Zr-based Bulk Metallic Glass Composites Research Articles

Mechanical properties and deformation behavior of Zr-based bulk metallic glass composites reinforced with tungsten fibers or tungsten powders

Mechanical properties and deformation behavior of Zr-based bulk metallic glass composites reinforced with tungsten fibers or tungsten powders

A modified maxwell-pulse thermoplastic constitutive model of in-situ Ta-particle reinforced Zr-based bulk metallic glass composites

The impact of different Ta contents on the mechanical properties and thermoplastic forming ability of in-situ Ta-particle reinforced Zr–Cu–Al–Ni bulk metallic glass composites was studied. The composition (Zr55Cu30Al10Ni5)94Ta6 with the best comprehensive performance was chose for a systematic investigation into its thermoplastic behavior in the supercooled liquid region (SLR), with quantitative analysis conducted by the strain rate sensitivity index and activation volume. The steady-state flow stress and the stress overshoot intensity were augmented with deformation temperature decreasing, strain rate increasing, and the addition of the secondary phase, leading to a transition from Newtonian to non-Newtonian flow regime. The addition of the secondary phase deteriorated the rheological properties of the material. To solve the problem that the Maxwell-Pulse constitutive model showed an inability to accurately describe the steady-state flow process. A modified constitutive relationship, introducing the effect of the volume fraction of Ta particles on viscosity and elastic modulus in the steady-state flow process which was ignored in Maxwell-pulse model, was established. The fitting results of the true stress-strain curves of the modified Maxwell-pulse constitutive model were in better agreement with the experimental date than those of the Maxwell-pulse constitutive model, with higher prediction accuracy. The modified constitutive model well predicted the thermoplastic deformation behavior of (Zr55Cu30Al10Ni5)94Ta6. The influence mechanism of Ta particles on the flow behavior was explained that Ta particles increased the viscosity of amorphous matrix, thereby hindering its flow and ultimately leading to an increase in flow stress.

Cryogenic thermal cycling induced simultaneous improvement of strength and ductility in a Zr-based bulk metallic glass composite

Preparing bulk metallic glass composites (BMGCs) is an effective way to improve the plasticity of bulk metallic glasses (BMGs). However, the enhancement of plasticity is usually at the cost of deterioration in strength. In this study, a series of BMGCs with the nominal composition of Zr48Cu48Al4 was prepared. Finely dispersed B2 CuZr crystals are embedded in a glassy matrix and subsequently, these composites were cryogenically cycled in liquid nitrogen followed by heating to various temperatures below the glass transition temperature. It was found that the samples after cryogenic thermal cycling (CTC) treated at an intermediate upper temperature shown a simultaneous improvement of yielding strength from 1680 MPa to 1832 MPa and plasticity from 5.6% to 9.1%. The enhancement of yielding strength is ascribed to the existence of the B19′ phase resulted from the partial martensitic transformation during the CTC treatment, while the improvement of plasticity is attributed to the higher free volume content and the larger “blocking effect” from the B19’ after the samples were treated by CTC. The combination of CTC treatment and precipitation of crystals provides a new strategy for improving the mechanical properties of the BMGs.

Preparation of tungsten-particle-reinforced Zr-based bulk metallic glass composites by two-step spark plasma sintering: microstructure evolution, densification mechanism and mechanical properties

Preparation of tungsten-particle-reinforced Zr-based bulk metallic glass composites by two-step spark plasma sintering: microstructure evolution, densification mechanism and mechanical properties

Toughening additive manufactured Zr-based bulk metallic glass composites by martensite phase transformation

Additive manufacturing technology based on laser powder bed fusion (LPBF) offers a novel approach for fabricating bulk metallic glass (BMG) products without restriction in size and geometry. Nevertheless, the BMGs prepared by LPBF usually suffered from less plasticity and poorer fracture toughness as compared to their cast counterparts due to partial crystallization in heat-affected zones (HAZs). Since crystallization in HAZs is hard to avoid completely in LPBF BMGs, it is desirable to design a suitable alloy system, in which only ductile crystalline phase, instead of brittle intermetallics, is formed in HAZs. This unique structure could effectively increase the toughness/plasticity of the LPBF BMGs. To achieve this goal, a quaternary BMG system with a composition of Zr47.5Cu45.5Al5Co2 is adopted and subjected to LPBF. It is found that nearly a single phase of B2-ZrCu is precipitated in HAZs, while a fully amorphous phase is formed in molten pools (MPs). This B2 phase reinforced BMG composite exhibits excellent mechanical properties with enhanced plasticity and toughness. Furthermore, it is easy to modulate the mechanical properties by altering the amount of the B2 phase via adjusting the laser energy input. Finally, the best combination of strength, plasticity, and notch toughness is obtained in the BMG composite containing 27.4% B2 phase and 72.6% amorphous phase, which exhibits yield strength (σs) of 1423 MPa, plastic strain (εp) of 4.65%, and notch toughness (Kq) of 53.9 MPa m1/2. Furthermore, a notable strain-hardening is also observed. The improvement of plasticity/toughness and appearance of strain-hardening behavior are mainly due to the martensite phase transformation from the B2 phase to the Cm phase during plastic deformation (i.e., the phase transformation-induced plasticity effect). The current work provides a guide for making advanced BMGs and BMG composites by additive manufacturing.

