Microstructure Of Titanium Alloy Research Articles

Analysis of the Elevated Temperature Plastic Flow Response of Ti-6Al-4V Produced via the Hydrogen Sintering and Phase Transformation (HSPT) Process

An analysis pertaining to hot deformation behavior was conducted on two unique titanium alloy microstructures. Each product was manufactured from commercially available blended elemental Ti-6Al-4V powder, consolidated by sintering in vacuum or hydrogen. The initial microstructures produced by these distinctive sintering atmospheres are represented by a coarse lamellar structure (produced by vacuum sintering) and a very fine lamellar structure [produced by Hydrogen Sintering Phase Transformation (HSPT)]. Performance of these materials was assessed by simulating representative titanium breakdown and conversion during thermomechanical processing through elevated temperature compression testing on a Gleeble® 3500 Hydrawedge II® system. Compression tests were performed on cylindrical specimens at sub and near-transus temperatures (850 °C, 900 °C, 950 °C, and 1000 °C) and at moderate strain rates of 0.01 and 0.10 s−1. The very fine lamellar microstructure exhibited similar flow behavior compared to the coarse lamellar structure, although with a typically slightly higher peak stress and greater degree of flow softening. In addition, the microstructure produced by HSPT retained a fine, equiaxed structure upon deformation, making it highly suitable for powder-based thermomechanically processed titanium alloy products.

Microstructure of titanium alloy modified by high-intensity implantation of low- and high-energy aluminium ions

This study focuses on the analysis of microstructural, elemental and phase compositions of surface and near-surface layers of titanium after the implantation of aluminium. A titanium alloy with a chemical composition close to commercially pure titanium (grade 2) was used as the target material. Ion implantation was performed using two modes of irradiation: 1. repetitively pulsed ion beams with a mean ion energy of 35 keV; 2. low-energy-focused ion beams of high intensity with a mean ion energy of 2.6 keV. The irradiation fluence reached 1.1 × 1018 ion/cm2 using the first mode and 1.6 × 1021 ion/cm2 using the second mode. In both cases, the beam itself heated the targets. The peak concentration of aluminium after the implantation of medium-energy ions was ~65 at.%, and the maximum depth of dopant penetration was 2.6 μm. On the contrary, in the case of high-intensity low-energy ion implantation, the surface concentration of dopant reached a maximum of 25 at.%, but the depth of penetration increased significantly and achieved 50 μm. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that fine-grained intermetallic phases, Ti3Al and TiAl, and solid solutions of various compositions were possibly formed after the medium-energy ion implantation. The mean grain size of the intermetallic phases was ~50 nm. XRD and TEM analyses in the case of low-energy high-intensity ion implantation demonstrated the formation of the ion-alloyed layer, which comprised intermetallic phase Ti3Al and solid solutions of aluminium in titanium. The grain size of Ti3Al phase can be 5 μm and more.

Quantitative analysis of interleaved degree in lamellar microstructure of titanium alloys

To establish the relationship between mechanical properties and microstructural features, it is necessary to comprehensively describe microstructural characterizations. In present study, an efficient and innovative quantitative method of interleaved degree in lamellar microstructure was developed. Firstly, four types of microstructural variables were defined as key factors that confirmed the microstructural features. Lath length (L) and variation coefficient for distribution of lath angle (CV) were measured to obtain dimension information of laths, and number of lath intersecting points per area (N) and uniformity of lath intersecting points (U) were defined to describe the lath distribution and the lath intersection complexity. Then, the microstructural variables were normalized based on multiple attribute decision-making. Finally, the equation of interleaved degree in lamellar microstructure was established based on entropy weight method. Present quantitative method was applied to analyze the interleaved degree of TC17 alloy containing a basketweave microstructure. It was shown that interleaved degree was higher at a deformation temperature of 930 °C, a height reduction of 40% and a strain rate of 0.1 s−1 and decreased with increasing cooling time. Besides, a model that can theoretically calculate fracture toughness based on tensile properties was utilized to prove the prediction ability of interleaved degree.

