Bulk Metallic Glass Matrix Research Articles

Effect of Cu content on microstructure and mechanical properties of in-situ β phases reinforced Ti/Zr-based bulk metallic glass matrix composite by selective laser melting (SLM)

In this study, non-toxic in-situ β phases of reinforced Ti/Zr-based bulk metallic glass matrix composites (BMGCs) of (Ti0.65Zr0.35)100-xCux (x = 5, 10, 15 at.%) are fabricated via selective laser melting. The effect of Cu content on phase formation, microstructure, and mechanical properties is investigated. The average volume fraction and width of the β phase decreases with increasing Cu content, while a more amorphous phase and the (Ti, Zr)2Cu phase forms. In the center zone of the molten pool, the β phase grows in the direction of the temperature gradient, and the amorphous phase distributes among the β phases. This occurs using: sphere morphology (for x = 5), a more continuous elongated sphere and network morphology (for x = 10), and network morphology (for x = 15), respectively. In the edge zone of the molten pool, due to the smaller cooling rate and the existence of a partially molten zone, the β phase becomes coarser, and an amorphous phase forms for more continuous networks. Furthermore, the hardness improves significantly with increasing Cu content. No crack is found for x = 5. Although the average volume fraction of the β phase for x = 5 is about 90 %, the compression yield strength is 1386 ± 64 MPa, reaching to an average level of conventionally fabricated counterparts, due to finer microstructure, and twinning and martensitic transformation of the β phase.

Tensile deformation mechanism of a bulk metallic glass matrix composite using in situ neutron diffraction

In situ neutron diffraction has been used to study the tensile deformation behaviors of a ZrTi-based bulk metallic glass matrix composites (BMGMC) at room temperature. The crystalline phase yielded prior to the amorphous phase during the tensile loading, and the glassy matrix bore more stress partition during the plastic deformation stage. A redistribution of the applied stress in dendrites occurred in the grains with an orientation of (110) and (200) during the plastic deformation. This work provides new insights into the tensile deformation mechanism of the BMGMCs at the microscopic level.

Versatile fabrication of bulk metallic glass composites reinforced by dissimilar secondary phase

Bulk metallic glass (BMG) matrix composites have attracted increasing attentions in the past decades, for combining the superior strength of BMGs with the excellent malleability of crystalline alloys. Insofar, increasing methods have been developed for the fabrication of BMG composites. However, versatile methods capable of fabricating high-performance BMG composites reinforced by diverse secondary phases remain lack. Here, the versatile fabrication of BMG composites reinforced by dissimilar crystalline alloy via ultrasonic vibration-assisted thermoplastic forming was reported. Wire gauze made of 304 stainless steel and Zr-based BMG were chosen as the secondary phase and the matrix, respectively. The as-prepared BMG composites exhibited metallurgical bonding at the interface between BMG and stainless steel, in contrast to the reference sample prepared by normal thermoplastic forming which exhibited merely mechanical bonding. The formation of metallurgical bonding was attributed to the self-cleaning effect induced by ultrasonic vibration which disposed the surface oxidation layer, and the enhanced atomic interdiffusion between BMG and stainless steel by ultrasonic vibration. The fracture toughness of the as-prepared BMG composites exhibited an improvement from 65 to 132 MPa m1/2. Based on fractography observation, the improved fracture toughness was attributed to the deflection of crack at the interfaces between BMG and stainless steel. These results prove the versatility of ultrasonic vibration-assisted thermoplastic forming in the fabrication of BMG composites.

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.

On the Inoculation and Phase Formation of Zr<sub>47.5</sub>Cu<sub>45.5</sub>Al<sub>5</sub>Co<sub>2</sub> and Zr<sub>65</sub>Cu<sub>15</sub>Al<sub>10</sub>Ni<sub>10</sub> Bulk Metallic Glass Matrix Composites

Bulk metallic glass matrix composites have emerged as new potential material for structural engineering applications owing to their superior strength, hardness and high elastic strain limit. However, their behaviour is dubious. They manifest brittleness and inferior ductility which limit their applications. Various methods have been proposed to overcome this problem. Out of these, introduction of foreign particles (inoculants) during solidification have been proposed as most effective. In this study, an effort has been made to delimit this drawback. A systematic tale has been presented which explain the evolution of microstructure in Zr47.5Cu45.5Al5Co2 and Zr65Cu15Al10Ni10 bulk metallic glass matrix composites with varying percentage of ZrC inoculant as analysed by secondary electron and back scatter electron imaging of as cast unetched samples. A support is provided to hypothesis that inoculation remain successful in promoting phase formation and crystallinity and improve toughness.