Constitutive modeling of Ta-rich particle reinforced Zr-based bulk metallic composites in the supercooled liquid region by using evolutionary artificial neural network

In this study, a series of in-situ Ta-rich particle reinforced Zr-based bulk metallic glass composites were successfully fabricated by arc-melting copper-mold spray casting. The effects of Ta content on the room temperature plasticity, compressive strength and thermoplastic formability were studied. (Zr55Cu30Al10Ni5)94Ta6 showed good comprehensive performance, and it was selected to systematically study the deformation behavior in the supercooled liquid region. Different from the strain softening after stress overshoot in bulk metallic glass, the composites showed work hardening in the late stage. Some classical constitutive models cannot accurately describe these phenomena. The back-propagation artificial neural network optimized by particle swarm optimization and genetic algorithm was used to establish the constitutive model. The particle-swarm-optimization back-propagation network with the optimal topology showed high accuracy and good generalization ability. The results predicted with this model were consistent with the experimental data, providing a powerful approach for describing the hot-deformation behavior of these Zr-based bulk metallic glass composites in the supercooled liquid region.

Laser additive manufacturing of laminated bulk metallic glass composite with desired strength-ductility combination

Introducing ductile crystalline dendrites into a glassy matrix to produce bulk metallic glass composites (BMGCs) is an effective way to improve the poor ductility of bulk metallic glasses (BMGs). However, the presence of soft crystalline phases tends to decrease the strength and causes the strength-ductility tradeoff. Here, relying on the flexible laser additive manufacturing (LAM) technique that allows the composition tailoring of each layer, we successfully fabricate a lamellated Zr-based BMGC constructed by the alternating superimposition of soft and hard layers. The lamellated BMGC shows an exceptional combination of yield strength (∼1.2 GPa) and ductility (∼5%). Such enhanced strength-ductility synergy is attributed to the asynchronous deformation at two scales, i.e., inter-laminar and intra-laminar, and the unique dual-scale Ta particles that uniformly distribute on the amorphous matrix. The lamellated structure design motif, enabled by the flexible LAM technology, provides a new window for the development of high-performance BMGCs. It is also applicable to the synergistic enhancement of strength and plasticity of other brittle metallic materials.

Enhanced plasticity in laser additive manufactured Nb-reinforced bulk metallic glass composite

The microstructures and mechanical properties of 50 wt% Nb-reinforced Zr-based bulk metallic glass composites, (BMGCs), manufactured via laser directed energy deposition (LDED) with two different laser powers, P , are investigated and compared with those of LDED manufactured monolithic bulk metallic glass (BMG). Results show that both BMGCs have a multi-component microstructure that includes dual-sized Nb particles and devitrification-induced nano crystals at the melt-pool boundaries whereas the monolithic BMG contains only the latter. The nanocrystals at the melt-pool boundaries embrittle the LDED manufactured monolithic BMG, which reflects as a higher yield strength but negligible plastic deformation in uniaxial compression. In contrast, both BMGCs undergo significant plastic deformation as the Nb-reinforcements, besides improving plasticity by arresting propagating shear bands, reduces the enthalpy of relaxation, Δ H rel , of the matrix and decreases the volume fraction of the nanocrystallites, V nc , at the melt-pool boundaries. However, amongst the two, the BMGC manufactured at higher P exhibits much higher shear band plasticity, despite having higher V nc and lower Δ H rel . This is rationalized by analyzing the load transfer characteristics of the Nb-BMG matrix interfaces in the two BMGCs. • LDED manufactured Nb-reinforced Zr-based BMGCs have significantly improved plasticity. • Nb induced plasticity improvement is achieved through limiting the structural relaxation of amorphous matrix. • Higher thermal diffusivity of Nb can minimize the devitrification induced brittle phases and thus enhance plasticity. • Partially dissolving Nb in the amorphous matrix by sufficient laser power can maximize shear band arresting capabilities.

