Two-phase Titanium Alloy Research Articles

Understanding the role of local texture variation on slip activity in a two-phase titanium alloy

During plastic deformation of engineering alloys with a hcp crystal structure, slip systems with different critical resolved shear stresses can be activated. In the case of two-phase titanium alloys such as Ti-6Al-4V, it is well established that various a→ and c→+a→ type slip systems can be activated in the α-phase, which dominates this alloy. However, their relative likelihood is less well established particularly when comparing prismatic a→ and basal a→ slip which are known to have similar critical resolved shear stress values. By combining EBSD-based grain orientation mapping and high-resolution digital image correlation, grain specific shear strain mapping and Burgers vector direction analysis was carried out after small levels of plasticity in two differently microtextured Ti-6Al-4V samples. This enabled the different types of strain heterogeneity and strain patterns to be linked to the underlying microstructure and microtexture. The detailed analysis shows that the dominance of a particular a→ type slip mode greatly varies with the local texture and that shear strain patterns extend across many grains when soft macrozones (clusters of similarly orientated grains) are present. The work highlights that the relative displacement ratio analysis significantly improves slip trace analysis in hcp crystals by reducing the cases of ambiguous solutions and that grain neighbourhood can have a greater impact on slip system activation than Schmid factor.

The Effect of TiN and DLC Anti-Wear Coatings on the Tribofilm Formation and Frictional Heat Phenomena in Coated Metals vs. WC-Co.

The aim of this work was to study the effect of anti-wear coatings on the selected frictional phenomena, i.a., frictional heating and tribofilm formation, of model tribological pairs. For this purpose, three popular metallic substrate materials were selected: AISI 316L and AISI 440B stainless steels, as well as Ti6Al4V two-phase titanium alloy. The substrates were tested in the dry sliding conditions in three states: uncoated, as well as titanium nitride (TiN) or diamond-like-carbon (DLC) coated. According to the results provided, under applied frictional conditions TiN coating, even if it is worn off the sample surface, contributes to excessive frictional heating of a tribological pair by altering the tribofilm formation. The analysis also showed that in some tribological pairs, rapid temperature alteration of a counter sample can be used to approximate the sliding distance after which the TiN coating becomes worn off. On the contrary, in all pairs tested, the DLC film became locally damaged, but it sustained its antifriction properties, contributing to low coefficients of friction (COFs) and the lowest frictional temperatures observed.

Effect of Annealing Process on Microstructure and Tensile Properties of TC16 Titanium Alloy after Rapid Heat Treatment

TC16 titanium alloy is a martensite α+β two-phase high strength titanium alloy, which can improve its structure and enhance properties through heat treatment. Effect of annealing process on microstructure and tensile properties of TC16 titanium alloy was investigated using optical microscope, scanning electron microscope and universe tensile test machine. The results show that when annealed at 720°C for 4h then furnace cooling to ambient temperature, the tensile strength of the TC16 alloy reaches nearly 900MPa,the elongation reaches 19.6% and the reduction of area reaches 65%, which present a good comprehensive performance.

Martensite Formation and Decomposition during Traditional and AM Processing of Two-Phase Titanium Alloys—An Overview

Titanium alloys have been considered as unique materials for many years. Even their microstructure and operational properties have been well known and described in details, the new technologies introduced—e.g., 3D printing—have restored the need for further research in this area. It is understood that martensitic transformation is usually applied in heat treatment of hardenable alloys (e.g., Fe alloys), but in the case of titanium alloys, it also occurs during the thermomechanical processing or advanced additive manufacturing. The paper summarizes previous knowledge on martensite formation and decomposition processes in two-phase titanium alloys. It emphasizes their important role in microstructure development during conventional and modern industrial processing.