Recognition and Quantification of Dual Phase Titanium Alloy Microstructures Using Convolutional Neural Networks

Recent advances in machine learning and image recognition tools/methods are being used to address fundamental challenges in materials engineering, such as the automated extraction of statistical information from dual phase titanium alloy microstructure images to support rapid engineering decision making. Initially, this work was performed by extracting dense layer outputs from a pretrained convolutional neural network (CNN), running the high dimensional image vectors through a principal component analysis, and fitting a logistic regression model for image classification. Kfold cross validation results reported a mean validation accuracy of 83% over 19 different material pedigrees. Furthermore, it was shown that fine-tuning the pre-trained network was able to improve image classification accuracy by nearly 10% over the baseline. These image classification models were then used to determine and justify statistically equivalent representative volume elements (SERVE). Lastly, a convolutional neural network was trained and validated to make quantitative predictions from a synthetic and real, two-phase image datasets. This paper explores the application of convolutional neural networks for microstructure analysis in the context of aerospace engineering and material quality.

О влиянии скорости деформирования на механическое поведение сплава титана Ti–3,5Al–1,1Zr–2,5V при растяжении

The authors studied the rate dependence of the deformation behavior of the circular section samples prepared from the Ti-3.5Al-1.1Zr-2.5V alloy under the uniaxial tension at room temperature. Samples 200 mm long were divided into three groups of five pieces each. The authors tested the first group of samples at a traverse rate of 0.05 mm/min, the second group - at a rate of 5mm/min, and the third group - at a rate of 500 mm/min. The evaluation of the titanium alloy microstructure in the undeformed state showed that the average grain size of the titanium α-phase was about 7 μm, and the grain boundaries were mostly angular, i.e. the neighboring grains were disordered by more than 15°. The mechanical tests showed that the nature of the titanium alloy deformation behavior did not depend on the loading rate. Despite this, the yield and strength limit increased with an increase in the strain rate, while the total strain value decreased. At the place of sample fracture, a neck was observed. The contraction coefficient did not depend on the tensile speed. The authors did not observe any qualitative changes in the mechanical behavior nature and the morphology of the surface of sample fractures (a cup fracture typical for viscous fracture). The study of samples microstructure justifies an increase in the deformability of samples with a decrease in the tensile rate. The width of the diffraction peaks of the samples tested at a lower speed was greater. The fluctuation of the obtained values of the diffraction lines’ width relative to the approximating straight line indicates the speed sensitivity of the grains of “hard” and “soft” orientations. This indicated the existence of the slip system activation sequence. Thus, first of all, “soft” grains are loaded, which are favorably oriented for easy prismatic sliding in the (100) and (110) planes. Then they harden, which contributes to the redistribution of the load on the “hard” grains with basic normals close to the axis of loading, which, at the initial stage, were deformed elastically.

Technological parameters for the production of steel and titanium blanks by the method of helical rolling

The article is devoted to the technology of producing steel and titanium blanks by the method of cross-helical rolling. The grades of the investigated alloys and technological processing modes are given. Studies of the effect of rolling parameters (deformation temperature, feed angle) on the production of round billets are presented. The general nature of the influence of technological factors of the process on the conditions of metal deformation is established. The change in the microstructure of titanium alloys after hot deformation was investigated. The expediency of using this method is substantiated.

Temperature and Microstructure Evolution in Gas Tungsten Arc Welding Wire Feed Additive Manufacturing of Ti-6Al-4V.

In the present study, the gas tungsten arc welding wire feed additive manufacturing process is simulated and its final microstructure predicted by microstructural modelling, which is validated by microstructural characterization. The Finite Element Method is used to solve the temperature field and microstructural evolution during a gas tungsten arc welding wire feed additive manufacturing process. The microstructure of titanium alloy Ti-6Al-4V is computed based on the temperature evolution in a density-based approach and coupled to a model that predicts the thickness of the α lath morphology. The work presented herein includes the first coupling of the process simulation and microstructural modelling, which have been studied separately in previous work by the authors. In addition, the results from simulations are presented and validated with qualitative and quantitative microstructural analyses. The coupling of the process simulation and microstructural modeling indicate promising results, since the microstructural analysis shows good agreement with the predicted alpha lath size.

Characterization of Microstructure and Texture Evolution in Ti664 Titanium Alloy After Multidirectional Forging and Annealing Treatments

In previous investigations, it was demonstrated that texturing of the microstructure in titanium alloy inevitably occurs after forging in one direction. In this work, the influence of multidirectional forging and annealing on the heterogeneity of the microstructure and crystallographic orientation of a new α + β titanium alloy (Ti-6Al-6Mo-4V) has been studied. A heterogeneous orientation distribution and morphology was observed in the microstructure, containing matrix β grains and α lamellae elongated along the deformation direction after multidirectional forging. Meanwhile, significant //axial direction (AD) and //AD textures were formed because of the special deformation mode. After annealing at 825°C, a more homogeneous microstructure was obtained, but the annealing had a limited effect on the texture components. The same texture components were found because of the texture inheritance effect, and the variation of the texture intensity contributed to the grain dissolution and recrystallization effect during subsequent annealing.

