4Cr 4Ti Alloy Research Articles

Strengthening caused by precipitates with different morphologies in Cu–Cr–Ti alloys: The role of dislocation bending angle

Addition of a small amount of Ti can significantly improve strength of Cu–Cr alloys. Previous work found that addition of Ti produced both spherical and cubic-shaped Cr particles. In this work, the hindering effect of Cr particles with different morphologies on dislocation was further studied. Transmission electron microscopy and high-resolution transmission electron microscopy were used to observe the bending angle of dislocations cutting through precipitated phase particles at about 108° or 54°. The angle of dislocations cutting through the spherical particles was 108° and that of the cubic particles was 54°. Theoretical calculations of dislocation bending angle to enhance strength determined that the bending angle of dislocations cutting cubic particles is about 54°. This study provides new insights for the design and preparation of high-strength and high-conductivity copper alloys.

Oxidation behavior of TiCr and TiMo alloys formed by low-energy pulsed electron beam impact

The titanium-based alloys with 2–3 at.% of chromium (TiCr) and molybdenum (TiMo) were produced on the top of titanium samples by means of the high-intense pulsed electron beam impact on the titanium with preliminary deposited Cr and Mo coatings. The TiCr and TiMo alloys were subjected to oxidation in open air atmosphere at temperature 600 °C. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy-disperse X-ray microanalysis (EDX) were used for structure and elemental composition determination in the samples. The analysis of oxygen depth profiles showed the increase in oxygen penetration depth in the case of TiCr alloy in comparable to pure titanium. The oxygen concentration corresponding to stoichiometry of the oxide phase TiO2 was found on the depth equaled to the thickness of the TiCr alloy that shows the enhancement of the diffusion of oxygen in the modified layer. The diffusion of oxygen at the temperature of 600 °C is enhanced by decomposition of the solid solutions based on bcc β-Ti phase with free chromium and molybdenum atoms releasing. The free molybdenum atoms take part in the stabilization of TiO2 anatase phase while the free chromium atoms form intermetallic compound TiCr2 preventing the sample from oxidation.

Effect of Hydrogen on Young’s Modulus and Internal Friction of V–4Ti–4Cr Alloy

Effect of Hydrogen on Young’s Modulus and Internal Friction of V–4Ti–4Cr Alloy

The structure and mechanical properties of Cr-based Cr-Ti alloy films

Previous studies have dealt with Cr and its alloy films that exhibit promising characteristics as surface modification layers for antiwear, anticorrosive, and decorative applications. However, the effect of Ti alloying on the structure and mechanical properties of Cr films has not been studied. This work aimed to the structure and mechanical properties of Cr-Ti alloy films in the Cr-rich side. To this end, pure Cr, Cr-6 at.% Ti, Cr-11 at.% Ti, Cr-16 at.% Ti, and Cr-21 at.% Ti alloy films were prepared by magnetron sputtering, and the structure and mechanical properties of the films were evaluated. The results indicated that all the films exhibited a Cr-based growth with body-centered cubic structure, and increasing the Ti content decreased the (110) orientation growth of Cr basis. Ti alloying increased the hardness of the films, while leaded to a monotonic decrease in the modulus of the films. The first-principles method was employed to demonstrate that the reduced modulus was determined by the Ti alloying degree, rather than the orientation evolution of the films. The analysis of H/E value suggested that the wear resistance of the films was improved by Ti alloying. The mechanical properties of present Cr-Ti alloy films, and other Cr-based alloy films or metallic glasses in publications were compared and discussed. We proposed that Ti alloying is a considerable way to explore advanced mechanical properties of Cr-based alloy films.