Laser additive manufacturing of Zr-based bulk metallic glass composite improved by TRIP effect

Laser additive manufacturing (LAM), as a fascinating technique, is equipped with the potential to fabricate bulk metallic glasses (BMGs) with arbitrary geometries. However, the serious thermal stress induced by the LAM process always causes the harmful cracks to be left inside the Zr-based BMGs with brittleness characteristics, which will lead to a sharp deterioration in fracture toughness. To solve this dilemma, B2 phase with excellent plasticity, realizing work-hardening through martensitic transformation, was precipitated during the cooling process of Zr 48 Cu 46.5 Al 4 Nb 1.5 BMG composite (BMGC). The deposited Zr-based BMGCs possess composite structures, i.e ., B2 phase is distributed in the partially crystallized glassy matrix. The TRIP effect provided by B2 phase can not only inhibit the generation of cracks, but also effectively avoid premature shearing-off through the sample to greatly improve the fracture strength.

Fracture toughness of a rejuvenated β-Ti reinforced bulk metallic glass matrix composite

• Cryothermal cycling is performed on embrittled bulk metallic glass composite. • Plasticity of BMGC examined using nanoindentation, DSC and compression tests. • Mode I notch toughness of CTC treated BMGC is same as brittle BMGC. • Rejuvenation is hampered by chemical short range ordering of constituents in amorphous matrix. A β-Ti dendrite reinforced Zr-based bulk metallic glass composite (BMGC) was found to be brittle when cast in a large size. The reasons for the embrittlement and the effectiveness of the cryothermal cycling (CTC) treatment in restoring the mode I fracture toughness are examined. Plasticity in all the CTC treated BMGC is estimated from the distribution and occurrence of pop-ins in nanoindentation tests and by measuring the magnitude of enthalpy of relaxation (Δ H rel ) via differential scanning calorimetry (DSC). This is further validated by examining the strain-to-failure ( ε f ) in compression tests. Mode I fracture behaviour of the as-cast embrittled BMGC and the CTC treated BMGC, which exhibits maximum plasticity, is examined. Results show that both BMGCs are equally brittle and exhibit 5 times lower notch toughness ( K QJ ) than their tougher counterpart. Post-facto imaging of the side surfaces reveals the absence of notch-tip plasticity in both BMGCs. The lack of notch tip plasticity of CTC treated BMGC, despite exhibiting signatures of plasticity in nanoindentation and higher Δ H rel is rationalized by reassessing the origin of pop-ins in nanoindentation tests and describing the variations in chemical and topological short range ordering during CTC, respectively. Implications of these results in terms of improving the fracture toughness of structurally relaxed BMGCs via CTC are discussed.

The micro-zones formation of Zr-based bulk metallic glass composite fabricated by laser 3D printing

In this study, a Zr-based bulk metallic glass composite (BMGC) was successfully fabricated by laser 3D printing with pre-laid powders. The results showed that the printed bulk metallic glass composite was composed primarily (82.5 vol%) of amorphous phase along with a small fraction of intermetallic compounds. The crystallization characteristics of different micro-zones in the as-printed BMGC were studied. It was found that the molten pool had a fully amorphous structure, while some nanocrystals were found in the re-melted zone, and both dendrites and nanocrystals were observed in the heat affected zone (HAZ). The nanoindentation results showed that the HAZ had the highest hardness, elastic modulus, and elastic recovery compared with the re-melted zone and molten pool zone. The forming mechanism of bulk metallic glasses composite was further studied by finite element analysis of the heating and cooling processes in laser 3D printing.

Mechanical properties and Weibull reliability analysis of tungsten-particle reinforced Zr-based bulk metallic glass composites

Tungsten-particle (Wp) reinforced Zr-based bulk metallic glass composites (Wp/BMGCs) were prepared by spark plasma sintering (SPS). The effects of the volume fraction of Wp on the densification and mechanical properties of the composites were studied. Weibull statistics were used to analyze the variability of compressive strength of Wp/BMGCs. The Weibull modulus (m) has a strong correlation with the volume fraction of Wp. The lower the volume fraction of Wp, the more uniform the compressive strength of the Wp/BMGCs, and the more reliable the materials should be in practical application.

