Ti-5553 Alloy Research Articles

Characterization of beta flecks and local solute segregation in Ti-17 alloy ingots produced by vacuum arc remelting

As a melt defect, beta flecks (β-flecks) may exist in many metastable β and α + β titanium alloys. In this work, the main characteristics of β-flecks, including detectability, macroscopic morphology, microstructural characteristics, and chemical composition, were investigated in an industrial-scale Ti-17 ingot produced by the vacuum arc remelting (VAR) process. The results show that β-flecks can be identified as dark areas in the ingot head through a specific heat treatment. Enrichment of Cr and Zr, along with deficiency of Mo, is found in the β-flecks, resulting in a lowered β transformation temperature (Tβ) and increased β phase stability in local areas. When soaked at temperatures from 45 to 15°C below Tβ, β-flecks can be distinctly visualized by adjusting the volume of α phase. Additionally, β-flecks exhibit continuous fluctuations in both chemical composition and microstructure, closely related to the size of the β-flecks. Based on the findings, it can be concluded that β-flecks may originate from residual segregated liquid during the final stage of solidification processes, forming as local defects in the final solidified microstructure. Analytical and numerical modeling provide insights into how solute elements segregate and evolve into β-fleck defects.

Dynamic Mechanical Behavior and Modified Johnson-Cook Model of Ti60 Alloy under High-temperature and High-strain-rate Conditions

Dynamic Mechanical Behavior and Modified Johnson-Cook Model of Ti60 Alloy under High-temperature and High-strain-rate Conditions

Microstructure and Texture Evolution of Ti65 Alloy during Thermomechanical Processing

Microstructure and Texture Evolution of Ti65 Alloy during Thermomechanical Processing

Influence of phase stability on postshock mechanical properties and microstructure evolution in Ti-17 alloy

There has been a growing surge of interest in examining the shock response of titanium alloys, owing to their considerable potential for military applications. The present study aims to reveal the influence of phase stability on the shock-induced mechanical response and substructure evolution of a metastable β titanium alloy, namely, Ti-17. This investigation included extensive work, such as plate impact tests, quasi-static reloading compression tests, and electron microscope analyses. The microstructural evaluations following the shock-wave loading unveil planar slip as the prevailing deformation mechanism in Ti-17 with a bimodal microstructure with stable α and β phases. However, when the shock stress exceeds 10 GPa, the activation of {101¯1}α nano-sized twins was observed, leading to improved reloading ductility. This implies a novel strategy to achieve excellent strength-plasticity compatibility in titanium alloys through appropriate shock-wave loading. Conversely, in Ti-17 with an equiaxed β microstructure, the metastability of the β phase leads to the activation of shock-induced α″ martensite, shock-induced ω, and planar slip. Two distinct forms of interaction involving the α″ laths, i.e., shear and truncation, were also observed. Phase stability greatly influences substructure evolution, which ultimately controls the reloading mechanical properties of the postshock Ti-17 alloy.

Bending properties and deformation micromechanisms of near-α titanium alloy sheets/foils considering initial texture characteristics and size effect

Clarifying the bending deformation behaviour of metal foils is essential for meeting the lightweighting requirements of metal honeycomb structures. This study selected Ti65 alloy specimens with various thicknesses and initial α-phase textures to conduct room-temperature three-point bending experiments. A detailed comparative analysis was performed on the bending deformation behaviour of Ti65 alloy sheets and foils. It reveals that in the foil specimens, the weakening effect of surface layer grains is significant. Under the influence of size effects, the springback angle of Ti65 alloy foils with coarse α-phase grains decreases markedly. Additionally, through various methods, including global Schmid factor analysis, lattice rotation analysis, and crystal plasticity finite element method simulations, the specific relationship between α-phase texture and the bending performance of Ti65 alloy foils was thoroughly investigated. The rolling process influences the bending performance of Ti65 alloy by determining the α-phase texture. Unidirectionally rolled Ti65 alloy products exhibit a transverse α-phase texture, which predisposes them to form transverse texture α-phase macrozones during bending. In contrast, cross-directionally rolled Ti65 alloy foils possess a basal α-phase texture biased toward the transverse direction. This not only helps avoid the formation of macrozones but also ensures coordinated deformation across the foil, resulting in superior bending performance.