Effect of introducing manganese as additive on microstructure, hydrogen storage properties and rate limiting step of Ti–Cr alloy

TiCr2 with adding different amount of Mn (0, 2, 4 and 8 wt.%) alloys have been investigated. All alloys have C14-type main phase (gray color in SEM) and Ti minor phase (dark gray color in SEM). Rietveld fitting results proved that the lattice parameter a and cell volume of C14-type phase decreased with increasing Mn content. The first hydrogenation measurement manifest that all alloys have best activation properties and could be activated without any prior heat treatment and hydrogen exposure. However, introducing Mn led to the decrease of the first hydrogen absorption rate of TiCr2 alloy, which may be due to the decrease of cell volume of C14-type main phase. The first hydrogenation properties at low temperature and effect of air exposure of the alloy were discussed. The results showed that the maximum hydrogen absorption capacity at 0 °C was obviously higher than that at room temperature. In addition, TiCr2 alloy doped with minor amounts of Mn after long-time air exposure showed better hydrogenation performance. This may be due to the Mn additive acting as a deoxidizer. Finally, the first hydrogenation kinetic mechanisms of all alloys at different temperature were also studied by using the rate limiting step.

Correlation between Microstructural Change and Irradiation Hardening Behavior of He-Irradiated V–Cr–Ti Alloys with Low Ti Addition

V–4Cr–xTi (x = 0 to 4) alloys were used to investigate the additional effect of Cr, Ti and interstitial impurities on the microstructural evolution in He-irradiated V–Cr–Ti alloys to minimize radioactivity after fusion neutron irradiation. Transmission electron microscopy and atom probe tomography were carried out to the He-irradiated specimens at 500 °C with 0.5 dpa at peak damage. A flash electro-polishing method for the FIB-extracted specimen was established for the ion-irradiated vanadium alloys. The microstructural evolution of the irradiation-induced titanium-oxycarbonitride, Ti(CON) precipitates was observed and was influenced by the effect of Ti addition on the Ti(CON) precipitation. Apparent Ti(CON) precipitates formed in V-4Cr-xTi with 2% addition of Ti. In the V-4Cr-1Ti alloy, a high density Ti enriched cluster was formed. The origin of the irradiation hardening increase resulted from the size distribution of Ti(CON) precipitation from the dispersed barrier-hardening theory.

New insights into ω-embrittlement in high misfit metastable β-titanium alloys: Mechanically-driven ω-mediated amorphization

ω-embrittlement is ubiquitous in metastable β-titanium (Ti) alloys, while the fundamental understanding on the damage-fracture mechanism hitherto remains elusive. In this study, we systematically investigate ω-embrittlement of high misfit Ti-10Cr (wt.%) alloys by coupling experiments and first-principles calculation. It is found that brittle cleavage-like fracture prevails in tensile samples, irrespective of the quenching or subsequent aging states. Microscopically, cracks nucleation and propagation proceed along slip bands, inside which ω-lattices are first disordered and then the localized (β + ω)-amorphous-like structures are developed in the shape of white patches. The underlying mechanism of mechanically-driven localized amorphization is that due to the remarkable covalent character of atomic bonding of ω-precipitates caused by composition partitioning of the Cr element, ω-precipitates impart extremely high energy barrier opposed to dislocation gliding and render dislocations pile-up ahead of ω-precipitates, thus leading to their lattice disordering. It is unveiled that the hydrostatic pressure, serving as the driving force for dislocations pile-up, plays a critical role in this unusual cleavage-like fracture of Ti-10Cr alloys caused by mechanically-driven ω-mediated localized amorphization. Accompanied by the transition from the co-operation of deformation twining and ordinary dislocation slip in the quenched Ti-10Cr alloys to the exclusive ordinary dislocation slip in the long-time aged Ti-10Cr samples, it is unexpected that the resulting tensile fracture strength monotonically decreases to a stress level of ~ 100 MPa. These findings provide new insights into the damage and fracture behavior of high misfit β-titanium alloys, such as Ti-Cr alloys.

Effect of Ti addition on the microstructure and properties of Cu–Cr alloy

The Cu–Cr–Ti alloys with different Ti contents were prepared by vacuum induction melting, solid solution, cold deformation, and ageing treatment. The microstructures, mechanical, and electrical properties of Cu–Cr–Ti alloys were investigated under different Ti contents. The results indicate that the increase of Ti content can improve the mechanical properties of Cu–Cr–Ti alloys, whereas its conductivity decreases significantly. After cold rolling by 80% and ageing at 500°C for 60 min, the Cu-0.3Cr-0.05Ti alloy with the hardness, electrical conductivity, and tensile strength are 162.6 HV, 82.2% IACS, and 510 MPa, respectively. The strengthening mechanism of the studied alloys is mainly attributed to the Orowan precipitation and dislocation strengthening. The addition of Ti in the ageing process can retard the growth and coarsen Cr precipitates.

