High Temperature Titanium Alloy Research Articles

Dynamic Recrystallization Modeling Considering Dynamic Transformation and Behavioral Analysis for a High-Temperature Titanium Alloy during Hot Deformation

Dynamic Recrystallization Modeling Considering Dynamic Transformation and Behavioral Analysis for a High-Temperature Titanium Alloy during Hot Deformation

Effects of pre-tension on the microstructural stability and mechanical properties of a near-alpha high temperature titanium alloy

Effects of pre-tension on the microstructural stability and mechanical properties of a near-alpha high temperature titanium alloy

Nfluence of Deformation Processing Modes on the Structure and Mechanical Properties of a High-Temperature Titanium Alloy of the Ti–Al–Zr–Si–Mo–Nb–Sn System

nfluence of Deformation Processing Modes on the Structure and Mechanical Properties of a High-Temperature Titanium Alloy of the Ti–Al–Zr–Si–Mo–Nb–Sn System

Superplastic deformation and macrozone behavior of the Ti60 high-temperature titanium alloy

Superplastic deformation and macrozone behavior of the Ti60 high-temperature titanium alloy

The Influence of Heat Treatment on the Tensile Creep Life of the TC25 Titanium Alloy.

High-temperature titanium alloys are significant materials in the aerospace field, and their service life largely depends on creep aging. However, the creep behavior of the TC25 titanium alloy at high temperatures has not been reported. Here, the creep behavior of TC25 before and after heat treatment at 550 °C under different stresses was investigated. It was found that heat treatment significantly enhanced the creep resistance of the TC25 alloy. An increase in creep stress increased the steady-state creep rate and reduced creep life. The smooth αp/βtrans grain boundaries and refined αs improved creep resistance, and the creep mechanism changed from grain boundary sliding to dislocation climbing after heat treatment. This research provides theoretical data support for the application of the TC25 alloy at high temperatures.

Effect of initial microstructure on hot deformation behavior of TC25G alloy: Comparison between basket-weave and equiaxed microstructure

The initial microstructure and its evolution during hot deformation are of critical importance with regard to the performance of high-temperature titanium alloys. This study is concerned with isothermal compression tests of the TC25G alloy with basket-weave and equiaxed microstructures. The tests were conducted at deformation temperatures in the α+β phase zone, with three strain rates and two height reductions. The findings indicate that the flow stress of the initial basket-weave microstructure is greater than that of the equiaxed microstructure at strain rates of 0.01 and 0.1 s⁻¹. A constitutive equation was developed and validated through experiments, which demonstrated variations in the stress exponent n and deformation activation energy Q between the two microstructures. And the predicted flow stress closely matched the experimental data, fulfilling engineering application requirements. Recrystallization was observed to increase with elevated deformation temperatures and recrystallized grains demonstrated a rapid growth rate following the loss of primary α phase constraint in the basket-weave microstructure. Higher deformation rates were found to enhance recrystallized grain boundaries within the equiaxed microstructure, although the grain size remained unaltered. TEM observations revealed that the lamellar α primary phase underwent spheroidization via grain boundary separation, with deformation in the basket-weave sample mainly due to lamellar α phase distortion. The secondary α phase present within the β phase acted as a reinforcement, impeding the movement of dislocations. In the equiaxed microstructure, deformation occurred in both the primary α and β phases, with the β phase exhibiting lower resistance to deformation due to recrystallization.

Simple formula learned via machine learning for creep rupture life prediction of high-temperature titanium alloys

Simple formula learned via machine learning for creep rupture life prediction of high-temperature titanium alloys

Unique grain refinement mechanism of graphene oxide reinforced high-temperature titanium alloy matrix composite

Grain refinement is an effective way to improve the comprehensive mechanical properties of titanium matrix composites. In this work, the strong grain refinement effect of GO on 600 ℃ high-temperature titanium alloy prepared by hot isostatic pressing was found. The refinement mechanism was studied by experimental analysis, first-principles calculation and cellular automaton simulation. The α grain size of the composite with 0.50 wt% GO decreased by 53.2 % compared with the matrix alloy. The direct effect of GO on grain refinement was weak. GO introduced C and O as α-stable elements to increase α phase content, resulting in the solid solubility of Si decreasing and fine (TiZr)6Si3 particles precipitating. (TiZr)6Si3 particles prevented dislocation from moving to accelerate continuous dynamic recrystallization nucleation and pinned grain boundary to inhibit grain growth. The results of cellular automaton simulation show that the inhibitory efficiency of (TiZr)6Si3 on grain growth was 4.7 times that of GO. The unique mechanism that GO promoted silicide particles precipitation and indirectly refined grain provided a design route for novel titanium matrix composites synergistically strengthened by two-dimensional nanosheets, in-situ nanoparticles and grain refinement.

