Bulk Metallic Glass Matrix Research Articles

The Microstructure of Zr-Based Bulk Metallic Glass and Glass Matrix Composite

The Microstructure of Zr-Based Bulk Metallic Glass and Glass Matrix Composite

In-situ synthesis and mechanical properties of Zr-based bulk metallic glass matrix composites manipulated by nitrogen additions

Abstract Our study investigates in-situ synthesis and mechanical properties of Zr-based bulk metallic glass (BMG) matrix composites via arc plasma-induced accelerated displacement reaction (APADR) process. The aluminum nitride precursor under arc plasma-induced ultra-high temperature results in higher contents of dissolved nitrogen as well as precipitation of zirconium nitride (ZrN) particles in a Zr-based amorphous matrix. The nitrogen in the matrix results in a decrease of crystallization resistance (lower T x and reduced glass-forming ability), but an increase of mechanical stability (a decrease of strain burst sizes). In particular, in-situ formed ZrN, which exhibits a homogeneous distribution and strong interfacial bonding with the matrix, causes an increase in compressive fracture strength and significant plastic deformation in the composite compared with the monolithic BMG. The formation of multiple shear bands and the enhancement of shear band interactions by the dissolved nitrogen as well as the in-situ formed ZrN particles were carefully confirmed by a statistical analysis on serrated flows. These results give us a guideline on how to manipulate nitrogen contents and fabricate in-situ BMG matrix composites with improved mechanical properties via APADR process.

Shear softening of Ta-containing metallic glass matrix composites upon dynamic loading

Abstract The deformation behaviors of in-situ Ti50Zr18Ni5Ta15Be12 bulk metallic glass matrix composites (MGMCs) were investigated upon quasi-static and dynamic loadings. The present MGMCs exhibit good quasi-static mechanical properties, combining high fracture strength (2460 MPa) with remarkable plasticity (20%) at the strain rate of 5×10−4 s−1. When the strain rate is higher than 3080 s−1, the strain rate effect of the yielding strength has an apparent negative strain rate sensitivity (SRS), which can be ascribed to the deteriorated ability of dendrites to impede the propagation of shear bands and the matrix-dominated fracture related to thermal softening at higher strain rates. Based on their deformation mechanisms, a constitutive relationship is obtained by cooperative shear model (CSM), which is employed to model the dynamic yielding stress behavior. The constitutive equations are established for describing the present MGMCs.

Dendrite size dependence of mechanical properties of in-situ Ti-based bulk metallic glass matrix composites

Abstract The relations between dendrite size and mechanical properties in an in-situ Ti-based bulk metallic glass composite (BMGC) have been investigated by using copper mold casting and semi-solid processing methods. Three Ti-based BMG composites with different dendrite sizes without changing glass matrix simultaneously were successfully obtained, which gives a new way to quantitively understand the relationship between dendrite size and mechanical properties. Results show that the yield strength decreases as the dendrite size increases and there exists an optimum dendrite size for both the plasticity and work hardening capacity.

Micromechanics constitutive model for predicting the stress–strain relations of particle toughened bulk metallic glass matrix composites

Abstract Based on the secant modulus and extended Mori-Tanaka method for dual ductile phases, a micromechanics model is proposed to predict the monotonic mechanical behaviors of bulk metallic glass matrix composites (BMGCs) toughened by particles. In this model, the deformation behaviors of the BMG matrix and particles are described by the use of the free volume model and the simple Ludwik flow equation, respectively, and Weng's homogenization frame is adopted to bridge the constituents and the composites. As compared to the existing relevant models, the present model is much more convenient for applying, and more readily to be extended. The developed model is applied with stain-controlled loading, and is verified by modeling the monotonic stress–strain relations of particle toughened BMGCs. The predictions were in good agreement with the experiments from the literature, which confirms that the developed analytical model is capable of successfully describing the mechanical properties, such as yield strength, stress hardening and strain softening elongation, of composites.

Modeling and simulation of microstructural evolution in Zr based Bulk Metallic Glass Matrix Composites during solidification

ABSTRACT Bulk metallic glass and their composites are unique new materials which have superior mechanical and structural properties as compared to existing conventional materials. Owing to this, they are potential candidates for tomorrow’s structural applications. However, they suffer from disadvantages of poor ductility and little or no toughness which render them brittle and they manifest catastrophic failure on the application of force. Their behavior is dubious and requires extensive experimentation to draw conclusive results. In present study, an effort has been made to overcome this pitfall by simulation. A quantitative mathematical model based on KGT theory has been developed to describe nucleation and growth of second phase dendrites from melt in glassy matrix during solidification. It yields information about numerical parameters necessary to understand the behaviour of each individual element in multicomponent sluggish slurry and their effect on final microstructural evolution. Model is programmed and simulated in MATLAB®. Its validation is done by comparison with identical curves reported in literature previously for similar alloys. Results indicate that the effect of incorporating all heat transfer coefficients at macroscopic level and diffusion coefficients at microscopic level play a vital role in refining the model and bringing it closer to actual experimental observations. Two types of hypo and eutectic systems namely Zr65Cu15Al10Ni10 and Zr47 . 5Cu45 . 5Al5Co2 respectively were studied. Simulation results were found to be in good agreement with prior simulated and experimental values.