Mechanistic origins of work hardening in shape memory alloy particle reinforced ex-situ bulk metallic glass matrix composites

All Bulk Metallic Glasses (BMGs) exhibit strain-softening or elastic-perfectly-plastic response under uniaxial loading. However, contrary to expectations, Shape Memory Alloy (SMA) reinforced BMG matrix composites show work hardening behavior in experiments. In this work, we elucidate the mechanistic origins of this work hardening behavior in representative SMA particle-reinforced ex-situ BMG martix composites through three-dimensional Finite Element Simulations. Results suggest that the synergistic effects of a) partial Austenite to Martensite phase transformation, and, b) elastic loading of the transformed Martensite, in the SMA particle, lead to the work hardening in the uniaxial response of the SMA reinforced BMG matrix composites.

Effect of isothermal annealing on mechanical performance and corrosion resistance of Ni-free Zr59Ti6Cu17.5Fe10Al7.5 bulk metallic glass

Ni-free Zr-Ti-Cu-Fe-Al bulk metallic glass (BMG) is regarded as a prospective candidate for practical applications. However, a high Ti content in the BMG causes a sharp deterioration of mechanical performance. Herein, the effects of isothermal annealing on the structure, mechanical performance, and corrosion resistance of the Zr59Ti6Cu17.5Fe10Al7.5 BMG are investigated. The alloy after a short-time annealing at 573 K shows admirable compressive strength and plasticity of 1910 MPa and 12.1%, respectively, which are much higher than 1733 MPa and 4.3% of the pristine BMG. This enhancement was ascribed to precipitation of ultrafine Al3Zr2 nanograins from the BMG matrix. However, the prolonged annealing induces propagation of nanocrystals and decreases free volume in the alloys, leading to the deterioration of mechanical performance. The electrochemical study demonstrates that the BMG maintains good corrosion resistance after the annealing. This work offers an avenue for designing high-performance Ni-free BMG-based alloys.

Numerical study on deformation behavior of bulk metallic glass composites via modified free-volume theory

A modified free-volume theory accounting for tensile and compressive strength asymmetry of bulk metallic glass (BMG) is implemented into finite element code as a user material subroutine. By means of representative volume element, systematical simulations are carried out to investigate the mechanical response as well as shear band evolution of BMG composites (BMGCs) under both tensile and compressive loadings. Comparison between experiments and simulations proves that this modified free volume model could yield acceptable prediction for both BMG matrix and BMGCs. Furthermore, free-volume is utilized to characterize the shear banding process of BMGCs, which is found to be dependent on volume fraction, shapes, orientation as well as yielding strength of particle materials. The present model could provide a computational tool to analyzing deformation behavior of BMGCs as well as designing new composites with high strength and plasticity.

Microstructural investigation and mechanical properties of rapidly solidified bulk nanocrystalline Fe-based alloys

In this work, the microstructure and mechanical properties of innovative, low cost, bulk metallic glass matrix composites with nominal composition of Fe79B20Cu1, Fe79B16Ti4Cu1, Fe79B16Mo4Cu1 and Fe79B16Mn4Cu1 (at. %) were investigated. The alloys were cast by using a rapid quenching technique and their microstructure was examined by means of X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). XRD analysis revealed the presence of nanocrystalinne α-Fe and Fe2B grains with mean diameters of less than 30 nm. TEM analysis confirmed that the alloys structure consisted of nanograins immersed in amorphous matrix. The hardness of the alloys varied from 723 HV2 for the Fe79B16Ti4Cu1 alloy to 1140 HV2 for the Fe79B20Cu1 alloy. The highest compression strength measured was 3908 MPa for the Fe79B20Cu1 alloy and the lowest 2703 MPa for the Fe79B16Mo4Cu1 alloy. The results clearly demonstrate that bulk, nanocrystalline composites with enhanced mechanical properties can be obtained directly during the manufacturing process.

