Ti Alloy Research Articles

Effect of Dispersed ZrO2 Particles on Microstructure Evolution and Superconducting Properties of Nb-Ti Alloy.

The influence of dispersed ZrO2 particles on the microstructure evolution and the superconducting properties of a Nb-Ti alloy was investigated. The studied materials were prepared by different methods including mechanical alloying (MA) and arc-melting. The obtained samples were studied by X-ray diffraction (XRD) and vibrating-sample magnetometer (VSM). It was found that ZrO2 particles can be successively introduced into an Fe-Nb matrix by MA. However, among all prepared samples with a nominal composition of Nb-47wt%Ti-5 wt% ZrO2, only the powders, which were prepared by MA of Nb-47wt%Ti and ZrO2 powders, exhibit superconductivity with critical parameters comparable to those observed in pristine Nb-47wt%Ti alloy. In particular, the determined upper critical field at 0 K μ0Hc2(0) is close to 15.6(1) T. This value is slightly higher than 15.3(3) T obtained for Nb-47wt%Ti and it can be ascribed to the presence of introduced ZrO2 particles in the Nb-Ti matrix.

Deformation mechanisms at the tip of internal fatigue cracks in vacuum and in the presence of an air environment in a Ti alloy

Ultrasonic fully reversed tension fatigue tests have been performed in the Very High Cycle Fatigue (VHCF) regime (NR>107−108cycles) on Ti-6Al4V specimens containing a controlled internal notch. Two sets of samples have been used. The first one contains a central chimney along the specimen longitudinal axis which brings air to the internal notch; in the second series the notches are not connected to the surface. The microstructure present below the fracture surface of the broken specimens has been studied by electron microscopy (EBSD, TKD and TEM). The formation of nanograins and nanovoids was observed below the surface of the cracks growing in a vacuum environment but not below the surface of cracks connected with ambient air. In the latter case extensive striations were observed. Below each striation the formation of tensile {101̄2} twins was observed.

Mathematical Modeling of Complex-Shape Forming of Ultrafine-Grained Ti Alloy and Subsequent Deposition of Protective High-Entropy Coatings

Mathematical Modeling of Complex-Shape Forming of Ultrafine-Grained Ti Alloy and Subsequent Deposition of Protective High-Entropy Coatings

Knowledge assisted machine learning to clarify pore influence on fatigue life of forging/additive hybrid manufactured Ti-17 alloy

Forging/additive hybrid manufactured Ti alloy parts suffer from relatively low fatigue life due to the existence of metallurgical defects in the transition zone, which also brings difficulty to fatigue life modeling. In this work, the synergistic effect of pore size and location on the rotating-bending fatigue life of hybrid manufactured Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) samples was systematically investigated with the combination of machine learning approaches and physical knowledge. A machine learning framework with a back propagation neural network and generative adversarial network (GAN) was constructed and employed on sparse and limited datasets. A general and interpretable model was obtained with a high level of 90% confidence. In general, the fatigue life of hybrid manufactured Ti-17 alloys decreases with pore size and increases with its distance to surface. Specifically, critical sizes were obtained for near-surface and in-depth pores that have negligible influence on fatigue life of hybrid manufactured samples with respect to pore-free samples. The present work thus provides a systematic platform for the evaluation of the fatigue performance of hybrid manufactured titanium alloys.

Sustainable alloy design: Fe-enhanced Ti alloys for superior mechanical performance in additive manufacturing

