Ti-based Bulk Metallic Glass Composites Research Articles

Tensile Deformation Mechanism of an In Situ Formed Ti-Based Bulk Metallic Glass Composites.

Ti-based bulk metallic glass composites (BMGMCs) containing an in situ formed metastable β phase normally exhibit enhanced plasticity attributed to induced phase transformation or twinning. However, the underlying deformation micromechanism remains controversial. This study investigates a novel deformation mechanism of Ti-based BMGMCs with a composition of Ti42.3Zr28Cu8.3Nb4.7Ni1.7Be15 (at%). The microstructures after tension were analyzed using advanced electron microscopy. The dendrites were homogeneously distributed in the glassy matrix with a volume fraction of 55 ± 2% and a size of 1~5 μm. The BMGMCs deformed in a serrated manner with a fracture strength (σf) of ~1710 MPa and a fracture strain of ~7.1%, accompanying strain hardening. The plastic deformation beyond yielding was achieved by a synergistic action, which includes shear banding, localized amorphization and a localized BCC (β-Ti) to HCP (α-Ti) structural transition. The localized amorphization was caused by high local strain rates during shear band extension from the amorphous matrix to the crystalline reinforcements. The localized structural transition from BCC to HCP resulted from accumulating concentrated stress during deformation. The synergistic action enriches our understanding of the deformation mechanism of Ti-based BMGMCs and also sheds light on material design and performance improvement.

Microstructure and Mechanical Properties of Multilayered Ti-Based Bulk Metallic Glass Composites Containing Various Thicknesses of Ti-Rich Laminates.

In order to optimize the balance between strength and toughness, a series of multilayered Ti-based bulk metallic glass composites (BMGCs) with varying thicknesses of Ti-rich layers were successfully fabricated. The findings reveal that with an increase in the thickness of the Ti-rich layers, both the flexural yield strength and ultimate strength decreased from 2066 MPa and 2717 MPa to 668 MPa and 1163 MPa, respectively. Conversely, there was a noticeable increase in flexural strain. The fracture toughness of these multilayered Ti-based BMGCs decreased as the thickness of the Ti-rich layers increased; nevertheless, it stabilized at approximately 80 MPa·m1/2 when the thickness reached 100 μm. It was observed that a shift in the dominant deformation mode may be accountable for this phenomenon. These noteworthy characteristics suggest that adjusting the thickness of Ti-rich layers in multilayered BMGCs can effectively optimize mechanical performance, shedding light on the manufacturing of novel BMGCs with high performance.

Simultaneously promoting strength and ductility by regulating TRIP effect in TiZrCuBeO bulk metallic glass composite

In this study, a novel series of Ti-based bulk metallic glass composites has been developed, exhibiting high specific strength and significant ductility (fracture strain exceeding 11 %). The TRIP effect of these composites was promoted by oxygen microalloying, ensuring uniform deformation under tensile loading. The outstanding mechanical properties could be attributed to the well-controlled metastability of the β phase, as well as the increased volume fraction and variants of martensite, effectively coordinating the micro-strain. It demonstrates that well-designed composition could significantly enhance the TRIP effect and ductility of bulk metallic glass composites, and prevent premature failure while preserving strength.

Boron-induced microstructure evolution and mechanical properties of in situ Ti-based bulk metallic glass composites

The effect of boron(B) on the glass-forming ability (GFA), microstructure evolution and mechanical properties of (Ti48Zr20Nb12Cu5Be15)100-xBx bulk metallic glass composites (x = 0, 0.3, 0.5, 1.0 and 3.0 at. %) alloys was investigated. With increasing boron content to 0.3 at.%, the dendrite size is refiner than that of the other alloys, the B0.3 alloy presents good ductility and high strength at ambient temperature, which is mainly attributed to the strong interaction between dislocations, shear bands and the dendrite/glass interface. When the boron content is lower or higher than the critical value of 0.3 %, multiple slide steps decrease. Once the B content exceeds its maximum solid solubility, the phase instability of β-Ti dendrites and the glass matrix decreases, and more needle-like TiB2 phases and irregular block-like ZrB2 phases within and between the dendrites suppress the initiation of shear bands, resulting in brittle fracture.