Mechanical and corrosion behaviour of in situ intermetallic phases reinforced Mg-based glass composite

ABSTRACTA (Mg65Cu10Ni10Y10Zn5)91Zr9 bulk metallic glass matrix composite, reinforced by in situ formed intermetallic phase, has been fabricated. In contrast to the monolithic Mg-based bulk metallic glasses (BMGs), the composite showed much higher fracture strength of 1039 MPa and a significant plastic strain of more than 5%. Moreover, the effect of in situ formed intermetallic phase on the corrosion behaviour of the composite was also studied. The results indicated that the corrosion resistance of the composite was only slightly lower than that of the monolithic Mg-based BMGs, but still much higher than that of the AZ31 magnesium alloy. This finding gives us a new clue to enhance the mechanical properties and corrosion resistance of Mg-based alloy by designing appropriate metallic glass composites.

Development of in-situ β-Ti reinforced Be-free Ti–based bulk metallic glass matrix composites

Abstract In this paper, in-situ β-Ti phase reinforced (Al, Ni, Be)-free Ti-based bulk metallic glass matrix composites (BMGMCs) were developed by microalloying Mo. The BMGMCs showed higher fracture strength and larger plastic strain than the monolithic glassy counterpart and other Be-free Ti-based BMGMCs, under both compression and bending tests. The ductile and soft β-Ti secondary phase appeared to hinder the rapid propagation of the main shear band, improving the plasticity. Furthermore, the size and interparticle spacing of the secondary β-Ti were very close to the processing zone size, further stabilizing the shear band against developing into cracks and thus improving mechanical properties. But under tension, no obvious ductilization was observed for the BMGMCs, maybe resulting from the lower volume fraction of β-Ti phase because of higher cooling rate during the fabrication for them. Further work should be focused on optimizing the composition and increasing the volume fraction of β-Ti phase and sample size.

Effects of Changes in Test Temperature on Tensile Properties and Notched Vs Fatigue Precracked Toughness of a Zr-Based BMG Composite

Tensile and fracture toughness behavior of a Zr-based bulk metallic glass matrix composite (BMGMC) containing a body-centered cubic crystalline phase was examined over temperatures from 77 K to 653 K (−196 °C to 380 °C). The BMGMC exhibited tensile plasticity at all test temperatures. The sample tested in tension at 173 K (−100 °C) exhibited work hardening but the remaining samples tested at higher temperatures exhibited work softening. EBSD analysis of the crystalline phase after tensile testing provides insight into active deformation mechanisms in the crystalline phase. At 603 K (330 °C), the dendrites exhibit significant plastic strain, with the dendrites oriented {101} parallel to the loading direction exhibiting the least amount of strain. Schmid factor analysis leads to the hypothesis that {110}〈111〉 dislocation mechanisms are active at this temperature. Additionally, measurements of dendrite shape as a function of macroscopic strain state in the tension experiments provide insight into cooperative deformation mechanisms in the composite. At low temperatures, the fracture toughness of the notch toughness samples exceeded that of fatigue precracked samples; but at and above room temperature, the toughness values of notched and fatigue precracked samples converge. These observations are rationalized based on the changes to the flow and fracture behavior of the glass and the crystalline phases over this temperature range. At low temperatures, the crystalline phase is sensitive to defects and changes in stress state that reduce its energy absorbing ability. At higher temperatures, both constituents possess lower strength and are less sensitive to defects, enabling more significant crack tip blunting in the fatigue precracked samples. This produces toughness values that are similar to those obtained for the notched samples.