The use of titanium (Ti) in the additive manufacturing (AM) industry has been steadily increasing. However, iron (Fe), a significant impurity originating from the sponge production process, is difficult to remove due to high energy requirements. Consequently, fully eliminating Fe from Ti is challenging and expensive. Understanding the role of Fe in Ti alloys and determining a maximum allowable threshold for AM is therefore critical. This knowledge could potentially relax current industry standards and enable the development of more sustainable Ti alloys. This study investigated the effect of Fe on the microstructure development and mechanical properties of Ti-Fe alloys, with a focus on their suitability for additive manufacturing. Through an in-situ alloying approach, Fe content was systematically increased from 0 to 3 wt%, leading to significant grain size reduction, from over 100 μm to less than 5 μm. These modifications in grain size and morphology, achieved by adjusting the Fe content in laser-based powder bed fusion (LPBF) fabricated Ti alloys, are directly related to substantial enhancements in the mechanical properties. The hardness increased from 171 to 366 HV, and the tensile strength effectively doubled from 426 to 1026 MPa while maintaining ductility. XRD analysis revealed the presence of a full α phase when the Fe content was ≤ 0.75 wt%. However, at higher Fe concentrations, small β peaks were observed. To identify the strengthening mechanisms, theoretical frameworks such as the Hall-Petch relationship and Labusch model were employed. Two significant inflection points were identified at Fe concentrations of 0.1 % and 1 wt%, indicating three important compositional ranges: Region #1 (Fe ≤ 0.1 wt%), Region #2 (0.1–1 wt% Fe), and Region #3 (1–3 wt% Fe). The strengthening mechanism in each region is discussed in detail.

Diffusion bonding of TC4/TB8 titanium alloys with an interlayer by regulating temperature: Microstructure and mechanical performance

Diffusion bonding of α+β type TC4 (Ti-6Al-4V) and metastable β type TB8 (Ti-15Mo-2.7Nb-3Al-0.2Si) alloys with interlayer addition was systematically investigated by regulating temperature, revealing the discrepancies in interfacial microstructure and mechanical performance of the joints. Microstructural evolution at the TC4/Ti interfaces and TB8/Ti interfaces can be attributed to atomic interdiffusion and α/β transformation depending on temperature. Additionally, 7 of the 12 α variants that comply with the Burgers orientation relationship with β parents at the transitional layer are identified. The elongation of the bonded samples upon the tensile direction perpendicular to the interfaces becomes decreased compared to that of samples subjected to the tensile direction parallel to the interfaces. The dislocation characteristics and fracture models are analyzed after plastic deformation. This study indicates that a two-step method (first high-temperature and short-duration, then low-temperature and long-duration) can optimize the microstructure and mechanical performance of joints for Ti alloys exposed to high temperatures.

Modeling and Prediction Method for Young’s Moduli of Ti Alloys Based on Residual Muti-layer Perceptron

Modeling and Prediction Method for Young’s Moduli of Ti Alloys Based on Residual Muti-layer Perceptron

Impact of fiber tortuosity on fatigue behavior of SiC fiber reinforced Ti alloy revealed by X-ray computed tomography

ABSTRACT X-ray computed tomography (CT) was used to investigate the fatigue crack growth behavior of continuous SiC fiber reinforced Ti alloy (SiCf/Ti). Based on the three-dimensional morphology of the fatigue crack and the tortuosity of the SiC fibers, we investigated the fatigue crack growth behavior and their dependence on the tortuosity of the fibers. The results revealed that the fatigue crack tends to intersect fibers with higher tortuosity compared to their straighter counterparts, which could explain the crack initiation position and its propagation behavior in continuous fiber reinforced composites.

Nonuniformity of Fatigue Properties of Two‐Sided Electron Beam Welded Joint of Superthick Titanium Alloy

ABSTRACTThe TC4 titanium (Ti) alloy has been widely utilized in various industries such as aerospace and shipbuilding, owing to its numerous advantages. Its exceptional properties have made it a material of choice for applications requiring high performance and reliability. The total weld thickness was 140 mm, and microstructures and high‐cycle fatigue properties were investigated at three different layers within the 140‐mm section. Experimental results show that the overlap area at two weld roots has the highest microhardness and largest nonuniformity of the overall joints, so the area is found to have the poorest high‐cycle fatigue properties. The microstructures in every layer of the weld metal of the joints were analyzed to determine the causes of the poor fatigue properties in the overlapping area at the weld roots. Significant amounts of α′ acicular microstructure are present in the weld metal of joints, while the overlap area at weld roots contains more α′ acicular microstructure with a finer size. Compared with other layers, the weld metal and base metal in Layer 2 (overlap area) have the largest microhardness gradient, where the stress concentration is more serious in the fatigue experimental process. Heat dissipation conditions was a critical factor for the inhomogeneity of microstructure and mechanical properties along the thickness direction of 140‐mm double‐sided electron beam welding joint. Fatigue damage (micropore) is formed at β phases in priority, and fatigue cracks propagate via series connection of micropores, indicative of transgranular ductile cracks.

