Β-phase Stability Research Articles

Dependency of mechanical properties in Ti-7Mo-3Al-3Cr-3Nb alloy on the β phase stability: Regulating primary α phase

In this study, the modification of the β-phase stability of Ti-7Mo-3Al-3Cr-3Nb alloy has been achieved by heat treatment at different temperatures. The synergy effects of primary α-phase and β-phase stability on the deformation behavior and mechanical properties were systematically studied based on these samples, combining the electron backscattering diffraction and transmission electron microscopy techniques. The content of the primary α-phase and stability of the β-phase increase when the heat treatment temperature is lowered from 860°C to 770°C, which increases the yield strength of the alloys. When the content of primary α-phase is less than 9%, high strength and ultra-high work-hardening rates can be simultaneously achieved, with maximum work-hardening reaching 12.75GPa and the ultimate tensile strengths reaching 846MPa. Stress-induced α′′ martensitic (SIM α′′) transformation is observed in all experimental samples during tensile deformation, and the trigger stress of martensitic transformation decreases with the decrease of β-phase stability. When the stability of the β-phase decreases, the quantity of SIM α′′ increases, while martensitic variants and twinned martensite increase to coordinate local strains. Meanwhile, as the strain increases, the martensite laths grow into martensite domains, which trigger martensite twins during deformation, and the interaction of the primary α-phase and β-phase deformation products will achieve different work-hardening rates. This study provides a possible strategy for the design and modification of new high-strength and 、work-hardening rate titanium alloys.

Fabrication of high performance BaSnO3/PVDF piezoelectric nanogenerator through high surface area BaSnO3 nanoparticle assisted β-phase stabilization of PVDF

Piezoelectric nanogenerators (PENGs) are becoming increasingly popular for energy generation and their use in smart electronics. In this study, a barium stannate (BaSnO3)-doped polyvinylidene fluoride (PVDF)-based PENG has been fabricated for the first time. The β-phase of PVDF was stabilized by optimizing the doping of BaSnO3 nanoparticles without the need for external electrical poling. The high surface area of the BaSnO3 nanoparticles promotes the nucleation of the polar β-phase in PVDF through electrostatic interaction. A low-cost solution casting method was used to prepare flexible BaSnO3/PVDF nanocomposite containing 5 wt% BaSnO3, which was then shaped and sandwiched between copper electrodes and protected with a thin PDMS layer to create the final PENG. The fabricated PENG can generate up to ∼41 V of voltage, ∼1.51 µA of current and ∼18.1 µW/cm2 of power density when ∼15.7 kPa pressure is applied by a human finger. The PENG can also charge capacitors, power up 16 LEDs in a series connection, and power other small electronics such as wristwatches, speakers, and calculators. Additionally, the PENG can activate the electrochromic material methyl viologen, which is commonly used in smart window applications.

Multiscale exploration of Ti-Nb-Zr-based alloys for enhanced bioimplant performance

Beta-titanium alloys (β-Ti alloys) with low elastic modulus are metallic materials of great technological interest for high-performance bioimplants. This study employs a comprehensive multiscale approach to investigate alloys from the Ti-Nb-Zr-Sn system, exhibiting desired bioimplant properties such as low elastic modulus and high β-phase stability. The multiscale strategy encompasses electronic structure calculations, integrating them with device simulations through a coupling of calculation of phase diagrams, density functional theory (DFT), machine learning (ML), and finite element analysis (FEA). Utilizing ML and DFT methodologies, we predict and analyze the elastic and electronic properties of the optimized ternary and quaternary alloys. DFT calculations point to elevated β-phase stability compared to omega-phase, suggesting a potential formation of orthorhombic martensite in the Ti-22Zr-11 Nb-4Sn (at%) alloy. Incorporating small amounts of Sn changes the nature of the bonds, resulting in structural and electronic stabilization of the beta-phase. FEA further validates the mechanical performance of the proposed alloys, demonstrating their potential compared to the well-established Ti-Nb-Ta-Zr (TNZT) alloy, a reference in the field. Our findings underscore the effectiveness of multiscale methodologies in advancing the understanding of alloy design for bioimplant applications. We conclude that this multiscale strategy not only elucidates the compositions of interest but also serves as a catalyst for innovation and progress in the field of bioimplantation.