Effect of loading pressure on mechanical properties and interface characteristics of 7056 Al alloy particle reinforced Zr-Al-Ni-Cu bulk metallic glass matrix composite prepared by spark plasma sintering

In this work, the particle-reinforced 7056 Al alloy/ Zr-Al-Ni-Cu metallic glass composites were successfully prepared by spark plasma sintering (SPS) combined with gas atomization at different loading pressures (45 and 400 MPa). No crystallization was observed throughout the composite and 7056 Al alloy particles were uniformly distributed in the glassy matrix. Due to enhanced densification, higher loading pressure (400 MPa) greatly increased the relative density of the composite from 95% to over 98% and its room-temperature compressive strength. When volume fraction of Al alloy was less than 10 vol%, the strength of the composite was higher than that of pure monolithic BMG obtained by SPS, and its plasticity was also improved. With the higher content of Al alloy, the plasticity of the composite continued to increase, but its strength decreased significantly. With the higher volume fraction of Al alloy (≥30 vol%), yield strength of the composites was accurately described by the iso-stress model. Interface characteristics were investigated by scanning electron microscopy (SEM), nanoindentation and high-resolution transmission electron microscopy (HRTEM). The increase in loading pressure from 45 to 400 MPa caused glassy matrix and Al alloy reinforcement to bond each other more tightly and destroyed the oxide layer at the interface, resulting in an effective increase in the bonding strength of the two-phase interface. A transition layer (∼15 nm) occurred at the interface, and some elements such as Zr, Mg and Zn diffused into the interface between glassy matrix and Al alloy particle.

Effect of L/D on penetration performance of tungsten fibre/Zr-based bulk metallic glass matrix composite rod

Tungsten fibre/Zr-based bulk metallic glass matrix composite (WF/Zr-MG) is a potential penetrator material. In the present paper, the effect of L/D on the penetration performance of WF/Zr-MG rod is studied. Experiments and finite element method (FEM) simulations of WF/Zr-MG and tungsten heavy alloy (WHA) rods with L/D of 18.33, 5.4, 3.89, 3.75 and 1.11 penetrating into armor steel targets (RHA) are conducted. The experimental results show that penetration efficiency (P/L) of WF/Zr-MG rods with L/D of 18.33, 5.4, 3.89 are higher than that of WHA rods with the same L/D, because the penetration process is long enough to include a steady state penetration self-sharpening. The steady state penetration self-sharpening results in less kinetic energy consumed of rods during penetration. Longitudinal splitting occurs in WF/Zr-MG rods with L/D of 3.75 during the penetration process, which results in a much lower P/L than that of WHA rods with L/D of 3.75. A jacket structure could prevent the longitudinal splitting and increase P/L of WF/Zr-MG rods. P/L of jacketed WF/Zr-MG rods with L/D of 1.11 is slightly lower than that of jacketed WHA rods with L/D of 1.11, because of its short penetration process without the steady state penetration self-sharpening. P/L curve fitted as a function of normalized impact velocity and L/D of the WF/Zr-MG rods into RHA shows the advantages of WF/Zr-MG rods over WHA rods increase with L/D.

Selective Laser Melting (SLM) of in-situ beta phase reinforced Ti/Zr-based bulk metallic glass matrix composite

In-situ ductile dendrite reinforcement is the most effective method to improve the plasticity of bulk metallic glasses. In this study, an in-situ beta phase reinforced Ti/Zr-based bulk metallic glass matrix composite (BMGC), (Ti0.65Zr0.35)90Cu10, was deposited via selective laser melting. Its microstructural characteristics and indentation deformation behaviors were investigated. There were fine and coarse microstructures in the BMGC, due to the existence of heat-affected zone, and they were finer than the microstructures of the BMGCs prepared using traditional technologies; the amorphous and beta phases could be coordinately deformed during the indentation process.

Retracted: Development of Bulk Metallic Glass Matrix Composites (BMGMC) by Additive Manufacturing: Modelling and Simulation – A Review: Part B

. Bulk metallic glasses (BMGs) and their composites (BMGMC) have emerged as competitive materials for structural engineering applications exhibiting superior tensile strength, hardness along with very high elastic strain limit. However, they suffer from a lack of ductility and subsequent low toughness due to the inherent brittleness of the glassy structure which render them to failure without appreciable yielding owing to mechanisms of rapid movement of shear bands all throughout the volume of the material. This severely limits their use in the manufacture of structural engineering parts. Various theories and mechanisms have been proposed to counter this effect. Introduction of secondary ductile phase in the form ofin-situnucleating and growing dendrites from melt during solidification have proved out to be best solution of this problem. Nucleation and growth of these ductile phases have been extensively studied over the last 16 years since their introduction for the first time in Zr-based BMGMC by Prof. Johnson at Caltech. Data about almost all types of phases appearing in different systems have been successfully reported. However, there is very little information available about the precise mechanism underlying their nucleation and growth during solidification in a copper mould during conventional vacuum casting and melt pool of additively manufactured parts. Various routes have been proposed to study this including experiments in microgravity, levitation in synchrotron light and modelling and simulation. In this report, which is Part B of two parts comprehensive overview, state of the art of development, manufacturing, characterisation and modelling and simulation of BMGMCs is described in detail. Evolution of microstructure in BMGMC during additive manufacturing have been presented with the aim to address fundamental problem of lack in ductility along with prediction of grain size and phase evolution with the help of advanced modelling and simulation techniques. It has been systematically proposed that 2 and 3 dimensional cellular automaton method combined with finite element (CAFE) tools programmed on MATLAB® and simulated on Ansys® would best be able to describe this phenomenon in most efficient way. Present part B focuses on methodology by which modelling and simulation can be adopted and applied to describe evolution of microstructure in this complex class of materials.