Effect of residual carbon on the microstructure and mechanical properties of spark plasma sintered Ti–Nb–Zr–Mn alloys

Herein, Ti–Nb–Zr–Mn alloys were prepared by ball milling and spark plasma sintering. The effect of residual carbon on the microstructure, phase composition, and mechanical properties of the as-prepared Ti–Nb–Zr–Mn alloys was systematically studied. The incorporation of stearic acid led to the presence of residual carbon, thereby resulting in the emergence of the FCC phase, encompassing both FCC Ti and carbon-deficient Ti2C. Subsequently, the ultimate tensile strength of the Ti–Nb–Zr–Mn alloys increased from 889 ± 13 MPa to 1166 ± 13 MPa, while the plasticity significantly decreased from 23.6 % to 3.8 %. Meanwhile, the elastic modulus and hardness exhibited an increase in correlation with higher stearic acid content. The Ti2C phase demonstrates significantly higher hardness and modulus compared to FCC Ti; however, it is brittle and carries the risk of reducing ductility and leading to brittle fracture. To achieve a synergistic match of low elastic modulus, high strength, and preferable ductility for metastable β Ti, careful regulation of the carbon content in the Ti alloys is essential.

Clarifying the formation of equiaxed grains and microstructural refinement in the additive manufacturing of Ti-Cu

Controlling microstructural evolution in metallic additive manufacturing (AM) is difficult, especially in producing refined as-built grains instead of coarse, directional grains. Traditional solutions involve adding inoculants to AM feedstocks, but titanium (Ti) alloys cannot employ this approach without producing detrimental secondary phases. Ti-Cu (Ti-copper) alloys offer a solution through constitutional supercooling and/or solid state thermal cycling under AM conditions. This work analyzes a compositionally graded directed energy deposition (DED) Ti-Cu build, single-melt laser tracks, and dilatometric heat treatments to evaluate if, when, and by what mechanism(s) microstructural refinement occurs. Refinement by inoculation of unmelted powder particles was also considered. Constitutional supercooling produced no net microstructural refinement as any equiaxed dendrites which form are remelted with new deposition. This finding agreed with solidification modeling of powder bed fusion-laser beam (PBF-LB) and DED builds. Solid state thermal cycling refined microstructures only during ex-situ dilatometric heat treatments, suggesting build parameter optimization is needed to achieve refinement in-situ. Accidental heterogeneous nucleation on unmelted Ti powder, originating from the different thermophysical properties of Ti and Cu, provided the most significant microstructural refinement. This work systematically assesses the microstructural refinement mechanisms of Ti-Cu in AM builds and offers insights into microstructural control in eutectoid alloys.

Reinforcement mechanism of in-situ TiB whiskers in bimorphic-bimodal titanium alloys

The precise mechanism of the in-situ TiB whisker formation process remains underexplored. In this work, we systematically investigated the formation process of in-situ TiB whiskers via spark plasma sintering of Ti68.8-xNb13.6Ni6Cu5.1Al6.5Bx (x = 0.5 and 1) alloys. The in-situ TiB whiskers evolved from cluster-like to whisker-like structures, together with formation of bimorphic-bimodal microstructures (BBM) in the sintered alloys during the sintering temperature range of 850–1150 °C. The resulting whisker-reinforced BBM Ti alloy achieved a compressive yield strength of 1297 MPa and a strain of 36.5 % at a sintering temperature of 1050 °C, representing a 10.5 % increase in yield strength compared to the BBM Ti alloy without whiskers. The whisker-like TiB acts as a bridge between the MTi2 (M = Cu, Ni) phase and the adjacent β-Ti, forming a continuous bond across these two-grain regions. This bond significantly increases resistance to dislocation movement, enhancing the alloy’s hardening capacity. In addition, the distinctive BBM structure allows for the incorporation of additional slip bands, further enhancing overall performance. At a sintering temperature of 1150 °C, the different thermal expansion coefficients of the MTi2 and TiB phases in the formation of voids negatively impacted the alloy's properties. Our work provides a new strategy for designing high-performance lightweight alloys.