Effects of Al addition and cryogenic cyclic treatment on impact toughness of phase-transformable Ti-based bulk metallic glass composites

• Al addition can significantly affect impact toughness of BMGCs at 298 and 77 K • Impact toughness of phase-tranformable BMGCs is sensitive to β-Ti phase stability • Deformation-induced martenstic transformation of β-Ti is largely restricted at 77 K • Cryogenic cyclic treatment affects toughness at 298 and 77 K in different ways • Impact toughness is dominated by crystals at 298 K but by glass matrix at 77 K Developing bulk metallic glass composites (BMGCs) with high toughness is vital for their practical application. However, the influence of different microstructures on the impact toughness of BMGCs is still unclear. The effects of Al addition and cryogenic cyclic treatment (CCT) on the Charpy impact toughness, a K , at 298 and 77 K of a series of phase-transformable BMGCs are investigated in this work. It is found that deformation-induced martensitic transformation (DIMT) of the β-Ti dendrites is the dominant toughening mechanism in the phase-transformable BMGCs at 298 K, but at 77 K, the toughness of BMGCs is primarily determined by the intrinsic toughness of the glass matrix. The addition of Al can moderately tune the β-Ti phase stability, which then affects the amount of DIMT and impact toughness of the BMGCs at 298 K. However, at 77 K, Al addition causes a monotonic decrease in the toughness of the BMGCs due to the embrittlement of the glass matrix. It is found that CCT can effectively rejuvenate the phase-transformable BMGCs, which results in an enhanced impact toughness at 298 K. However, the toughness at 77 K monotonously decreases with increasing the number of CCT cycles, suggesting that the rejuvenation of the glass matrix affects the toughness at both 298 and 77 K of BMGCs, but in dramatically different ways. These findings reveal the influence of microstructures and CCT on the impact toughness of BMGCs and provide insights that could be useful for designing tougher BMGs and BMGCs.

Energy-releasing and phase transitions of Ti-based bulk metallic glass composites during heating

The energy-releasing and phase transitions of Ti-based bulk metallic glass composites (BMGCs) during heating largely remain elusive. Here, the effects of cooling rates and compositional changes on energy-releasing and phase transitions of two BMGCs containing relatively stable β-Ti crystals or metastable β-Ti crystals are investigated. With decreasing the cooling rates, both BMGCs transform from non-equilibrium BMGCs to quasi-equilibrium BMGCs. Moreover, decreasing the Co content reduces the phase stability of β-Ti. DSC heating, isothermal ω-Ti precipitates in β-Ti crystals before Tg, and as the temperature above Tx, the glass matrix undergoes crystallization. With decreasing the cooling rates, both the relaxation and crystallization enthalpies decrease, but which can be significantly enhanced by decreasing the Co content, suggesting that BMGCs with unstable β-Ti dendrites are of better energy-releasing properties. These findings not only reveal the energy changes and phase transitions of BMGCs during heating, but also promote their practical applications as energy-releasing materials.

Non-monotonic influence of cryogenic thermal cycling on rejuvenation and impact toughness of Ti-based bulk metallic glass composites

Cryogenic thermal cycling (CTC) can alter the energy states of bulk metallic glasses (BMGs) and their composites (BMGCs), but the fundamental mechanisms of CTC and their effects on mechanical properties are largely remain elusive. Herein, the effects of CTC on structural evolution and impact toughness, aK, of Ti-based BMGCs containing β-Ti dendrites are investigated. It is found that either rejuvenation or relaxation alternately dominates the structural evolution of the glass matrix, causing a non-monotonic rejuvenation. At 298 K, a more rejuvenated state causes a synergistic toughening by both of the glass matrix and dendrites, and the aK variation trend of BMGCs is the same as the non-monotonic rejuvenation. However, at 77 K, the aK variation trend of BMGCs is just opposite as the non-monotonic rejuvenation of the glass matrix. The rejuvenation/relaxation during CTC are correlated with the impact toughness, which provides a basis for improving toughness of BMGCs by CTC.

