Constitutive model for a new kind of metastable β titanium alloy during hot deformation

The constitutive model was developed to describe the relationship among flow stress,strain,strain rate,and deformation temperature completely,based on the characteristics of flow stress curves for a new kind of metastable β Ti2448 titanium alloy from isothermal hot compression tests,in a wide range of temperatures（1023-1123 K） and strain rates（63-0.001 s-1）.During this process,the adopted hyperbolic sine function based on the unified viscoplasticity theory was used to model the flow behavior of alloy undergoing flow softening caused by dynamic recovery（DRV） at high strain rates（≥1 s-1）.The standard Avrami equation was adopted to represent the softening mechanism attributed to dynamic recrystallization（DRX） at low strain rates（1 s-1）.Additionally,the material constants were determined by optimization strategy,which is a new method to solve the nonlinear constitutive equation.The stress—strain curves predicted by the developed constitutive model agree well with the experimental results,which con-rms that the developed constitutive model can give an accurate estimate of the-ow stress of Ti2448 titanium alloy and provide an effective method to model the flow behavior of metastable β titanium alloys during hot deformation.

Effect of Different Sizes of α Phase on Tensile Properties of Metastable β Titanium Alloy Ti-5.5Cr-5Al-4Mo-3Nb-2Zr

To study the relationship between the microstructure and tensile properties of the novel metastable β titanium alloy Ti-5.5Cr-5Al-4Mo-3Nb-2Zr,a heat treatment process of ABFCA(solid solution in α+βregion with subsequent furnace cooling followed by aging treatment finally)was designed,by which α phases of different sizes can be precipitated in the β matrix.The results show that the microstructure obtained by this heat treatment process is composed of primary α(α_(p))phase,submicro rod-like α(α_(r))phase and secondary α(α_(s))phase.The alloy with multi-scale α phase has an excellent balance between strength and ductility.The elongation is about 18.3% at the ultimate tensile strength of 1125.4 MPa.The relationship between the strength of the alloy and the α phase was established.The strength of the alloy is proportional to the power of‒1/2 of the average spacing and width of α phase.The α_(s) phase with a smaller size and phase spacing can greatly improve the strength of the alloy by hindering dislocation slip.The transmission electron microscope analysis shows that there is a large amount of dislocation accumulation at the α/β interfaces,and many deformation twins are found in the α_(p) phase after tensile deformation.When the dislocation slip is hindered,twins occur at the stress concentration location,and twins can initiate some dislocations that are difficult to slip.Meanwhile,the plastic strain is distributed uniformly among the α_(p),α_(r),α_(s) phases and β matrix,thereby enhancing the ductility of the alloy.

On the nature of a peculiar initial yield behavior in metastable β titanium alloy Ti-5Al-5Mo-5V-3Cr-0.5Fe with different initial microstructures

The compressive yielding phenomenon of titanium alloys is not as focused and sufficiently ascertain as the tensile yielding phenomenon.In the present work,the peculiar compressive yielding behavior and the different dynamic responses of three different initial microstructures(singleβ,clavateβand lamellarβ)were investigated in an attractive metastableβtitanium alloy Ti-5553 using electron microscopes/crystallographic calculation/crystal plastic finite element simulation.Results reveal that the distinct compressive yielding behavior,steep peaks of sudden drop in the initial stage(very small true strain 0.03)of stress loading have appeared in the compression stress-strain curves except for the lamellarβinitial microstructure.Dislocation slip is the essential mechanism of the initial yielding behavior.Interlaced multiple-slip bands formed in the singleβinitial microstructure during the warm deformation process.A small quantity of single slip bands was observed in the deformed clavateβinitial microstructure.The abundant varied nano/ultrafineβsprecipitates were nucleated dynamically and dispersedly in all the three deformed initial microstructures.The multiple-slip bands formation and substantial nanoscaleβsresult in the highest peak of flow stress for singleβinitial microstructure.The compressive slip bands are formed early in the elastic–plastic deformation stage.As the increasing strain,the sample showed a significant compressive bulge,or eventually forming a strong adiabatic shear band or crack.These results are expected to provide a reference for the study of deformation behavior and mechanical properties of metastableβtitanium alloys.