Effect of solution and cooling methods on the high-temperature mechanical behavior of Ti60 alloy

The influence of solution treatment temperature and cooling rate on the mechanical behavior of Ti60 alloy at 600℃ was investigated. Five different solution treatment temperatures and five different cooling methods were used for the Ti60 alloy. The study revealed that, at the same solution treatment temperature the ultimate tensile strength (UTS) and elongation (Z%) of the water-quenched (WQ) microstructure were 32 % and 61 % higher, respectively, compared to the furnace-cooled (FC) microstructure. The WQ microstructure exhibited significantly superior strength and ductility. This phenomenon was primarily attributed to the differences in microstructural morphology caused by varying cooling methods. The effects of different cooling methods on high-temperature tensile behavior were discussed in terms of fracture morphology, high-angle grain boundaries, and void distribution. On the other hand, the UTS of the air-cooled (AC) microstructure initially increased and then decreased with decreasing solution treatment temperature, while the UTS of the FC microstructure decreased with decreasing solution treatment temperature. This phenomenon was mainly due to the competing effects of effective slip length (colony size) and elemental distribution. The correlation between solution treatment temperature and cooling rate parameters and high-temperature mechanical properties was established using the response surface methodology (RSM). The optimized solution cooling scheme was determined to be at 1012℃ with a cooling rate of 4238℃/min.

High temperature tensile creep behavior and microstructure evolution of Ti60 alloy rolled sheet

In this work, the high temperature tensile creep test of 2mm Ti60 alloy rolled sheet was carried out, and the creep behavior and microstructure evolution were studied. The initial microstructure of the 2mm Ti60 alloy rolled sheet is mainly composed of primary α phase and secondary α phase, and there are many dislocations and dynamic recrystallization (DRX) inside the rolled sheet. According to Norton-Bailey law, the creep stress exponent at 600 °C is calculated to be 3.6, and creep activation energy at 200MPa is calculated to be 286.4kJ/mol. It implies that the creep mechanism of the rolled sheet includes dislocation slip and dislocation climb. The initial Ti60 alloy rolled sheet has the {0001}<10-10>α texture. Stretching along the RD makes the texture direction gradually change from B-type (<0001>//ND) to T-type (<0001>//TD). Whether it is the B-type texture or T-type texture, the (0001) plane of the α phase always exhibits a basal texture state parallel to the tensile stress direction, contributing a good tensile creep property of this alloy sheet.

Effects of solution treatment on microstructure and properties of Ti-5.7Al-3.9Sn-0.91Mo-3.4Zr-0.40Si-0.38Nb-0.95Ta titanium alloy

This study investigated the effects of solution treatments under various conditions on the matrix and silicides microstructure and their impact on the mechanical properties of high-temperature Ti60 (Ti-5.7Al-3.9Sn-0.91Mo-3.4Zr-0.40Si-0.38Nb-0.95Ta) titanium alloy. The microstructure evolution during solution treatments was characterized, and the tensile properties at 600 °C and room temperature (RT) were investigated. The results show that the fraction and grain size of martensite and silicides can be tailored through solution treatments. With increasing solution temperature, the fraction of primary α (αp) phase and silicides decreases, while that of the transformed β (βt) microstructure increases. After solution treatment at 1025 °C, the yield strength (YS) and ultimate tensile strength (UTS) reach 685.0 MPa and 900.8 MPa, respectively, at 600 °C, increasing by 18.0% and 27.0%, respectively, compared to the initial state. The elongation (EL) remains at 16.2%. The strengthening mechanisms of Ti60 alloy include grain boundary strengthening of the αp phase and martensite formed during rapid cooling, as well as precipitation strengthening of the silicides. With increasing solution temperature from 950 °C to 1025 °C, the fraction of martensite strengthening increases from 38.4% to 89.3%, while the fraction of precipitation strengthening of silicides decreases from 3.63% to 1.17%.

