Bulk Metallic Glass Matrix Research Articles

Combined effect of isothermal annealing and pre-compression on mechanical properties of Cu36Zr48Al8Ag8 bulk metallic glass

The combined effects of isothermal annealing and pre-compression on the mechanical properties of Cu36Zr48Al8Ag8 bulk metallic glass (BMG) were investigated. The as-cast specimens were first annealed at 743 K for 10 min, and then pre-compressed under 800 MPa for 1, 3, 5 and 10 h, respectively. The results indicated that annealing resulted in the formation of nanocrystals with a diameter of ~10 nm in the amorphous matrix and a drastic decrease of the free volume, leading to complete loss of the plasticity of the BMG. Applying pre-compression under a stress of 800 MPa for a proper duration (5 h) resumed part of the lost free volume in the BMG matrix and therefore partially recovered the plasticity. A very long period of pre-compression (10 h) decreased the free volume again, which was caused by the excessive crystal growth.

Wear behaviour of Zr-based in situ bulk metallic glass matrix composites

Zr-based bulk metallic glass (BMG) and its in situ BMG matrix composites with diameter of 3 mm were fabricated by conventional Cu-mould casting method and the dry sliding wear behaviour of the BMG and composites was investigated. Compared to the pure BMG, the composites exhibited a markedly improved wear resistance from 10 to 48% due to the existence of various volume fractions of the ductile β-Zr dendritic phase embedded in the glassy matrix. The composites showed lower friction coefficient and wear rate than the pure BMG. Meanwhile, the surface wearing of the composite with a proper amount of β-Zr dendrites was less severe compared to that of the pure BMG. The worn surface of the composite was covered with mild grooves and some fine wear debris, which exhibited the characteristic of a mild abrasive wear. The improvement of the wear resistance of the composite with the proper amount of β-Zr crystalline phase is attributed to the fact that the β-Zr crystalline phase distributed in the amorphous matrix has some effective load bearing, plastic deformation and work hardening ability to decrease strain accumulation and the release of strain energy in the glassy matrix, restrict the expanding of shear bands and cracks, and occur plastic deformation homogeneously.

Towards an understanding of tensile deformation in Ti-based bulk metallic glass matrix composites with BCC dendrites.

The microstructure and tension ductility of a series of Ti-based bulk metallic glass matrix composite (BMGMC) is investigated by changing content of the β stabilizing element vanadium while holding the volume fraction of dendritic phase constant. The ability to change only one variable in these novel composites has previously been difficult, leading to uninvestigated areas regarding how composition affects properties. It is shown that the tension ductility can range from near zero percent to over ten percent simply by changing the amount of vanadium in the dendritic phase. This approach may prove useful for the future development of these alloys, which have largely been developed experimentally using trial and error.

Multi-scale Characterisation of the 3D Microstructure of a Thermally-Shocked Bulk Metallic Glass Matrix Composite.

Bulk metallic glass matrix composites (BMGMCs) are a new class of metal alloys which have significantly increased ductility and impact toughness, resulting from the ductile crystalline phases distributed uniformly within the amorphous matrix. However, the 3D structures and their morphologies of such composite at nano and micrometre scale have never been reported before. We have used high density electric currents to thermally shock a Zr-Ti based BMGMC to different temperatures, and used X-ray microtomography, FIB-SEM nanotomography and neutron diffraction to reveal the morphologies, compositions, volume fractions and thermal stabilities of the nano and microstructures. Understanding of these is essential for optimizing the design of BMGMCs and developing viable manufacturing methods.