Estimating single-crystal elastic constants of polycrystalline β metastable titanium alloy: A Bayesian inference analysis based on high energy X-ray diffraction and micromechanical modeling

A two-phase near-β titanium alloy (Ti–10V–2Fe–3Al, or Ti-1023) in its as-forged state is employed to illustrate the feasibility of a Bayesian framework to identify single-crystal elastic constants (SEC). High Energy X-ray diffraction (HE-XRD) obtained at the Diamond synchrotron source are used to characterize the evolution of lattice strains for various grain orientations during in situ specimen loading in the elastic regime. On the other hand, specimen behavior and grain deformation are estimated using the elastic self-consistent (ELSC) homogenization scheme. The XRD data and micromechanical modelling are revisited with a Bayesian framework. The effect of different material parameters (crystallographic and morphological textures, phase volume fraction) of the micromechanical model and the biases introduced by the XRD data on the identification of the SEC of the β phase are systematically investigated. In this respect, all the three cubic elastic constants of the β phase (C11β,C12β,C44β) in the Ti-1023 alloy have been derived with their uncertainties. The grain aspect ratio in the ELSC model, which is often not considered in the literature, is found to be an important parameter in affecting the identified SEC. The Bayesian inference suggests a high probability for non-spherical grains (aspect ratio of ∼3.8±0.8) : C11β=92.6±19.1GPa,C12β=82.5±16.3GPa,C44β=43.5±7.1GPa. The uncertainty obtained by Bayesian approach lies in the range of ~1-3 GPa for the shear modulus μ′=C11β−C12β2, and ~7 GPa for the shear modulus μ″=C44β, while it is significantly larger in the case of the bulk modulus C11β+2C12β3 (~17-24 GPa).

Efficiency of Microstructure Refinement in Ti-Based Alloys

The influence of various factors on the efficiency of microstructure refinement in two-phase titanium alloys with respect to a well-known Ti-6Al-4V alloy was discussed. The kinetics of microstructure evolution in titanium alloys with a lamellar type α/β microstructure during large plastic deformation depends mainly on temperature and strain rate, type of the initial microstructure, thickness of the α lamellae, path of deformation and chemical composition. Each parameter should be controlled to provide the most efficient microstructure refinement during conventional metalforming methods.

Constitutive Model of TC21 Titanium Alloy Based On BPNN

TC21 alloy is a new two-phase titanium alloy with good comprehensive properties of high strength, toughness and damage tolerance. The isothermal thermal compression deformation test of TC21 titanium alloy is carried out on the Gleeble-3500 thermal simulation test machine. Based on the stress-strain data at different temperatures and strain rates, the constitutive relation model of TC21 alloy was established by using BPNN(Back Propagation Neural Network), which has high prediction and generalization ability, and the predicted flow stress value is very close to the experimental data.

Structure and Properties of High-Strength Titanium Alloy Ti-6.5Al-3Mo-2.5V-4Nb-1Cr-1Fe-2.5Zr Welded Joints

As intensive work is underway in leading material science centers in the USA, EU, Russia, and China, both to modernize existing titanium alloys and to create new ones, the E.O. Paton Electric Welding Institute of the National Academy of Sciences of Ukraine developed titanium alloys T110 (Ti-5.5Al-1.2Mo-1.2V-4Nb-2Fe-0.5Zr system) and T120 (Ti-6.5Al-3Mo-2.5V-4Nb-1Cr-1Fe-2.5Zr system), which according to their characteristics, belong to the group of modern two-phase high-alloyed alloys characterized by high strength and good ductility. With more and more attention is being paid to the expansion in the usage of welded structures and assemblies of high strength titanium alloys with UTS ≥ 1100 MPa, there’s urgent need in studying best ways to obtain welded joints from such alloys. The weldability of two-phase high-alloyed titanium alloys, the use of which can give big reduction in structural weight, is significantly worse than low-alloyed alloys, therefore for a new alloy it is necessary to ensure the possibility of obtaining welded joints with a strength of at least 90% compared to the strength of base material. The aim of this work is to study the influence of the welding thermal cycle and reducing of weld metal alloying degree on the structure and mechanical properties of welded joints of high-strength titanium alloy Ti-6.5Al-3Mo-2.5V-4Nb-1Cr-1Fe-2.5Zr with tensile strength more than 1200 MPa, as well as assessment of it welded joints properties in comparison with other high-strength titanium alloys.

Comparison of Different Thermo-Chemical Treatments Methods of Ti-6Al-4V Alloy in Terms of Tribological and Corrosion Properties.