Laser Cladding of a Ti–Zr–Mo–Ta–Nb–B Composite Coating on Ti60 Alloy to Improve Wear Resistance

To improve the wear resistance of the Ti60 alloy, laser cladding was used to obtain a composite coating containing a high-entropy (Ti0.2Zr0.2Mo0.2Ta0.2Nb0.2)B2 boride phase, with Ti, Zr, Mo, Ta, Nb, and B powders as the raw materials. The microstructure and wear characteristics of the coating were studied using XRD, SEM, EDS, and the pin-on-disc friction wear technique. The results show that the coating mainly consists of six phases: (Ti0.2Zr0.2Mo0.2Ta0.2Nb0.2)B2, ZrB2, TiB, TiZr, Ti1.83 Zr0.17, and Ti0.67Zr0.67Nb0.67. The average microhardness of the coating was 1062.9 HV0.1 due to the occurrence of the high-entropy, high-hardness (Ti0.2Zr0.2Mo0.2Ta0.2Nb0.2)B2 boride phase, which was about 2.9 times that of the Ti60 alloy substrate. The coating significantly improved the wear resistance of the Ti60 alloy substrate, and the mass wear rate was about 1/11 that of the Ti60 alloy substrate. The main types of wear affecting the coating were abrasive, adhesive, and oxidation wear, while the main wear affecting the Ti60 alloy matrix was abrasive wear, accompanied by a small amount of adhesive and oxidation wear.

Effects of Thermal Exposure Temperature on Room-Temperature Tensile Properties of Ti65 Alloy.

As a critical material for high-temperature components of aero-engines, the mechanical properties of Ti65 alloy, subjected to high-temperature and long-term thermal exposure, directly affect its service safety. The room-temperature tensile properties of the Ti65 alloy after thermal exposure to temperatures ranging from 450 °C to 650 °C for 100 h were investigated. The results indicate that as the thermal exposure temperature increases, the strength of Ti65 alloy initially increases and then decreases, while ductility exhibits a decreasing trend. The strength of the thermally exposed alloy positively correlates with the size and content of the α2 phase. The ductility of the thermally exposed alloy is comprehensively influenced by the surface oxidation behavior, α2 phase, and silicides. After the prolonged thermal exposure, stress concentration at the crack tips within the oxide layer was enhanced with the increased thickness of the surface TiO2 oxide layer, leading to premature fracture due to reduced alloy ductility. Furthermore, the α2 phase in the matrix promotes the planar slip of dislocations, while silicides at the α/β phase boundaries hinder dislocation motion, causing dislocation pile-ups. Both behaviors facilitate crack nucleation and deteriorate alloy ductility.

Cooling rate effects on microstructure and diffusion behaviour in Ti65 alloy: Insights from a modified diffusion model

In the continuous cooling process, the growth of the equiaxed α-phase grains in near-α high-temperature titanium alloys is controlled by the diffusion of alloying elements. Establishing a specific connection between the cooling rate and the diffusion behaviour of alloying elements aids in the precise prediction of the evolution of equiaxed α-phase grain size. This study meticulously controlled the cooling rate during the two-phase region annealing treatment of the Ti65 alloy. Using EPMA technology, the diffusion behaviour of solute elements during cooling was accurately characterized. The study found that slowing the cooling rate promotes the coarsening of the lamellar secondary α-phase grains and the growth of the primary equiaxed α-phase grains. At higher annealing temperatures, the growth of equiaxed α-phase grains can occur at faster cooling rates, while coarse lamellar secondary α-phase grains can be retained at slower cooling rates. The diffusion behaviour of solute elements Al, Ta, Mo, and W between the α-phase and transformed β-phase matrix is significantly influenced by the cooling rate, thus they are considered as the controlling elements for the growth of the equiaxed α-phase grains. Based on the diffusion behaviours of these controlling elements, their single-element diffusion models were categorized and integrated for predicting the grain size of the equiaxed α-phase. The predictions from the revised diffusion model show an excellent agreement with the actual results, with an error margin of about 5%.