Microstructural effects on strain rate and dwell sensitivity in dual-phase titanium alloys

In this study, stress relaxation tests are performed to determine and compare the strain rate sensitivity of different α−β titanium alloy microstructures using discrete dislocation plasticity (DDP) and crystal plasticity finite element (CPFE) simulations. The anisotropic α and β phase properties of alloy Ti-6242 are explicitly included in both the thermally-activated DDP and CPFE models together with direct dislocation penetration across material-interfaces in the DDP model. Equiaxed pure α, colony, Widmanstatten and basketweave microstructures are simulated together with an analysis of the effect of α grain size and dislocation penetration on rate sensitivity. It is demonstrated that alloy morphology and texture significantly influence microstructural material rate sensitivity in agreement with experimental evidence in the literature, whereas dislocation penetration is found not to be as significant as previously considered for small deformations. The mechanistic cause of these effects is argued to be changes in dislocation mean free path and the total propensity for plastic slip in the specimen. Comparing DDP results with corresponding CPFE simulations, it is shown that discrete aspects of slip and hardening mechanisms have to be accounted for to capture experimentally observed rate sensitivity. Finally, the dwell sensitivity in a polycrystalline dual-phase titanium alloy specimen is shown to be strongly dependent on its microstructure.

Research on Three-Roll Screw Rolling Process for Ti6Al4V Titanium Alloy Bar

Abstract The effects of both the microstructure and the original grain size on three-roll screw rolling process of Ti6Al4V titanium alloy bar were studied in the present work. The microstructure of Ti6Al4V titanium bar had a great influence on the mechanical properties of the rolling bar. When the original size was large, the grains were apparently refined but the microstructure was uneven. But for semi-finished titanium bar composed of fine equiaxed grains, the grains after rolling were fine and uniform. During the rolling process, the Ti6Al4V titanium alloy microstructure changed from equiaxed structure to the basket-weave one. After annealing at 800℃ for 1.5 hours and then cooling in air, the average tensile strength decreased from 984 MPa to 964 MPa; while after annealing at 950℃ for 1.5 hours and then cooling by water, and aging at 540℃ for 6 hours then cooling by air, the average tensile strength increased from 979 MPa to 1107 MPa.

A Data Analytics Approach to Discovering Unique Microstructural Configurations Susceptible to Fatigue

Principal component analysis and fuzzy c-means clustering algorithms were applied to slip-induced strain and geometric metric data in an attempt to discover unique microstructural configurations and their frequencies of occurrence in statistically representative instantiations of a titanium alloy microstructure. Grain-averaged fatigue indicator parameters were calculated for the same instantiation. The fatigue indicator parameters strongly correlated with the spatial location of the microstructural configurations in the principal components space. The fuzzy c-means clustering method identified clusters of data that varied in terms of their average fatigue indicator parameters. Furthermore, the number of points in each cluster was inversely correlated to the average fatigue indicator parameter. This analysis demonstrates that data-driven methods have significant potential for providing unbiased determination of unique microstructural configurations and their frequencies of occurrence in a given volume from the point of view of strain localization and fatigue crack initiation.

Crystallographic orientation evolution during the development of tri-modal microstructure in the hot working of TA15 titanium alloy

The crystallographic orientation evolution and its dependence on processing parameters during the development of tri-modal microstructure of titanium alloy were studied by the thermal-mechanical processing tests and electron backscatter diffraction (EBSD) examination. It is found that the development of tri-modal microstructure undergoes two stages: firstly, bimodal microstructure consisting of equiaxed α (αp) and transformed β matrix (βt: a mix of secondary α phase (αs) and β phase) is formed after first-stage near-β forging; then, the tri-modal microstructure consisting of αp, lamellar α phase (αl) and βt are obtained after the following heat treatment. The equiaxed α in final tri-modal microstructure does not follow the Burgers orientation relationship (OR) with β phase. Its crystallographic orientation is hardly influenced by the hot processing parameters. The lamellar α in tri-modal microstructure is right the undissolved secondary α of bimodal microstructure (obtained after first step) during the heating process of the second step. Both of them keep the Burgers OR with β phase, however, the dissolution of secondary α present selectivity to some extent making the variant selection degree of lamellar α greater than that of secondary α. The variant selection degree of lamellar α in tri-modal microstructure decreases with increasing the cooling rate, deformation degree and strain rate of near-β forging. The secondary α in tri-modal microstructure is precipitated from β phase and obeys the Burgers OR with β phase during the cooling process of the second step. The existing lamellar α plays a strengthening role in the variant selection during its precipitation. While the cooling rate, deformation degree and strain rate of near-β forging show limited effect on the probabilities of each type of misorientation and variant selection degree of secondary α.