Radiation shielding properties of low-density Ti-based bulk metallic glass composites: a computational study

Bulk metallic glasses (BMGs), a new class of structural and functional materials with unique physical and chemical features like high corrosion resistance, high yield strength, low elastic modulus, and transparency to visible light, indicate they could be potential shield against unwanted radiations. This study presents an attempt to investigate radiation shielding efficiencies of a few titanium (Ti)-based BMGs with low densities of range 4.43–5.15 g/cm3. Different shielding properties viz., attenuation coefficients (μ m and μ), half and tenth value layers (HVL and TVL), mean free path (λ), effective atomic number (Zeff), buildup factors (EBF and EABF), and fast neutron removal cross-section (Σ R ) were evaluated in 0.015 − 15 MeV energy range using Phy-X/PSD software. The interaction of charged particles (i.e., H1 and He+2 ions) with BMG samples was investigated in terms of mass stopping power (MSP) and projected range (PR) by deploying Monte Carlo-based SRIM software. The five-parametric geometric-progression (G-P) fitting method was employed to calculate EBF and EABF, whereas Zeff values were calculated through atomic to electronic cross-section ratio. Further, obtained results were compared with two conventional shielding materials: lead (Pb) and heavy concrete (StMg). We found that among 8 BMGs, sample Ti41.9Zr36.3V12.1Cu6.3Be3.4(S1) with the lowest Ti and highest Zr-composition by mass (41.9% and 36.3%, respectively) exhibited the best gamma-rays, fast neutrons, and H1/He+2 ions shielding characteristics with the highest μ m (0.02–15 MeV), μ (0.015−0.2 MeV), Zeff (0.015–0.06 MeV) and Σ R . These values were higher than that of StMg, but lower than those of Pb. Moreover, S1 exhibited the lowest values of HVL, TVL, and λ in 0.015 − 0.2 MeV region for gamma-rays and also has the lowest MSP and PR values for H1/He+2 ions. However, the lowest EBF and EABF values belonged to BMG S1 in intermediate energy region (0.1−2 MeV) only. But, the sample Ti90Al6V4(S7) was the worst among all BMGs and StMg. Thus, low-density Ti-based BMGs have better performances towards gamma-rays, fast neutrons, and H1/He+2 ions shielding and hence the potential to replace conventional StMgs and toxic Pb-based materials.

Cryogenic wear behaviors of a metastable Ti-based bulk metallic glass composite

• The BMGC shows a 48% improvement of wear resistance at 113 K compared to 233 K. • The martensitic transformation was abnormally suppressed after sliding at 113 K. • A strain-dominated transformation is confirmed by inducing a pre-notch by FIB. • The confining effect of metallic glass influences the wear/transformation behaviors. Bulk metallic glass composites (BMGCs) are proven to be excellent candidates for cryogenic engineering applications due to their remarkable combination of strength, ductility and toughness. However, few efforts have been done to estimate their wear behaviors that are closely correlated to their practical service. Here, we report an improvement of ∼ 48% in wear resistance for a Ti-based BMGC at the cryogenic temperature of 113 K as compared to the case at 233 K. A pronounced martensitic transformation ( β -Ti→ α ″-Ti) was found to coordinate deformation underneath the worn surface at 233 K but was significantly suppressed at 113 K. This temperature-dependent structural evolution is clarified by artificially inducing a pre-notch by FIB cutting on a β -Ti crystal, demonstrating a strain-dominated martensitic transformation in the BMGC. The improved wear resistance and suppressed martensitic transformation in BMGC at 113 K is associated with the increased strength and strong confinement of metallic glass on metastable crystalline phase at the cryogenic temperature. The current work clarifies the superior cryogenic wear resistance of metastable BMGCs, making them excellent candidates for safety-critical wear applications at cryogenic temperatures.

Versatile Medium Entropy Ti-Based Bulk Metallic Glass Composites.