Tuning α precipitation via post-heat treatments in direct energy deposited metastable β Ti-5Al-5Mo-5V-3Cr alloy and its impact on mechanical properties

In this study, the strength and ductility of a direct energy deposited (DEDed) metastable β Ti-5Al-5Mo-5 V-3Cr (wt%, Ti-5553) alloy was explored by tuning the formation of various α microstructures through post-heat treatments. The microstructure of DEDed Ti-5553 with and without post-heat treatments was systematically studied using scanning electron microscopy, three-dimensional (3D) focused ion beam-scanning electron microscopy tomography, transmission electron microscopy, scanning transmission electron microscopy, and atom probe tomography. Nanoscale ω phase and O′ phase particles were observed in the as-built DEDed Ti-5553 without post-heat treatment for the first time. By altering the aging temperatures and heating rates during post-heat treatments, various microstructural evolution pathways were activated, leading to α microstructures with different sizescales, morphologies, and number densities. By fast heating and isothermal aging at 600°C for 2 hours, refined α microstructure was formed through the pseudospinodal decomposition mechanism. While slow heating (at the heating rates of 5 °C/min or 0.5 °C/min) to 600°C and isothermal aging for 2 hours, super-refined α microstructures were produced respectively, primarily via ω-assisted and O′-assisted α precipitation mechanisms. By fast heating to and isothermal aging at 700°C, fine-scaled intragranular α microstructure was formed, dramatically different in morphology and sizescale from the coarse α microstructure formed in the casted Ti-5553, which is suspected to be related to the indirect influence of nanoscale isothermal ω phase particles formed during the DED process and the excess oxygen introduced during the DED process. With fast heating to and isothermal aging at 800°C, coarse α microstructure forms through the classical nucleation and growth mechanism. Various α microstructures led to a drastic change of mechanical properties with improvements up to a 55 % increase in hardness and 92 % increase in tensile yield strength, compared with as-built DEDed Ti-5553. Our work indicates the feasibility of achieving tailored mechanical properties in DEDed metastable β-Ti alloys by tuning α microstructures through selectively activating various phase transformation mechanisms via post-heat treatments.

Effect of Cr on microstructure and high temperature oxidation resistance of Ti-Al-Si composite coatings prepared by two-step hot-dipping + pre-oxidation method on Ti65 alloy

Titanium alloys have a thermal barrier temperature of 600℃, however, the preparation of Ti-Al-Si coating is one of the effective methods to improve the high temperature oxidation resistance of titanium alloys. Due to the preferential combination of Si and Ti, it is difficult to form a Ti-Al alloy phase layer with excellent oxidation resistance at high temperature. In order to solve this problem, the two-step hot-dipping + pre-oxidation method was creatively used to prepare Ti-Al-Si composite coatings, and a small amount of Cr was added to improve the high temperature oxidation resistance of the coatings. The phase structure of the coating was analyzed by XRD. The microstructure of the coating was characterized by SEM. EDS was used to analyze the content and distribution of elements in the coating. The results shown that the Cr-added Ti-Al-Si composite coatings were in the sequence of Ti3Al layer, TiAl layer, TiAl2 + Ti5Si3 layer, Ti(Al,Si,Cr)3 layer, L-(Al,Si) layer, and Al2O3 layer from the substrate. Cr segregated on the Ti(Al,Si,Cr)3 phase boundary, and promoted the selective oxidation of Al to form Al2O3. The dense and continuous Ti-Al binary intermetallic layer can prevent cracks from spreading to the substrate, which further improves the high temperature oxidation resistance.

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Investment Casting Ti-1300 Alloy

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Investment Casting Ti-1300 Alloy

An Investigation of the Effect of Novel Mono/Bi-Layered PVD-Coated WC Tools on the Machinability of Ti-5Al-5V-5Mo-3Cr.

