Ti64 Alloy Research Articles

Advanced phenomenological models guided heat treating processes for LPBF Ti-6Al-4V alloy

Ti-6Al-4V (Ti64) alloy produced by laser powder bed fusion (LPBF) technique consists of an α′-martensite phase, which is usually brittle. Hence, heat treatments are required to promote the α՛→α+β and/or α→β transformations for microstructural optimization to achieve balances between strength and ductility. To guide the selection of heat treatment parameters for the design of LPBF Ti64 microstructures exhibiting optimized strength and ductility, this work explores the suitability of a Johnson-Mehl-Avrami-Kolmogorov (JMAK) and Lifshitz-Slyozov-Wagner (LSW) models. The work showed that the JMAK model can effectively model the heat treatment processes to predict volume fraction of constituent phases in LPBF Ti64. The transformation kinetics was predicted by an extended non-isothermal JMAK model based on differential scanning calorimetry (DSC) experimental data recorded during continuous heating. Moreover, hardness, as a mechanical property index, was measured for a set of specimens. The hardness initially decreased, then remained constant, and finally slightly increased with the increase in β phase fraction and underlying evolution of microstructure. When the β phase fraction was small < 3%, hardness decreased with the continuous coarsening of α lath during heat treatment process. The measured hardness and α lath width for the specimens followed the Hall-Petch relationship. Moreover, the α lath width and heat treatment time at a given temperature were found to undergo the LSW model. Hardness became independent on the β phase fraction of 3-8%, owing to the competition between α lath coarsening and solution strengthening. The hardness slightly increased when the β phase fraction was greater than 8%, because solid solution strengthening of the α phase played a dominant role over the coarsening of α lath width. The experimentally verified JMAK and LSW models are therefore discussed as effective tools to guide the selection of heat treatment parameters for designing the microstructure and hardness/strength of LPBF Ti64 alloy.

Lack of fusion-induced cracking effect on tensile and fatigue behaviours of laser powder-bed fusion-processed Ti-6Al-4V implant

In the laser powder-bed fusion (L-PBF) of Ti-6Al-4 V (Ti64) alloy, cracking defects often caused by lack-of-fusion (LoF) defects cannot be avoided. These defects strongly impact the structural stability of Ti64 implants. In this work, the influence of LoF defects on the tensile and fatigue behaviours of Ti64 implants at different energy densities is evaluated. Three primary approaches were used to characterise the LoF defects in the 10 mm gauge volume of near-net-shaped produced hourglass samples: Image-J software, scanning electron microscopy (SEM), and X-ray computed tomography (µ-CT). A low-cycle fatigue (LCF) test at a stress ratio of −1 and an extensive fractography study of the fractured Ti64 samples were used to investigate the LoF porosity-induced cracking and fatigue effect. The tensile properties of Ti64 samples processed by the L-PBF are generally more affected by microstructural changes resulting from variations in energy density than by LoF defects. A fine microstructure enhances tensile strength, while a coarser microstructure favours ductility. This is evident in samples LPBF-AD and LPBF-BD1, which demonstrate finer and coarser microstructures but show the lowest (8.31 %) and highest ductility (17.58 %), respectively. The best and worst fatigue performance samples were LPBF-AD (600 MPa) and LPBF-BD2 (200 MPa), respectively, and LoF defects significantly impactedthis finding. Moreover, it has been demonstrated that cracks originate and propagate faster from the surfacethan the internal sites. As a result, the former demonstratesa negative effect on the fatigue life of L-PBF-processed Ti64 samples under cyclic loading. The sub-surface morphologies and pore formation with different energy densities are rationalised by high-fidelity thermal-fluid dynamics simulations.

Performance evaluation of a low-cost Ti-Mo-Fe (TMF8) as a replacement for Ti-6Al-4V for internal fixation implants used in mandibular angular fractures: a finite element analysis study

Stainless steel and titanium-based alloys have been the gold standard when it comes to permanent implants and magnesium-based alloys have been the best option for bioresorbable alloys. Ti-6Al-4V, Ti-64, with its 110 GPa Young’s Modulus is the most commonly employed alloy to manufacture biomedical implants used for treatment of fractures of skeleton. Recently, researchers have developed a new low-cost and toxic Vanadium-free alternative to this alloy, Ti-3Mo-0.5Fe at.%, namely TMF8. This alloy has a 25% lesser Young’s Modulus compared to Ti-6Al-4V and also demonstrated acceptable mechanical properties while possessing better cell proliferation results. The lower Young’s Modulus can aid in lowering stress shielding effects while its cytocompatibility could enhance healing. This work, therefore, tries to use finite element analyses to compare these two alloys (Ti-64 and TMF8) from a practical structural point of view to analyse the advantages and disadvantages of this new alloy and how a low-cost biocompatible alternative (TMF8) can actually prove to be a more viable option. The analyses confirm that TMF8 shows almost similar biomechanics performance to Ti-64 alloy (and in acceptable range) in bone plate fixation of mandibular angular fracture treatment.Graphical

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.