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%.

Evolution of microstructure and mechanical properties of Ti65 high-temperature titanium alloy after additive manufacturing and annealing

Ti65 was prepared by Laser Direct Energy Deposition (LDED) and subjected to Annealing Heat Treatment (AHT). The microstructure and mechanical properties of different specimens were evaluated. The results indicated that the prior β columnar crystals had a strong [0001] texture along the grain growth direction. The coarsening or spheroidization of α lath was attributed to the splitting of lamellar α, subsequent non-directional growth, element migration, and Ostwald ripening. The isotropy of the specimen annealed at 950 °C was caused by trimodal microstructure, discontinuous grain boundary α (αGB), precipitates dissolution, and low-angle grain boundary. A mathematical model was established to predict yield strength (YS) and microhardness based on the α lath thickness. The microhardness-strength correlation of LDED Ti65 followed an empirically derived model (Tabor's relationship). Improvements to the original models of the microhardness-strength relationship for Ti65, in conjunction with the strain-hardening effect and α orientation, made it possible to use these models to predict the strength of LDED Ti65 parts and improve the accuracy of the predicted values. Simultaneously, the model can provide data support for the industrial application of Ti65 or, where appropriate, provide a reference for other technical production (material applications).

Effects of Ta and Nb on high-temperature oxidation properties of Ti-6Al-3.5Sn-4Hf-0.4Si-X alloys

In previous studies, we identified Ta and Nb as the crucial elements affecting the high-temperature oxidation resistance of titanium alloys. To investigate their impact on microstructure evolution and oxidation resistance, we employed a constant temperature oxidation method at 700°C. The results demonstrate that Ta and Nb elements effectively inhibit oxygen diffusion and adsorption on the alloy surface, promote the formation of Al2O3 in the oxide film, and enhance its density. Notably, Ti-6Al-3.5Sn-4Hf-0.4Si-3Ta alloy exhibits exceptional antioxidation performance with an oxidation weight gain of only 0.4884 mg/cm2 after 100 hours of constant temperature oxidation at 700°C, an oxide film thickness of merely 1.047 μm, and a significant proportion (36.29 %) of O atoms combined with Al in the oxide film. The statement is in line with our previous computational findings and serves as a research foundation for the advancement of high-temperature titanium alloys.

Effect of thermal exposure on microstructure and mechanical properties of Ti65 high-temperature titanium alloy deposited by laser direct energy deposition

Industrial design and new product development benefit from the adaptable processing approach offered by laser direct energy deposition (LDED). In this paper, a novel Ti65 alloy was successfully prepared by LDED and subjected to thermal exposure at 650 °C and 750 °C, respectively. The results showed that the as-deposited microstructure varies in different regions due to the cooling rate. Silicide precipitation was observed at the α/β interface, and a coherent α2 phase was generated in the matrix after thermal exposure at 650 °C. Two-scale silicides were observed at the α/β interface and inside the α laths after thermal exposure at 750 °C. The as-deposited ultimate tensile strength (UTS) was 1058 MPa and 690 MPa at room temperature and 650 °C, respectively. After thermal exposure at 650 °C, the room temperature UTS was 1135 MPa, and the elongation (EL) at 650 °C was 27.5 %. After thermal exposure at 750 °C, the room temperature EL was 11.05 %, and both UTS and EL at 650 °C showed a decrease. The quantitative analysis showed that silicide precipitation was primarily responsible for the strengthening mechanism of the specimens thermally exposed at 650 °C at room temperature. The results provide scientific data for the manufacture of Ti65 alloy with excellent mechanical properties, laying the foundation for its application in aerospace.