The Ti-5Al-5V-5Mo-3Cr (Ti-5553) alloy is a relatively novel difficult-to-cut material with limited machinability and tool life analysis available in the literature, and hence requires further investigation. This study focuses on the machining and tribological performance of Ti-5553 under high-speed finish turning (150 m/min, 175 m/min, and 200 m/min) via novel mono/bi-layered PVD-coated WC tools. A base AlTiN coating is used as the reference monolayer coating, with AlCrN, diamond-like ta-C, and TiAlSiN coatings each deposited on top of a base AlTiN coating, totaling four separate coated tools (one monolayer and three bi-layer). Tool life, cutting forces, workpiece surface quality, and tribological chip analysis are among the subjects of investigation in this study. Overall, the AlTiN/AlCrN coated tool outperformed all the other combinations: an improvement of ~19% in terms of tool life in reference to the base AlTiN coating when averaging across the three speeds; lowest surface roughness values: ~0.30, 0.33, and 0.64 µm; as well as the lowest chip back surface roughness values: ~0.80, 0.68, and 0.81 µm at 150, 175, and 200 m/min, respectively. These results indicate that the AlTiN/AlCrN coating is an excellent candidate for industrial applications involving high-speed machining of Ti-5553.

Effect of current intensity on molten pool and solidification in vacuum arc remelting process of Ti60 alloy

Current intensity is a critical parameter in the vacuum arc remelting (VAR) process, significantly impacting the molten pool, solidification structure, and ultimately, the quality of the ingot. This study establishes a transient electromagnetic-fluid-thermal-solidified coupled model to examine the effects of current intensity on the shape of molten pool and the solidification process of Ti60 alloy ingots produced by VAR process. Findings indicate that with the increase in current intensity, there is a corresponding rise in the magnetic induction intensity, current density, and Lorentz force. This enhancement leads to more vigorous flow in the liquid phase, creating a vortex flow opposing to the ingot's center at the boundary, influenced by the strong current. As a consequence, the molten pool's shape tends to shift from a “V” shape to a “U” shape, and the depth of molten pool increases while the mushy zone thickness diminishes. For instance, at 17000 A, the depth of molten pool surges by 57.43%, and the mushy zone thickness contracts by 62.01% compared to 5000 A. Over time, the depth of molten pool gradually decreases, with its reduction range ( Δh) within 400 to 6000 s inversely related to current intensity. At 17000 A, Δh is 23.71% less than at 5000 A. Furthermore, elevating the current intensity results in a higher temperature gradient within the ingot and a marked reduction in local solidification time, particularly in the ingot's central area.

Understanding deformation and fracture mechanism of Ti-55531 alloy under complex loading conditions: a case of pre-tensioned torsion

Understanding deformation and fracture mechanism of Ti-55531 alloy under complex loading conditions: a case of pre-tensioned torsion

Experimental investigation on surface integrity and fatigue performance of Ti60 alloy under ultrasonic impact treatment

The surface integrity and fatigue properties of Ti60 alloy under different ultrasonic impact processes were investigated. Ultrasonic impact treatment (UIT) with various parameters enhanced the surface integrity of the turned specimen. The Ra values of the UIT specimens were all less than 0.380 μm, with the surface stress concentration factor (Kst) values ranging from 1.075 to 1.120. The compressive residual stress values of the UIT specimens were enhanced, leading to the localization of the maximum residual stress (σrsm) in the subsurface. Increases in surface residual stress (σs) values exceeded 21.9 % and σrsm values were improved by more than 74.4 % compared to the turned specimen. The microhardness values showed improvement after UIT, with surface microhardness (HVs) values ranging from 408.5 HV0.025 to 461.6 HV0.025. The orientation of the grains was deflected in UIT specimens, and the depths of the plastic deformation layer (hp) values experienced increases of more than 17 times. The fatigue life (Nf) value of the Comb. U2 with the best surface integrity was approximately 9328.4 % higher than that of turned and about 4362.1 % higher than that of Comb. U1 with the worst surface integrity among the UIT specimens. Observing the fatigue fractures, the crack initiation locations of the UIT specimens were relocated to the subsurface at a distance of more than 150 μm from the surface. A higher fatigue life of the specimen was achieved when there was better surface integrity and when the fatigue crack source was located further away from the surface. The crack source in the UIT specimen exhibited a large and irregular shape, and there were numerous small, evenly distributed dimples and a limited number of cleavage planes in fatigue instantaneous fracture region. Additionally, it was found that the subsurface fatigue life prediction model demonstrates superior accuracy for shorter fatigue life.

