent Talents in University of Fujian Province,China (No.JA10013)。
文摘Effects of pressure on lattice parameters, electronic, thermodynamic and mechanical properties of the fully ordered Ti_(2)AlNb orthorhombic phase were studied using first-principles calculations based on density functional theory(DFT). The bonding nature for ordering orthorhombic Ti_(2)AlNb was revealed quantitatively through the electronic structure analyzing. The external pressures play limited roles in the elastic anisotropy of the alloy due to the outstanding dynamical and mechanical stabilities under pressure. However, the shear modulus of O phase manifests anisotropic, where {010} shear planes are the easiest planes to cleave among the principal planes under all pressures.The heat capacities, volume expansions and thermal expansion coefficients were calculated using the quasi-harmonic approximation model based on the phonon dispersion curves. Meanwhile, the bulk modulus, Young’s modulus,shear modulus and the hardness are promptly enhanced under pressure. The predicted results give hints to design Ti_(2)AlNb-based alloy as high-pressure applications.
基金financially supported by the National Natural Science Foundation of China(No.51401058)the Transformation Project of Major Scientific and Technological Achievements of Shanxi Province(No.2012KTCG04-14)the Science and Technology Innovation Team Project of Shanxi Province of China(No.2012KCT-23)
文摘Abstract The α ＋ β→β phase transformation kinetics of Ti-1300 alloy during continuous heating at different heating rates were investigated using dilatometric method. Results show that the curves of the α ＋ β→β phase transformation exhibit a typical S-shaped pattern, which indicates that the α ＋ β→β phase transformation is a nucleation-growth-controlled process. The overall activation energy of the α ＋ β→β transformation of the alloy is 797 kJ·mol^-1. The nucleation and growth mechanism of the α ＋ β→β transformation was also investigated using the non-isothermal Avrami exponent. The Avrami exponent during α ＋ β→β transformation process significantly changes with transformed volume fraction increasing, which indicates that the α ＋ β→β transformation mechanism in the Ti-1300 alloy varies at different sections.
基金financially supported by the Natural Science Foundation of China(No.51828102)the Natural Science Foundation of Hunan Province(No.2018JJ3649)+1 种基金The Project of Innovation-driven Plan in Central South University(No.2019CX026)financial support from the Australian Research Council(No.DP190102243).
文摘The effects of temperature and Ti content on the deformation mechanisms of pure Zr and Zr-Ti alloys were investigated by transmission electron microscopy.The results indicate the existence of a relation between deformation-induced phase transformation from a hexagonal close-packed structure to a facecentered cubic structure and{10■1}deformation twinning.That is,when one is suppressed,the other will be promoted.The phase transformation was suppressed while the{10■1}compressive twinning was promoted with increasing the rolling temperature and/or Ti content.This can be attributed to the activation of basal<a>dislocations at high temperature and the increased stacking fault energy with Ti content.
基金financially supported by the National Natural Science Foundation of China(Nos.51271010 and 21301075)the Senior Intellectuals Fund of Jiangsu University(13JDG098)
文摘Precipitation response of a recently developed β-type Ti-25Nb-2Mo-4Sn alloy （wt%） during aging was investigated in detail. Experimental results indicate that the metastable co or equilibrium α phase can form alternatively even under the same aging condition, depending on the condition prior to the aging, i.e., solution treatment or severe cold rolling. This provides, for the first time, the direct evidence for the competition between ω and α in aged β-type Ti alloys. This peculiar aging response is found to be closely related to high-density dislocations and grain boundaries which suppress the formation of ω but favor the precipitation of fine α phase.
基金financially supported by the Industry,Education and Research Projects of the China Aviation Industrial(No.cxy2012BH04)
文摘The effects of heat treatments on the phase transformation behavior of Ti49Ni49.5Fe1V0.5and Ti48Ni48.5Fe1V2.5 alloys were investigated. The results indicate that the alloys subjected to different heat treatments have B2 structure at room temperature. All the specimens exhibit a twostage B2 → R → B19r martensitic transformation on cooling, but a B19’ → B2 one-stage reverse martensitic transformation on heating except aged A1 alloy, which undergoes an abnormal two-stage transformation upon heating. The phase transformation temperatures are affected by heat treatments and V content, which can be attributed to the variation of the second-phase particles content in the matrix.
文摘TEM examination proves that the second phase particle within the as-forged Ti-55alloy consists of either bright or dark 'matrix' (nano-Nd3Sn) and some small dark blocks (SnO) dispersed in the 'matrix'. The HREM observation shows that the nanoNd3Sn phase is roughly spherical and about 3-15nm in diameter, and the grain boundaries with atout 1nm width are 'gas-like' structure.