An ultra-strong Ti-based bulk metallic glass composite was developed via the transformation-induced plasticity (TRIP) effect to enhance both the ductility and work-hardening capability of the amorphous matrix. The functionally graded composites with a continuous gradient microstructure were obtained. It was found that the austenitic center possesses good plasticity and toughness. Furthermore, the amorphous surface exhibited high strength and hardness, as well as excellent wear corrosion resistance. Compared with the Ti-6Al-4V alloy, bulk metallic glass composites (BMGCs) exhibit better spontaneous passivation behavior during the potential dynamic polarization. No crystallization was observed on the friction surface, indicating their good friction-reduction and anti-wear properties.

Mechanical properties and fracture behaviour of in situ dendrite-intermetallic Ti-based bulk metallic glass composites

The multiphase Ti-based bulk metallic glass composites (BMGCs) consisting of β-Ti dendrites, island-like Ti2Cu intermetallic phases and glassy matrix were designed, and their mechanical properties were investigated by room temperature compression tests. The effect of brittle intermetallic Ti2Cu phase on the mechanical properties and fracture mechanism of multiphase BMGCs was also discussed. Microstructure was adjusted by minor Sn addition and the characteristic sizes of the β-Ti dendrites and glassy matrix decreased with the increase of Sn content. Under compressive loading, the yield strength increased from approximately 1056 MPa to 1429 MPa. The increased yield strength was ascribed to the size effect of the glassy matrix, solid solution strengthening of the β-Ti dendrites and precipitation of the Ti2Cu intermetallic phase. The fracture behaviour was related to the slip bands generating within the dendritic arms and the micro-cavities originating from the interface between the Ti2Cu intermetallic phase and glassy matrix. The existence of the brittle intermetallic phase will not deteriorate the mechanical properties of Ti-based BMGCs. The results may provide an insight into tuning microstructure of the multiphase Ti-based BMGCs to achieve excellent mechanical properties.

Enhanced mechanical properties of dendrite-reinforced Ti-based bulk metallic glass composites by tuning the microstructure

Ti-based bulk metallic glass composites (BMGCs) with the microstructure consisting of micro-scale β-Ti dendrites and nano-scale interdendritic glassy matrix were prepared via suction casting. Effects of minor Sn addition on mechanical behavior of the BMGCs were investigated. It was found that the Sn addition presented “dual effects” on mechanical properties of the dendrites in the BMGCs, i.e., solid solution strengthening and increase of Young's modulus. As a result, remarkably enhanced strength without reducing plasticity could be achieved for the BMGCs. The BMGCs exhibited a unique plastic deformation mode, which was attributed to the presence of the glassy matrix in nano-scale. The results might give some hints for improving the mechanical properties of dendrite-reinforced Ti-based BMGCs by tuning the microstructure.

High strength in-situ beta reinforced Ti-based bulk metallic glass composite produced by laser Powder Bed Fusion using elemental powder mixture

A Ti-based in-situ beta (β) reinforced Ti61.75Zr33.25Cu5 bulk metallic glass composite (BMGC) with unique hybrid microstructure and enhanced mechanical properties were produced using laser Powder Bed Fusion (L-PBF) with elemental powder mixture. The Ti61.75Zr33.25Cu5 BMGC possessed high compressive strength of 1.9 GPa with total strain exceeding 13%, and its microstructure was composed of fine primary β dendrite and amorphous phase in the inter-dendrite. The undissolved Zr particle induced stress accumulation near the particle interface that affected the local shear behavior in the β dendrite and promoted slip bands multiplication. The inhomogeneous distribution of amorphous phase divided the BMGC into strong and weak domains and caused strain partition, leading to back stress strain hardening of the BMGC. It is also found that there exist dispersed ω particles and ω laths in the primary β dendrites during the L-PBF and the deformation process, respectively, leading to high strength but limited plasticity of the BMGC. Further improving the mechanical properties of the BMGC can be achieved by hindering the ω formation through alloying method. This work provides a guidance on the design of novel additively manufactured BMGCs with outstanding mechanical properties using low cost elemental powder mixture.