Titanium and its alloys are characterized by high mechanical strength, good corrosion resistance, high biocompatibility and relatively low Young’s modulus. For many years, one of the most commonly used and described titanium alloys has been Ti-6Al-4V. The great interest in this two-phase titanium alloy is due to the broad possibilities of shaping its mechanical and physico-chemical properties using modern surface engineering techniques. The high coefficient of friction and tendency to galling are the most important drawbacks limiting the application of this material in many areas. In this regard, such methods as carburizing, nitriding, oxidation, and the synthesis of thin films using physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods may significantly improve the tribological properties of titanium alloys. The influence of thermo-chemical treatment (oxidation, carburizing and nitriding) on tribological properties and corrosion resistance of Ti-6Al-4V alloy is presented in this paper. The results include metallographic studies, analysis of tribological and mechanical properties and corrosion resistance as well. They indicate significant improvements in mechanical properties manifested by a twofold increase in hardness and improved corrosion resistance for the oxidation process. The carburizing was most important for reducing the coefficient of friction and wear rate. The nitriding process had the least effect on the properties of Ti-6Al-4V alloy.

Revisiting the lamellar globularization behavior of a two-phase titanium alloy from the perspective of deformation modes

Abstract The correlation between lamellar globularization and deformation modes during the primary hot processing of titanium alloy was evaluated by means of uniaxial compression, tension, torsion and plane strain compression tests. The microstructure evolution features and underlying globularization mechanisms were comparatively studied via Electron Backscattered Diffraction technique. Noticeable divergences of globularization response are captured in different deformation modes, especially for the globularized fractions and the critical strain. In the face of the strain applied is less than the critical globularization value (0.4−0.63) under uniaxial compression, the lamellae can be still globularized under tension or torsion deformation. But the growth rate of globularized fraction is more sluggish under tension than that under torsion deformation. The lamellae separation at early tension deformation preferentially occurs at junctions of lamellae without destroying Burgers Orientation relationship and significant orientation fluctuation. Shear deformation can facilitate the formation of intra-α boundaries and its distribution uniformity, which could make the lamellae grow up into globularized particles and improve the globularization heterogeneity. It is envisaged that the results obtained can provide guidance for the technology scheme and route design of primary hot working of titanium alloy aiming at the homogeneous equiaxed grains.

A dislocation-based model for the microstructure evolution and the flow stress of a Ti5553 alloy

The plastic deformation at high temperatures of two-phase titanium alloys is modelled using a mesoscale approach to describe the complex interactions between different populations of dislocation densities. The static and dynamic recovery, as well as of continuous dynamic recrystallization, is modelled. The flow stresses of both α and β phases are calculated using constitutive equations combined with a load partitioning model between the α and β phases. The dislocation populations are separated into three categories, named mobile, immobile and walls, and separated rate equations are developed for each reaction between them. Several microstructure features are calculated, such as mean subgrain size, grain size, dislocation densities and boundary misorientation. Additionally, glide velocity is also estimated. Hot compression experiments of a Ti-5553 alloy at temperatures between 1073 K and 1193 K and strain rates between 0.001 s−1 and 10 s−1 are used for validation. The flow softening observed in the α+β domain is attributed to the change in load partitioning. Moreover, the decrease in grain and subgrain size with the increase in strain rate and decrease in temperature is well predicted by the proposed model as well as the evolution of a fully static recrystallized microstructure into a continuous dynamic recrystallized one.

Rheological Behavior of a VT23 Alloy during Deformation in a Wide Temperature Range

Upsetting tests of a two-phase VT23 titanium alloy are carried out in the temperature range 700–1200°C. The phase composition of the alloy after deformation on a plastometer is studied by X-ray diffraction. Experimental plastic flow curves are plotted.