文摘High resolution electron microscopy studies of rure earth-rich phase particles in a melt-quenched Ti-5Al-4Sn-2Zr-1MO-0.25Si-1Nd alloy indicate that the α-Ti matrix crystallizes prior to the rare earth-rich phase particles. According to a new nucleation model, the heteropeneous nucleation of the rare earth-rich phase particles at the matrix interface is easier than the homogeneous nucleation off the interface matrix, which is consistent with the results of the HREM obseroations.
基金Project(50571063) supported by the National Natural Science Foundation of ChinaProject(04JC14054) supported by the Science and Technology Committee of Shanghai, China
文摘The energetic, electronic structure and elastic property of β-type Ti1-xXx (X=Nb and Mo, x=0.041 7, 0.062 5, 0.125 0, 0.187 5, 0.250 0, 0.312 5 and 0.375) binary alloys were calculated by the method of supercell and augmented plane waves plus local orbitals within generalized gradient approximation. The elastic moduli of the polycrystals for these Ti1-xXx alloys were calculated from the elastic constants of the single crystal by the Voigt-Reuss-Hill averaging method. Based on the calculated results, the influence of X content on the phase stability and elastic property of β-type Ti1-xXx alloys was investigated. The results show that the phase stability, tetragonal shear constant C′, bulk modulus, elastic modulus and shear modulus of β-type Ti1-xXx alloys increase with an increase of X content monotonously. When the valence electron number of β-type Ti1-xXx alloys is around 4.10, i.e. the content of Nb is 9.87% (molar fraction) in the Ti-Nb alloy and Mo is 4.77% (molar fraction) in Ti-Mo alloy, the tetragonal shear constant is nearly zero. The Ti1-xXx alloys achieve low phase stability and low elastic modulus when the tetragonal shear constant reaches nearly zero. In addition, the phase stability of β-type Ti1-xXx alloys was discussed together with the calculated electronic structure.
文摘The morphologies of the Nd-rich phase particles in the Ti-5Al-4Sn-2Zn -1Mo-0.25Si-1Nd alloy after high temperature deformation are investigaied by optical microscope and transmission electron microscope. It is found that the Nd-rich phase particles are 1.0～14 μm in diameter and uniformly distributed in ihe matrix, and the majority of the particles are elliptical. Under high temperature deformaiton, high stress concentration occurs on the particles, the particles near to sphericity are obtained.
文摘The high temperature oxidation behaviors of Ti Cr alloys containing 18% ～ 35% Cr with Laves phase TiCr 2 were investigated at 650 ～ 780?℃ for exposure up to 104?h. The results reveal that chromium content has critical significance to the oxidation resistance of the alloys. The scaling rates of the alloys with less than 21% Cr are higher than those measured for pure titanium, but for the alloys with more than 26% Cr their scaling rate is lowered by 1～2 times, under the same oxidizing conditions. Both an external and an internal oxidation layers were observed. The oxidation resistance enhancement by chromium alloying is contributed to the formation of a continuous and compact chromic oxide interleaf in the scale. Oxidation temperature significantly affects the scaling rates of Ti Cr alloys, and the mass gain is doubled with a temperature change from 650?℃ to 700?℃ or from 700?℃ to 780?℃, for the same exposure duration. TiCr 2 shows no negative influence on the high temperature oxidation resistance of the alloys.
文摘The effects of applied tensile strain on the coherent α_2→O-phase transformation in Ti-Al-Nb alloys are explored bycomputer simulation using a phase-field method. The focus is on the influence of the applied strain direction onthe microstructure and volume fraction of the O-phase precipitates. It is found that altering applied strain directioncan modify microstructure of Ti-25Al-10～12Nb (at. pct) alloy during α_2→O-phase transformation effectively andfull laminate microstructure in the Ti-25Al-10Nb (at. pct) alloy can be realized by an applied strain only along thedirection 30°away from the α_2 phase <1010> in magnitude equivalent to the stress-free transformation strain. Thesimulation also shows that not only the magnitude of applied strain but also the applied strain direction influencesthe O-phase volume fraction and the effect of strain direction on the volume fraction is up to 25%.