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.

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.

Cryogenic temperature tensile properties of laser powder bed fused Ti-6Al-4V

Unnotched and notched tensile properties of Ti-6Al-4V (Ti64) alloy, additively manufactured using the laser powder bed fusion (LPBF) technique, at cryogenic temperatures of 90, 77 and 20 K were investigated. The LPBF process parameter combination was chosen such that the investigated alloy has not only a minimum in porosity, but also an equiaxed prior β microstructure, which predominantly contains acicular α/α’ lath structure in basket-weave morphology, that results in a high strength and ductility combination as well as insignificant mechanical anisotropy at room temperature (300 K). Tensile tests revealed that the yield (σy) and tensile (σu) strengths of LPBF Ti64 are superior while elongation to failure (ef) is comparable to those of the conventionally manufactured (CM) Ti64 down to 77 K, owing to the fine α/α’ lath microstructure in the former. While the progressive reduction of <a>-basal and prismatic dislocation slip activity with decreasing deformation temperature enables a steep rise in σy, the unnotched specimens fractured catastrophically without macroscopic yielding at 20 K. Detailed postmortem analyses revealed the absence of significant twinning-based deformation in LPBF Ti64, in stark contrast to the CM ones at cryogenic temperatures. Instead, deformation kink bands with varying sizes and misorientation were found to be increasingly active within the prior β grains. A large misorientation at the kink band boundary within the β grain leads to void nucleation followed by crack growth, which eventually results in brittle failure at 20 K. While relatively notch insensitive from 300 to 77 K, LPBF Ti64 was notch brittle at 20 K. These results highlight the importance of the unique hierarchical micro- and meso-structural features of LPBF Ti64 on the tensile mechanical behavior, especially at cryogenic temperatures.

Micromechanical testing and microstructure analysis of as-welded and post-weld heat-treated Ti-6Al-4V alloy

The microstructural evolutions and variations in mechanical performance of electron beam welded (EBW) Ti-6Al-4V (Ti64) alloy have been investigated. The effects of heat treatment on the microstructure of welded samples have been studied after post-welding solution treatment and ageing. The martensitic phase α′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\alpha }{\\prime}$$\\end{document} has been confirmed using transmission electron microscopy (TEM). Electron backscatter diffraction (EBSD) has been used to investigate the phase and grain morphology. Results showed that the martensitic α′ phase coarsened, the size of heat-affected zone (HAZ) changed and grains in the base materials (BMs) had grown after the post-weld heat treatments (PWHT). The tensile behaviour of electron beam welded Ti64 has been investigated using in situ tensile testing monitored by optical microscopy. The deformation and failure were directly revealed during the in situ tensile process. Results showed that the EBW Ti64 samples have different failure locations after receiving different post-weld heat treatments. The relationship between the post-weld heat treatments, microstructural evolution and mechanical properties of EBW Ti64 were investigated. Thermodynamic databases were used to predict mechanical properties—including the yield strengths—of the titanium alloy for different grain sizes, representing different post-weld heat treatment operations, and these were embedded into a finite element modelling framework to simulate the tensile testing specimens to understand the mechanical fields experienced such as stresses and strains, just prior to failure.

Investigation on the thermal deformation mechanisms and constitutive model of Ti-55511 titanium alloy

This study presents a comprehensive analysis of the hot deformation behavior of the Ti-55511 alloy over a temperature range of 700 °C–950 °C and strain rates from 0.001 s⁻1 to 1 s⁻1, utilizing isothermal compression testing alongside electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The investigation focuses on the influence of various hot deformation parameters on the microstructural evolution of distinct phase regions within the alloy. At higher strain rates (0.1 s⁻1 to 1 s⁻1), the primary softening mechanisms for β grains in the α+β two-phase region are identified as continuous dynamic recrystallization (CDRX) and dynamic recovery (DRV), while in the β single-phase region, discontinuous dynamic recrystallization (DDRX) and DRV predominate. Conversely, at lower strain rates (0.001 s⁻1 to 0.01 s⁻1), the softening of β grains in the two-phase region is primarily governed by DRV, whereas in the single-phase region, DDRX and CDRX are the dominant mechanisms. Additionally, based on stress-strain data corrected for friction and temperature effects, an elastoplastic constitutive model is developed, incorporating strain rate and temperature to predict peak stress in the two-phase regions of the Ti-55511 alloy. This examination of the thermal deformation behavior and microstructural evolution of the Ti-55511 alloy provides significant theoretical and practical insights for optimizing the manufacturing processes of aviation die forging, tailoring microstructures, and enhancing hot working techniques.

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.

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.