Applications Of Bulk Metallic Glasses Research Articles

Consolidation and wear resistance of Fe based bulk metallic glass composites by spark plasma sintering

High densification and wear resistance are essential for the application of Fe-based bulk metallic glass composites. In this work, Fe-based composites were fabricated by spark plasma sintering. Firstly, under the pressure of 150 MPa, all samples achieved high densification, the microcontact pressure between powder particles decreased with increasing density. Then, as the sintering temperature was increased from 350 °C to 450 °C, the crystalline phases were identified as Fe3Si and Fe2B. The hard borides improved the hardness and wear resistance of composites. Finally, at sintering temperature of 400 °C, the sample exhibited the highest micro-Vickers hardness of 1168.8 Hv and the lowest friction coefficient of 0.59, the coefficient of friction was lower than that of bearing steel. FeSiB BMG composites showed dominant abrasive and oxidative wear mechanisms. FeSiB composites showed excellent hardness and wear resistance, which extends the potential application of bulk metallic glass in the field of engineering structural materials.

Recent development in the application of bulk metallic glasses

Over the past decades, considerable efforts have been made in the commercial application of bulk metallic glasses (BMGs). Despite great challenges faced by the industrial players, significant progress has been achieved, and millions of commercial products for various kinds of applications have been shipped around the world. Here in this paper, we shall present the alloys suitable for the actual products in the application and discuss the merits of the processing technique of BMGs over the existing processing techniques and materials. Most importantly we demonstrate the typical examples of products over the past few years. Finally, future directions of the industrialization of BMGs are also discussed.

The effect of minor alloying on the glass forming ability and crystallization reaction of Ti32.8Zr30.2Cu9M5.3Be22.7 (M=Fe, Co, and Ni) bulk metallic glass

Glass forming ability (GFA) is critically important for large-scale processing and application of bulk metallic glasses (BMGs). It is now widely accepted that the compositions of BMGs with excellent GFA can be located in off-eutectic regions, where the melts have high stability and primary crystallization plays an important role. In this study we reported that the thermodynamic properties of Ti32.8Zr30.2Cu9Fe5.3Be22.7, Ti32.8Zr30.2Cu9Co5.3Be22.7 and Ti32.8Zr30.2Cu9Ni5.3Be22.7 BMGs to understand the origin of the GFA in these glass-forming systems. It is present that these off-eutectic TiZr-based alloys have high thermomechanical stability and the GFA can be improved by manipulating the primary crystallization through minor alloying. The icosahedron-like short-range ordered arrangement improves the stability of the supercooled liquid, and the (Ti, Zr)2M phase with complex structure formed by minor alloying slows down the nucleation and growth of crystal phase, synergistically contributing to better GFA.

Compositions design of Co-Fe-based bulk metallic alloys

Glass forming ability (GFA) is one of the key factors hindering the application of bulk metallic glasses (BMGs). In this paper, a cluster-related method was used to design good glass-formers in the complex Co-Fe-based system. A novel Co-centered Co-Mo binary topologically packed cluster Co-Co8Mo4 with 12-coordination number was found and used. The basic ternary composition in Co-Mo-B system is calculated based on an intersection of cluster lines B-B2Co8 and Co-Co8Mo4. Based on this, a series of novel Co-Fe-based glass-formers with high GFA, were quickly designed using the method of similar element replacement and microalloying. The best glass-former is (Co27.5Fe27.5Mo12.2Cr12.2B16P4.6)98Y2. The source of high GFA of designed glass-formers was also discussed. The results of this paper would offer researchers a novel insight in understanding the source of high GFA of Co/Fe-based system, and lay a solid foundation for exploring Co/Fe-Mo-based glass-formers via newly found Co-Mo binary cluster.