Characterization of hot deformation and microstructure evolution of a new metastableβtitanium alloy

The hot deformation characteristics of as-forged Ti−3.5Al−5Mo−6V−3Cr−2Sn−0.5Fe−0.1B−0.1C alloy within a temperature range from 750 to 910℃and a strain rate range from 0.001 to 1 s^(-1) were investigated by hot compression tests.The stress−strain curves show that the flow stress decreases with the increase of temperature and the decrease of strain rate.The microstructure is sensitive to deformation parameters.The dynamic recrystallization(DRX)grains appear while the temperature reaches 790℃at a constant strain rate of 0.001 s^(-1) and strain rate is not higher than 0.1 s^(-1) at a constant temperature of 910℃.The work-hardening rateθis calculated and it is found that DRX prefers to happen at high temperature and low strain rate.The constitutive equation and processing map were obtained.The average activation energy of the alloy is 242.78 kJ/mol and there are few unstable regions on the processing map,which indicates excellent hot workability.At the strain rate of 0.1 s^(-1),the stress−strain curves show an abnormal shape where there are two stress peaks simultaneously.This can be attributed to the alternation of hardening effect,which results from the continuous dynamic recrystallization(CDRX)and the rotation of DRX grains,and dynamic softening mechanism.

Microstructure and mechanical properties of new metastable β type titanium alloy

A new metastable β type titanium alloy called TB-13 with the combination of excellent strength and ductility was developed successfully.In order to develop a perspective on this new alloy,the influence of several commonly used heat treatments on the microstructure and properties was studied.In solution-treated and quenched samples,a low-temperature aging at 480°C results in the precipitation of finerαphase.The precipitation of coarserαphase plate at higher aging temperature(560°C)leads to the increase of tensile ductility but reduction of strength.During low-temperature aging at 300°C,quite homogeneous distribution of fine isothermalωphase particles was found.The isothermalωphase provides nucleation sites forαphase during two-step aging process and makesαphase extremely fine and disperse uniformly in β matrix.Thus,TB-13 alloy is strengthened and its mechanical properties are improved.

Slip behavior of Bi-modal structure in a metastable β titanium alloy during tensile deformation

β titanium alloys with bi-modal structure which exhibit improved strength-ductility combination and fatigue property are widely used in aviation and aerospace industry.However,owing to the small size of primary α(αp) and nano-scaled multi variant distribution of secondary α platelets(αs),investigating the deformation behavior is really a challenging work.In this work,by applying transmission electron microscopy(TEM),the slip behavior in αp and transformed β matrix with different tensile strain was studied.After α/β solution treatment,the initial dislocation slips on {110} plane with <1 1 1> direction in β matrix.During furtherdeformation,(110),(101) and(1 1 2) multi slip is generated which shows a long straight cro s sing configuration.Dislocation cell is exhibited in β matrix at tensile strain above 20 %.Diffe rent from the solid solution treated sample,high density wavy dislocations are generated in transformedβ matrix.High fraction fine as hinders dislocation motion in β matrix effectively which in turn dominates the strength of the alloy.In primary α phase(αp),a core-shell structure is formed during deformation.Both pyramidal a+c slip and prismatic/basal a slip are generated in the shell layer.In core region,plastic deformation is governed by prismatic/basal a slip.Formation of the core-shell structure is the physical origin of the improved ductility.On one hand,the work hardening layer(shell) improves the strength of αp,which could deform compatibly with the hard transformed β matrix.Meanwhile,the center area(core) deforms homogeneously which will sustain plastic strain effectively and increase the ductility.This paper studies the slip behavior and reveals the origin of the improved strength-ductility combination in Bi-modal structure on a microscopic way,which will give theoretical advises for developing the next generation high strength β titanium alloys.

Effect of thermo-mechanical processing on microstructure and electrochemical behavior of Ti-Nb-Zr-V new metastable β titanium biomedical alloy

The influence of thermo-mechanical processing (TMP) on the microstructure and the electrochemical behavior of new metastableβ alloy Ti?20.6Nb?13.6Zr?0.5V (TNZV) was investigated. The TMP included hot working in belowβ transus, solution heat treatments at the same temperature and different cooling rates in addition to aging. Depending upon the TMP conditions, a wide range of microstructures with varying spatial distributions and morphologies of equiaxed/elongatedα andβ phases were attained, allowing for a wide range of electrochemical properties to be achieved. The corrosion behavior of the studied alloy was evaluated in a Ringer’s solution at 37 °C via open circuit potential?time and potentiodynamic polarization measurements.

Evolution of microstructure, phase composition, and tensile properties of severely cold deformed titanium metastable β alloy in rapid continuous heating

Influence of severe cold deformation of titanium alloy Ti-1.5%A1-6.8%Mo-4.5%Fe in metastable β condition on the evolution of phase composition, microstructure, and tensile properties during continuous rapid heating was studied. As-deformed alloy was characterized by quasi-amorphous single-phase β condition with an abnormal temperature dependence of electric resistance that was normalized after 48 h exposure at room temperature as a result of isothermal ω phase precipitation. Subsequent rapid heating with a rate of 5 ℃/s caused recovery and recrystallization. Tensile properties of the alloy after different treatments were determined and discussed.

