Near-alpha Titanium Alloy Research Articles

Characterization and Growth Kinetics of Borides Layers on Near-Alpha Titanium Alloys.

Pack boriding with CeO2 was performed on the powder metallurgical (PM) near-α type titanium alloy at a temperature of 1273-1373 K for 5-15 h followed by air cooling. The microstructure analysis showed that the boride layer on the surface of the alloy was mainly composed of a monolithic TiB2 outer layer, inner whisker TiB and sub-micron sized flake-like TiB layer. The growth kinetics of the TiB2 and TiB layers obeyed the parabolic diffusion model. The diffusion coefficient of boron in the boride layers obtained in the present study was well within the ranges reported in the literature. The activation energies of boron in the TiB2 and TiB layers during the pack boriding were estimated to be 166.4 kJ/mol and 122.8 kJ/mol, respectively. Friction tests showed that alloys borided at moderate temperatures and times had lower friction coefficients, which may have been due to the fine grain strengthening effect of TiB whiskers. The alloy borided at 1273 K for 10 h had a minimum friction coefficient of 0.73.

The Influence of Si on the High-Temperature Oxidation of Near-alpha Titanium Alloys

The Influence of Si on the High-Temperature Oxidation of Near-alpha Titanium Alloys

Flow behavior and dynamic recrystallization mechanism of a new near-alpha titanium alloy Ti-0.3Mo-0.8Ni-2Al-1.5Zr

A new near-α titanium alloy Ti-0.3Mo-0.8Ni-2Al-1.5Zr was designed based on Ti-0.3Mo-0.8Ni (TA10). The hot compression tests were carried out at temperatures of 800–970 °C and strain rates of 0.01–5 s−1. The results show that the flow softening phenomenon in the α + β phase region is more distinct than that in the single β phase region. The Arrhenius constitutive models based on strain compensation in the α+β phase region and β phase region were established respectively, and the correlation coefficient between the predicted flow peak stress values and the experimental values reached 0.99365. The hot processing map of the alloy was established, the processing parameters of the peak efficiency: 800 ≤ T ≤ 818 °C, 0.01 ≤ ε˙ ≤ 0.0235 s−1, and 960 ≤ T ≤ 970 °C, 0.01 ≤ ε˙ ≤ 0.0213 s−1. The microstructure evolution and deformation mechanism of the compressed specimens were researched by electron backscatter diffraction (EBSD) technique. There were two nucleation mechanisms for dynamic recrystallization (DRX): sub-grains growth nucleation and high angle grain boundaries (HAGBs) bulging nucleation, the former was continuous dynamic recrystallization (CDRX), and the latter was discontinuous dynamic recrystallization (DDRX). The flow stress in the α+β phase region was softened by CDRX and dynamic recovery (DRV), while the principal deformation mechanisms in the β phase region are DRV and DDRX. The dislocation strain energy and recrystallization ability at different temperatures were quantitatively analyzed by the kernel average misorientation (KAM) and the geometrically necessary dislocation (GND), and the results showed that more complete recrystallization occurred at lower temperature in the α + β phase region. The HCP slip was principally completed by prismatic ⟨a⟩ and pyramidal ⟨c+a⟩ slip systems during the hot compression, while BCC was a mixed mode of {110}, {112} and {113} multiple slips.

Strong correlation between high temperature oxidation resistance and nitrogen mass gain during near alpha titanium alloys exposure in air

Nitrogen is known to play a role in the oxidation of titanium and titanium alloys in air. This paper shows the strong correlation between the high temperature oxidation kinetics of eight near-alpha titanium alloys, in the class of Ti6242S, exposed for 3000 h in air at 650 °C. Nuclear reaction analysis (NRA) was used to quantify and locate the nitrogen inside the material. An excellent linear correlation between the total mass gain measured by gravimetry and the nitrogen mass gain measured by NRA is revealed: less the alloys oxidize, more the nitrogen in involved in the oxidation process.