Insight into phase stability and thermoelectric properties of semiconducting iron silicides with manganese substitution: β-Fe1−xMnxSi2 (0≤x≤0.05)

Metal-doped iron silicides (β-FeSi2) are promising thermoelectric materials for high-temperature applications. However, the addition of metal dopants usually causes the formation of secondary metallic phases, resulting in the degradation of thermopower. Here we report the stability of semiconducting β-phase (higher than 95 %) of Mn-doped β-FeSi2 obtained at Mn concentration from 1 % to 5 %, where the samples were prepared through direct arc melting and heat treatment process. The carrier density remarkably increases with Mn content, but the mobility decreases. The electrical resistivity significantly decreases with Mn content. The Seebeck coefficient of Mn-doped samples is improved and stable at high-temperature regions because of the reduction of the bipolar effect and β-phase stability. The thermal conductivity slightly increases with Mn. As a result, the maximum thermoelectric power factor PF = 970 μWm−1K−2 and dimensionless figure of merit ZT = 0.12 at 800 K are obtained in a 3 % Mn-doped sample. The stability of β-phase and the improved carrier density are the origins of enhanced thermoelectric properties, where the Seebeck coefficient is improved, and the electrical resistivity is reduced. Our study provides insight into the importance of phase stability for enhancing thermoelectric transport in Mn-doped β-FeSi2.

Effects of hatch spacing on densification, microstructural and mechanical properties of β-solidifying γ-TiAl alloy fabricated by laser powder bed fusion

β-solidifying γ‑titanium aluminide (γ-TiAl) alloys, which typically contain β-phase stabilizers such as Nb and Cr, hold great promise for the aerospace industry and can potentially be processed through additive manufacturing to realize performance unachievable using conventional methods. However, the effects of laser powder bed fusion (L-PBF) parameters on the characteristics of the thus obtained samples remain underexplored. To address this gap, we herein examined the effects of hatch spacing on the densification, microstructural, and mechanical properties of L-PBF-fabricated Ti-44Al-6Nb-1.2Cr (at.%) alloy samples, revealing that the strong influence on thermal history induced the variation in densification and formation of two microstructure types. 0.01 mm hatch spacing resulted in repetitive slow cooling and sufficiently remelting, thus suppressing crack formation, promoting high densification, and inducing a complex phase transformation involving the formation of a basket-weave-structured α2 phase and the 〈001〉 alignment of the β phase along the build direction. 0.06 mm hatch spacing resulted in rapid cooling and insufficient heat accumulation, favoring the massive phase transformation, a jagged morphology α2 phase with a randomly distributed crystallographic texture. Hardness was mainly correlated with phase constitution and volume fraction, whereas compressive properties were jointly determined by additional effects of multiple factors such as grain size and crystallographic texture. This work provides the fundamental insights required to suppress defect formation in β-solidifying γ-TiAl alloys and tailor their microstructure for mechanical property enhancement.

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.

The Effect of Solution Treatment Duration on the Microstructural and Mechanical Properties of a Cold-Deformed-by-Rolling Ti-Nb-Zr-Ta-Sn-Fe Alloy.

The study presented in this paper is focused on the effect of varying the solution treatment duration on both the microstructural and mechanical properties of a cold-deformed by rolling Ti-30Nb-12Zr-5Ta-2Sn-1.25Fe (wt.%) alloy, referred to as TNZTSF. Cold-crucible induction using the levitation synthesis technique, conducted under an argon-controlled atmosphere, was employed to fabricate the TNZTSF alloy. After synthesis, the alloy underwent cold deformation by rolling, reaching a total deformation degree (total applied thickness reduction) of 60%. Subsequently, a solution treatment was conducted at 850 °C, with varying treatment durations ranging from 2 to 30 min in 2 min increments. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were utilized for the structural analysis, while the mechanical properties were assessed using both tensile and hardness testing. The findings indicate that (i) in both the cold-deformed-by-rolling and solution-treated states, the TNZTSF alloy exhibits a microstructure consisting of a single β-Ti phase; (ii) in the solution-treated state, the microstructure reveals a rise in the average grain size and a decline in the internal average microstrain as the duration of the solution treatment increases; and (iii) owing to the β-phase stability, a favorable mix of elevated strength and considerable ductility properties can be achieved.