Glass-forming ability, thermal stability of B2 CuZr phase, and crystallization kinetics for rapidly solidified Cu–Zr–Zn alloys

The glass-forming ability (GFA) of (Cu0.5Zr0.5)100-xZnx (x = 1.5, 2.5, 4.5, 7, 10, and 14 at %) metallic glasses (MGs) was studied. With increasing Zn content, the GFA of CuZr-based MGs gradually increases, enabling the fabrication of Cu–Zr–Zn bulk metallic glasses (BMGs) and metallic glass matrix composites. The enhancement of GFA with Zn addition to the CuZr binary alloy is well explained by considering topological instability and electronic criteria. Upon annealing of Cu–Zr–Zn MGs Cu10Zr7 and subsequent CuZr2 crystals precipitate in the glassy matrix, being followed by the nucleation of B2 CuZr crystals. It is shown that Zn addition can effectively stabilize B2 CuZr phase to lower temperatures. Analysis of the crystallization kinetics of Cu–Zr–Zn MGs under isothermal conditions shows that the dominated crystallization mechanism is the interface-controlled two- or three-dimensional growth with different nucleation rates.

Controlling crystallization process and thermal stability of a binary Cu–Zr bulk metallic glass via minor element addition

In this paper, the effect of minor element addition on the initial structural evolution during crystallization in a simple binary Cu–Zr bulk metallic glass (BMG) forming liquid has been investigated by using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Despite no changes in the completely crystallized products, the remarkable opposite impacts on the supercooled liquid region (SLR) and crystallization reaction rate constant [Formula: see text] are observed as a result of minor selective additions of an affine element, i.e., Sn and an immiscible element, i.e., Nb into the Cu–Zr BMG alloy, respectively. Furthermore, it is demonstrated that the primary devitrification pathway and crystalline phases are simultaneously modified, which leads to significant changes in kinetics of atomic rearrangement and thus thermal stability of this material. Such a finding offers a promising way to control the type of primary crystalline phases of BMG-forming metallic supercooled liquids to synthesize novel BMGs or BMG matrix composites for structural or functional applications.

Dynamic mechanical behavior of a Zr-based bulk metallic glass composite

Dynamic mechanical analysis (DMA) was used to study the viscoelastic properties of a Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 (LM2) bulk metallic glass (BMG) matrix composite. The temperature spectrum and the frequency spectrum were tested by three point bending. We revealed that the relaxation process of the LM2 composite is different from the single amorphous alloys. The unique superimposition of glass transition (α-relaxation) and β-phase transformation during DMA results in double peaks on the loss modulus evolution and a plateau on the storage modulus evolution. The numerical analysis of the isothermal spectrum suggests that the dynamic relaxation behavior of the LM2 composite cannot be described by a single classical relaxation model. A coupling model is instead proposed to well quantify the coupling effect of the α-relaxation and β-phase transformation in the LM2 BMG composite. Our findings provide an insight into understanding the more complex structural relaxation of BMG composite than monolithic BMGs.

Development and microstructure optimization of Mg-based metallic glass matrix composites with in situ B2-NiTi dispersoids

Abstract In this paper, we designed a novel processing method and successfully developed in situ precipitated B2-NiTi shape-memory-alloy reinforced Mg-based bulk metallic glass matrix composites (BMGMCs). The composites exhibited improved fracture strength in both compressive and flexural modes and large plastic deformation in compressive mode compared with those of its monolithic glassy counterpart. The stress-induced martensitic transformation of B2-NiTi in this system caused the composite to exhibit work-hardening behavior, especially during compression. The microstructure of the composite was optimized by decreasing the size and increasing the volume fraction of the B2-NiTi phase, to obtain better mechanical properties. This novel in situ method is applicable to fabricating various BMGMCs, making it a breakthrough for designing ductile work-hardenable BMGMCs.

Infrared thermal processing history of a Ti-based bulk metallic glass matrix composite manufactured via semi-solid forging

A method for using non-contact infrared thermal imaging for determining the processing history of bulk metallic glass matrix composites (BMGMCs) during semi-solid forging is presented. The technique allows for the first estimations of the relevant parameters associated with semi-solid forging, including the heating profile, forging temperatures, cooling rates, and formability parameters. The processing parameters are correlated with microstructure and a new forging viscosity estimation is developed and compared with other techniques. The research offers a new strategy for thermal measurements that is widely applicable to other manufacturing processes.