Effect of particle size on dynamic mechanical behaviors of W particles/Zr-based bulk metallic glass composites

The effect of particle size on the dynamic mechanical behavior of W particle /Zr-based bulk metallic glass composites (Wp/BMGCs) was investigated by split Hopkinson pressure bar (SHPB) and finite element method (FEM). The yield strength decreases with the increase of W particles size under quasi-static compression, while the fracture strain increases. The BMGC with 60% Wp shows the highest fracture strain, and the BMG matrix shows a uniform rheological characteristic which is different from the brittle fracture characteristic. Under dynamic compression, the yield strength of the BMGCs does not show obvious strain rate sensitivity, and the dynamic fracture strain is significantly lower than the quasi-static fracture strain. With the increase of the W particles size, the cladding on the BMG matrix weakened, and the fracture mode changed from fragmentation to shear fracture. We consider that the combination of interface debonding and cleavage fracture was the very reason for the changed fracture mode. It is found that the Ansys/LS-DYNA code is able to predict the response of the Wp/BMGCs in the element mesh if special care is taken, and good agreement is in general obtained between the numerical simulations and experimental results.

A real-time TEM study of the deformation mechanisms in β-Ti reinforced bulk metallic glass composites

The deformation mechanisms in a β-Ti reinforced Zr-based bulk metallic glass composite (BMGC) are studied by extracting submicron sized tensile coupons of the crystalline and amorphous phase in their monolithic and bilaminate composite forms and tensile testing them inside a TEM. Results show that the monolithic BCC crystalline phase and amorphous phase have high yield strains, owing to small length scale effects, but undergo negligible post-yield elongation before failure. However, the ductility of the bilaminate composite is significantly higher (~12.4%), provided the thickness of its amorphous portion is < 100 nm. Real time videos, which are supplemented by molecular dynamics simulations, show that the negligible post yield elongation of the monolithic BCC crystalline phase is caused by planar slip on one of the {110} planes. However, the bilaminate composite form exhibits strain hardening, despite the occurrence of planar slip, as dislocations pile up at the impervious amorphous/crystalline interface, which in turn, activates slip on other {110} planes. Strain hardening in the crystalline phase ceases when a shear band nucleated in the amorphous phase penetrates the dendrite along one of the slip planes. These mechanisms are extended to explain the flow behavior of β-Ti reinforced BMGCs and strategies to improve the ductility are discussed.

Controllable additive manufacturing of gradient bulk metallic glass composite with high strength and tensile ductility

Introducing ductile crystalline dendrites into glassy matrix to produce in situ bulk metallic glass composites (BMGCs) is an effective strategy to enhance the ductility of bulk metallic glasses (BMGs). However, the microstructural control of the crystalline dendrites is a challenge, and potent toughening of BMGs often requires a high volume fraction of the crystalline phase that impairs the strength and causes the strength-ductility tradeoff. Moreover, existing processing techniques of BMGCs mostly rely on liquid metal casting, which imposes an inherent size limitation due to the required rapid cooling for glass formation. Here we fabricate a multi-layered Zr-based BMGC with a well-controlled gradient in volume fraction of the crystalline dendrites via laser additive manufacturing (LAM) that allows site-specific control of the cooling rate and the resultant microstructure. The gradient BMGC shows an exceptional combination of yield strength (>1.3 GPa) and tensile ductility (~13%). Such enhanced strength-ductility synergy is attributed to the synergetic strengthening from the interaction of the adjacent layers and the asynchronous deformation mode associated with the heterogeneous microstructure. The gradient or functionally-graded structure design motif, enabled by the versatile LAM technology, opens a new window to the development of high-performance BMGCs on a large scale for structural applications.

Developing in-situ Zr-based bulk metallic glass composites from multi-cluster competition strategy

The mechanism of structural evolution and phase formation for in-situ bulk metallic glass composites (BMGCs) remains unclear and needs to be described via a comprehensive strategy. Herein, four chemical compositions (named as ZN10, ZN30, ZN50, and ZN70, respectively) were designed and used as base alloys for exploring the microstructures and mechanical properties from the thermodynamic and structural points of view. A pseudo-binary (ZrNb)-(CuNiAl) phase diagram was constructed to predict the relationship between structural evolutions and chemical compositions. Phase formation and composition distributions of bulk metallic glasses (BMGs) and in-situ BMGCs were carefully investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) equipped with an energy-dispersive spectrometer (EDS). Based on experimental results, the structural evolutions were analyzed and discussed in details, showing the evolution from the atomic-scale ordered clusters to micro-scale phase precipitation in the supercooled liquid. Furthermore, the compressive mechanical tests of as-cast samples were performed to unveil the correlation between microstructures and deformation behaviors of different alloys. It is believed that the proposed strategy and experimental results can deepen the understanding of the formation of BMGs and in-situ BMGCs associated with atomic-scale ordered structures, and provide new insights to design in-situ BMGCs from the structural perspective.