Understanding the beneficial microalloying elements in Fe-based bulk metallic glasses via clusters

Glass forming ability (GFA) is one of the key factors hindering the application of bulk metallic glasses (BMGs). Microalloying has shown beneficial effects on GFA. However, the mechanism is still unclear. A new guidance via clusters was applied to understand and quickly choose beneficial microalloying elements for enhancing GFA which might help build a foundation for further quantitative analysis of minor alloying via clusters. Under the guidance, a series of beneficial microalloying elements could be quickly discovered, verified and understood. The results show that the beneficial microalloying elements for enhancing GFA should be chosen under the condition of bringing in new types of topologically efficiently packed clusters.

Improved Prediction and Understanding of Glass-Forming Ability Based on Random Forest Algorithm

As an ideal material, bulk metallic glass (MG) has a wide range of applications because of its unique properties such as structural, functional and biomedical materials. However, it is difficult to predict the glass-forming ability (GFA) even given the criteria in theory and this problem greatly limits the application of bulk MG in industrial field. In this work, the proposed model uses the random forest classification method which is one of machine learning methods to solve the GFA prediction for binary metallic alloys. Compared with the previous SVM algorithm models of all features combinations, this new model is successfully constructed based on the random forest classification method with a new combination of features and it obtains better prediction results. Simultaneously, it further shows the degree of feature parameters influence on GFA. Finally, a normalized evaluation indicator of binary alloy for machine learning model performance is put forward for the first time. The result shows that the application of machine learning in MGs is valuable.

Improving glass forming ability of off-eutectic metallic glass formers by manipulating primary crystallization reactions

Glass forming ability (GFA) is critically important for large-scale applications of bulk metallic glasses with maximized functionalities at low costs in materials and processing. Traditionally, excellent glass formers usually have compositions in eutectic regions where liquid phases have high stability and low liquid temperatures while GFA of off-eutectic alloys is largely limited by primary crystallization. In this study we reported that the GFA of Ni-based off-eutectic alloys can be dramatically improved by manipulating the primary crystallization reaction through minor alloying. As a result, a novel Ni60Pd20P14Si2B4 metallic glass with excellent GFA is developed by substituting P in Ni60Pd20P20 using 2 at.% Si and 4 at.% B. The minor alloying leads to the transition of the primary crystallization from a tetragonal (Ni, Pd)3P phase to a chemically modulated complex monoclinic phase. The enhanced GFA results in the largest achievable processing diameter (25 mm) of Ni-based bulk metallic glasses, which is more than four times larger than that of Ni60Pd20P20. The complex crystal structure of the primary crystalline phase with chemical modulation and a large unit cell leads to slow crystal growth, and hence the improved stability of supercooled liquid for better GFA.

Improving Glass Forming Ability of Off-Eutectic Metallic Glass Formers by Manipulating Primary Crystallization Reactions

Glass forming ability (GFA) is critically important for large-scale applications of bulk metallic glasses with maximized functionalities at low costs in materials and processing. Traditionally, excellent glass formers usually have compositions in eutectic regions where liquid phases have high stability and low liquid temperatures while GFA of off-eutectic alloys is largely limited by primary crystallization. In this study we reported that the GFA of Ni-based off-eutectic alloys can be dramatically improved by manipulating the primary crystallization reaction through minor alloying. As a result, a novel Ni60Pd20P14Si2B4 metallic glass with excellent GFA is developed by substituting P in Ni60Pd20P14Si2B4 using 2 at.% Si and 4 at.% B. The minor alloying leads to the transition of the primary crystallization from a tetragonal (Ni, Pd)3P phase to a chemically modulated complex monoclinic phase. The enhanced GFA results in the largest achievable processing diameter (25 mm) of Ni-based bulk metallic glasses, which is more than four times larger than that of Ni60Pd20P14Si2B4 . The complex crystal structure of the primary crystalline phase with chemical modulation and a large unit cell leads to slow crystallization kinetics from high barrier energy for crystal nucleation and growth, and hence the improved glass forming ability.