On low-temperature strength and tensile ductility of bulk metallic glass composites containing stable or shape memory β-Ti crystals

Bulk metallic glass composites (BMGCs) with in-situ formed crystals can display tensile ductility at room temperature, overcoming brittleness of monolithic bulk metallic glasses (BMGs). However, the ductility and toughness of BMGCs severely deteriorate at low temperatures, which has been a longstanding bottleneck hindering their low-temperature applications. Here, the low-temperature tensile properties of two Ti-based BMGCs containing stable β-Ti crystals with dislocation-mediated plasticity (Fe1) or shape memory β-Ti crystals (Fe0) were investigated. With temperature decreasing from 298 to 77 K, the strength of Fe1 increases but its tensile ductility decreases. In comparison, the shape memory Fe0 BMGC exhibits a simultaneous enhancement of strength and tensile ductility as temperature decreases from 298 to 143 K. The superior low-temperature properties of Fe0 are attributed to its combined structure of a glassy matrix and shape memory crystals. As temperature decreasing, the glassy matrix possesses an increased strength which softens as shear bands form, and the shape memory crystals are more inclined to deformation-induced martensitic transformation. Therefore, the combination of characteristic properties of metallic glasses and shape memory crystals in shape memory BMGCs can successfully overcome the low-temperature brittleness. These findings are believed to facilitate the development of BMGCs with superior low-temperature properties and promote their applications at low temperatures.

Double toughening Ti-based bulk metallic glass composite with high toughness, strength and tensile ductility via phase engineering

The popular strategy of overcoming the brittle fracture of bulk metallic glasses (BMGs) is to develop BMG composites (BMGCs). Most BMGCs consist of a single crystalline phase and glassy phase, and they display enhanced plasticities. However, these BMGCs usually display a trade-off in strength, ductility and fracture toughness as most engineering structural materials, which severely hampers their industrial application. To obtain a pronounced combination in tensile strength, tensile ductility and fracture toughness, the multiphase reinforced dispersive Ti-based BMG composite was successfully prepared via phase engineering. The as-prepared BMGC consists of β-phase, α-phase and glassy phase. The composite manifested the tensile mechanical properties with the yield strength of ~ 1410 MPa, ultimate tensile strength of ~ 1625 MPa, and tensile ductility of ~ 3.6%, and fracture toughness of ~ 110 MPa∙m1/2. The outstanding tensile properties are attributed to the double toughening of α-phase and β-phase. The high fracture toughness is ascribed to that the coarser dual crystalline phases lead to the devious crack propagation and crack bridging. Our work highlights a novel route for developing high-performance BMGCs.

Deformation behavior of metallic glass composites and plasticity accommodation at microstructural length-scales

Bulk metallic glass matrix composites represent a unique microstructural design strategy for overcoming the strength/ductility trade-off in structural alloys. Site-specific mechanical behavior of a Ti-based bulk metallic glass composite was evaluated at microstructural length-scale. The micro-pillars on the amorphous matrix showed an average yield point of 1.9 GPa followed by serrated plastic deformation characteristic of shear banding. In contrast, micro-pillars on the crystalline dendritic phase showed a much lower yield strength of 0.72 GPa on average for the four different crystallographic orientations chosen, smooth plastic flow with no recognizable load burst, and stable strain-hardening after yield point. A number of micro-pillars were made at the interface between the glassy matrix and the crystalline dendrite. The mixed micro-pillars showed homogeneous deformation and greater plasticity which was attributed to their smaller stored elastic energy. Shear bands initiated in the amorphous matrix were arrested by the crystalline dendrite, which accommodated plasticity through slip bands and dislocations pile-ups. The interface remained intact after plastic deformation, with no observable signs of devitrification in the amorphous phase.

