Ti64 Alloy Research Articles

Coupling CALPHAD Method and Entropy-Driven Design for the Development of an Advanced Lightweight High-Temperature Al-Ti-Ta Alloy

In this study, a new lightweight Al-Ti-Ta alloy was developed through a synergistic approach, combining CALPHAD methodology and entropy-driven design. Following compositional optimization, the Al87.5Ti6.25Ta6.25 (at.%) alloy was fabricated and isothermally heat-treated at 475 °C for 24 h to attain equilibrium. X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) analyses revealed a dual-phase microstructure comprising a 50 vol.% FCC matrix enriched in Al and 50 vol.% Al3(Ti,Ta)-type intermetallic phase (IP). Notably, the FCC phase exhibited a high-melting transition temperature of 660 °C, surpassing conventional Al-Si cast alloys. Phase-specific nanomechanical properties were evaluated using Nanoindentation. Microindentation tests demonstrated exceptional microhardness of approximately 3300 MPa. These results indicate the alloy’s superior hardness compared to conventional alloys such as Al-Si (A390), 7075 Al alloy, and CP-Ti, even exceeding Ti-64 alloy at a 15% lower density. The alloy’s stability under prolonged heat treatment at 475 °C, reflected by stable phases, microstructure, and mechanical properties, highlights its enhanced thermal stability, which can be attributed to entropy-driven phase stabilization. This study underscores the effectiveness of integrating entropy-driven design strategy with CALPHAD predictions for the accelerated development of advanced Al-based alloys.

Modeling complex polycrystalline alloys using a Generative Adversarial Network enabled computational platform

Creating statistically equivalent virtual microstructures (SEVM) for polycrystalline materials with complex microstructures that encompass multi-modal morphological and crystallographic distributions is a challenging enterprise. Cold spray-formed (CSF) AA7050 alloy containing coarse-grained prior particles and ultra-fine grains (UFG) and additively manufactured (AM) Ti64 alloys with alpha laths in beta substrates. The paper introduces an approach strategically integrating a Generative Adversarial Network (GAN) for multi-modal microstructures with a synthetic microstructure builder DREAM.3D for packing grains conforming to statistics in electron backscatter diffraction (EBSD) maps for generating SEVMs of CSF and AM alloy microstructures. A robust multiscale model is subsequently developed for self-consistent coupling of crystal plasticity finite element model (CPFEM) for coarse-grained crystals with an upscaled constitutive model for UFGs. Sub-volume elements are simulated for efficient computations and their responses are averaged for overall stress-strain response. The methods developed are important for image-based micromechanical modeling that is necessary for microstructure-property relations.

Assessment on heat treatment and machinability of DMLS-processed Ti64 alloy

Assessment on heat treatment and machinability of DMLS-processed Ti64 alloy

Influence of Al and Ti Alloying and Annealing on the Microstructure and Compressive Properties of Cr-Fe-Ni Multi-Principal Element Alloy

This study meticulously examines the influence of aluminum (Al) and titanium (Ti) on the genesis of self-generated ordered phases in high-entropy alloys (HEAs), a class of materials that has garnered considerable attention due to their exceptional multifunctionality and versatile compositional palette. By meticulously tuning the concentrations of Al and Ti, this research delves into the modulation of the in situ self-generated ordered phases’ quantity and distribution within the alloy matrix. The annealing heat treatment outcomes revealed that the strategic incorporation of Al and Ti elements facilitates a phase transformation in the Cr-Fe-Ni medium-entropy alloy, transitioning from a BCC (body-centered cubic) phase to a BCC + FCC (face-centered cubic) phase. Concurrently, this manipulation precipitates the emergence of novel phases, including B2, L21, and σ. This orchestrated phase evolution enacts a synergistic enhancement in mechanical properties through second-phase strengthening and solid solution strengthening, culminating in a marked improvement in the compressive properties of the HEA.