基金support from the National Natural Science Foundation of China (Nos. 51601078 and 51201147)the National Key R&D Program of China (Grant No. 2016YFB0701302)+1 种基金the Informalization Construction Program of Chinese Academy of Science (INFO-115-B01)Shenyang Supercomputer Centers for the computational resource of Chinese Academy of Science
文摘A quantitative phase field method of multi-component diffusion-controlled phase transformations coupled with the Kim-Kim-Suzuki model was applied to study the effect of initial particle size distribution （PSD） in 3D and space distribution in 2D on dissolution of α particles in Ti-6Al-4V alloy below β transus temperature in real time and length scale. The thermodynamic and mobility data were obtained from Thermo-Calc and DICTRA softwares, respectively. The results show that the volume fractions of α particles decay with time as： f =feq ＋ （f0 -feq） exp（-Ktn） for four cases of PSD. The sequence of dissolution kinetics from fast to slow is： uniform PSD, normal PSD, lognormal PSD and bimodal PSD. The space distribution is found to be a major factor affecting the dissolution kinetics and the microstructures. When the distance of the particles is less than critical value, the dissolution rates reduce with the decrease in distance. The Al and V concentration fields around the particles appear more obvious soft impingement.
文摘The site occupations of the alloying elements of O phase in Ti 2AlNb based intermetallics are clarified. The ordering behaviours of the O phase in Ti y Al z Nb( y ≥ 25%, mole fraction) orthorhombic alloys are also investigated with a Bragg Williams model. In the temperature range where the O phases exist, the order parameters change with the alloy composition and temperature continuously, and the first order transition character is very "
文摘Ti 48 Al 52 foils were examined by high resolution electron microscopy and electron microscopy. It was found that a Ti 2Al phase does exist in the sample tested, which is different from Ti 2AlN or Ti 2AlC phase. There is some further research to be carried out. Firstly, the precise crystal structure of Ti 2Al is to be determined, especially the atom arrangement of the (0001) plane. Secondly, the structure of interface between Ti 2Al and Ti 3Al should be obtained so as to interpret their relation when they grow from the TiAl matrix in more detail.
基金Project supported by Natural Science Foundation of Shanxi Province (2007011067)
文摘Al-Ti-C master alloy was prepared by SHS (Self-propagating High temperature Synthesis)-melting technique. Effect of yttrium addition level on the microstructures of the master alloy was studied by XRD, SEM and EDS. The experimental results show that the addition of 1.0% Y is beneficial to the formation of TiC particles; Al-Ti-C-1.0Y consists of rod-like and blocky TiAl3, TiC, Al3Y and α-Al matrix. Y is found around TiC particles in Al-Ti-C-0.5Y master alloy while blocky (AlTiY) phase appears in Al-Ti-C-1.0Y master alloy. Al3Y with dendritic morphology and small blocky Al2Y except for TiC are found in Al-Ti-C-2-0Y master alloy.
文摘By means of optical microscope , scanning electron microscope （SEM） and transmission electron microscope （TEM）, the process of densification, the characterization of phase transformation and the microstructure for spark plasma sintering （SPS） nano hard phase Ti（C,N）-based cermet were investigated. It is found that the spark plasma sintering （SPS） enables the nano hard phase Ti（C,N）-based cermet to densify rapidly, however, the full densification of the sintered samples can not be obtained. The rate of phase transformation is significantly quick. When being sintered at 1 200 ℃ for 8 min, Mo2C is completely dissolved, and TiN dissolves into TiC entirely and disappears. Above 1 200 ℃, Ti（C,N） begins to decompose and the atoms of C and N separate from Ti（C,N） resulting in the generation of N2 and the graphite. Due to the denitrification and the graphitization, the density and the hardness of sintered samples are rather low. The distribution of grain size of the sample sintered at 1 350 ℃ covers a wide range of 90500 nm, and most of the grain size are about 200 nm. The hard phase is not of typical core-rim structure. Oxides on the surface of particles can not be fully removed and present in sample as titanium oxide TiO2. Graphite exists in band-like shape.
文摘The thermal stability of the rare earth rich phase particles in α, α+β and β phase regions of Ti 5Al 4Sn 2Zr 1Mo 0 25Si 1Nd(Ti 55) high temperature titanium alloy heat treated was studied. Under conditions of 600～980 ℃/1～100 h and 1050～1500 ℃/1～10 h, the average particle size ranges from 3 34 to 4 20 μm, the circularity shape factor from 0 619 to 0 759, and the volume fraction from 1 4% to 1 8%. The results show that nearly no change is found for the size, shape, and volume fraction of the particles in the alloy, and the rare earth rich phase particles exhibit thermal stability.