Retracted: Development of Bulk Metallic Glass Matrix Composites (BMGMC) by Additive Manufacturing: Modelling and Simulation – A Review: Part A

Bulk metallic glasses (BMGs) and their composites (BMGMC) have emerged as competitive materials for structural engineering applications exhibiting superior tensile strength, hardness along with very high elastic strain limit. However, they suffer from a lack of ductility and subsequent low toughness due to the inherent brittleness of the glassy structure which render them to failure without appreciable yielding owing to mechanisms of rapid movement of shear bands all throughout the volume of the material. This severely limits their use in fabricating structural and machinery parts. Various mechanisms have been proposed to counter this effect. Introduction of secondary ductile phase in the form ofin-situnucleating and growing dendrites from melt during solidification have proved out to be best solution of this problem. Nucleation and growth of these ductile phases have been extensively studied over the last 16 years since their introduction for the first time in Zr-based BMGMC by Prof. Johnson at Caltech. Data about almost all types of phases appearing in different systems have been successfully reported. However, there is very little information available about the precise mechanism underlying their nucleation and growth during solidification in a copper mould during conventional vacuum casting and melt pool of additively manufactured parts. Various routes have been proposed to study this including experiments in microgravity, levitation in synchrotron light and modelling and simulation. In this report consisting of two parts which is a preamble of author’s PhD Project, a concise review about evolution of microstructure in BMGMC during additive manufacturing have been presented with the aim to address fundamental problem of lack in ductility along with prediction of grain size and phase evolution with the help of advanced modelling and simulation techniques. It has been systematically proposed that 2 and 3 dimensional cellular automaton method combined with finite element (CAFE) tools programmed on MATLAB® and simulated on Ansys® would best be able to describe this phenomenon in most efficient way. Present part consists of general introduction of bulk metallic glass matrix composites (BMGMC), problem of lack of ductility in them, measures to counter it, success stories and their additive manufacturing.

Rejuvenation of Zr-based bulk metallic glass matrix composite upon deep cryogenic cycling

The rejuvenation behavior of Ta-rich particle reinforced Zr-based bulk metallic glass matrix composites upon deep cryogenic cycling treatment has been studied. The composite can be rejuvenated resulting in a higher enthalpy of relaxation and lower density. The internal stress generated from both the intrinsic heterogeneity in amorphous matrix and the interfaces between the matrix and Ta-rich phase should contribute to the rejuvenation behavior. The composite structure can generate a 4 times higher internal stress than that from the intrinsic heterogeneity, which causes the more rejuvenated state of the composites compared with the monolithic counterpart. With a higher volume fraction of Ta-rich phase, both the increment in enthalpy of relaxation and free volume between as-cast and thermal treated state increases almost linearly. The rejuvenated samples show better plasticity compared with as-cast counterparts because of more induced free volume.

Stability of the B2 CuZr phase in Cu-Zr-Al-Sc bulk metallic glass matrix composites

This study investigates the effect, that replacing Zr in a glass-forming Cu47.5Zr47.5Al5 alloy by Sc (0–2 at.%) has on the phase formation as well as on the thermal and mechanical properties. Even though it is not reflected in the thermal data, the glass-forming ability (GFA) is significantly reduced. This originates from the increased tendency to precipitate the shape-memory phase B2 CuZr(Sc), which, in turn, promotes the formation of bulk metallic glass (BMG) matrix composites. Sc appears to be very effective in stabilizing the B2 crystals because it forms the stable B2 CuSc phase with a similar lattice constant like B2 CuZr. By adjusting the casting parameters, the composite microstructure of Cu47.5Zr46.5Al5Sc1 can be controlled to a certain extent. The yield strength and the plasticity of the present composites depend on the crystalline volume fraction. In-situ high-energy X-ray diffraction reveals that deformation proceeds in three stages: (i) martensitic transformation of the B2 phase, (ii) yielding of the amorphous phase and continuing martensitic transformation, (iii) completion of the phase transformation and plastic deformation of all phases. Our work suggests that Sc is a promising candidate to adjust the microstructure and, thus, the mechanical properties of CuZr-based composites consisting of a glassy matrix and shape-memory crystals.