Multi-scale dispersion strengthening for high-temperature titanium alloys: Strength preservation and softening mechanisms

The long-lasting expectation “the hotter the engine, the better” calls for the development of high-temperature metallic alloys. Although the high specific strengths of titanium alloys are compelling for such applications, their deleterious softening beyond 600 °C imposes serious limitations. Much has been known for decades regarding the phase metallurgy for precipitation strengthening design in titanium alloys, however, the other facile strength promotion mechanism, dispersion strengthening, remains comparatively less-explored and unutilized. The present research concerns the multi-scale dispersion strengthening in titanium alloys, with mechanistic emphases on the critical plasticity micro-events that affect strength preservation. Due to the simultaneous introduction of intragranular dispersoids and intergranular reinforcers, the current titanium alloys present superior engineering tensile strength of 519 MPa at 700 °C. Throughout the examined 25–800 °C temperature range, noticeable softening induced by the thermal activation occurs above 600 °C, accompanied by evident strength loss. The temperature-dependence transition of dominated softening mechanisms from dynamic recovery to dynamic recrystallization has been clarified by theoretical calculations. Furthermore, the strengthening effect of multi-scale architectures is underpinned as the enhanced dislocation strengthening owing to the introduction of thermally-stable heterointerfaces, which could generically guide the design of similar heat-resistant titanium alloys.

High-temperature “Inverse” Hall-Petch relationship and fracture behavior of TA15 alloy

The Hall-Petch relationship is important for material design at room temperature. However, it is not well studied at high temperatures. In this work, the influence of different microstructures on the high-temperature mechanical behavior and corresponding softening mechanisms of high-temperature titanium alloy TA15 (Ti-6.5Al-2Zr-1Mo-1 V, wt.%) were studied. Specimens with duplex, Widmanstätten, and coarse Widmanstätten microstructures were obtained through powder metallurgy. High-temperature tensile tests were carried out between 500 and 650°C. It was found that the fracture mode of the Widmanstätten microstructure was transgranular at 500 °C and 550 °C, but intergranular at 600 °C and 650 °C. EBSD analysis revealed that the high-temperature deformation was facilitated by several mechanisms including GB softening, GB migration, grains rotation, and activation of multiple slip systems. High temperature nanoindentation indicated sofenting of individual grains with increasing temperature. In-situ tensile testing under SEM revealed deformation was primarily in grain interior at room temperature, and GBs played a significant role at 650℃. The GB behavior at high temperatures is believed responsible for the inverse Hall-Petch relationship. These findings provide a new perspective for improving the high-temperature mechanical properties and microstructure control of titanium and its alloys.

The mechanism for annealing-induced ductile to brittle transition in a high-temperature titanium alloy and its mitigation

By investigating the relation between microstructure evolution and tensile responses of a BTi6431S alloy at room temperature and 700 °C, this study finds an annealing-induced ductile-to-brittle transition phenomenon in the near-α titanium alloy. The high strength of the as-received BTi6431S alloy is rooted in the high dislocation density and collective dislocation behavior in the α phase. However, after annealing at 650 °C, the alloy exhibits brittle fracture at room temperature. Using multiscale characterization methods, we attribute this phenomenon to the presence of brittle precipitates and the change of dislocation structures near the surface of BTi6431S titanium alloy. Silicides are generated in the vicinity of the surface region due to the relatively high dislocation density on the surface after the rolling process. The room temperature ductility can be restored by removing the near-surface area. When the alloy is tested at 700 °C, most of the near-surface brittle silicides and dislocations can be eliminated, because the deformation is mainly affected by dislocation behavior and dynamic recrystallization at high temperature. The findings in this study can advance the understanding of alloying effects on the mechanical behavior of high-temperature titanium alloy. The results suggest that inhibiting silicide formation and controlling the environmental temperature during service are potential approaches for maintaining the mechanical performance of this near-α titanium alloy.

Insights into microstructural stability and embrittlement of TC25 high temperature titanium alloy subjected to thermal exposure

High temperature titanium alloys are being urgently developed owing to the requirements of advanced aerospace industry. Performance of the alloys in service under high-temperature environments always attracts great attention. In this study, variations of microstructure and mechanical property in TC25 (Ti-6.5Al-2Mo-1Zr-1Sn-1 W-0.2Si) dual-phase high temperature titanium alloy subjected to thermal exposure have been systematically investigated by coupling microstructural characterization, compositional analyses and mechanical measurement. It is found that strength is significantly enhanced while ductility is sharply degraded when the alloy is thermally exposed at 550 °C for a long duration of 100 h. Microstructural observations manifest that ternary α-needles (αt) are drastically precipitated from β-ligaments inside transformed β-matrix (βtrans) whilst α2 (Ti3Al)-phase is produced from primary α-phase (αp) through ordered transformation. The precipitation of αt-needles is promoted by β-phase metastability resulting from insufficient element partitioning in the initial microstructure. The β-phase stability also renders αt-precipitation encounter size effect of β-ligaments, where the precipitation is suppressed when β-ligaments are thin in size. Both precipitation of αt-needles and α2-phase triggers precipitation-hardening effect, which results in strain localization and thereby regresses alloy ductility. However, further analysis indicates that compared with α2-phase, αt-precipitation plays more adverse role in embrittlement in the current alloy. This is different from thermal-exposed behavior of most of high temperature titanium alloys reported in literatures. These findings enrich our fundamental understanding on thermal stability of high temperature titanium alloys, and provide plausible implication to improve high temperature performance via controlling phase precipitation.