Evolution on the Microstructure and Mechanical Properties of a New Multicomponent Near-Alpha Titanium Alloy after Rolling and Heat Treatments

Near-alpha titanium alloys are widely used in aeroengine blades due to their excellent specific strength and mechanical properties. The mechanical properties of near-α titanium alloys are closely related to the evolution of the microstructure and precipitates. In this paper, the microstructure and mechanical properties of a new type of multi-component near-α titanium alloy sheet after rolling, 700 °C aging, and 800 °C aging were studied. The results show that the strength of the alloy after aging at 700 °C increases from 1156 MPa to 1304 MPa, respectively, but decreases to 1246 MPa with the aging temperature increasing. The ductility of the alloy aged at 700 °C is lower than that of the rolled state, but the ductility increases slightly with the aging temperature increasing. The effect of aging heat treatment on the microstructure and precipitation behavior of alloy plates has been studied and compared with alloys before aging. After heat treatment, the content of primary α decreases from 25% to 5%, respectively. Two kinds of silicide precipitate at different positions, with the large-size spherical silicide being (Ti, Zr, Nb)5Si3, and the small-size fusiform silicide being (Ti, Zr, Nb)6Si3, respectively. Ti3Al was precipitated in the primary α phase, during the aging process. The silicides exhibit the strengthening effect on the alloy, but the effect weakens when the silicides grow up. The loss in ductility is mainly attributed to the precipitation of the α2 phase after aging treatment. However, ductility is improved after applying higher aging temperatures as the size of the α2 phase becomes smaller, and the distribution of them tends to become dispersed.

Microstructural effects on fatigue crack initiation mechanisms in a near-alpha titanium alloy

The role of different microstructural constituents on crack initiation in two-phase titanium alloys is still an area of great controversy. The present study investigates the effects of primary α volume fraction and concomitant macrozones on two different fatigue crack initiation modes concurrently observed in a near-α titanium alloy. Statistically representative regions were monitored in quasi-in-situ studies by interrupting fatigue testing to detect slip trace formation leading to crack initiation. In addition, high-resolution 2D strain maps were generated to quantify in-plane shear strains of slip traces related to microstructural features. The detailed analysis demonstrates that at 90% of the proof stress basal 〈a〉 slip plays a crucial role in crack initiation, regardless of whether cracking is transgranular or intergranular. In addition, a distinct shift from transgranular to intergranular crack initiation was observed with increasing αp fraction driven by the increased number of αp/αp grain boundaries. The high-resolution 2D strain mapping suggest that these intergranular cracks initiated from a burst of basal 〈a〉 slip starting from (0001) twist grain boundaries but penetrating one side of the grain pair in case of a partial (0001) twist grain boundary. From these observations, a new criterion for intergranular cracking is proposed based on a geometrical grain boundary parameter and the preference of neighbouring αp grain pair well aligned for basal 〈a〉 slip. It was found that while (0001) twist grain boundaries increase with increasing αp fraction, macrozones do not further enhance their frequency. However, macrozones of hard orientated grains did enhance transgranular crack formation by potentially higher local stress and increasing slip length over clustered αp grains with low misorientation reducing the requirement for out-of-plane shear.

Impact fracture characteristics of multilayer laminate based on near-alpha titanium alloy

Titanium near-alpha alloy Ti-6Аl-2Zr-1.2Мо-1.3V was used to manufacture a multilayer laminate by diffusion bonding. The laminate consisted of thirteen sheets stacked relative to each other in a way that they all had common rolling direction. The influence of cutting orientation of specimens on the mechanical behavior under impact loading of the laminate was determined. The results of quantitative assessment of the impact fracture characteristics for the studied specimens was analyzed. The transverse specimens had a higher impact strength value in comparison to the longitudinal specimens. The results of fractographic studies showed the presence of minor delaminations on the surfaces of fractured specimens.

Low cycle fatigue behavior of near-alpha titanium alloys used in deep-driving submersible: Ti-6Al-3 Nb-2Zr-1Mo vs. Ti-6Al-4 V ELI

The low cycle fatigue (LCF) of Ti-6Al-3 Nb-2Zr-1Mo and Ti-6Al-4 V ELI with a bimodal structure were compared at different total strain amplitudes (∆εt/2) from 0.5 % to 1.0 %. Because the Ti-6Al-3 Nb-2Zr-1Mo exhibited a higher tensile elongation, but a lower yield strength than Ti-6Al-4 V ELI, it displayed a slightly longer fatigue life than Ti-6Al-4 V ELI when ∆εt/2 was larger than 0.7 % (plastic deformation predominated), while its fatigue life became shorter when ∆εt/2 was less than 0.7 % (elastic deformation predominated). Both Ti-6Al-3 Nb-2Zr-1Mo and Ti-6Al-4 V ELI showed a continuous cyclic softening behavior due to the rearrangement or mutual annihilation of initial dislocations during cyclic deformation, and the variation of cyclic softening rate depended on ∆εt/2 was consistent with the variation of fatigue life depended on ∆εt/2. In cyclic deformation, the prismatic and basal slips were easier to activate, and the dislocation bands were denser and more homogeneous in the Ti-6Al-3 Nb-2Zr-1Mo than that in the Ti-6Al-4 V ELI due to the actual Al content in former was smaller than that in latter, which was beneficial to reduce local stress concentration and prolong fatigue life.