Gradient Titanium Alloy with Bioactive Hydroxyapatite Porous Structures for Potential Biomedical Applications.

Hard bone disease is a clinical problem affecting more than 20 million people annually worldwide, with significant health, social, and economic consequences. For successful integration of any implant, the key aspects are bone regeneration, osseointegration at the bone-implant interface, and the mitigation of inflammation. The purpose of this research work is to demonstrate an innovative material system and method of biomaterial preparation for regenerative medicine. A number of studies were carried out for both hydroxyapatite powder and composites. Wet-precipitated synthesized hydroxyapatite was compared to commercial products through accurate physicochemical studies that confirmed the high purity of the obtained calcium phosphate without any impurities. Ti/HAp composites before and after sintering were compared by XRF, XRD, SEM, EDS, PSA, and roughness measurements, and the Vickers microhardness was analyzed. The fabrication of the biomaterial was based on a bottom-up approach, which involved fabricating HAp particles with specific morphologies using powder metallurgy (PM) to sinter Ti composites. The resulting gradient structures consisting of two compositions (5%HAp%5CMC and 10%HAp10%CMC) mimic the structure of bone tissue. The created pores of 10-100 µm in size will allow bone cells to penetrate the implant and regenerate bone. In turn, the introduction of hydroxyapatite into the material reduces the microhardness of the composite and introduces properties such as bioactivity. The developed composite material contains a combination of Ti alloy and hydroxyapatite (HAp), creating an excellent biomaterial that promotes bone growth and eliminates the problem of implant loosening by integrating it into the bone. This material requires further research, especially biological research. However, it shows promising potential for further experiments.

Machine learning algorithms for optimization of magnetocaloric effect in all-d-metal Heusler alloys

This study examines the application of machine learning algorithms, specifically the Random Forest regression model, to optimize the magnetocaloric effect in all-d-metal Heusler alloys. The model was trained using descriptors related to the mean properties of individual atoms, the properties of simple compounds in their ground state, and measures of chemical disorder. It demonstrated high accuracy in predicting structural properties, while exhibiting moderate accuracy in predicting magnetic properties. To identify optimal alloy compositions, a genetic algorithm was used to find those with the greatest differences in magnetization during martensitic transitions. Using this combined approach, the Ni–Co–Mn–Ti alloy system was thoroughly explored, resulting in the discovery of an alloy with a maximum magnetization difference. These results are consistent with previous research based on density functional theory and highlight the effectiveness of integrating machine learning with genetic algorithms for the discovery of new materials with outstanding magnetocaloric properties. The study emphasizes the need for further refinement of models capable of accurately predicting complex magnetic interactions, which is essential for fully leveraging the potential of all-d-metal Heusler alloys in practical applications.

Hierarchical deformation and anisotropic behavior of (α+β) Ti alloys: A microstructure-informed multiscale constitutive model study

In this study, the hierarchical deformation and anisotropic behavior of (α+β) Ti alloys are investigated using a novel microstructure-informed multiscale constitutive model. State-of-the-art crystal plasticity finite element (CPFE) models, due to their emphasis on a single length scale, are inadequate for capturing the complex hierarchical behavior of additively manufactured (AM) (α+β) Ti alloys, which are characterized by columnar grains and lamellar subgrain features at distinct length scales. To overcome this limitation, a decoupled multiscale framework was developed, integrating representative volume elements (RVEs) for both the columnar grain structure at the higher length scale and the lamellar subgrain microstructure at the lower length scale, with equal emphasis on each. The material behaviors at these scales were modeled using an anisotropic classical plasticity model and a mechanism-based CPFE model, respectively. The framework was experimentally validated for Directed Energy Deposition (DED) manufactured Ti-6Al-4V. It was then used to investigate microscopic stress/strain fields, deformation localizations at grain and subgrain levels, and stress partitioning among neighboring grains. From the insights gained a new theory of anisotropy for AM (α+β) Ti alloys is proposed.