Microstructural analysis of titanium alloys based on high-temperature phase reconstruction

The microstructural evolution of titanium alloys under high-temperature conditions plays a key role in determining their mechanical properties and hot working behavior. This research presents an advanced method for calibrating β phase reconstruction software using in situ testing on Grade 2 titanium, which achieves accurate reconstruction of the parent β phase microstructure. In addition, unique microstructural observations in the forging of Ti-6246 titanium alloy are highlighted, demonstrating the influence of deformation parameters on the resulting β phase grain structures. Using advanced techniques such as electron backscatter diffraction and Burgers orientation relationship-based software, the research elucidates the behavior of these phases under varying thermal and deformation conditions. In Grade 2 titanium, significant grain growth and phase transformation dynamics were observed upon heating beyond the β-transus temperature during in situ calibration of β phase reconstruction software. The analysis demonstrates the effectiveness of the software in precise reconstructing the parent β phase microstructure based on the orientation of the inherited αs phase. Furthermore, the evaluation of hot forming parameters in Ti-6246 alloy shows the influence of deformation temperature and strain rate on the resulting microstructure. Finite element method analysis coupled with dynamic material modeling elucidates the distribution of temperature, strain rate, and effective strain during forging, which aids in the qualitative assessment of hot workability. Microstructural observations in Ti-6246 alloy forging highlight the presence of elongated colonies of αs phase precipitates, indicative of localized strain intensities and deformation temperatures. In addition, EBSD analysis coupled with β phase reconstruction reveals distinct microstructural features in different regions of the forging. In particular, regions subjected to higher strain rates exhibit elongated β phase grains with pronounced disorientation gradients, suggesting intense deformation. Conversely, optimal forging conditions lead to the appearance of unreinforced axisymmetric β phase grains, indicating dynamic recovery processes. Pole figure analysis further emphasizes the Burgers crystallographic relationship between the αs and β phases, confirming that deformation during forging occurs exclusively within the β phase. These results provide valuable insights into the microstructural evolution in titanium alloys under high-temperature conditions, which are essential for optimizing hot working processes and improving mechanical properties.Graphical abstract

Oxidation behavior of Ti55 alloy and TiBw/Ti55 composites and antioxidation mechanism of TiBw in composites at 960–1000 °C

The oxidation behavior of Ti55 alloy and TiBw/Ti55 composites at temperatures ranging from 960 to 1000 °C was investigated by characterizing the surface and cross-section microstructure of specimens. Results showed that TiBw reinforcement accelerated the occurrence of Ti6O/Ti3O by dissolving oxygen in titanium in the starting oxidation stage, and the Ti6O/Ti3O transformed into TiO2 with the progression of oxidation. Meanwhile, TiBw reinforcement promoted the formation of (101) crystal planes to be beneficial to the growth of TiO2 twins. The cross-sectional characterization showed that the oxide layer of Ti55 alloy and TiBw/Ti55 composites from outside to inside was TiO2+Al2O3, TiO2, Ti-Sn compounds, Ti6O/Ti3O in sequence, which was confirmed by calculating the standard Gibbs free energy of the oxide nucleation. The TiBw reinforcement accelerated the occurrence of suboxides Ti6O/Ti3O by dissolving oxygen in titanium, and promoted the formation of (101) crystal planes which were beneficial to the growth of TiO2 twins. The optimal addition of TiBw induced the TiO2 twins, promoted the random orientation of oxides and refined the oxide size of the TiBw/Ti55 composites with 3.5 % volume fractions of TiBw, resulting in the best resistance against oxidation.