Formation of a composite structure in Ti-Cr alloys using reversible hydrogen alloying

The aim of this work is to study the regularities of the influence of hydrogen doping on the course of phase and structural transformations in Ti-Cr alloys. The influence of the amount of hydrogen on the preferred sites of intermetallic separation was studied. The influence of hydrogen on the lines of variable solubility of the state diagram Ti-Cr is studied. The possibility of controlling the process of structure formation in titanium alloys with p-eutectoid-forming stabilizers by additional alloying with hydrogen and obtaining such types of structures that are not typical for them with traditional methods of technological influence is shown.

Fabrication of Be-Ta Ti Alloys without Pre-Alloyed Powders via SLM

In this study, we sucsess the fabrication of dense compornent of Ti-20at.%X (X = Cr and Nb) alloys by Selected laser melting (SLM) pwocess, from a mixture of poweder element powders. The volume rasio of pore and non-molten particles is dependent of the enegy density. The difficulty of fabrication of Ti-X alloy comporment is dependent of melting temperature of X element. Thus, Ti-20at.%Cr alloys, which has the lowest melting temperature of X is easier to monufacture of dense comporment. The Ti-20at.%Cr alloys and Ti-20at.%Nb comprise β-Ti single-phase components without any non-molten particles and macroscopic defects. In addtion, the {001}〈100〉 crystallographic texture of these Ti-Cr and Ti-Nb alloys can be controlled effectively by optimizing the SLM parameters. This means that the SLM is key techmelogy of controlling of Young’s modulus and shape at the same time because Young's modulus of be-ta phase in Ti alloys is strongly related to the crystal orientation.

Irradiation Hardening Behavior of He-Irradiated V–Cr–Ti Alloys with Low Ti Addition

A set of V–(4–8)Cr–(0–4)Ti alloys was fabricated to survey an optimum composition to reduce the radioactivity of V–Cr–Ti alloys. These alloys were subjected to nano-indenter tests before and after 2-MeV He-ion irradiation at 500 °C and 700 °C with 0.5 dpa at peak damage to investigate the effect of Cr and Ti addition and gas impurities for irradiation hardening behavior in V–Cr–Ti alloys. Cr and Ti addition to V–Cr–Ti alloys for solid–solution hardening remains small in the unirradiated V–(4–8)Cr–(0–4)Ti alloys. Irradiation hardening occurred for all V–Cr–Ti alloys. The V–4Cr–1Ti alloy shows the highest irradiation hardening among all V–Cr–Ti alloys and the gas impurity was enhanced to increase the irradiation hardening. These results may arise from the formation of Ti(CON) precipitate that was produced by He-ion irradiation. Irradiation hardening of V–Cr–1Ti did not depend significantly on Cr addition. Consequently, for irradiation hardening and void-swelling suppression, the optimum composition of V–Cr–Ti alloys for structural materials of fusion reactor engineering is proposed to be a highly purified V–(6–8)Cr–2Ti alloy.

Recrystallization and structure-property correlation in V–Ti–Ta alloys

Abstract The deformation and recrystallization behaviour with associated microstructural and textural evolutions, precipitation formation and dissolution behaviour, and structure-property correlations have been investigated in V–Ti–Ta alloy system. Recrystallization temperature in this system was found to be in the range of 1250–1300 °C, 200 °C higher than reference V–4Ti–4Cr alloy. Substitutional solid solution strengthening by Ta was found to be the dominant strengthening mechanism. In addition, Ta was also found to influence the precipitation behaviour of V–Ti–Ta alloys. Synchrotron XRD and TEM-EDS results indicated the composition of precipitate to be (Ti,Ta)CON in contrast to V–Ti–Cr system where no Cr is found in the precipitates. Theoretical calculations based on thermodynamics and experimental evidence are presented which indicate desirable enhanced precipitate stability in this system due to presence of Ta. Deformation texture of the alloy was found to exhibit prominent θ-fibre, whereas the recrystallized texture had shown predominant γ-fibre texture.