Microstructure and mechanical properties of laser-deposited Ti65 near-alpha titanium alloy

Microstructure and mechanical properties of laser-deposited Ti65 near-alpha titanium alloy

Achieving high tensile strength-ductility synergy of a fully-lamellar structured near alpha titanium alloy at extra-low temperatures

The previous study has indicated that a near alpha titanium alloy of an equiaxed microstructure could hardly exhibit a desirable ductility at 20 K. This study aimed at achieving a promising balance of superhigh strength and excellent ductility of a Ti−3Al−3Mo−3Zr (wt%) alloy in cryogenic temperature field. Temperature dependence of tensile properties and deformation behavior was investigated systematically. It was found that the ultimate tensile strength (UTS) and elongation-to-fracture (EI) jumped from 730 MPa and 19.0% at 298 K to 1300 MPa and 23.0% at 77 K, respectively. Ultrahigh UTS up to 1600 MPa and an acceptable EI of 13.5% were achieved at 20 K. The ultrahigh UTS at 77 and 20 K was considered to be attributed to the sharp increase of CRSS of slip and the Hall-Petch effect of {101̅2}< 101̅1̅> twinning. The enhanced ductility at 77 K was owing to the improved strain hardening ability from large-scale twinning and prismatic and basal slips. Besides, a serrated plastic flow took place at 20 K, which was essentially because the intermittent start of twinning brought about alternate stress jump and cliff-like drop. A fully-lamellar microstructure is suggested to synchronously enhance the strength and ductility of a near-alpha titanium alloy at extra-low temperatures.

High temperature fatigue behavior of a near-alpha titanium alloy

High-cycle and very-high-cycle fatigue at 450 °C in near-α titanium with bi-modal microstructure are investigated. Stress-life duality appears with one data group spanning from 105 to 107 and the other from 107 to 109 cycles, characterized by surface and subsurface cracking, respectively. Misfit strain induced by the high misorientation of a particular primary α-grain relative to its surroundings, termed as local texture, promotes the subsurface fatigue-crack initiation. Fatigue strength increases up to 100 MPa owing to cyclic pre-strain at 450 °C, but the duality remains. Strain hardening by activation of prismatic <a> slip is responsible for the improved fatigue strength.

Effect of heat treatment on microstructure and mechanical properties of laser-deposited Ti65 near-alpha titanium alloy

Effect of heat treatment on microstructure and mechanical properties of laser-deposited Ti65 near-alpha titanium alloy

Microstructure and microtexture evolution of hot-rolled Ti-6321 alloy at different post-annealing temperatures

The microstructure and microtexture evolution of a near-alpha titanium alloy Ti-6321 during the post-annealing process after the hot-rolling were investigated. The microstructure of the hot-rolled plate developed differently at distinct annealing temperatures and the macrozone sizes and morphologies changed at the same time. The results showed that the recrystallization process was not fully achieved after hot-rolling and macrozones had formed after the hot-rolling process with its longitudinal direction extending nearly parallel to the rolling direction and exhibited strong transverse basal texture. After post-annealing, the recrystallization, α grain globularization, coarsening as well as the αp→β→αs phase transformation occurred depending on the temperatures, resulting in the decrease of density and size of macrozones and weakening of< 0001 > ||TD texture component. Variant selection and the influence of αp contributed to the texture inheritance, whereas globularization, β grain growth, and new variant formation led to the orientation spread of αs.

Microstructural Effects on Fatigue Crack Initiation Mechanisms in a Near-Alpha Titanium Alloy

Microstructural Effects on Fatigue Crack Initiation Mechanisms in a Near-Alpha Titanium Alloy

Low Cycle Fatigue Behavior of Near-Alpha Titanium Alloys Used in Deep-Driving Submersible: Ti-6al-3nb-2zr-1mo vs. Ti-6al-4v Eli

Low Cycle Fatigue Behavior of Near-Alpha Titanium Alloys Used in Deep-Driving Submersible: Ti-6al-3nb-2zr-1mo vs. Ti-6al-4v Eli

SMITHS Ti-6Al-2Sn-4Zr-2Mo-Si

Abstract Smiths Ti-6Al-2Sn-4Zr-2Mo-Si is a near-alpha titanium alloy that was developed for use at elevated temperatures. It exhibits high strength and toughness, excellent creep resistance, and high temperature stability at temperatures up 550 °C (1020 °F). This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as casting, heat treating, and joining. Filing Code: Ti-185. Producer or source: Smiths Metal Centres Limited.