Aging characteristics of new metastable beta titanium alloy

The aging characteristics including microstructures and properties were investigated for a new metastable beta titanium alloy named Ti-B20 subjected to different solution treatments. Microstructural examination shows that precipitate-free zones,which are present in the many metastable beta titanium alloys,are not produced in the aged new alloy. The decrease of yield stress with the increase of aging temperature is due to the coarsening of alpha platelet. Furthermore,the age hardening effect of the new alloy strengthens with the increase of solution treatment temperature. These aging characteristics are attributed to the relatively lower concentration of beta stabilizer in the new alloy.

Microstructural influences on the high cycle fatigue life dispersion and damage mechanism in a metastable β titanium alloy

In this work,the effect of microstructure features on the high-cycle fatigue behavior of Ti-7Mo-3Nb-3Cr-3Al(Ti-7333)alloy is investigated.Fatigue tests were carried out at room temperature in lab air atmosphere using a sinusoidal wave at a frequency of 120 Hz and a stress ratio of 0.1.Results show that the fatigue strength is closely related to the microstructure features,especially theα_(p) percentage.The Ti-7333 alloy with a lowerα_(p) percentage exhibits a higher scatter in fatigue data.The bimodal fatigue behavior and the duality of the S-N curve are reported in the Ti-7333 alloy with relatively lowerα_(p) percentage.Crack initiation region shows the compoundα_(p)/βfacets.Facetedα_(p) particles show crystallographic orientation and morphology dependence characteristics.Crack-initiation was accompanied by faceting process across elongatedα_(p) particles or multiple adjacentα_(p) particles.These particles generally oriented for basal slip result in near basal facets.Fatigue crack can also initiate at elongatedα_(p) particle well oriented for prismatic slip.Theβfacet is in close correspondence to{110}or{112}plane with high Schmid factor.Based on the fracture observation and FIB-CS analysis,three classes of fatigue-critical microstructural configurations are deduced.A phenomenological model for the formation ofα_(p) facet in the bimodal microstructure is proposed.This work provides an insight into the fatigue damage process of theβprecipitate strengthened metastableβtitanium alloys.

Precipitation of metastable phases and its effect on electrical resistivity of Al-0.96Mg_2Si alloy during aging

The precipitation behavior and its influence on the electrical resistivity of the Al-0.96Mg2Si alloy during aging were investigated with in-situ resistivity measurement and transmission electron microscopy （TEM）. The precipitates of the peak aged alloy include both β＂ and if, but the amount ratio of β＂ to β＂ varies with the aging temperature and time increasing. The precipitates during aging at 175 ℃ are dominated by needle-like β＂ phases （including pre-β＂ phase）, the size of which increases with the time prolonging, but does not increase substantially after further aging. The evolution of electrical conductivity is directly related to such microstructural evolution. However, the hardness of the alloy stays at the peak value for a long term. When the alloy is aged at 195 ℃, the ratio of β＂ to β＇ becomes the main factor to influence relative resistivity （Ap） value. The higher the temperature is, the smaller the ratio is, and the faster the Ap value decreases. Moreover, the hardness peak drops with the decrease of the ratio. With the size and distribution parameters measured from TEM images, a semi-quantitative relationship between precipitates and the electrical resistivity was established.

Recent innovations in laser additive manufacturing of titanium alloys

Titanium(Ti)alloys are widely used in high-tech fields like aerospace and biomedical engineering.Laser additive manufacturing(LAM),as an innovative technology,is the key driver for the development of Ti alloys.Despite the significant advancements in LAM of Ti alloys,there remain challenges that need further research and development efforts.To recap the potential of LAM high-performance Ti alloy,this article systematically reviews LAM Ti alloys with up-to-date information on process,materials,and properties.Several feasible solutions to advance LAM Ti alloys are reviewed,including intelligent process parameters optimization,LAM process innovation with auxiliary fields and novel Ti alloys customization for LAM.The auxiliary energy fields(e.g.thermal,acoustic,mechanical deformation and magnetic fields)can affect the melt pool dynamics and solidification behaviour during LAM of Ti alloys,altering microstructures and mechanical performances.Different kinds of novel Ti alloys customized for LAM,like peritecticα-Ti,eutectoid(α+β)-Ti,hybrid(α+β)-Ti,isomorphousβ-Ti and eutecticβ-Ti alloys are reviewed in detail.Furthermore,machine learning in accelerating the LAM process optimization and new materials development is also outlooked.This review summarizes the material properties and performance envelops and benchmarks the research achievements in LAM of Ti alloys.In addition,the perspectives and further trends in LAM of Ti alloys are also highlighted.