Fabrication of a Zr-based bulk metallic glass surface with extreme wettability

Unlike the high surface energy of traditional metallic materials, metallic glass with amorphous structure have a lower surface energy with a different wettability of solid surfaces. In this work, the micro-nano hierarchical structures were constructed on the Zr55Cu30Ni5Al10 bulk metallic glass (BMG) surface by electrochemical corrosion and then modified with stearic acid to form both superhydrophobic and superlipophilic surfaces. After the optimized modification conditions, the water contact angle was as high as 169.6 ± 3.5° with a low water sliding angle of 5° and the contact angle of oil on the alloy surface was 5°, respectively. The present work would open a window for the application of bulk metallic glasses in nondestructive liquid transportation and oil-water separation.

Quantitative evaluation of hidden hierarchical pores in laser additive manufactured bulk metallic glasses via computed tomography

Laser additive manufacturing (LAM) technology presents a great chance to break through the size limitation and realize the wide applications of bulk metallic glasses (BMGs). However, one of the inherent problems associated with this technical route is the unavoidable hidden pore defects, which is detrimental to the mechanical properties of the BMGs. In the present study, a comprehensive investigation of hidden pore defects in a typical model BMG Zr51Ti5Cu25Ni10Al9 fabricated by LAM is performed by using the computed tomography (CT) technology. The overall porosity of the LAMed BMG samples is found to be increased with increasing laser power. However, the variation trends of the proportions for different-size pores are not the same. Specifically, the proportions of larger pores are increased with the consumption of small ones as the laser power increasing. This opposite evolution trends of pores with the increasing laser power is analyzed from the Marangoni effect in the molten pool flow.

High-throughput screening of laser additive manufactured metallic glass via ultrasonic wave

Laser additive manufacturing (LAM) technology provides an opportunity to fabricate bulk metallic glasses (BMGs) without any dimensional constraint and achieve the large-scale applications of BMGs. However, flaws, such as cracks, gas porosity, and crystalline phases, are always formed accompanied by the process of LAM, which seriously worsens the mechanical and physical properties of the resulting BMGs. Here, we present a novel method that involves ultrasonic wave technique to high-throughput screen the optimum process parameters for the LAM of BMG. A parameter library, constituted by a series of rectangular BMG samples, is rapidly fabricated by the LAM method under continuously changed combinations of laser power and travel speed. The ultrasonic attenuation factor, which is sensitive to the flaws, is used as the monitor to screen the parameters of the BMGs fabricated by the LAM. Using this approach, the laser power of 1300 W and travel speed of 600 mm/min are estimated as the optimum parameter combination for the LAM of a Zr51Ti5Ni10Cu25Al9 (Zr51) BMG with the slightest flaws. The amorphous-phase dominated microstructure and the sufficiently high tensile strength of the subsequent fabricated large-sized Zr51 BMG sample verify this optimum parameter combination.

Achieving stable plastic flows in a Zr-based bulk metallic glass under tailored mixed-mode (I/II) loading conditions

The achievement of stable plastic flows plays a key role for practical structural applications of bulk metallic glasses (BMGs). In this work, by designing complex stress fields through tailored double-side notches, stable plastic flows in a Zr-based BMG were achieved under mixed-mode (I/II) loading conditions. The deformation behavior of the notched BMG specimens, including the shear-banding and fracture behaviors, was examined and correlated to the designed complex stress fields. The findings have shown that the stable plastic flows were mainly caused by the introducing of mode-II component under the mixed-mode (I/II) loading conditions. Increase of the mode-II component can result in not only more stable plastic flows, but also larger bearing loads. The present findings are of significance in uncovering the plastic deformation mechanisms of BMGs under mixed-mode loading conditions and in designing BMG structures with better mechanical performance.