Microstructural evolution and mechanical properties of Al-4Ni-0.4V alloyed with Zr and Ti at elevated temperatures

The influence of Zr and Ti alloying on the microstructural evolution and mechanical properties of an Al-4Ni-0.4V alloy at elevated temperatures was investigated. The results showed that the coarsening rate of the eutectic Al3Ni phase in the Al-4Ni-0.4V-0.2Zr-0.2Ti alloy decreased from 21.1 nm3/s in the Al-4Ni-0.4V alloy to 7.4 nm3/s after annealing at 350 °C for 0 h to 120 h. The tensile strength, yield strength, and elongation at room temperature of the annealed Al-4Ni-0.4V-0.2Zr-0.2Ti alloy (350 °C, 8 h) were 181 MPa, 108 MPa, and 27.2 %, respectively. After tensile test at 350 °C, these values of the annealed Al-4Ni-0.4V-0.2Zr-0.2Ti alloy were 108 MPa, 72 MPa, and 29.8 %, respectively. Transmission electron microscopy results revealed the precipitation of the L12 ordered structure of the Al3M (M = Zr, V, Ti) phase, approximately 2 nm in size, in the α-Al after annealing. These phases exhibited excellent lattice matching with the α-Al and considerable precipitation strengthening. Segregation of Zr, V, and Ti elements at the α-Al/Al3Ni interface hindered Ni diffusion in the matrix, thereby reducing Al3Ni phase coarsening. Moreover, the Al3M phase precipitated at the interface exhibited favorable matching with the lattice planes of the α-Al and Al3Ni phase, which improved the thermal stability of the eutectic structure and the mechanical properties at elevated temperatures.

Exploring the Impact of Heat Treatment on Residual Stress, Microstructure, and Mechanical Behavior of Laser Powder Bed Fusion Additively Manufactured Ti-6Al-2Sn-4Zr-2Mo Alloy

In the field of additive manufacturing (AM), a promising alloy that is gaining attention is the near-α Ti-6Al-2Sn-4Zr-2Mo (Ti6242) alloy. This alloy is known for its remarkable resistance to creep and corrosion at elevated temperatures. However, the production of Ti6242 components via Laser-based AM technologies faced with several challenges, such as the formation of residual stress in the as-built state that originates from the nature of these processes. Therefore, this study has a dual objective: first, to evaluate the microstructure and residual stresses in the as-built Ti6242 produced through laser powder bed fusion. Secondly, to investigate the impact of a promising post heat treatment on mitigating residual stresses, inducing alterations in the microhardness of the Ti6242 alloy and its ductility, phase transformations and microstructure evolution. The as-built specimen exhibited a significant residual stress of 1357 MPa, which was caused by the pronounced temperature gradients experienced during the fabrication process. It is interesting to note that this promising post heat treatment was highly effective in eliminating 99% of the residual stress. After heat treatment, the amount of α' present in the as-built specimen decreased. This resulted in the activation of diffusion of elements such as molybdenum, causing a proportion of the α' to decompose into the more ductile α+β structure. Additionally, it is revealed that the microstructural changes and relieved stresses from the heat treatment process caused a lower microhardness and a higher ductility under compressive loading, as the elongation and toughness reached 20.5% and 23.255 kJ/mm3 in the heat-treated samples, respectively. The outcomes of this work facilitate the use of this alloy in the production of complex shape components through laser-based AM technologies.

Alpha-case promotes fatigue cracks initiation from the surface in heat treated Ti-6Al-4V fabricated by Laser Powder Bed Fusion

This research investigates the effect of the formation of an oxygen-stabilised titanium alpha layer – called alpha-case at the surface – on the fatigue properties of Ti-6Al-4V (Ti64) alloy components produced by Laser Powder Bed Fusion (L-PBF). Three post processing heat treatments with different controlled atmospheres were carried out on samples with as-built surfaces to evaluate how differences in alpha-case layer thickness and hardness affect the material’s susceptibility to surface embrittlement and its overall fatigue performance. The investigation includes bulk and subsurface microstructural analysis, surface characterisation by X-ray computed tomography (XCT), and fatigue testing. Key findings show that alpha-case layers can reduce the fatigue resistance of L-PBF fabricated Ti64. The presence of a 70±3 µm thick alpha-case layer was found to promote crack initiation. This is emphasised by a higher density of initiated cracks, thus leading to a reduction in fatigue life. Conversely, thinner alpha-case layers were found to have a reduced impact on the fatigue performance, highlighting the critical role of post processing heat treatments in modulating the fatigue resistance of the material. The use of XCT to characterise the surfaces of the specimens in 3D confirms that fatigue cracks primarily initiate at surface notches, highlighting the predominance of as-built surfaces over microstructure in determining the fatigue resistance of L-PBF Ti64 components.