Effects of hydrogen as a solid solution element on the deformation behavior of a near-alpha titanium alloy

The effects of hydrogen on the room-temperature mechanical properties and the deformation behavior of near-alpha alloy Ti–6Al–3Nb–2Zr–1Mo were systematically investigated. It was found that hydrogen addition increased the strength and plasticity of titanium alloy, while the impact toughness firstly increased for the sample with 65 wppm hydrogen and then decreased at higher hydrogen content. The strength was increased due to the pinning effect and the solid-solution strengthening effect of hydrogen, while the plasticity was improved by the increase of dislocation mobility and the breakage of beta laths. The increase of impact toughness at 65wppm hydrogen resulted from the enhancement of dislocation motion and multiplication, but further increasing hydrogen addition would reduce impact toughness by decreasing the cohesion strength at interfaces and grain boundaries and the breakage of beta laths. In addition, deformation behaviors of titanium alloys with different hydrogen content were discussed. Hydrogen inhibited twinning and enhanced dislocation slip to some extent. Cross-slip was hindered and planar slip was favored due to the decrease of stacking fault energy after hydrogenation. Further, basal slip and pyramidal slip were activated while prismatic slip was suppressed by hydrogen addition.

High-speed nanoindentation mapping of a near-alpha titanium alloy made by additive manufacturing

Titanium alloys are widely used in additive manufacturing, but their complex microstructures and related micromechanical properties have not been fully explored. Here, we employ high-speed nanoindentation mapping, electron probe microanalysis, and electron backscatter diffraction to characterize as-deposited and heat-treated Ti–6Al–2Zr–Mo–V alloys. Our results show the correlations between mechanical contrasts (hardness and elastic modulus) and phase contrasts (α and β). The hardness and elastic modulus of the α and β phases are increased due to the element redistribution after annealing (Al diffuses from β to α; Mo and V diffuse from α to β). We use a K-means clustering algorithm to analyze the nanoindentation dataset and correlate the mechanical property maps to the distribution of α and β phases. Our study employs the emerging high-speed nanoindentation mapping to give a better understanding of the microstructure–mechanical property relationship of additive manufactured multiphase alloys across length scales.

Stress corrosion cracking and fracture behaviors of gaseous-hydrogenated Titanium alloy Ti-6321 during slow strain rate tests

The stress corrosion cracking (SCC) behavior of gaseous-hydrogenated near-alpha titanium alloy Ti-6321 in the range of 20 ∼ 210 wppm (ppm by weight) was investigated using slow strain rate test (SSRT). Optical Microscopy (OM), Scanning Electron Microscopy (SEM), as well as Transmission Electron Microscopy (TEM), were utilized to observe the microstructures of raw materials, fracture surfaces, cross-sectional areas of fracture surfaces, and the microstructures after deformation; Electron Backscattered Diffraction (EBSD) method was used to analyze the grain orientations so as to analyze the fracture behavior. The results showed that the Ti-6321 alloy revealed no SCC susceptibility in this range, and the material exhibited softening effect when hydrogen content was 65wppm and a hardening effect when hydrogen content exceeded 65wppm. With the increase of hydrogen concentration, the elongation increased because the mobility of dislocations and the nucleation of twins were simultaneously enhanced by hydrogen. In addition, microvoids’ growth and nucleation were inhibited by hydrogen in the matrix.

Quantifying the effect of oxygen on micro-mechanical properties of a near-alpha titanium alloy

Titanium alloys are widely used in the aerospace industry, yet oxygen ingress can severely degrade the mechanical properties of titanium alloy components. Atom probe tomography (APT), electron probe microanalysis (EPMA) and nanoindentation were used to characterise the oxygen-rich layer on an in-service jet engine compressor disc, manufactured from the titanium alloy TIMETAL 834. Oxygen ingress was quantified and related to changes in mechanical properties through nanoindentation studies. The relationship between oxygen concentration, microstructure, crystal orientation and hardness has been explored through correlative hardness mapping, EPMA and electron backscatter diffraction (EBSD). It has been found that the hardening effects of microstructure and crystallography are only significant at very low-oxygen concentrations, whereas interstitial solid solution hardening dominates by order of magnitude for higher oxygen concentrations. The role of microstructure on oxygen ingress has been studied and oxygen ingress along a potential α/β interface was directly observed on the nanoscale using APT.