Enhancing the compressive and tensile properties of Ti-based glassy matrix composites with Nb addition

Abstract Combining copper mold suction-casting and copper mold pouring-casting techniques, in-situ Ti-based bulk metallic glass matrix composites (Ti 0.45 Zr 0.31 Be 0.17 Cu 0.07 ) 100 − x Nb x ( x = 4, 6, 8 and 10) with Φ = 3 mm and composites ( x = 6, 8 and 10) with Φ = 8 mm are fabricated in order to perform compressive and tensile tests, respectively. The volume and size of crystalline β -Ti(Zr, Nb) dendrites of these composites increase with the increasing Nb content, resulting in the improvement of compressive and tensile properties of the composites. Among these composites, Ti 40.5 Zr 27.9 Be 15.3 Cu 6.3 Nb 10 ( x = 10) has the highest compressive ultimate strength of 2756 MPa and plastic strain of 39.5%; meanwhile, it possesses a high tensile ultimate strength of 1428 MPa and a large tensile plasticity of 7.7%. As indicated by the SEM micrographs, in compressive tests, the more branched the dendrites, the more shear bands, and the higher compressive strength and plasticity of these composites. In tensile tests of Ti 40.5 Zr 27.9 Be 15.3 Cu 6.3 Nb 10 ( x = 10), ductile fracture features, including the macroscopic necking, fracture of ligament, vein patterns and sliding traces, are observed. The reason of the excellent mechanical properties of the measured composites is that the propagation of shear bands and cracks are impeded by β -Ti(Zr, Nb) dendrites, and then be confined in a small space.

Triple-yieldable multiphase reinforced bulk metallic glass matrix composites under tension

Abstract Multiphase (Ta-rich phase, B2 and B19′-CuZr) reinforced bulk metallic glass matrix composites (BMGMCs) were successfully developed. The Ta-rich phase appeared not only to hinder the propagation of shear bands, but also to act as a nucleant for the B2 and B19′ phases to homogenize their distribution. The composites showed superior tensile plasticity, work-hardening, and a unique triple yielding behavior. The martensitic transformation of B2-CuZr, the deformation of the Ta-rich phase, and the twinning and detwinning of B19′-CuZr all contributed to these mechanical properties. The present novel BMGMC is expected to lead to a breakthrough in designing work-hardenable and ductile BMGMCs.

The Fracture Processes of Mg81Ni8Zn5Y6 Bulk Metallic Glass Matrix Composite with a Long-period Stacking Ordered Structure

Mg81Ni8Zn5Y6 bulk metallic glass matrix composite samples with long-period stacking ordered(LPSO) structure were fabricated by conventional Cu-mold casting method and the shear scenarios of them were investigated under uniaxial compressive loading with different stresses. The phase formation and spatial microstructure of the alloy were investigated by using X-ray diffraction and scanning electron microscopy. The fracture scenarios were analyzed based on the observation of the lateral surfaces and the fracture surfaces. Six stages can be outlined as stress concentration, embryonic shear bands formation, mature shear bands formation, shear bands propagation, shear band multiplication and shear-off. The influence of the LPSO phase on the fracture mechanism of the Mg-based amorphous matrix composite during the fracture process was systemically described.

Design of Bulk Metallic Glasses and Glass Matrix Composites Near Intermetallic Composition by the Principle of Competitive Growth

Design of Bulk Metallic Glasses and Glass Matrix Composites Near Intermetallic Composition by the Principle of Competitive Growth

Fabrication and mechanical properties of bulk metallic glass matrix composites by in-situ dealloying method

Abstract In-situ Ti-reinforced Mg-based (MT-D) and in-situ Ta-reinforced Zr-based (ZT-D) bulk metallic glass matrix composites (BMGMCs) were prepared by a novel dealloying method, which contains an element-selective leaching process in a metallic melt. The BMGMCs exhibit better mechanical properties, including higher fracture strength and larger plastic strain, than their monolithic glassy counterparts or similar BMGMCs by ex-situ dispersing or conventional arc-melting methods. The differences of Young's modulus between the dispersoids and the glassy matrix for these BMGMCs generate stress concentration at the interface, which is considered to suppress the propagation of the single main shear band and initiate multiple shear bands to accommodate the plastic deformation. Furthermore, the fine size of dispersoids for these BMGMCs, caused by low reaction temperature during dealloying in the metallic melt, results in more interfaces with the matrix for further improvement of mechanical properties. In addition, the low reaction temperature can also contribute to less composition fluctuation of the matrix to maintain the glass-forming ability of itself, which can introduce no undesired phases to degrade the mechanical properties. This novel in-situ dealloying method is believed to make a breakthrough in designing ductile BMGMCs with fine-sized secondary particles.