Severe plastic deformation induced precipitation of the ordered α2-Ti3Al phase in Ti–5Al–2Sn–2Zr–4Mo–4Cr

The typical two-phase titanium alloy of Ti–5Al–2Sn–2Zr–4Mo–4Cr was subjected to severe plastic deformation (SPD) by using high energy shot peening (HESP) at room temperature. Here, we experimentally investigated the SPD-induced atomic diffusion and phase transformation in the HESP processed Ti–5Al–2Sn–2Zr–4Mo–4Cr. The experimental results revealed that the ellipsoid-shaped precipitates with about 30–50 nm in thickness occurred in the surface layer of the HESP processed Ti–5Al–2Sn–2Zr–4Mo–4Cr, which was characterized to be the ordered α2-Ti3Al phase with the D019 crystal structure. The underlying formation mechanism of these ordered α2-Ti3Al precipitates was attributed to the SPD-induced atomic diffusion behaviors at room temperature, i.e., SPD-induced diffusive phase transformation, significantly different from the conventional ordering transformation driven by thermodynamics at high temperature. During HESP, the extremely high stress and strain level provided the potential conditions for precipitation of α2-Ti3Al phase; meanwhile, the generation of high-density dislocations accelerated the atomic diffusion, thereby promoting the nucleation of α2-Ti3Al phase. Furthermore, the significant reduction of grain size to nanometer contributed to the stability of α2-Ti3Al phase at room temperature.

Enhanced formability and forming efficiency for two-phase titanium alloys by Fast light Alloys Stamping Technology (FAST)

During hot stamping of titanium alloys, insufficient forming temperatures result in limited material formability, whereas temperatures approaching the β phase transus also result in reduced formability due to phase transformation, grain coarsening and oxidation during the long-time heating. To solve this problem, Fast light Alloys Stamping Technology (FAST) is proposed in this paper, where fast heating is employed. Effects of heating parameters on the formability and post-form strength were studied by tensile tests. Forming of a wing stiffener was performed to validate this new process. Results show that microstructure of TC4 alloy after fast heating was in nonequilibrium state, which could enhance ductility significantly compared with the equilibrium state. When TC4 alloy was first heated to 950 °C with heating rate of 100 °C/s and then cooled to 700 °C, the elongation at 700 °C was more than 3 times that of a slow heating rate with soaking. Nano-scaled martensite with high dislocation density transformed from β phase was observed under fast heating condition. A complex shaped wing stiffener was successfully formed from TC4 titanium alloy in less than 70 s including heating, transfer and forming, and the post-form strength was almost the same with the initial blank.

Effect of grinding parameters on microstructure evolution of TC21 titanium alloy with bimodal starting microstructure

Abstract This study aims to investigate the deformation behavior of two-phase titanium alloy Ti–6Al–3Mo–2Zr–2Sn–2Nb–1Cr (TC21) during grind hardening (GH) process. According to dynamic material modeling (DMM) combine Kumar’s instability criterion, the processing maps were constructed to discuss processing properties of material. Results suggest that the ideal processing region is in the temperature of 880 °C, strain rate range 10−3-0.03s−1. The evolution mechanism of α phase was revealed using TEM microstructural analysis under different grinding conditions. It is interesting that, some secondary-precipitated α phase with approximate orientation usually combine to form lamellar α colonies, while some ones with different orientations split to short rod-like or globular structure particularly at higher grinding depth. The optimum grinding parameters for TC21 is at grinding depth range 60–90 μm, wheel speed of 20 m s−1 followed by aging treatment. Most of all, the GH technology has a significantly advantage than heat treatment for exhibiting higher micro-hardness and lower friction coefficient.

The influence of heat treatment on the formation of the structure and the level of mechanical properties of high-alloyed titanium alloy

The paper investigates the possibility of increasing the strength of the experimental high-alloyed titanium alloy due to various methods of thermal action, leading to a change in its phase composition and intragrain structure. Changes in mechanical properties in correlation with the change in structure in the annealed, tempered and heat-hardened state are reviewed. It is shown that by controlling phase transformations in highalloyed two-phase titanium alloys, it is possible to realize high-strength state with satisfactory plastic characteristics. The optimal complex of mechanical properties is provided by heat treatment, which leads to the creation of a two-phase heterogeneous structure with a developed bimodal intragrain structure.