Synthesis and characterization of carbon-based MWCNT combined with CaO to improve the surface characteristics of DED-processed Ti64 alloy machined under MQL conditions

The capacity of additive manufacturing (AM) to create intricate geometries and minimise material waste has drawn a lot of attention. Nevertheless, post-processing steps like machining are frequently needed for AM components to improve their functional surfaces. High temperatures are produced at the tool-workpiece-chip contacts during cutting operations, which lowers tool life and efficiency. Although petroleum-based cutting fluids (CFs) are commonly used to control these temperatures, they pose environmental, health, and cost concerns. Minimum quantity lubrication (MQL) with vegetable oil (VO) has emerged as a promising alternative that offers improved machining performance and environmental friendliness. However, MQL’s effectiveness of MQL may be limited under aggressive machining conditions, necessitating the use of nanoparticles (NPs) to enhance performance. In this investigation, the wettability, dynamic viscosity, density, and thermal conductivity of multi walled carbon nanotubes (MWCNT) at varying wt. concentrations (0.25% to 1.25%) are examined. Following that, the milling tests are conducted in the following conditions: dry, flood, MQL (CaO), and nanofluid-MQL (N-MQL). The outcomes show that the addition of NPs to CaO reduces the contact angle to 15.53° at 1.00 wt%, indicating better wettability. Furthermore, the incorporation of MWCNTs results in a significant improvement in the dynamic viscosity, thermal conductivity, and density of the VO. N-MQL, on the other hand, results in an enhancement in surface quality in contrast to other cutting strategies.

Investigation of the synergetic effect of oleophilic textured surfaces and MoS2 at different loads on the tribological performance of Ti64 alloy

In this research study, surface modification of Ti64 alloy was carried out using laser surface texturing (LST). The investigation aims to explore the effects of loads, oleophilic textured surfaces, and MoS2 as a solid lubricant on the friction and wear reduction of Ti64 alloy and AISI 52100 steel tribo-pairs. Three types of LST textures (Circular, triangular, and square textures) were created on the Ti64 alloy. Subsequently, tribological experiments were performed using a ball-on-disc universal tribometer at loads of 5, 10, and 15N with a 15 Hz frequency. The worn surface was analyzed using various methods, including optical microscopy, 3D-profilometer, FESEM, EDAX analysis, and Raman spectroscopy. The study compared the coefficient of friction (COF) and wear behavior of non-textured surfaces (NTS) with those of textured surfaces (TS) under both dry sliding conditions (DSC) and lubricated sliding conditions (LSC). The results demonstrated a significant reduction in the COF and wear coefficients on the TS. Specifically, the circular texture (CiT) exhibited a remarkable reduction of 39.3%, 63.83%, and 83.6% in wear coefficients compared to the NTS tested under DSC and LSC (using pure PAO-4 and PAO-4 + 1% wt MoS2) with sliding load of 15N. DSC showed abrasion, adhesion, and delamination wear, while LSC displayed mild adhesion, delamination, and tribo-layer formation on NTS and TS. The analysis indicated that the use of LST and solid lubricant nanoparticles on a Ti64 alloy would result in improved service life and better endurance in cutting tools and tribo-mating parts.

The texture evolution near the shear band and corresponding impact on the microvoid nucleation and crack propagation of Ti6242s alloys under high strain rates

This study investigates the texture evolution near the adiabatic shear bands (ASBs) and its impact of on the adiabatic shear failure mechanism, focusing on microvoid nucleation and crack propagation in Ti6242s alloy with an equiaxed α microstructure under high strain rates, using a split Hopkinson pressure bar (SHPB) for the experiments. To achieve this, the initial microstructure was used to enable the texture with the c-axis perpendicular to the loading direction. After compression, the initial texture transformed into two main texture components through different mechanisms. One texture component, aligned parallel to the loading direction, is strongly associated with the {10 1‾ 2} tensile twins, which were widely distributed near the ASBs with their c-axis are 85° to the parent grains in the initial microstructure. The other texture component, with its c-axis perpendicular to the ASB, is formed by the basal slip activation during adiabatic shear deformation. Besides, it should be noted that twinning resulted in the formation of hard grains (with the c-axis of α-grains parallel to the loading direction), increasing the number of hard-soft grain boundaries. A key finding of this paper is the presence of numerous microvoids near the ASB mainly initiated at soft-hard grain boundaries (approximately 65 %), attributed to stress concentration at the boundaries of soft-hard grains, making these boundaries potential nucleation sites for microvoids. Additionally, basal slip bands in the equiaxed α grains provide rapid channels, accelerating the crack propagation rate. This study provides new insights into refining the adiabatic shear failure mechanism under dynamic loading.