A novel magnetic field assisted powder arc additive manufacturing for Ti60 titanium alloy: Method, microstructure and mechanical properties

Due to the rapid heating-cooling process and unstable keyhole, pore defects are easily formed during the high energy beam-powder additive manufacturing (AM) process, posing great challenges to the high-performance manufacturing of aerospace components. Using an arc with lower energy density as a heat source can effectively avoid these defects, but its matching raw materials are limited to wire. In this paper, a novel magnetic field assisted powder arc additive manufacturing (MFA-PAAM) method has been proposed, which combines arc heat source and powder raw material to achieve dense metal parts. A transverse magnetic field (TMF) was introduced to solve the powder spattering problem which impacts the stability of the PAAM process, by regulating the direction of the arc plasma flow and the arc pressure. The unique melting behavior of the powder under arc heating was captured by a high-speed camera, which can be summarized into two steps: balling and adsorption by the molten pool. And the well-formed and fully dense Ti60 high-temperature titanium alloy wall components were successfully manufactured using the self-developed equipment. The microstructure of the thin-wall component is dominated by basket-weave distributed α laths and few β sheets remaining at their boundaries. A layered periodic distribution along the building direction was observed, which is mainly distinguished from the content and morphology of the β phase. The average ultimate tensile strength (UTS) and elongation to failure in the travelling direction are 1003.2 MPa and 15.1%, while the average UTS and elongation along the building direction are 1009.3 MPa and 16.6%, respectively. The fracture morphologies in both directions are characterized by ductile fracture. The MFA-PAAM technique shows great potential for fabricating materials that are difficult to be drawn into wires with high efficiency and performance.

Influence of pre-heating on TIG-welding thermal cycle of high-temperature titanium alloy of TI‒AL‒ZR‒SN‒MO‒NB‒SI system

Influence of pre-heating on TIG-welding thermal cycle of high-temperature titanium alloy of TI‒AL‒ZR‒SN‒MO‒NB‒SI system

Influence of quenching plus aging on microstructures and mechanical properties evolutions for Ti-Al-Sn-Zr-Mo-Si-Nb-Ta-Er-C near-α high temperature titanium alloys

The microstructures and mechanical properties of β-forged and as-heat treated high temperature titanium alloys were carefully investigated. Heat treatments with solution processes varying from 940℃～1010℃ and aging at 650℃ after water quenching were adopted. After forging, prior β grains were squashed and elongated. The content of the primary α phase decreased with increasing solution temperatures, while the content of the transformed β structures increased. After water quenching plus aging processes, super-fine secondary α lamellas with widths of 80～400 nm precipitated in transformed β structure. Secondary nano-scale silicides with a size of ～82 nm re-precipitated. More α2 phase particles with a mean size of 8.00 nm were dispersively and uniformly precipitated. After heat treatment at 1000℃, the room temperature ultimate strength and yielding strength were enhanced by 241 MPa and 228 MPa, reaching 1256 MPa and 1151 MPa, respectively. The high temperature ultimate strength and yielding strength were enhanced by 119 MPa and 128 MPa, reaching 756 MPa and 669 MPa, respectively. The high temperature elongation increased to 13.6%. The excellent mechanical properties compared to the previously studied were ascribed to the precipitation of super-fine secondary α lamellas in βt, dispersed nano-scale silicides and α2 particles, and the superior mixing proportion of Pα and βt acquired after optimization of heat treatments.

Microstructure and Mechanical Properties Evolution of High-Temperature Titanium Alloys with In Situ Synthesized TiB Whiskers

Microstructure and Mechanical Properties Evolution of High-Temperature Titanium Alloys with In Situ Synthesized TiB Whiskers