Intrinsic correlation of the plasticity with liquid behavior of bulk metallic glass forming alloys

Nowadays, plasticizing has become a critical issue for the engineering application of bulk metallic glasses (BMGs). What is the origin of plastic flow and how to evaluate the plasticity of BMGs with a unified standard are still open questions. Here we report a universal fragility criterion to scale the plasticity of BMGs from the equilibrium liquids and supercooled liquids. Based on our experimentally measured and previously reported viscosities at superheated and supercooled region for 51 glasses, the plasticity (ε) of BMGs has been found to positively correlate to the supercooling liquid fragility (m) with the equation of ε = 92exp[− 73/(m−15)], where ε is the plastic strain and m the fragility near glass transition temperature, but negatively correlate to the fragile-to-strong (F-S) transition tendency characterized by F-S transition factor and temperature. The intrinsic mechanism of the plasticity can be well interpreted in the frame of structural relaxation theory. This work provides a new insight into the microscopic essence of the plasticity of glassy solids and a universal approach to scale the fluidity of metallic glasses.

Mechanical properties of Zr-based bulk metallic glass parts fabricated by laser-foil-printing additive manufacturing

The application of bulk metallic glasses (BMGs) has been traditionally limited to parts with small dimensions and simple geometries, due to the requirement of fast cooling during the conventional process of casting. This research exemplifies a promising additive manufacturing method, i.e., laser-foil-printing (LFP), to fabricate high-quality BMG parts with large dimensions and complex geometries. In this study, Zr52.5Ti5Al10Ni14.6Cu17.9 BMG parts were fabricated by LFP technology in which MG foils are laser welded layer-by-layer upon a substrate. The mechanical properties of the fabricated BMG parts were measured using micro-indentation, tensile test and four-point bending test, and compared to as-cast BMG parts. Through LFP, as rapid cooling rates can be achieved, fully amorphous and nearly fully dense BMG parts without cracking have been successfully made. The glass transition temperature, crystallization temperature, and melting temperature of the fabricated parts are nearly the same as those of the as-cast parts. Additionally, the fabricated BMG parts exhibit mechanical properties, including micro-hardness, tensile strength, and flexural strength, comparable to the as-cast BMG parts.

Design of Fe-Based Bulk Metallic Glasses with Improved Wear Resistance.

The application of bulk metallic glasses (BMGs) as advanced wear-resistant materials has remained limited despite optimistic expectations. In this work, we develop a series of novel Fe-based BMGs with improved wear resistance by altering the Cr and Mo contents in an Fe-Cr-Mo-C-B-Y glass-forming system. Experimental results demonstrate that increasing Cr and Mo contents enhance the thermal stability and hardness ( Hv) of the resulting BMGs without reducing their fracture toughness ( Kc). The enhanced hardness is mainly attributed to the increased fraction of the stiff (Cr,Mo)-C covalent bonds in the resultant BMGs, as revealed by X-ray photoelectron spectrograph measurement. Worn surface/subsurface observations and stress field modeling reveal the activity of two kinds of wear mechanisms, i.e., hardness-controlled abrasion wear and toughness-controlled fatigue wear. We further clarify the enhanced wear performance of the Fe-based BMGs according to an effective indicator Kc3/4 Hv1/2 that correlates positively with the wear resistance of the samples. The optimal Fe-based BMG sample possessed versatile properties, including a strong glass-forming ability (i.e., a critical diameter of 8 mm), a high hardness of 1335 Hv, and a very low specific wear rate of ∼1.3 × 10-6 mm3 N-1 m-1, which represents one of the most outstanding Fe-based BMGs reported thus far.

Effect of complex stress fields on the plastic energy accumulation in a Zr-based bulk metallic glass

In the practical applications of bulk metallic glasses (BMGs) as structural materials, they always deform under complex stress states. In this work, some single-side-notched BMG specimens with varying notch radii and geometries were fabricated, and tested under tensile loadings. The effect of complex stress fields on the accumulation of plastic energy in the notched BMG specimens was examined and discussed. The results show that the notched BMGs can dissipate more plastic energy before fracture than conventional tensile specimens which have a relatively-uniform stress distribution. To accumulate more plastic energy, it necessitates high orders of stress concentration to initiate more shear bands and appropriate distribution of complex stress fields to confine their propagations. The present findings are of significance for practical structural-applications of BMGs, where complex stress fields are usually presented.