Suppression of discontinuous precipitation by Fe addition in Cu–Ti alloys

Suppression of discontinuous precipitation by Fe addition in Cu–Ti alloys

Titanium Surface Synergy: Strontium Incorporation and Controlled Disorder Nanotopography Optimize Osteoinduction.

Osteoporotic fractures and arthritis represent a major socioeconomic health burden. Fragility fracture fixation and joint replacement are often undertaken using titanium (Ti) or Ti alloy implants. Ideally these should induce bone formation and reduce osteoclast formation. Nanoscale topographies are potent inducers of osteogenesis, and strontium (Sr) has both osteogenic and antiosteoclastic effects. We incorporated strontium into a titanium surface with an osteogenic disordered nanoscale topography. The surface comprises 120 nm diameter, 100 nm deep pits in a near-square order with deliberate offset from the center pit position up to ±50 nm, providing a pattern with an average center-center pit spacing of 300 nm (called near-square 50, NSQ50). Several surfaces were assessed, including NSQ50 alone, strontium incorporated alone, and combined, compared with control surfaces. We assessed the surfaces using a human bone marrow stromal cell (BMSC)/ bone marrow hematopoietic cell (BHSC) coculture capable of osteogenesis and osteoclastogenesis. The samples eluted Sr over long-term culture, and uptake of Sr was better with eluted Sr than with Sr added to the culture media. The NSQ50 pattern in Ti was osteogenic, and addition of Sr elution increased osteogenesis further for both flat and NSQ50 samples. Interestingly, BMSCs on all Ti samples did not secrete the receptor activator of nuclear factor kappa-Β ligand (RANKL) or macrophage colony-stimulating factor (M-CSF) while secreting osteoprotegrin (OPG) at high levels. This meant that no osteoclast formation was observed on any Ti surface. Therefore, using Sr-incorporated nanotopographical imprinting, we generated highly osteogenic Ti surfaces that inhibited osteoclast formation.

Asynchronous Spheroidization of the Lamellar Structure in a Near-α Ti Alloy

Asynchronous Spheroidization of the Lamellar Structure in a Near-α Ti Alloy

Corrosion Behavior of SLMed Ti6Al4V-Equine Bone Nanocomposites

Ti6Al4V is one of the most widely used Ti alloys in biomedical applications, such as orthopedic and dental implants, due to its excellent mechanical properties, biocompatibility, and high corrosion resistance. Metal implants require high bonding strength between the implant and bone for long-term use in the human body; Hydroxyapatite (HAp) has generally been used as it can be expected to provide high osseointegration. However, in this study, Equine Bone (EB), which is a biowaste with a similar chemical composition to HAp and is environmentally friendly, was used instead. Ti6Al4V and EB were mixed through ball milling and then fabricated into Ti6Al4V-0.05EB composites using Selective Laser Melting (SLM). During the SLM process, localized high thermal gradients and rapid cooling rates leads to high strength and low ductility, making it challenging to use as a biomaterial. To overcome these issues, heat treatment was performed at temperatures corresponding to the β phase transformation. Subsequently, to evaluate the corrosion behavior after implantation in the body, the corrosion resistance of the Ti6Al4V-0.05EB nanocomposites was assessed through potentiodynamic polarization tests in a 0.9% NaCl solution, which simulates the physiological environment of the human body. Additionally, the effects of EB addition and heat treatment temperature on the corrosion behavior were also observed.

Comparison study on the effect of oxygen, nitrogen and hydrogen absorption on phase transformation and mechanical properties of quenched CP Ti and Ti6Al4V alloy

Microstructures and mechanical properties of commercial pure Ti and Ti6Al4V metal were studied after water quenching. The nitrogen (N), oxygen (O) and hydrogen (H) analysis was conducted on the quenched samples to establish the effect of impurities on phase transformation and mechanical properties. It was found that despite some negligible increment on the impurities, they could not be attributed to structural change but rather stabilization of the metastable FCC induced by rapid cooling. The formation of the metastable FCC phases was attributed to stresses induced by high cooling rates upon water quenching. Quenching from high temperatures has a significant effect on the crystal structure, microstructure and mechanical properties.