Ti-Zr-V-Cu-Be BMGMCs Processed by Semi-Solid Processing

Compared with monolithic bulk-metallic glasses at room temperature, in-situ two-phase bulk metallic glass matrix composites (BMGMCs) exhibit improved toughness. However, most of in-situ BMGMCs are developed through extremely rapid cooling, during which the solidification process cannot be controlled effectively. As a consequence, the microstructures of in situ two-phase composites, even with the same composition, vary from one to another, highly depend on the cooling rate. In the present investigation, the Ti-Zr-V-Cu-Be BMGMCs was prepared by using copper mould suction process, and the evolution of microstructures at semi-solid stage was investigated. The results indicated that microstructures of billets, produced by copper mould suction and water quenching after isothermal holding at semi-solid stage, mainly contained β-Ti phase and glass matrix. Isothermal holding temperature and time interval determined the final morphology of β-Ti phase. Compression tests showed that semi-solid processing could further improve ductility of BMGMCs effectively.

A study on the corrosion behavior of the in-situ Ti-based bulk metallic glass matrix composites in acid solutions

Corrosion behavior of the in-situ Ti-based bulk metallic glass matrix composites (BMGMCs) with a nominal composition of Ti42.3Zr29.1Cu6.6Nb6Be16 was studied in HCl and H2SO4 solutions with different concentrations. Potentiodynamic polarization tests indicated that at the lower solution concentration the corrosion current densities barely changed and their values were in the 10−7 - 10−8order of magnitude. However, corrosion current densities increased as the acid concentrations increased. Additionally, stable passivation films formed in the chloride-free solutions after polarization, but passive film breakdown and pitting corrosion were observed in HCl solution. Furthermore, the selective dissolution occurred in the amorphous matrix. Protective oxide films were enriched with Ti, Zr, and Nb oxides according to the XPS analysis after polarization on the surface. For a comprehensively study on the corrosion resistance of the BMGMCs, there also compared corrosion behavior of the composites with 316 stainless steel, Ti-6Al-4V and Zr-45Ti-5Al-3V alloys. It presents us a new reference value on the application of amorphous composites in their functioning environments.

A meso-mechanical constitutive model of bulk metallic glass composites considering the local failure of matrix

Referring to the existing experimental investigation, a meso-mechanical constitutive model is constructed to describe the deformation and failure of bulk metallic glass composites under the monotonic uniaxial tensile and compressive loading conditions. Firstly, a free volume based constitutive model considering the failure mechanisms of bulk metallic glass and a unified visco-plastic model are employed for the bulk metallic glass matrix and toughening phase, respectively. To effectively reflect the local failure occurring in the bulk metallic glass matrix of the composites, a new two-leveled homogenization method is developed by extending the traditional Mori-Tanaka's method. Then, the algorithmic tangent operators for both of bulk metallic glass matrix and toughening phase are derived; the numerical integration algorithm of proposed model is also developed. Finally, the effectiveness of proposed model is validated by predicting the deformation and failure of bulk metallic glass composites under the monotonic tension and compression, respectively. Comparison of predicted results and corresponding experimental ones demonstrates that the proposed model can predict the deformation and local failure of bulk metallic glass composites well.

Effect of Nb content on corrosion behavior of Ti-based bulk metallic glass composites in different solutions

The effect of Nb content on the corrosion behavior of in-situ (Ti0.45Zr0.31Be0.17Cu0.07)100−xNbx (x = 4, 6, 8, 10, and 12) was evaluated in 0.5 mol/L H2SO4, 0.6 mol/L NaCl, and 1 mol/L NaOH solutions. A dual-phase microstructure which composed of an amorphous matrix and dendrites was observed. Electrochemical measurements in each corrosion medium showed the same trend. The corrosion resistance first increased and then decreased with the addition of Nb content from 4 to 12 at.%. The results show the best corrosion resistance in terms of × = 8 for the alloys. Notably, Nb addition improved the pitting-corrosion resistance of samples in a chloride-containing solution, whereas spontaneous passivation occurred in chloride-free solutions. A preferential solution was observed in the amorphous matrix region in NaCl solution, but a part of dark spots and dents appeared on the surface after the polarization in chloride-free solutions. X-ray photoelectron spectroscopic measurements showed that Nb addition promoted the formation of metal oxide on the surface film, thus inducing a superior corrosion resistance for the bulk metallic glass matrix composites.