Microstructure characterization and nano & micro hardness of tri-modal microstructure of titanium alloy under different hot working conditions

In this work, the dependences of tri-modal microstructure parameters and corresponding nano & micro hardness on through-process processing parameters were quantitatively studied during the three-step thermo-mechanical processing of TA15 titanium alloy. It is found that the processing parameters of first step, especially for the deformation temperature and strain rate, mainly affect primary equiaxed α (αp) through the α→β phase transformation and the competition between dynamic recovery and dynamic recrystallization. The second processing step primarily affects the content and thickness of lamellar α (αl). In the third processing step, compared with low-temperature aging, normal annealing provides sufficient driving force for αl and secondary lamellar α (αs) growing, which leads to thicker αl and αs. As for the nano & micro hardness, in one sample undergoing different process, transformed β matrix (βt) is always harder than αl and αs due to the interfacial-strengthening effect. In addition, with increasing strain rate of the first step, αp becomes harder due to the constantly enhanced work hardening effect while the hardness of βt varies little because of the competition between interfacial strengthening and distribution disorder degree. However, the nano hardness of αl decreases firstly and then increases with strain rate, which presents the same trend with the micro hardness of integrated hardness at different processing conditions.

Surface chemistry and microstructure of metallic biomaterials for hip and knee endoprostheses

The surface chemistry and microstructures of titanium alloys (both new and used) and CoCrMo alloys used for hip and knee endoprostheses were determined using SEM (morphology), EBSD (phase analysis), AES and XPS (surface chemistry). Two new and two used endoprostheses were studied. The SEM SE and BE images showed their microstructures, while the EBSD provided the phases of the materials. During the production of the hip and knee endoprostheses, these materials are subject to severe thermomechanical treatments and physicochemical processes that are decisive for CoCrMo alloys.The AES and XPS results showed that thin oxide films on (a) Ti6Al4V are primarily a mixture of TiO2 with a small amount of Al2O3, while the V is depleted, (b) Ti6Al7Nb is primarily a mixture of TiO2 with a small amount of Al2O3 and Nb2O5, and (c) the CoCrMo alloy is primarily a mixture of Cr2O3 with small amounts of Co and Mo oxides.The thin oxide film on the CoCrMo alloy should prevent intergranular corrosion and improve the biocompatibility. The thin oxide films on the Ti alloys prevent further corrosion, improve the biocompatibility, and affect the osseointegration.

TC4 Titanium Alloy Microstructure and Properties Influenced by High Frequency Scan of Electron Beam

In order to improve the HV hardness and microstructure on the surface of TC4 titanium alloy, the high frequency scan of electron beam (EB) was introduced to treat TC4 titanium alloy. For excellent parameters, the EB energy, focus current and scan times, which will influence the HV hardness and microstructures, were studied. After high frequency scan of electron beam treatment, the HV hardness, modified layer depth and microstructures of TC4 titanium alloy were analyzed. Results show that the HV hardness on the TC4 surface treated by the high frequency scan of electron beam can be increased by almost 40 MPa compared with that of the original material. With improved energy of EB, the depth layer influenced is increased. The focus current adjusted in a narrow range can acquire comparatively better HV hardness on the surface. When the scan times are increased, the HV hardness decreases, and the grains grow up.

The Influence of the Technological Parameters of Rolling in the Helical Rollers and Longitudinal Wedge Mill on the Quality of Two-Phase Titanium Alloy

This article presents a new technology of obtaining the flat products with an ultrafine structure. The ultrafine-grained structure is obtained by using severe plastic deformation which is developed by the helical rollers. The stress-strain state (SSS) of the workpiece during rolling process in the helical rollers and longitudinal wedge mill is investigated in this scientific paper. The quantitative data has been obtained by the finite element method and MSC.SuperForge software; as well as the basic SSS distribution patterns, the temperature in simulating the rolling in the helical rollers and longitudinal wedge mill with different number of passes and the single reduction have been established. The rational technology of rolling the two-phase titanium alloys was developed and tested in the laboratory. The special attention is paid to analysis of the influence of the rolling conditions in the helical rollers and longitudinal wedge mill on the formation of VT6 titanium alloy microstructure.