Microstructure and tensile properties of transient liquid phase (TLP) sintering repaired Ti–6Al–4V alloys with large area hole defect

Repairing defects in titanium alloy components is economically justified due to their high cost. In this work, Ti–6Al–4V samples with large area hole defects are repaired by transient liquid-phase sintering. The microstructure and tensile properties after repair have been investigated. The factors of different base powder morphology and the ratio of braze metal are also studied. The results show that by using spherical Ti64 alloy powder with 40 wt% TiZrCuNi braze alloy powder, an overall repair effect with high-density repair zone and good interface combination can be obtained at 960 °C for 3 h. The tensile strength of the as-repaired exceeds that of the matrix, but the elongation is lower than that of the matrix. Finally, the repair experiment conducted at various angles demonstrates this technique's strong practical feasibility.

The effects of forging strategies on microstructures and mechanical properties of a Ti–5Al–5Mo–5V–1Cr–1Fe near β-titanium alloy

The present study systematically investigated the influence of forging strategies on the microstructures and deformation behaviors of a Ti–5Al–5Mo–5V–1Cr–1Fe (Ti-55511) near β-titanium alloy. Microstructure analysis revealed that the as-cast alloy exhibited a basket-weave structure predominantly comprised of lamellar α phase. Three different forging methods were used to adjust the morphology of the primary α phase during the final two forging steps: 1) dual-phase (825 °C) + dual-phase forging (DD sample), 2) dual-phase + β single-phase (900 °C) forging (DS sample), and 3) β single-phase + dual-phase forging (SD sample). After standard heat treatment, the DD samples exhibited equiaxed αp due to sufficient deformation in dual-phase region, while DS samples transformed into lamellar shape due to αp reforming during the cooling process of the final β single-phase forging. In contrast, the SD samples displayed short-rod αp due to reforming in the single-phase region and insufficient deformation in the dual-phase region. All these αp and βt phases can hinder dislocation motion to enhance the strength. The DS sample exhibited the best combination of strength, ductility, and impact toughness. During tensile deformation, planar dislocation slip and {101‾1} twinning were dominant in the αp, while wave slip occurred in the βt phase. The fracture behavior transitioned from brittle to ductile after forging and heat treatment. Overall, this study offers a practical and effective method for optimizing the mechanical properties of the Ti-55511 alloy.

Enhancing Tribological Characteristics of Titanium Grade-5 Alloy through HVOF Thermal-Sprayed WC-Co Nano Coatings by TOPSIS and Golden Jack Optimization Algorithm.

Thermal spray coatings have emerged as a pivotal technology in materials engineering, primarily for augmenting the characteristics related to wear and tribology of metallic substrates. This study aimes to delve into applying High-Velocity Oxygen Fuel (HVOF) thermalsprayed WC-Co nanocoatings on Titanium Grade-5 alloy (Ti64). The coating process, utilizing nano-sized WC-Co powder, undergoes systematic optimization of HVOF parameters, encompassing the flow rate of carrier gas, powder feed rate, and nozzle distance. Experimental assessments via Pin-on-Disc (PoD) tests encompass Loss of Wear (WL), Friction Coefficient (CoF), and Frictional Force (FF). Later, an exhaustive optimization of responses is conductede using the Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS) method and the golden jack optimization algorithm (GJOA). Outcomes show a substantial increase in WL, CoF, and FF with a rise in the carrier gas and powder feed rate. However, with increasing spraying distance of powder, the WL, CoF, and FF tend to lower due to higher bonding, which leads to increased wear resistance. The ideal parametric settings achieved from TOPSIS and GJOA are 245 mm of spray distance, 30 gpm rate of powder feed, and 11 lpm of carrier gas flow rate. The powder feed rate contributes 88.99% to the control action, as seen from ANOVA. The confirmation experiment presents that the WL, CoF, and FF output responses are 42.33, 27.97, and 9.38% less than the mean of experimental data. These results highlight the HVOF process in spraying WC-Co nanocoatings to fortify the durability and performance of Ti64 alloy that can be patented for diverse engineering applications.

Effect of primary α phase fraction on deformation mechanism of Ti-1023 alloy at room temperature

The fraction and morphology of α phase have important effects on the mechanical properties and deformation mechanism of Ti-1023 alloy. Here, the tensile stress-strain curves and deformation mechanisms with the fraction of α phase are discussed in detail. As α phase fraction decreases from 67.5 % to 12.6 %, there is a negative correlation coefficient between the yield strength and α phase volume fraction of Ti-1023 alloy, and its fitting equation is obtained. When the fraction of α phase is decreased to 12.6 %, the elongation and ultimate tensile strength of the alloy are 31.09 % and 845.52 MPa, as well as a transition from single to double yielding phenomenon, which is caused by stress-induced martensitic transformation (SIMT). When the fraction of α phase is high, the deformation mechanism is dominated by dislocation slip and mechanical twinning of the α phase. When the fraction of α phase is low, the deformation mechanism is dominated by mechanical twinning of the β matrix and stress-induced martensitic transformation (SIMT). The relationship between α phase fraction and deformation mechanism and mechanical properties of Ti-1023 in α+β dual phase region is studied, which provides a template to guide the development of comprehensive mechanical properties of metastable β titanium alloy in α+β dual phase region.