A micromechanics-based incremental damage theory of bulk metallic glass matrix composites

Based on the Mori–Tanaka’s mean field concept, a micromechanics-based incremental damage theory was developed to investigate the mechanical performance of bulk metallic glass matrix composites under tension. Firstly, the shear band was considered to be a microcrack, and therefore a spherical fictitious inclusion-containing microcracks and the surrounding bulk metallic glass matrix were constructed. Based on the equivalence between the effective elasticity of microcrack-containing media and porous material, the volume fraction of the fictitious inclusion could be determined by the density of microcracks generated during a strain increment. The stress-based Weibull probability distribution function and percolation theory were applied to describe the microcrack evolution that results in the progressive damaging of bulk metallic glass composites. Based on the present model, the impact of shear bands on the tensile ductility was discussed for the composites with various microstructures. The predictions are in fairly good agreement with the experimental data, demonstrating that the developed analytical model is capable of successfully capturing the main features, such as yield strength, strain hardening, and stress softening elongation, of particle-toughened bulk metallic glass. The main conclusions will shed some light on optimizing the microstructures in effectively improving the tensile ductility of bulk metallic glass composites.

Numerical study of shear banding evolution in bulk metallic glass composites

In this article, a systematic simulation was performed to demonstrate the detailed shear banding evolution in bulk metallic glass (BMG) composites subjected to the tension, and the relation between microstructures and tensile ductility was therefore elucidated. Free volume was adopted as an internal state variable to characterize the shear banding nucleation, growth and coalescence in BMG matrix with the help of free volume theory, which was incorporated into ABAQUS finite element method (FEM) code as a user material subroutine. The present numerical method was firstly verified by comparing with the corresponding experimental results, and then parameter analyses were conducted to discuss the impacts of particle volume fraction, particle shape, particle orientation and particle yielding strength on the enhancement efficiency of the tensile ductility of BMG composites.

Strong work-hardening behavior induced by the solid solution strengthening of dendrites in TiZr-based bulk metallic glass matrix composites

A series of TiZr-based bulk metallic glass matrix composites (BMGMCs) with distinguished mechanical properties are successfully fabricated by adding different volume fractions of Ta (Ti38.8Zr28.8Cu6.2Be16.2Nb10 as the basic composition, denoted as Ta0.0–Ta8.0). Along with the growth of precipitated phase, typical dendritic morphology is fully developed in the TiZr-based BMGMCs of Ta8.0. Energy-dispersive spectrometry analysis of the dendrites and glass matrix indicates that the metallic elements of Nb and Ta should preferentially form solid solution into dendrites. The chaotic structure of high-temperature precipitate phase is trapped down by the rapid cooling of the copper-mould. The detected lattice distortions in the dendrites are attributed to the strong solid solution strengthening of the metallicelements of Ti, Zr, Nb, and Ta. These lattice distortions increase the resistance of the dislocation motion and pin the dislocations, thus the strength and hardness of dendrite increase. Dendrites create a strong barrier for the shear band propagation and generate multiple shear bands after solid solution strengthening, thereby providing the TiZr-based BMGMCs with greatly improved capacity to sustain plastic deformation and resistance to brittle fracture. Thus, the TiZr-based BMGMCs possess distinguished work-hardening capability. Among these TiZr-based BMGMCs, the sample Ta0.5 possesses the largest plastic strain (εp) at 20.3% and ultimate strength (σmax) of 2613MPa during compressive loading. In addition, the sample of Ta0.5 exhibits work-hardening up to an ultrahigh tensile strength of 1680MPa during the tensile process, and then progressively softens until it fractures at a strain of 10.2%.