Metastable β-Phase Ti–Nb Alloys Fabricated by Powder Metallurgy: Effect of Nb on Superelasticity and Deformation Behavior

This study investigates the effect of Nb concentration on the mechanical properties, superelasticity, as well as deformation behavior of metastable β-phase Ti–Nb alloys produced via powder metallurgy. The alloys were fabricated through mechanical alloying, followed by consolidation using hot pressing. The resulting microstructure comprises fine β-phase grains with TiC carbide precipitates at the grain boundaries. The study reveals non-linear variations in the values of yield strength for the manufactured materials, which were attributed to the occurrence of various deformation mechanisms activated during the loading. It was found that the mechanisms change with the increasing concentration of Nb in the manner: stress-induced martensitic transformation, twinning, slip. However, all these mechanisms were activated at a reduced concentration of Nb compared to the materials obtained by casting technology previously reported in the literature. This is most probably associated with the elevated oxygen content, which affects the stability of the parent β-phase. The study revealed that superelasticity in Ti–Nb-based alloys prepared using powder metallurgy may be achieved by reducing the content of β-stabilizing elements compared to alloys obtained by conventional technologies. In this study, the Ti–14Nb (at. pct) alloy exhibited the best superelasticity, whereas conventionally fabricated Ti–Nb alloys displayed superelasticity at an Nb concentration of approximately 26 at. pct. The developed material exhibited a non-conventional, one-stage yielding behavior, resulting in a superelastic response at significantly higher stresses compared to conventionally fabricated Ti–Nb alloys.

Effect of 105 MeV gold ion irradiation on dielectric properties of PVC/PVDF@BaZrO3 nanohybrid thin film

The PVC/PVDF@BaZrO3 nanohybrid thin films were prepared by solution grown method. The dielectric constant of the films was higher due to BaZrO3 incorporation in the PVC/PVDF matrix. The PVDF and PVC/PVDF nanohybrid films were irradiated with 105 MeV Au2+ ion beam under vacuum condition at room temperature with two ion fluence. The irradiated thin film of PVC/PVDF@BaZrO3 exhibits relatively low dielectric constant with low loss at different temperature because of thermodynamic stability of β-phase. However, almost complete amorphization was observed in BaZrO3 filler in PVC/PVDF@BaZrO3 nanohybrid samples. After being irradiated with a 105 MeV Au2+ ion beam, the (ϵ′) dielectric constant, FTIR and SEM parameters were used to evaluate changes in dielectric and structural properties for all the samples. In FTIR spectra, new peaks appeared at 1705 cm−1, disappeared or minutely shifted due to high energy of ion beam. It is interesting to note that BaZrO3 phase becomes amorphized through 105 MeV Au2+ ion irradiation that causes an increased dielectric constant along with cross-linking effect of nanohybrid films.

Physical, mechanical, and corrosion properties of Ti–12Mo and Ti–15Mo alloys fabricated by elemental blend and mechanical alloying techniques

Ti–Mo alloys have received increased attention and concern in several applications, especially in biomedical, because of their appropriate properties, non-toxicity, and reasonable cost. This work investigated the different Mo powder content (12 and 15 wt%) fabricated by elemental blended and mechanical alloying. The microstructure, density, microhardness, compressive, wear, and corrosion properties were characterized. It was found that the volume fraction of β-phase increases with increasing Mo content to around 85%, mainly due to the robust β-phase stabilizer effect. Moreover, the microhardness and compressive properties were enhanced with Mo addition and MA fabrication by 11.5 and 27%, respectively, mainly due to solid solution strengthening, plastic deformation, high dislocations, and lattice defects. However, the strain at failure decreased with decreasing sintered density and increasing porosity. From this study, the corrosion rate decreased with decreasing the porosity, reaching 0.226 × 10−3 mm/year for Ti–12Mo alloy fabricated by elemental blend with a minimum porosity of 3.6%. Ti–Mo alloys can also tolerate properties and impurities, making them suitable for biomedical applications.