A novel strategy to break through the strength-ductility trade-off of titanium matrix composites

This study used a solution blending method to coat Ti64 alloy particles with an organopolysilazane (OPSZ) precursor, creating (TiC + Ti3Si)/Ti64 composites via spark plasma sintering (SPS). During SPS, OPSZ decomposes, releasing silicon, carbon, and nitrogen. Nitrogen exits as NH3 and N2, while carbon and silicon partially dissolve in the matrix and partially react with titanium to form TiC and Ti3Si particles. The composite with 0.5 wt% OPSZ exhibited a tensile strength of 1135 MPa and an elongation of 19.0 %, 18.2 % and 28.5 % higher than commercial Ti64 alloy, respectively. The strength increase is attributed to grain refinement, solid solution strengthening, Orowan strengthening, and L phase strengthening. The improved ductility results from fine precipitates promoting dislocation multiplication, the dislocation storage effect of the interface L-phase, and matrix purification by H2 and NH3 from OPSZ decomposition.

Laser powder bed fusion of metastable β titanium alloys: Enhanced strength and plasticity through simultaneous activation of multiple deformation mechanisms

The excellent mechanical properties of metastable β titanium alloys make them suitable for use in aerospace and biomedical fields. However, the deformation mechanisms of these alloys are currently limited to slip/twinning or twinning/transformation-induced plasticity (TRIP) based on β phase stability, hindering high strength and plasticity. In this study, we regulated the laser powder bed fusion (LPBF) parameters to control ω phase density and β phase stability, thereby simultaneously triggering slip/twinning/TRIP deformation mechanisms and resulting in a high strength-plastic metastable β titanium alloy. The results demonstrated that reducing laser energy density decreased the ω phase fraction, leading to a decrease in β phase stability. The formation of the ω phase in specimens with low energy density increased the strain requirements for TRIP to occur, promoting dislocation slip and twinning initiation under low strain conditions. Due to TRIP effect activation at high strains, the α′ phase rather than the α″ phase became the transformation product, subsequently promoting twin formation within the α′ phase during further deformation. Generation of dislocation/twinning/TRIP and twins in the α’ phase resulted in an LPBF-ed metastable β Ti-1023 alloy with excellent strength and plasticity, which surpassed previous research findings for LPBF metastable β titanium alloys and overcame the strength-plasticity trade-off observed in traditional metal materials.

Designing a Refractory Binary Alloy with Low Oxygen Solubility

Refractory metals such as Ti, Zr, Hf, V, Nb, and Ta can dissolve oxygen up to 33 %, 29 %, 20 %, 17 %, 9 %, and 5.7 %, respectively, at high temperatures. The high solubility of oxygen causes brittleness in these metals. When designing a refractory high entropy alloy, efforts should be focused on reducing oxygen solubility. We find that the high solubility of oxygen is related to the thermodynamic stability of oxygen interstitials in pure refractory metals. To understand the impact of alloy composition on oxygen solubility in refractory alloys, we examine the thermodynamic stability of oxygen interstitials across various refractory binary alloys. Using first-principles Density Functional Theory (DFT), we calculate the Oxygen Interstitial Formation Energy (OIFE) of nine refractory metals and their 24 equiatomic binary alloys. The OIFE is determined by the bond strength between oxygen and the nearest neighbor (NN) metal atoms. It is a strong function of the nature of NN atoms that surround the interstitial site rather than the overall composition of the alloy. For a given alloy, the OIFE can vary based on the NN atoms around the oxygen interstitial. These observations indicate that an alloy with even a small amount of metal of high oxygen affinity (or highly negative OIFE), like Ti, can result in the high stability of oxygen in specific interstitial sites where the nearest neighbors are predominantly Ti atoms. It also explains Re as a choice of alloying elements to ductilize W instead of Ti. Although both Ti and Re alloying in W similarly improve its ductility, Ti’s tendency to stabilize oxygen interstitials makes the W-Ti alloy brittle, while Re does not stabilize oxygen interstitials.