The cryogenic mechanical property deviation of Ti-based bulk metallic glass composite induced by interstitial element

Although most bulk metallic glass composites (BMGCs) will undergo ductile-to-brittle transition at cryogenic temperature, significant low temperature compression and tensile ductility have been found in a BMGC with the composition of Ti48Zr20Nb12Cu5Be15. In present work, the cryogenic mechanical behavior of BMGCs containing interstitial element was studied for understanding the multiple reinforcement of BMGCs in low temperature environment and for explaining the differences in cryogenic properties of BMGCs. Results show that the Ti-based BMGC will be much more sensitive to impurity elements in cryogenic environment than that at room temperature. Besides, the increase in yield strength of BMGCs with the decrease of temperature is not simply due to the dislocations motion in the dendrites becomes more difficult. Low temperature environment can strengthen the glassy matrix as well as increase the strength of dendrites. Results imply Ti48Zr20Nb12Cu5Be15 BMGC can be a kind of promising materials for low-temperature applications.

Enhancing the plasticity of a Ti-based bulk metallic glass composite by cryogenic cycling treatments

Abstract The effect of cryogenic cycling treatments on the thermal and mechanical properties of a Ti-based bulk metallic glass (BMG) composite was investigated. Even though the macroscopic structures of the dendrite-phase and glass-matrix remain unchanged, the treated samples exhibited a rejuvenation behavior in terms of a higher relaxation enthalpy, which leads to an enhancement of plasticity as high as 90%. Different from the monolithic BMGs, in which rejuvenation has been attributed to the nanoscale structural heterogeneity, rejuvenation in BMG composite is induced by the crystal/amorphous heterogeneous microstructures. The increasing defects around the interfaces may promote formation of multiple shear bands and accommodation of plastic deformation. This work shows clearly that the cryogenic cycling treatments could be an effective and controllable way to modulate mechanical properties of BMG composites.

Designing new work-hardenable ductile Ti-based multilayered bulk metallic glass composites with ex-situ and in-situ hybrid strategy

To overcome the trade-off between the devisable microstructure and the excellent tensile ductility of bulk metallic glass composites (BMGCs), a novel ex-situ and in-situ hybrid strategy is successfully proposed to design a series of the work-hardenable ductile Ti-based multilayered BMGCs (ML-BMGCs). The as-prepared ML-BMGCs, consisting of α-phases, β-phases and amorphous phases, exhibit a controllable multilayered structure of the Ti layers and the amorphous layers with alternative distribution. The size and volume fraction of the crystalline phases are tuned by Nb microalloying. It is found that the ML-BMGCs possess a suitable size and volume fraction of the crystalline phases when Nb microalloying content are 5% (at.) or 8% (at.), and they obtain an optimum combination of the specific strength of 243 MPa g kg­1 or 216 MPa g kg−1, and tensile plasticity of 4.33%±0.1% or 5.10%±0.1%. The deformation mechanism of the as-prepared ML-BMGCs during tension is also revealed. The ex-situ Ti layers and in-situ dendrites together effectively serve as absorbers to suppress the propagation of shear bands and multiply shear bands. And the deformation of ex-situ α-Ti phases by dislocation slip and the transformation from in-situ metastable β-Ti phase to orthorhombic α"-Ti during tension impart significant work-hardening capability to the ML-BMGCs. The present study provides a guidance of developing novel high-performance BMGCs with a controllable microstructure.

Strengthening Ti-based bulk metallic glass composites containing phase transformable β-Ti via Al addition

Ti-based bulk metallic glass composites (BMGCs) containing deformation-induced phase-transformable β-Ti can exhibit large tensile plasticity with superior work-hardening capability, but they generally yield at very low stresses. In this work, Ti-based (Ti0.474Zr0.34Cu0.06Be0.126)100-xAlx BMGCs with modulated β-Ti phase stability have been developed. The yield strength of BMGCs can be significantly enhanced via Al addition, and the tensile plasticity can also be improved by adding 4 at.% of Al. The strong strengthening effect arises from the enhanced phase stability of β-Ti and more covalent-like bonding introduced by Al addition. The current findings provide an effective method to strengthen BMGCs containing phase-transformable β-Ti.