Effects of aluminum and oxygen additions on quenched-in compositional fluctuations, dynamic atomic shuffling, and their resultant diffusionless isothermal [formula omitted] transformation in ternary Ti–V-based alloys with bcc structure

Diffusionless isothermal ω transformation is a recently discovered ω transformation that occurs isothermally during aging near room temperature in Ti alloys with a bcc (β-phase) structure. Unlike conventional displacive phase transitions, the diffusionless isothermal ω transformation occurs in locally unstable nanoscale β-phase regions formed by quenched-in statistical compositional fluctuations. In the present study, the effects of Al and oxygen additions in ternary β-phase Ti–V-based alloys on the diffusionless isothermal ω transformation and its attempt process, called dynamic atomic shuffling, were studied. Elastic constant and internal friction measurements for Ti–16.6V–2.1Al and Ti–17.5V–2.5O (at.%) alloy single crystals and analysis of quenched-in compositional fluctuations using the thermodynamic theory of fluctuations indicated that the oxygen addition increases the β-phase stability, and it selectively increases the activation energy of dynamic atomic shuffling in locally unstable Ti-rich regions, which is caused by the strong attractive interaction between Ti and oxygen elements. As a result, oxygen addition suppresses the diffusionless isothermal ω transformation that occurs during aging at 298 K. In contrast, low β-phase stability, which promotes ω-phase nucleation, is retained by Al addition. Furthermore, dynamic atomic shuffling with a low activation energy is retained even though the average activation energy is enhanced by the Al addition, originating from the relatively weak atomic interaction between Ti and Al. Therefore, the diffusionless isothermal ω transformation cannot be suppressed by Al addition.

Corrosion resistance of β-phase titanium alloys under simulated inflammatory conditions: Exploring the relevance of biocompatible alloying elements

In this study we compared the corrosion behavior of single β-phase alloys: (i) Ti-29Nb-13Ta-4.6Zr and (ii) Ti-45Nb, that contain similar amount of β-phase stabilizers. Corrosion resistance was analyzed in the PBS+H2O2 solution, which simulates the conditions as can be found during post-operative inflammation. Results of electrochemical impedance spectroscopy, and ion-release measurements revealed that Ti-29Nb-13Ta-4.6Zr alloy demonstrated significantly higher corrosion resistance compared to Ti-45Nb. Post-immersion microscopic analysis demonstrated that a thinner layer of oxidation products was formed on Ti-29Nb-13Ta-4.6Zr alloy surface. Overall results allowed to exclude the beneficial role of Nb in tailoring corrosion resistance of Ti-29Nb-13Ta-4.6Zr under simulated inflammatory conditions.

Investigation of ion transport properties in Er–W co-doped La2Mo2O9 electrolytes

Here we present the structural, vibrational, dielectric as well as ionic transport properties in a series of La2-xErxMo1.7W0·3O9 (for 0 ≤ x ≤ 0.5). Stabilization of cubic β-phase at room temperature was achieved by doping, evident from XRD and conductivity plots. Raman analysis suggests a change in phase structure and deformation in Mo-polyhedra due to doping. Ionic conductivity of 10 mol% Er-doped sample was found to be 3.6 × 10−2 S/cm similar to that of pure La2Mo2O9 at 700 °C. Two different conduction mechanisms prevail: Arrhenius type below 450 °C and Vogel-Tammann-Fulcher (VTF) type above 450 °C. Dielectric constant and loss studies indicate the presence of two dielectric relaxations in the co-doped samples with different relaxation times attributed to the short-range diffusion of oxygen ions between different sites, i.e., O (1) ↔ O (2) and O (1) ↔ O (3). Electric modulus studies suggests that the relaxation mechanism is independent of temperature and composition.

Effect of interlayer cooling on the microstructure and mechanical properties of titanium alloys fabricated using directed energy deposition

The effect of interlayer cooling in directed energy deposition on the microstructure and mechanical properties of two titanium alloys (Ti–6Al–4 V and Ti–2.5Fe–4.5Al–0.25Si) was investigated in this study. On the one hand, the general process of directed energy deposition provided sufficient time for element partitioning, resulting in the formation of the isothermal ω. On the other hand, interlayer cooling interfered with element partitioning and isothermal ω formation. It induced the formation of the supersaturated α. The isothermal ω or supersaturated α, generated based on the fabrication conditions, significantly influenced the mechanical properties of these alloys. The higher the β-phase stability of the alloy, the greater is the change in its mechanical properties depending on the fabrication conditions. This study provides guidelines for the design of new alloys manufactured using directed energy deposition.