Computational micromechanics analysis of toughening mechanisms of particle-reinforced bulk metallic glass composites

Based on the interaction between the dislocation-sliding and shear-banding, numerical simulations were performed to elucidate the toughening mechanisms of bulk metallic glass (BMG) composites under tension. During the numerical modeling, the free volume theory was applied for the BMG matrix, and free volume density acts as an internal state variable to describe the evolution of shear banding. While the mechanism-based strain gradient plasticity theory was adopted to describe the crystalline second phase, and dislocation density was employed to track the dislocation sliding. With the aid of the user material subroutines (UMAT) in the ABAQUS code, these theories were implemented for predicting the tensile deformation of BMG composites. Numerical results showed that the proposed model could successfully describe the enhanced ductility of BMGs by introducing varied sized of crystalline particles. The predictions were in good agreement with the experimental results. Additionally, the toughing micro-mechanism was clearly clarified from the strong interaction between the dislocation propagation and shear bands. It is further noted that the tensile ductility of a BMG composite is very sensitive to the parameters of the back stress, Taylor factor and particle size. The present results will shed some light on optimizing the microstructures in effectively improving the tensile ductility of BMG composites.

Dynamic shear punch behavior of tungsten fiber reinforced Zr-based bulk metallic glass matrix composites

Dynamic shear punch tests were carried out on the tungsten fiber reinforced Zr-based bulk metallic glass composites. The experimental results show that with the increasing fiber volume fraction, the failure mode of the composites switches from shear to tensile fracture. A new failure criterion, based on the Tsai-Hill criterion and the unified failure criterion for bulk metallic glasses, is proposed to characterize fracture behavior of this bulk metallic glass composite. It is found that the shear-to-normal strength ratio α controls the transition of failure mode of this metallic glass composite. The underlying mechanism of the transition of failure mode is discussed as well.

Effect of compositional tailoring on the glass-forming ability and mechanical properties of TiZr-based bulk metallic glass matrix composites

A large amount of free volume (FV) or the precipitation of ductile dendrites from the glass matrix generally leads to the enhanced plasticity of bulk metallic glasses (BMGs). In this study, the structural relaxation enthalpy ΔHrel (the measure of FV amount) is found to increase after adding Nb or Fe to the glass matrix. As a result, a series of centimeter-scale plastic BMGs is fabricated. Among these TiZr-based BMGs, the sample (Ti32.8Zr30.2Cu9Ni5.3Be22.7)0.9Nb10 (at%) possesses the largest plastic strain (εp) of 8.3% and ultimate strength (σmax) of 2080MPa. By further precisely tailoring the composition, a TiZr-based BMG matrix composite (BMGMC) (Ti38.8Zr28.8Cu6.2Be16.2Nb10, at%) possessing both the precipitation of β-Ti and β-Zr dendrites simultaneously has been fabricated. The TiZr-based BMGMC has both the distinguished plastic strain (εp) of 12% and ultimate strength (σmax) of 2150MPa. The values of yielding strength (σy) significantly decreased with the increase of suction casting diameter, whereas the work-hardening phenomenon is more obvious. Therefore, a critical size and volume fractions corresponding to the best mechanical properties of TiZr-based BMGMC should exist. The ductile dendrites are crucial to impeding shear band propagation and generating multiple shear bands in the glass matrix. Results indicate that a large amount of lattice distortions, pile-ups of dislocations and shear steps can be attributed to distinguished plasticity, and these constitute the deformation mechanism of TiZr-based BMGMC.

Shape Memory Behavior of Zr-Cu-Al Bulk Metallic Glass Matrix Composite

Zr-Cu-Al bulk metallic glass matrix composite with the intermetallic compound ZrCu (B2) phase was fabricated. The effect of the ZrCu phase on mechanical properties and deformation behavior of the composite was investigated by compressive test. Also, phase transformation behavior of the ZrCu phase was analyzed by X-ray diffraction. Furthermore, macroscopic shape memory behavior was investigated using the composite by three point bending test. As the results, it was found that the mechanical properties of the composite depend on the volume fraction of the precipitated ZrCu phase. Compressive strength and yield stress of the composite decrease with increase of volume fraction of the ZrCu phase. On the other hand, plastic strain increases with increase of volume fraction of the ZrCu phase. In addition, it was confirmed that a stress-induced martensitic transformation of the ZrCu phase occurs by compressive stress loading. Furthermore, it was found that the composite with high volume fraction of the ZrCu phase exhibits shape memory effect.