Competing roles of microstructure and defects on the mechanical properties of laser-powder bed fused Ti-6Al-2Sn-4Zr-2Mo alloy

AbstractUsing different volumetric energy densities ($${E}_{\text{v}}$$ E v ), the microstructure, texture, and defect evolution in laser-powder bed fused (PBF-LB/M) Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) alloy is studied. PBF-LB/M Ti-6242 rods were manufactured using different $${E}_{\text{v}}$$ E v ranging from 41.67 to 66.67 J/mm3. The $${E}_{\text{v}}$$ E v is varied by setting the scan speed to 1000 mm/s, 1200 mm/s, 1400 mm/s, and 1600 mm/s. The mechanical properties (yield strength, tensile strength, and strain at fracture) were then studied under quasi-static loading conditions. It is observed that the strength of the sample printed using the lowest $${E}_{\text{v}}$$ E v is lower than the other conditions due to the formation of the lack of fusion defects. In addition, the sample printed with the highest $${E}_{\text{v}}$$ E v consists of redeposited process by-products that result in the lowest ductility. The microstructure and texture of the samples were studied using electron backscatter diffraction. The results show that microstructural features including α′ lath width, dislocation density, and lath orientation (texture) were almost identical under different $${E}_{\text{v}}$$ E v . Therefore, the variations in mechanical properties may not controlled completely by the microstructure. The defect analysis is conducted employing X-ray computed tomography. The defect characteristics change from keyhole to lack of fusion by varying the $${E}_{\text{v}}$$ E v . The volume fraction of defects in the samples is in the range of 0.0005–0.007%, which seems to be negligible. However, the fractography analysis shows the dominance of defects in controlling the mechanical properties. This study proves the sensitivity of PBF-LB/M Ti-6242 to defects as the mechanical properties were defect-driven rather than microstructure-driven.

Strain rate affects the deformation mechanism of a Ti-55511 titanium alloy: Modeling of constitutive model and 3D processing map using machine learning

The constitutive model and processing map are effective tools for analyzing the hot deformation behavior of titanium alloys. The stress-strain curves of the Ti-5Al-5Mo-5V-1Cr-1Fe alloy were obtained through the Gleeble thermal simulation experiment. The deformation microstructures at different strain rates were characterized by EBSD and TEM. According to the stress-strain curve, the constitutive models were established by using the Arrhenius equation and the BP artificial neural network (BP-ANN). The constitutive model constructed by BP-ANN has higher fitting accuracy, with the Pearson’s R of 0.99902 and the MAPE of 5.499 %. The 3D processing map of the Ti-55511 alloy was constructed by the BP-ANN constitutive model, which takes temperature, strain, and strain rate as variables. In the processing map, the deformation mechanism is dynamic recovery when the power dissipation efficiency is 0.2–0.33, and the deformation mechanism is dynamic recrystallization when the efficiency is 0.33–0.5. At temperatures of 1123 K and 1153 K and the strain of 0.4, the deformation mechanism is dynamic recovery at the strain rate of 1 s−1. At the strain rate of 0.1 s−1, the deformation mechanism is dynamic recrystallization. This is due to the fact that the higher strain rate prevents dislocations from rearranging, thereby inhibiting dynamic recrystallization behavior.

In-situ investigation of coordinated deformation behavior of Ti-6242S alloy with duplex microstructure

In this work, the coordinated deformation behavior related to slip activation, slip transfer and microcrack growth of Ti-6242S alloy with duplex microstructure was investigated through the in-situ tensile testing. It was found that the deformation process of duplex microstructure can be divided into three stages: slip deformation, the formation of slip band and microcrack nucleation, crack propagation and fracture. And single slip was the dominant slip mode, and multiple slip was the auxiliary slip mode. During the initial tensile stage, the slip lines appearing within colony α were shallower than those within primary α owing to the hindering of α/β interface. The slips penetrated across the entire colony region by straight line. This was because there existed a Burgers orientation relationship between lamellar α and β layer, and the orientation of lamellar α was similar. Meanwhile, the common crystal plane between adjacent grains can still provide good condition for slip transfer when the grain boundary was greater than 15°. Moreover, the slip transfer between adjacent slip systems was more prone to occur when there existed good geometric compatibility and high Schmid factor of exit slip system, which provided coordinated deformation between adjacent grains and avoided stress concentration. However, due to the existence of incompatible deformation, the cracks were generated at the stress concentration areas and then grew along the grain boundary or localized slip band.