Effect of ion beam treatment (Ar+, E = 30 keV) on the microstructure of titanium alloys

The effect of continuous Ar+ ion beams (E = 30 keV, j = 400 μA/cm2; F = 5·1016 cm-2) on the hardness and microstructure of the Gr2-titanium-based and Ti-6Al-4V alloys after cold working and subsequent recrystallization annealing is studied. It has been found that the initial microstructure of the annealed alloys in the equilibrium state, which consisted of recrystallized equiaxed grains, does not change after irradiation; thus the hardness of the irradiated samples is comparable with that of the initial samples. The initial fine fiber structure of the deformed Ti-6Al-4V alloy changes insignificantly after both annealing (T = 790°C, 30 min) and ion irradiation under used conditions. In contrast to that, the effect of rapid radiation annealing of the cold-worked titanium Gr2 alloy with beams of accelerated ions of inert gas at low temperatures (lower by 130°C than the conventional annealing temperature of these alloys at 680°C) and for a shorter time (9 min instead of 35 min, τirr ∼ 20 s) has been revealed. The result is the formation of a uniform recrystallized structure with equiaxed fine grains 5-10 μm in size in the entire volume of the 3-mm-thick samples, despite the fact that the average projected range of 30-keV Ar+ ions in titanium is only 20 nm.

Effect of Different Heat Treatments on Microstructure and Mechanical Properties of Ti6Al4V Titanium Alloy

This paper analyzed the microstructure of Ti6Al4V titanium alloy after different heat treatments. The tensile experiment and instrumented impact test were performed. The relationship among the microstructure, impact fracture characteristic and mechanical properties was analyzed by metallurgical microscope and environment scanning electron microscope (ESEM). Results show that the microstructure, mechanical properties and impact toughness of Ti6Al4V titanium alloy are affected by the solution and aging treatment. The yield strength and ultimate tensile strength are improved remarkably. The ductility increases firstly, and then decrease. The good comprehensive properties can be obtained when the Ti6Al4V titanium alloy is treated under the condition of 960 °C/1 h + WQ and 500 °C/4 h + AC. σ0.2 is 1050 MPa, σb is 1120 MPa and Ak is 46.22 J·cm−2. The microstructure of the titanium alloy after solution and aging treatment consists of the β matrix and the precipitation of the α-phase. The lamellar β-phase and the α-phase structure of the small needle plexiform can enhance comprehensive properties.

Selective laser melting of titanium alloy: investigation of mechanical properties and microstructure

This article presents the mechanical properties and microstructure of titanium alloy after selective laser melting (SLM). Titanium alloys are ideal material for selective laser melting (SLM), because they are expensive and difficult to machinery using traditional technologies. The application of SLM in the biomedical area has been slow due to the stringent performance criteria and concerns related to personification and part quality. In this article we focused on the manufacture by SLM and determination of microstructure and mechanical properties of titanium alloy (Ti Grade 2 Powder) using tensile tests and X-ray diffraction. The results reveal that the alloy exhibits a pronounced the homogeneous microstructure and high mechanical strength.

Fatigue hot spot simulation for two Widmanstätten titanium microstructures

A simulated microstructure-sensitive fatigue study has been performed for two titanium alloy microstructures. The investigated materials exhibit a Widmanstätten structure and include the α–β alloy Ti–6Al–4V and the near β alloy Ti-18 in a β-annealed, slow-cooled, and aged condition (BASCA). In other work [1], crystal plasticity models implemented into ABAQUS (2011) [2] UserMATerial subroutines have been calibrated to experimental cyclic deformation data for both materials. The current study utilizes calibrated crystal plasticity models to simulate fatigue loading of varying microstructures for each material to study the influence of key morphological and crystallographic aspects on the fatigue performance, e.g., the mean colony size, phase volume fraction, and crystallographic texture. Localized stress and plastic strain are studied via computation of fatigue indicator parameters (FIPs), which represent the driving force for fatigue crack formation and early propagation in the microstructure. The maximum FIP values are sampled over several stochastic simulations and are utilized to determine extreme value statistical distributions which demonstrate the trends in the microstructural influence on fatigue performance. Marked radial correlation functions developed by Przybyla and McDowell [3] have also been employed to study the correlation between favorably oriented slip systems and the extreme value FIP locations within the instantiated microstructures. The simulation results suggest that reduced lamellar colony sizes, reduced α-phase, and a transverse texture within a reference plane normal to the applied uniaxial loading direction can enhance resistance to formation and early growth of fatigue cracks.