Bubbles and precipitates formation and effects on the hardening of irradiated vanadium alloys

This paper investigated the formation of bubbles and precipitates and the hardening effects in V–4Cr–4Ti alloy after irradiation of He and H ions and post-irradiation annealing. Microstructures observation shows that small bubbles formed in as-irradiated samples, and, during the post-irradiation annealing, lath-like precipitates formed and small bubbles grew upon. It was found that bubbles surrounding precipitates were significantly smaller than those away from, and tended to align along the precipitates. Composition analysis shows that the precipitates comprised TiO with FCC structure. The effects of bubbles and precipitates on hardening were evaluated by the nanoindentation test, as well as the dispersed barrier model that explicitly considered the small bubbles in as-irradiated sample, large bubbles and TiO precipitates in post-irradiated annealed samples. Compared with the as-irradiated samples, the higher hardness in post-irradiated annealed samples is attributed to the co-existence of bubbles and precipitates.

Effect of aging process on the microstructure and properties of Cu–Cr–Ti alloy

The effect of aging treatment on the microstructure of Cu–Cr–Ti alloy was studied by Scanning electron microscope (SEM) and Transmission electron microscope (TEM), and its electrical conductivity, microhardness and tensile strength were also measured. The results showed that the Cu–Cr–Ti alloy had a microhardness of 166 H V, tensile strength of 551 MPa and electrical conductivity of 78.2%IACS after being solution treated at 960 °C, 80% cold rolled and aged at 500 °C for 1 h. TEM characterization revealed that the precipitates were fully coherent with copper matrix after aging at 450 °C for 1 h. Two precipitates of face-centered cubic (fcc) and body-centered cubic (bcc) Cr structures existed in the matrix at the same time after aging at 500 °C for 1 h, and the existence of ordered phases accelerated the transformation from fcc to bcc. After aging at 550 °C for 1 h, the relationship between precipitates and the matrix transformed into a semi-coherent relationship, and the strength gradually deteriorated.

Effect of micro-alloying element Ti on mechanical properties of Cu–Cr alloy

The mechanical properties and microstructure of Cu–Cr and Cu–Cr–Ti alloys after aging treatment were investigated via hardness measurements, electron backscattered diffraction analysis, and transmission electron microscopy. The results show that the hardness, yield strength, and softening temperature of the Cu–Cr–Ti alloy significantly improved. The interface of the Cu matrix and Cr-rich precipitates was semi-coherent as determined by calculations, and the strengthening mechanism of the Cr precipitates was via the Orowan strengthening relation. A high dislocation density was observed in the matrix, which was because of impediment by fine Cr precipitates in the Cu–Cr–Ti alloy. The effects of dislocation strengthening, solid-solution strengthening, and precipitate strengthening were shown to remarkably enhance the yield strength.

Structures and energetics of semicoherent interfaces of precipitates in hcp/bcc systems: A molecular dynamics study

α/β (hcp/bcc) interfaces are of great importance in the microstructure development and the mechanical properties of titanium and zirconium alloys. This work contributes to the study of interface energetics and interfacial structures of the precipitate in the hcp/bcc system based on a simulation study using molecular statics (MS) and molecular dynamics (MD). The input orientation relationship (OR) was calculated based on the O-line criterion. Based on the energy of the interfaces containing the invariant line (IL), two preferred facets were determined by the Wulff construction, which explained the observed orientations of the habit plane (HP) and the side facet (SF). The deviation of the observed precipitate morphology from the equilibrium shape was discussed in terms of interface kinetics. The structures of the interfaces surrounding a three-dimensional (3D) precipitate, including the preferred facets and the end face, were obtained at the atomic level. The simulated dislocation structures and atomic structures in these interfaces are in good agreement with those of the experimental observations for Ti-Cr alloys. A method was suggested for modifying the O-cell structure with the guidance of the relaxed structure, yielding consistency between the calculated dislocation structure based on the generalized O-element approach and the simulation results.