Effect of carbon ions beam irradiation on structural and dielectric properties of Poly(vinylidene fluoride–trifluoroethylene) P(VDF-TrFE) copolymer

P(VDF-TrFE) have been irradiated by 70 MeV carbon ions beam under vacuum at room temperature with various ion fluences. FT-IR, SEM-EDS and dielectric parameters are used to evaluate induced changes in electrical and structural properties. The ion fluence rate of 1×1012 ions/cm2, 2×1012 ions/cm2 and 20×1012 ions/cm2 have been used to study the irradiation effect on P(VDF-TrFE). FT-IR spectra represent the maximum absorption at 1177 cm−1. In FT-IR spectra, new peaks appeared at 1284 cm−1 and 1343 cm−1, while the peaks at 1284 cm−1 and 1343 cm−1 disappeared or minutely shifted. EDS pattern support the semi-crystalline nature of P(VDF-TrFE). SEM images show the destruction of regular packed structure due to dominance of oxidation reaction during exposure of ion beam. The irradiated samples exhibit relatively low dielectric permittivity and loss due to thermodynamic stability of β-phase. The anomaly of dielectric properties at low temperature is due to the freezing chain motions.

Microstructure evolution and deformation mechanism of α+β dual-phase Ti-xNb-yTa-2Zr alloys with high performance

• Microstructure of the alloys is more sensitive to Nb rather than Ta. A slight difference in Nb content will affect the morphology of martensite and even induce ω phase transformation, resulting in completely different mechanical responses of the alloy. • The as-cast Ti-3Nb-13Ta-2Zr alloy shows the highest compressive strength (227 ±10 MPa), and compressive strain (74.3% ± 0.4%). • Nb and Ta content strongly affects Young's modulus and tensile properties of the alloys after rolling. The as-rolled Ti-3Nb-13Ta-2Zr alloy exhibits much lower modulus due to lower Nb content as well as more α"-martensite and β-phase, and a good combination of low modulus and high strength among all the designed alloys. Biomedical β-phase Ti-Nb-Ta-Zr alloys usually exhibit low elastic modulus with inadequate strength. In the present work, a series of newly developed dual-phase Ti- x Nb- y Ta-2Zr (wt.%) alloys with high performance were investigated in which the stability of β-phase was reduced under the guidelines of ab initio calculations and d-electronic theory. The effects of Nb and Ta contents on the microstructure, compressive and tensile properties were investigated. Results demonstrate that the designed Ti- x Nb- y Ta-2Zr alloys exhibit typical characteristics of α+β dual-phase microstructure. The microstructure of the alloys is more sensitive to Nb rather than Ta. The as-cast alloys exhibit needle-like α′ martensite at a lower Nb content of 3 wt.% and lamellar α′ martensite at an Nb content of 5 wt.%. Among the alloys, the Ti-3Nb-13Ta-2Zr alloy shows the highest compressive strength (2270 ± 10 MPa) and compressive strain (74.3% ± 0.4%). This superior performance is due to the combination of α+β dual-phase microstructure and stress-induced α" martensite. Besides, lattice distortion caused by Ta element also contributes to the compressive properties. Nb and Ta contents of the alloys strongly affect Young's modulus and tensile properties after rolling. The as-rolled Ti-3Nb-13Ta-2Zr alloy exhibits much lower modulus due to lower Nb content as well as more α" martensite and β phase with a good combination of low modulus and high strength among all the designed alloys. Atom probe tomography analysis reveals the element partitioning between the α and β phases in which Ta concentration is higher than Nb in the α phase. Also, the concentration of Ta is lower than that of Nb in the β phase, indicating that the β-stability of Nb is higher than that of Ta. This work proposes modern α+β dual-phase Ti- x Nb- y Ta-2Zr alloys as a new concept to design novel biomedical Ti alloys with high performance.