The Evolution of Microstructures and the Properties of Bulk Metallic Glass with Consubstantial Composition Laser Welding

A Zr55Cu30Ni5Al10 plate-like bulk metallic glass (BMG) was prepared using copper mold suction casting. Additionally, alloy powders with the same nominal composition were synthesized. The alloy powders were welded or melted to the cleaned surface of the BMG with a laser beam acceleration voltage of 60 kV, a beam current range from 60 to 100 mA, a welding speed of 60 mm/s, as well as an impulse width of 3.0 ms. The effect of consubstantial composition welding on the microstructures and properties was investigated. The molten and subsequently solidified metallic mixtures remain an amorphous structure, but the enthalpy of the welded or melted position varies due to the combination of the micro-structural relaxation and nano-crystals precipitated during the energy inputs. The surface layers of the BMG can be significantly intensified after welding processes; however, the heat-affected zones (HAZs) exhibit a slight degradation in mechanical properties with respect to the BMG matrix. This study has important reference value for specialists working on the promotion of applications of BMGs.

Excellent plasticity of a new Ti-based metallic glass matrix composite upon dynamic loading

Abstract Quasi-static and dynamic compressive properties of in-situ Ti 60 Zr 14 V 12 Cu 4 Be 10 bulk metallic glass matrix composites containing ductile dendrites were investigated. Upon quasi-static compressive loading, the composite exhibits a high fracture strength of ~2,600 MPa, combined with a considerable plasticity of ~40% at room temperature. However, upon dynamic loading, an excellent plasticity of ~16% can be obtained due to the abundant dislocations and severe lattice distortions within dendrites and multiplication of shear bands within the glass matrix analyzed by transmission-electron microscopy. A constitutive relationship is obtained by Johnson-Cook plasticity model, which is employed to model the dynamic flow stress behavior. In addition, under dynamic compression, the adiabatic temperature rise increases with increasing strain rates, resulting in that the softening effect within the glass matrix is obviously enhanced during deformation.

Meso-mechanical constitutive model of bulk metallic glass matrix composites

Abstract Based on the existing experimental observations and extended Mori-Tanaka (M-T) method, a new meso-mechanical constitutive model is proposed to predict the monotonic tensile or compressive deformation of bulk metallic glass (BMG) matrix composites with toughening phases. In the proposed model, the deformation behaviors of the BMG matrix and toughening phase are described by using the extended free volume model and unified visco-plastic model, respectively, and corresponding algorithmic tangent operators are also derived. The proposed model is verified by predicting the monotonic tensile or compressive stress-strain responses of the BMG composites with an in-situ dendrite and different ex-situ toughening particles, respectively. Comparison of predicted results and experimental ones demonstrates that the proposed meso-mechanical constitutive model describes both the strain hardening and softening features of the BMG composites reasonably. The simulations agree with the experiments well.

Three-dimensional imaging of shear bands in bulk metallic glass composites.

The mechanism of the increase in ductility in bulk metallic glass matrix composites over monolithic bulk metallic glasses is to date little understood, primarily because the interplay between dislocations in the crystalline phase and shear bands in the glass could neither be imaged nor modelled in a validated way. To overcome this roadblock, we show that shear bands can be imaged in three dimensions by atom probe tomography from density variations in the reconstructed atomic density, which density-functional theory suggests being a local-work function effect. Imaging of near-interface shear bands in Ti48 Zr20 V12 Cu5 Be15 bulk metallic glass matrix composite permits measurement of their composition, thickness, branching and interactions with the dendrite interface. These results confirm that shear bands here nucleate from stress concentrations in the glass due to intense, localized plastic deformation in the dendrites rather than intrinsic structural inhomogeneities.

Work-hardenable Mg-based bulk metallic glass matrix composites reinforced by ex-situ porous shape-memory-alloy particles

Abstract Porous NiTi shape-memory-alloy particle-reinforced Mg-based bulk metallic glass matrix composites were prepared by an ex-situ method. The composites show a larger plastic strain, higher fracture strength and obvious work-hardening behavior compared with their monolithic glassy counterparts. The ex-situ porous NiTi particles hinder the rapid propagation of shear bands, which generates multiplied shear bands, like other ductile metal particles, and undergo a stress-induced martensitic transformation, which is unique and contributes to work hardening. Local regions within one porous particle satisfy the optimal conditions of bulk metallic glass matrix composite structure, i.e., the average particle size and mean inter-particle spacing are close to the processing zone size, and thereby further improve the plasticity by localized plastic deformation.

Microstructural Control via Copious Nucleation Manipulated by In Situ Formed Nucleants: Large-Sized and Ductile Metallic Glass Composites.

A novel strategy to control the precipitation behavior of the austenitic phase, and to obtain large-sized, transformation-induced, plasticity-reinforced bulk metallic glass matrix composites, with good tensile properties, is proposed. By inducing heterogeneous nucleation of the transformable reinforcement via potent nucleants formed in situ, the characteristics of the austenitic phase are well manipulated.