Microstructure evolution and strengthening mechanism of high -performance powder metallurgy TA15 titanium alloy by hot rolling

Hot deformation of sintered billets by powder metallurgy(PM)is an effective preparation technique for titanium alloys,which is more significant for high-alloying alloys.In this study,Ti–6.5Al–2Zr–Mo–V(TA15)titanium alloy plates were prepared by cold press-ing sintering combined with high-temperature hot rolling.The microstructure and mechanical properties under different process paramet-ers were investigated.Optical microscope,electron backscatter diffraction,and others were applied to characterize the microstructure evolution and mechanical properties strengthening mechanism.The results showed that the chemical compositions were uniformly dif-fused without segregation during sintering,and the closing of the matrix craters was accelerated by increasing the sintering temperature.The block was hot rolled at 1200℃ with an 80%reduction under only two passes without annealing.The strength and elongation of the plate at 20–25℃ after solution and aging were 1247 MPa and 14.0%,respectively,which were increased by 24.5%and 40.0%,respect-ively,compared with the as-sintered alloy at 1300℃.The microstructure was significantly refined by continuous dynamic recrystalliza-tion,which was completed by the rotation and dislocation absorption of the substructure surrounded by low-angle grain boundaries.After hot rolling combined with heat treatment,the strength and plasticity of PM-TA15 were significantly improved,which resulted from the dense,uniform,and fine recrystallization structure and the synergistic effect of multiple slip systems.

Comparison of electrochemical behaviors of Ti-5Al-2Sn-4Zr-4Mo-2Cr-1Fe and Ti-6Al-4V titanium alloys in NaNO_(3) solution

The Ti-5Al-2Sn-4Zr-4Mo-2Cr-1Fe(β-CEZ)alloy is considered as a potential structural material in the aviation industry due to its outstanding strength and corrosion resistance.Electrochemical machining(ECM)is an efficient and low-cost technology for manufacturing theβ-CEZ alloy.In ECM,the machining parameter selection and tool design are based on the electrochemical dissolution behavior of the materials.In this study,the electrochemical dissolution behaviors of theβ-CEZ and Ti-6Al-4V(TC4)alloys in NaNO3solution are discussed.The open circuit potential(OCP),Tafel polarization,potentiodynamic polarization,electrochemical impedance spectroscopy(EIS),and current efficiency curves of theβ-CEZ and TC4 alloys are analyzed.The results show that,compared to the TC4 alloy,the passivation film structure is denser and the charge transfer resistance in the dissolution process is greater for theβ-CEZ alloy.Moreover,the dissolved surface morphology of the two titanium-based alloys under different current densities are analyzed.Under low current densities,theβ-CEZ alloy surface comprises dissolution pits and dissolved products,while the TC4 alloy surface comprises a porous honeycomb structure.Under high current densities,the surface waviness of both the alloys improves and the TC4 alloy surface is flatter and smoother than theβ-CEZ alloy surface.Finally,the electrochemical dissolution models ofβ-CEZ and TC4 alloys are proposed.

EXPLOITATION AND APPLICATIONS OF METASTABLE AUSTENITE MATRIX WEAR ALLOYS

Fe based cast alloys with double phases structure of m etastable austenite m atrix an d eutecticcarbide M7 C3 were provided with the excellent properties of high abrasion resistance andhigher i m pact toughness . An i m portant reason of high abrasion resistance is hard ness violentincreasing on the m atrix surface because of w ear easily induced m artensite transfor m ation . The exploitation and applications of m etastable austenite m atrix wear alloys of Fe C Cr Nisyste m and Fe C Cr Mn system were described in this paper . The excellent properties of thesealloys w ill be sufficiently indicated by authors’exa m ples . To exploit a class of these alloyswith high abrasion resistance and various im pact toughness for m eeting the requirem ent of dif ferent environ ment , the proble m of the structure design of metastable austenite m atrix wearalloy w as also described in this paper .

Microstructure Evolution in a Rapidly Solidified Cu85Fe15 Alloy Undercooled into the Metastable Miscibility Gap

A model has been developed to describe the microstructure evolution in the atomized droplets of Cu-Fe alloy during cooling through the metastable miscibility gap. Calculations have been performed for Cu85Fe15 alloy to investigate the process of liquid-liquid phase transformation. The numerical results indicate that the minority phase droplets are nucleated in a temperature region around the peak of the supersaturation. The average radius of the Fe-rlch droplets decreases and the number density of the minority phase droplets increases with decreasing the atomized droplet size. The simulated results were compared with the experimental ones. The kinetic process of the liquid-liquid phase transformation was discussed in detail.