Microstructural characterisation and mechanical properties of Ti-5Al-5V-5Mo-3Cr built by wire and arc additive manufacture

ABSTRACT The as-deposited microstructure and mechanical properties of the near-β titanium alloy Ti-5Al-5V-5Mo-3Cr (Ti-5553) produced by wire-arc additive manufacture (WAAM) were investigated, to understand its microstructural evolution under WAAM deposition conditions and to establish correlations between the microstructure features formed and the thermal cycles experienced during deposition. The ‘as-deposited’ Ti-5553 WAAM material exhibited higher tensile strengths than other as-deposited additively manufactured Ti-5553 deposits previously reported in the literature, but had significant anisotropy in elongation, as a consequence of the coarse and columnar β-grain structure that formed on solidification, which exhibited a strong cube texture. The multiple reheating cycles, inherent to the WAAM process, were recorded using a novel ‘harpoon’ thermocouple technique, and the α precipitation evolution was related to the thermal history. Electron probe microanalysis chemical maps revealed significant solute microsegregation during solidification, which influenced the subsequent precipitation due to its effect on the local β-phase stability. As each layer experienced more reheating cycles, the microstructure evolution could be ‘time resolved’ and the α laths were found to precipitate in a specific sequence of nucleation sites, starting at the β-grain boundaries and then inter-dendritically, where there was lower matrix β stability. However, after the reheating peak temperature was insufficiently high to have any further effect, the microstructure consisted of a relatively uniform distribution of α laths.

Influence of Β-Phase Stability Affected by Heat Treatment and Elastoplastic Deformation on Mechanical Characteristics and Microstructure of the Titanium Alloy Ti-5al-5v-2mo-Cr

Influence of Β-Phase Stability Affected by Heat Treatment and Elastoplastic Deformation on Mechanical Characteristics and Microstructure of the Titanium Alloy Ti-5al-5v-2mo-Cr

Microstructure transition gradients in titanium dissimilar alloy (Ti-5Al-5V-5Mo-3Cr/Ti-6Al-4V) tailored wire-arc additively manufactured components

The nature of the chemical mixing and microstructure gradients that occur across the interface transition, when manufacturing tailored components with the two high-performance dissimilar titanium alloys (Ti-6Al-4V (Ti-64) and Ti-5Al-5V-5Mo-3Cr (Ti-5553)) by the wire-arc additive manufacturing (WAAM) process, are reported. It has been shown that a relatively long-range chemical gradient occurs during the transition between layers produced with the two different titanium alloys, due to convective mixing in the melt pool between the substrate layers and new alloy wire. This resulted in a stepwise exponential decay composition profile normal to the layers, the width of which can be described by a simple dilution law, with steep local composition gradients seen within the boundary layers at the fusion boundary of each individual layer. The alloy-alloy composition gradients had little effect on the β-grain structure. However, they strongly influenced the transformation microstructure, due to their effect on the parent β-phase stability and the β → α transformation kinetics and reaction sequence. The microstructure gradient seen on transitioning from Ti-64 → Ti-5553 was significantly more abrupt, compared to when depositing the two alloys in the reverse order. Under WAAM thermal conditions, Ti-64 appears to be more sensitive to the effect of adding β-stabilising elements than when Ti-5553 is diluted by Ti-64, because at high cooling rates, stabilisation of the β phase readily suppresses α nucleation when cooling through the β transus, and the normal Ti-64 lamellar transformation microstructure is abruptly replaced by finer scale α laths generated by precipitation during subsequent reheating cycles.

Effect of Fe addition on glass-forming ability, thermal stability of B2 CuZr phase and crystallization kinetics for CuZr-based amorphous alloys

The glass-forming ability (GFA), thermal stability and crystallization kinetics of (Cu0.5Zr0.5)100-xFex (x = 2.5, 5, 7.5, 10 and 12.5 at.%) amorphous alloys were studied in detail. As Fe concentration increases, the GFA and thermal stability decrease first and then increase. The excessive Fe addition significantly deteriorates the GFA due to the precipitation of the FeZr2 phase. Interestingly, with increasing Fe concentration, the crystallization products gradually transit from Cu10Zr7 and CuZr2 to B2 CuZr phase, indicating that Fe addition can effectively enhance the thermal stability of B2 phase. Simulation results show that Fe atoms may be dissolved into the B2 lattice substituting Cu sites and decrease the formation energy, which is similar to Co–or Zn-added CuZr-based alloys. Non-isothermal crystallization behaviors of Cu–Zr–Fe amorphous alloys are well described by the Šesták-Berggren (SB) model instead of the John-Mehl-Avrami (JMA) model due to the multi-phase formation (low Fe concentration) or the nucleation and growth of B2 phase (high Fe concentration). These results could help with the understanding of further stabilizing B2 CuZr phase and the fabrication of high-performance CuZr-based composites.