Designing Bulk Metallic Glass Composites with Enhanced Formability and Plasticity

To address the main stumbling-block of bulk metallic glasses (BMGs), i.e., room temperature brittleness, designing BMG matrix composites has been attracted extensive attention. Up to date, BMG composites in various alloy systems have been successfully developed by forming crystalline phases embedded in the amorphous matrix through either ex-situ or in-situ methods. In this paper, a brief review of our recent work in this topic will be presented and the novel approaches to improving composite formability and mechanical properties will also be highlighted. The main purpose of this manuscript is not to offer a comprehensive review of all the BMG composites, but instead focuses will be placed on illustrating recently developed advanced BMG composites including Fe-based BMG composite with no metalloids, Al-based BMG composite and BMG composites reinforced by the TRIP (transformation-induced plasticity) effects. The basic ideas and related mechanisms underlying the development of these novel BMG composites will be discussed.

Dry Sliding Tribological Properties of a Dendrite-reinforced Zr-based Bulk Metallic Glass Matrix Composite

In-situ dendrite-reinforced metallic glass matrix (MGM) composites with the composition of Zr58.5Ti14.3Nb5.2Cu6.1Ni4.9Be11.0 were prepared with a vacuum arc melter by the copper mold suction casting. Effect of different normal loads and sliding velocities on the tribological properties of MGM composites was studied. The results showed that the friction coefficient and wear rate of composites initially descended with increasing the normal load and reached a minimum of 0.339 and 1.826 × 10−4 mm3/(N m) at 10 N, respectively, then ascended. Similarly, the friction coefficient and wear rate of composites initially decreased with the increase in the sliding velocity and reached a minimum of 0.330 and 2.389 × 10−4 mm3/(N m) at 0.4 m/s and 0.3 m/s, respectively, then raised. The wear mechanism of composites was mainly adhesive wear accompanied by abrasive wear at lower normal load and sliding velocity. However, the wear mechanism of composites was abrasive wear and adhesive wear as well as delamination at higher normal load and sliding velocity due to the nucleation and propagation of surface and subsurface cracks during the wear process. The flake-like and particle-like wear debris was the dominant shapes of debris observed.

Investigation of the microcrack evolution in a Ti-based bulk metallic glass matrix composite

The initiation and evolution behavior of the shear-bands and microcracks in a Ti-based metallic-glass–matrix composite (MGMC) were investigated by using an in-situ tensile test under transmission electron microscopy (TEM). It was found that the plastic deformation of the Ti-based MGMC related with the generation of the plastic deformation zone in crystalline and shear deformation zone in glass phase near the crack tip. The dendrites can suppress the propagation of the shear band effectively. Before the rapid propagation of cracks, the extending of plastic deformation zone and shear deformation zone ahead of crack tip is the main pattern in the composite.

Microyielding of Core-Shell Crystal Dendrites in a Bulk-metallic-glass Matrix Composite

In-situ synchrotron x-ray experiments have been used to follow the evolution of the diffraction peaks for crystalline dendrites embedded in a bulk metallic glass matrix subjected to a compressive loading-unloading cycle. We observe irreversible diffraction-peak splitting even though the load does not go beyond half of the bulk yield strength. The chemical analysis coupled with the transmission electron microscopy mapping suggests that the observed peak splitting originates from the chemical heterogeneity between the core (major peak) and the stiffer shell (minor peak) of the dendrites. A molecular dynamics model has been developed to compare the hkl-dependent microyielding of the bulk metallic-glass matrix composite. The complementary diffraction measurements and the simulation results suggest that the interface, as Maxwell damper, between the amorphous matrix and the (211) crystalline planes relax under prolonged load that causes a delay in the reload curve which ultimately catches up with the original path.