Enhanced Plasticity of Cu-Zr-Ti Bulk Metallic Glass and Its Correlation with Fragility

Inadequate room-temperature plasticity limits the application of bulk metallic glasses (BMGs). This study focuses on enhancing the plasticity of BMGs for widening their applications. Composition modification of Cu60Zr25Ti15 through the minor addition of Ni is the approach adopted in this study. A systematic increase in mechanical properties is observed with increasing Ni content (up to 5 at. pct), followed by a decrease thereafter. Values of yield stress (2425 MPa), fracture stress (2513 MPa), maximum stress (2725 MPa), and plastic strain (16 pct) exhibited by (Cu60Zr25Ti15)95Ni5 BMGs are higher than those reported in the literature for Cu-BMGs (high Cu content). Analysis of the glass transition region indicated that the enthalpy values of the exothermic heat flow prior to glass transition (ΔHbg) and the fragility parameter (m) are well correlated with the plasticity of the alloys. The increasing fragility parameter and exothermic enthalpy correspond to higher free volume. Therefore, high plasticity values can be attributed to the free volume modification (creation and distribution) caused by Ni addition. This free volume modification initiates shear bands and promotes their branching; consequent interactions among them increase the resistance to shear band propagation and, thereby, delay the fracture.

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.

Thermoplastic Micro-Forming of Bulk Metallic Glasses: A Review

Bulk metallic glasses are a fascinating class of metallic alloys with an isotropic amorphous structure that is rapidly quenched from liquid melts. The absence of a crystalline micro-structure endows them with a portfolio of properties such as high strength, high elasticity, and excellent corrosion resistance. Whereas the limited plasticity and hence poor workability at ambient temperature impede the structural application of bulk metallic glasses, the unique superplasticity within the supercooled liquid region opens an alternative window of so-called thermoplastic forming, which allows precise and versatile net-shaping of complex geometries on length scales ranging from nanometers to centimeters that were previously unachievable with conventional crystalline metal processing. Thermoplastic forming not only breaks through the bottleneck of the manufacture of bulk metallic glasses at ambient temperature but also offers an alluring prospect in micro-engineering applications. This paper comprehensively reviews some pivotal aspects of bulk metallic glasses during thermoplastic micro-forming, including an in-depth understanding of the crystallization kinetics of bulk metallic glasses and the thermoplastic processing time window, the thermoplastic forming map that clarifies the relationship between the flow characteristics and the formability, the interfacial friction in micro-forming and novel forming methods to improve the formability, and the potential applications of the hot-embossed micro-patterns/components.

Understanding of micro-alloying on plasticity in Cu46Zr47−xAl7Dyx (0≤ x ≤ 8) bulk metallic glasses under compression: Based on mechanical relaxations and theoretical analysis

Lacking of plasticity at ambient temperature severely hinders the wide applications of bulk metallic glasses, and a significant challenge is to improve the plasticity. Based on the metallurgical physics, micro-alloying can be applied to adjust metallic glasses plasticity. In the current work, dynamic mechanical relaxation of Cu46Zr47−xAl7Dyx (0 ≤ x ≤ 8) bulk metallic glasses has been investigated experimentally by dynamic mechanical analysis. Compressive tests have been performed to investigate mechanical properties of the Cu-based bulk metallic glasses at both ambient as well as cryogenic temperatures. The results indicated that by modifying the chemical composition, plastic deformation and dynamic mechanical relaxation processes are changed. The influence of Dysprosium (Dy) on plastic deformation is possibly related to the Johari-Goldstein (JG) relaxation in the metallic glasses. A kinetic model which may be predict the mechanical relaxation behavior and atomic mobility of the metallic glasses. In addition, experimental analyses show that thermal properties can be affected by the Dy addition of the Cu-based bulk metallic glasses. Our investigations demonstrated that micro-alloying of Dy could play an important role to influence the Cu46Zr47−xAl7Dyx bulk metallic glasses plasticity. In order to explain this behavior, the quasi-point defects theory was used to describe the microstructural heterogeneity. We postulate that the compressive plasticity is directly associated with local heterogeneity and relaxation modes for metallic glasses.