Microstructure, phase formation and properties of rapid solidified Al–Fe–Cr–Ti alloys

Improvements in the mechanical strength of Al–Fe–Cr–Ti alloys have been demonstrated when non-equilibrium microstructures are developed. This paper investigated the effect of cooling rate and composition on the phase formation, microstructure and properties of new Al96.6Fe1.5Cr1.7Ti0.2 and Al91.6Fe4.9Cr2.2Ti1.3 (at.-%) alloys. Wedge-shaped samples produced by suction casting were characterised by optical, scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, energy dispersive X-ray spectroscopy and microhardness. The results showed that the morphology and size of the phases precedent of the flower-like phases change from small, spherical particles to large flower-like phases with decreasing the cooling rate. The presence of intermetallic phases Al13Fe4, Al13Cr2 and Al3Ti in the Al91.6Fe4.9Cr2.2Ti1.3 alloy, resulted in a hardness 1.6 times higher compared to the Al96.6Fe1.5Cr1.7Ti0.2 alloy.

Bond strength of commercial veneering porcelain to experimental cast Ti-Cr alloy

This study evaluated bond strengths of three commercial veneering porcelains to experimental cast titanium-chromium (Ti-Cr) alloy and commercially pure titanium (cp-Ti) via three-point bending test. After the bending test, the fractured specimens were analyzed using an electron probe microanalyzer (EPMA). The Ti-Cr specimens showed lower bond strengths than the cp-Ti specimens, irrespective of the layering porcelain material; however, all the strengths exceeded the minimum requirement of ISO 9693-1:2012 (>25 MPa). EPMA revealed that titanium and/or chromium elements were detected on the debonded porcelain surface of the Ti-Cr and cp-Ti specimens in the case of the higher bond strength. Contrastingly, the residual porcelain was retained on the metallic surface in the case of the lower bond strength. Although porcelain bonding to the titanium alloy is influenced by porcelain type, the Ti-Cr alloy could be feasible for porcelain-fused-to-metal restorations.

Role of germanium in microstructural development of powder metallurgy Ti-20Cr-xGe alloys

This paper investigates the microstructural changes after incorporating germanium (Ge) into a Ti-20Cr alloy fabricated by powder metallurgy. A positive correlation between Ge compositions and density of the sintered alloys was revealed, with limited effects on the grain size. The microstructure comprised equiaxed β phase grains and nodules of eutectoid phases (α + TiCr2). Alloying more Ge to Ti-20Cr produced more α phase and broadened the nodules. This coarsening is believed to be the consequence of increasing (α-β) interfacial area, which serves as the nucleation site for TiCr2. The largest proportion of α phase (~14 vol%) was obtained in the Ti-20Cr-3Ge alloy, together with the formation of Ti5Ge3 intermetallic. The microstructural changes after Ge additions increase hardness by up to 13%, which may enhance the wear resistance of the alloys providing a promising alternative for dental implants.

Deuterium permeation through the low-activated V–4Cr–4Ti alloy under plasma irradiation

Abstract Vanadium-based alloys are considered as candidate structural materials for nuclear fusion and fast nuclear reactors. Some properties of vanadium alloys are especially advantageous for nuclear fusion facilities, namely, a fast decay of induced activity, resistance to liquid lithium media and high-temperature strength. At the same time, V-alloys absorb and dissolve hydrogen isotopes in large quantities, and the mobility of dissolved hydrogen is high even at cryogenic temperatures. Thus, vanadium and its alloys, as some other metals of the fifth group (Nb, Ta), are characterized by high hydrogen permeability. This allows their usage as membranes for the diffusive purification of hydrogen isotopes. Under plasma irradiation of an inlet surface of such membranes, suprathermal hydrogen atoms and ions with quite high possibility penetrate through the adsorption barrier and diffusing inside materials bulk can reach an outlet surface. This paper aims to study the plasma-driven permeation (PDP) of deuterium through V–4Cr–4Ti alloy. It was shown that the permeation probability of deuterium under plasma irradiation for V–4Cr–4Ti alloy varies in a range of χ = 0.03 ÷ 0.12 for T = 600 ÷ 800 K, which leaves open the possibility of such alloys usage for hydrogen isotopes purification in the fusion reactor exhaust.