Comparison of sub-grain scale digital image correlation calculated using commercial and open-source software packages

High-resolution strain mapping is an increasingly prominent technique for characterising the deformation behaviour of metals. In this study, HRDIC analysis was performed on materials exhibiting either more or less intense planar slip, using different software packages to highlight any issues that might arise depending on the algorithm that is used to calculate the displacements. The differences between the algorithms were investigated using frequency distributions, strain profiling and Burgers vector direction analysis to determine their significance in terms of any subsequent interpretation of the data. A dilute zirconium alloy showed maximum strain concentrations of <4.5 and similar to previous comparison studies of different software packages on optical images, little difference was observed in the resulting strain maps. However, in a more highly alloyed two-phase titanium alloy with significant planar slip and strain values of up to 20 times the applied strain, one of the algorithms had difficulty tracking the features particularly at low strains when the difference between the strain in a slip trace is markedly higher than that in the neighbouring region. The consequences of inaccurate displacement data around a slip trace region were highlighted by an incorrect prediction of the Burgers vector when using the relative displacement ratio for slip system identification.

Understanding the Role of Local Texture Variation on Slip Activity in a Two-Phase Titanium Alloy

During plastic deformation of engineering alloys with a hcp crystal structure, slip systems with different critical resolved shear stresses can be activated. In the case of a two-phase titanium alloys such as Ti-6Al-4V, it is well established that various [[EQUATION]] and [[EQUATION]] type slip systems can be activated in the α-phase, which dominates this alloy. However, their relative likelihood is less well established particularly when comparing prismatic [[EQUATION]] and basal [[EQUATION]] slip which are known to have similar critical resolved shear stress values. By combining EBSD-based grain orientation mapping and high-resolution digital image correlation, grain specific shear strain mapping and Burgers vector direction analysis was carried out after small levels of plasticity in two differently microtextured Ti-6Al-4V samples. This enabled the different types of strain heterogeneity and strain patterns to be linked to the underlying microstructure and microtexture. The detailed analysis shows that the dominance of a particular [[EQUATION]] type slip mode greatly varies with the local texture and that shear strain patterns extend across many grains when soft macrozones (clusters of similarly orientated grains) are present. The work highlights that the relative displacement ratio analysis significantly improves slip trace analysis in hcp crystals by reducing the cases of ambiguous solutions and that grain neighbourhood can have a greater impact on slip system activation than Schmid factor.

Cyclic creep behaviour of two-phase Ti-6Al-2Mo-2Cr alloy

One of the important criteria for selection titanium alloys for discs and blades of turbine engine compressor is their fatigue and creep strength at room and elevated temperature. Fatigue and creep properties of two-phase titanium alloys show strong dependence on microstructure, especially morphology of the α and β phases which can be controlled to certain extent by proper selection of hot working and heat treatment conditions. Quantitative description of two-phase titanium alloys behaviour under loading and environmental conditions leading to combined creep and fatigue processes has been always very challenging task due to large number of factors affecting deformation and fracture behaviour of the material. In the course of the research cyclic creep behaviour of Ti-6Al-2Mo-2Cr alloy (VT3-1) was investigated and compared to low-cycle fatigue and static creep properties at the temperature of 450°C. Microstructure of the alloy was varied by means of the heat treatment. Constant load tensile creep tests were carried out. Tension-tension cyclic loading was applied at the constant stress ratio with and without hold time at maximum load. The effect of test parameters on the creep-fatigue life at elevated temperature was estimated. Characteristic features of fracture surfaces were identified by scanning electron microscopy methods.

The heterogeneous globularization related to crystal and geometrical orientation of two-phase titanium alloys with a colony microstructure

Understanding the heterogeneous globularization phenomena and the underlying mechanisms is important to process design for primary hot working of titanium alloys. To this end, hot compression of a TA15 titanium alloy with initially colony structure was carried out at 900 °C and strain rate of 0.1 s−1 on a Gleeble thermal simulator. Comprehensive electron back scatter diffraction (EBSD) examination was conducted to check how the heterogeneous microstructural developments were affected by the geometrical and crystal orientations of the colony. A crystal plasticity model was employed to quantify the heterogeneous deformation and orientation evolution during compression. The heterogeneous globularization behavior is interpreted from the orientation perspective by relating the orientation spread within alpha lamellae to the slip activation, strain partitioning in the constituent phases as well as microstructural phenomena such as deformation banding and dynamic recrystallization. The activation of the prism and basal slips in alpha phase and strain partitioning between the alpha and beta phases would enhance the orientation spread, which accounts for the relatively high globularization efficiency in inclined colonies.