Effect of infiltrating time on interfacial reaction and properties of tungsten particles reinforced Zr-based bulk metallic glass composites

The tungsten particles reinforced Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit 1 alloy) bulk metallic glass composites (BMGCs) were prepared by the melt infiltrating casting method with the infiltrating time of 1, 5 and 10 min, respectively. The changes of interfacial reaction and compression properties of the bulk metallic glass composites with different infiltrating times were studied. Results show that with the increase of infiltrating time, tiny nanocrystals are generated at the interfacial boundary of tungsten particles and the amorphous matrix, and the size of tiny crystals increases with the infiltrating time. When the infiltrating time is 10 min, polygonal crystals with a larger size are also generated within the amorphous matrix. The compressive strength of the composites also increases with the infiltrating time. When the infiltrating time is 10 min, the compressive strength of the composite reaches 2,030 MPa and the compression strain is 44%. The fracture morphology of the composite materials is in a vein-like pattern and the melting phenomenon is found on the fracture surface. In addition, the density of the shear bands during the compressive tests of the composite materials increases with the infiltrating time.

Dynamic compressive mechanical properties of the spiral tungsten wire reinforced Zr-based bulk metallic glass composites

In this study, bulk metallic glass composite (BMGC) reinforced with a novel spiral structure of tungsten wires was prepared. The composite exhibits a high ultimate strength of 2830 MPa and a large plasticity of 26% under quasi-static compression. The dynamic compressive mechanical properties of this BMGC were also systematically investigated by split Hopkinson pressure bar technique. It is found that the yield stress of the composite under uniaxial compression increases firstly and then decreases with increasing the strain rate. To describe the strain-rate dependence of the yielding behavior of the composite, a constitutive model considering adiabatic shear localization was established. Furthermore, the deformation and fracture behaviors of the composite under quasi-static and dynamic compression were discussed in detail. Different from the tungsten fiber reinforced bulk metallic glass composites (BMGCs), the spiral tungsten wire reinforced BMGC fractured in a shear mode, which is distinctly favorable to the self-sharpening capability. These findings could deepen the understanding of deformation behaviors and failure modes of BMGCs and promote their applications.

Enhancing dynamic mechanical properties of bulk metallic glass composites via deformation-induced martensitic transformation

Due to the lack of plastic strain accommodation and work-hardening capability, brittleness still dominates dynamic deformation in most bulk metallic glass composites (BMGCs). Herein, we present a series of Zr-based BMGCs characterized with a unique combination of fracture strain of ~15%, ultimate strength of ~1550 MPa and unusual two-stage work-hardening behavior upon dynamic loading. The strain-induced martensitic transformation occurred, not only homogenizes the dynamic plastic flow, but also compensates the amorphous work-softening. Our work highlights a novel route for developing high-performance BMGCs for high-speed applications, and sheds new insights on the deformation mechanisms of BMGCs.

Additive Manufactured Large Zr-Based Bulk Metallic Glass Composites with Desired Deformation Ability and Corrosion Resistance.

Zr-based bulk metallic glasses have been attracting tremendous interest of researchers because of their unique combination of mechanical and chemical properties. However, their application is limited as large-scale production is difficult due to the limitation of cooling rate. Recently, additive manufacturing technology has been proposed as a new solution for fabricating bulk metallic glasses without size limitation. In this study, selective laser melting technology was used to prepare Zr60Fe10Cu20Al10 bulk metallic glass. The laser parameters for fabricating full dense amorphous specimens were investigated. The mechanical and corrosion resistance properties of the prepared samples were measured by micro-compression and electrochemical corrosion testing, respectively. Lastly, Zr60Fe10Cu20Al10 bulk metallic glass (BMG) with dispersed nano-crystals was made, and good deformation ability was revealed during micro-compression test. The corrosion resistance decreased a bit due to the crystalline phases. The results provide a promising route for manufacturing large and complex bulk metallic glasses with better mechanical property and acceptable corrosion resistance.