Non-equilibrium microstructure and the metastable phase of Al-9.6wt%Mg Alloy solidification under high pressure

The non-equilibrium microstructure and a new metastable phase of Al-9.6wt%Mg alloy solidified at 6 GPa were studied by optical microscope,differential scanning calorimetry,X-ray diffraction and transmission electron microscope.The results showed that dendrite microstructure was refined,and the solid solubility of Mg in α-Al phase increased greatly.Correspondingly,the lattice parameter of α-Al phase increased.Al3Mg2 phases disappeared under high pressure solidification.In particular,a metastable phase with small size(20 nm or so) was produced in the alloy,its melting temperature range was 464～518.2 ℃,which was higher than that of Al3Mg2 phase(453～465 ℃) under normal pressure.These metastable phases located in the interdendritic position.It was the first time that the metastable phase was found in Al-Mg alloy at a high pressure of 6 GPa.The formation mechanism of the metastable phases was discussed.

Preparation and Properties of Cu-Containing High-entropy Alloy Nitride Films by Magnetron Sputtering on Titanium Alloy

Magnetron sputtering deposition with regulated Cu target power was used for depositing Cu-containing high-entropy alloy nitride(Cu-(HEA)N)films on TC4 titanium alloy substrates.The microscopic morphologies,surface compositions,and thicknesses of the films were characterized using SEM+EDS;the anti-corrosion,wear resistance and antibacterial properties of the films in simulated seawater were investigated.The experimental results show that all four Cu-(HEA)N films are uniformly dense and contained nanoparticles.The film with Cu doping come into contact with oxygen in the air to form cuprous oxide.The corrosion resistance of the(HEA)N film without Cu doping on titanium alloy is better than the films with Cu doping.The Cu-(HEA)N film with Cu target power of 16 W shows the best wear resistance and antibacterial performance,which is attributed to the fact that Cu can reduce the coefficient of friction and exacerbate corrosion,and the formation of cuprous oxide has antibacterial properties.The findings of this study provide insights for engineering applications of TC4 in the marine field.

Tribological Behaviors of Electroless Nickel-Boron Coating on Titanium Alloy Surface

Titanium alloys are excellent structural materials in engineering fields,but their poor tribological properties limit their further applications.Electroless plating is an effective method to enhance the tribological performance of alloys,but it is difficult to efficiently apply to titanium alloys,due to titanium alloy’s strong chemical activity.In this work,the electroless Nickel-Boron(Ni-B)coating was successfully deposited on the surface of titanium alloy(Ti-6AL-4V)via a new pre-treatment process.Then,linearly reciprocating sliding wear tests were performed to evaluate the tribological behaviors of titanium alloy and its electroless Ni-B coatings.It was found that the Ni-B coatings can decrease the wear rate of the titanium alloy from 19.89×10^(−3)mm^(3)to 0.41×10^(−3)mm^(3),which attributes to the much higher hardness of Ni-B coatings.After heat treatment,the hardness of Ni-B coating further increases corresponding to coating crystallization and hard phase formation.However,heat treatment does not improve the tribological performance of Ni-B coating,due to the fact that higher brittleness and more severe oxidative wear exacerbate the damage of heat-treated coatings.Furthermore,the Ni-B coatings heat-treated both in air and nitrogen almost present the same tribological performance.The finding of this work on electroless coating would further extend the practical applications of titanium alloys in the engineering fields.

A review on advances of high-throughput experimental technology for titanium alloys

Ti alloys,as leading lightweight and high-strength metallic materials,exhibit significant application potential in aerospace,marine engineering,biomedical,and other industries.However,the lack of fundamental understanding of the microstructure−property relationship results in prolonged research and development(R&D)cycles,hindering the optimization of the performance of Ti alloys.Recently,the advent of high-throughput experimental(HTE)technology has shown promise in facilitating the efficient and demand-driven development of next-generation Ti alloys.This work reviews the latest advancements in HTE technology for Ti alloys.The high-throughput preparation(HTP)techniques commonly used in the fabrication of Ti alloys are addressed,including diffusion multiple,additive manufacturing(AM),vapor deposition and others.The current applications of high-throughput characterization(HTC)techniques in Ti alloys are shown.Finally,the research achievements in HTE technology for Ti alloys are summarized and the challenges faced in their industrial application are discussed.