Fabrication Of Bulk Metallic Glass Research Articles

A novel hybrid approach to develop bioresorbable material

The need for bioresorbable implants that are able to dissolve within the body is rising, unlike their traditional counterparts. Bulk metallic glasses (BMGs) can perhaps serve this need, since they possess incredible properties, including high biocompatibility by virtue of their amorphous structure and absence of dislocations. However, the fabrication of BMGs is challenging, since, to achieve an amorphous structure, fast cooling is a pre-requisite which is very difficult to achieve for casting due to the fact that fast cooling rate and adequate rate of filling of the mold possess a trade-off relationship. Therefore, purpose of this work is to develop a simple novel hybrid approach that is cost effective and attempts to synthesize BMG based on Mg–Ca–Zn constituent. Synthesis of bioresorbable material was attempted by hybridizing friction stir processing (FSP) technique with gas tungsten arc welding (GTAW). FSP was performed with Magnesium as base material and Calcium granules as reinforcement. After FSP, GTAW process was performed by using Zn as filler material. The added Ca and Zn were found to effectively intermix with the Mg matrix in the FSP and GTAW steps, respectively. Especially, a relatively invariable distribution of Ca phases was observed in the stirred microstructure after FSP. Finally, a wide bead consisting of mixed dendritic and columnar cast structure was obtained. The current work is expected to alleviate the physiological issues pertaining to orthopaedic fixations and decrease the need for secondary surgeries in geriatric fractures.

Additive manufacturing of a compliant mechanism using Zr-based bulk metallic glass

• Additively manufactured moving structure with a compliant mechanism using bulk metallic glass. • Zr-based bulk metallic glasses demonstrate excellent resilience for compliant mechanisms. • The nominal rotational elastic motion can be increased by roughly 300% compared to Ti6Al4V in an exemplary compliant mechanism. Compliant mechanisms offer several advantages compared to rigid mechanisms, such as lower friction, backlash, and reduced part count which makes them attractive for structural and medical applications. However, their motion is limited by the elastic properties of the used material. Bulk metallic glasses offer a unique combination of high strength and large elastic deformation which suggests a high potential for the application in compliant mechanisms. This unique property profile originates from the amorphous structure, which results from the rapid cooling of tailored glass-forming alloy compositions. Recently, additive manufacturing via laser powder bed fusion established as a pivotal technology to overcome the limitations of size and complexity during the fabrication of bulk metallic glasses. This work presents the fabrication of a compliant mechanism via laser powder bed fusion that utilizes the unique elastic properties of the Zr 59.3 Cu 28.8 Al 10.4 Nb 1.5 bulk metallic glass forming alloy in combination with the geometrical freedom of additive manufacturing.

3D pore structure characterization and hardness in a powder bed fusion-processed fully amorphous Zr-based bulk metallic glass

Recently, fabrication of bulk metallic glasses (BMGs) components with complex shapes has been realized using laser powder bed fusion (PBF). Initial defects such as porosity inherent to the PBF process can significantly degrade the mechanical integrity of the BMGs components. In spite of intensive studies on pore structures in 3D-printed crystalline alloys, pore structures in 3D-printed fully amorphous BMGs have not been characterized due to the difficulties in achieving large-scale fully amorphous structures. In the present work, the pore characteristics of PBF-processed fully amorphous Zr-based BMGs were systematically studied. The amorphous structure of the printed parts was first verified using X-ray diffraction (XRD). A non-destructive high-resolution X-ray micro-computed tomography (micro-CT) technique was then applied to evaluate the inner 3D pore structure, while microstructures below the resolution of X-ray micro-CT were examined in 2D using scanning electron microscopy (SEM). The printed amorphous parts can reach a total volumetric porosity as small as 0.45%. The distribution of pore size and pore sphericity were evaluated for the PBF-processed BMGs samples with different porosities, where two observed pore features were irregular large lack-of-fusion pores, and smaller gas-induced round pores. Furthermore, correlations were found between porosity, pore size and morphology. Finally, hardness tests at various loads revealed that while the intrinsic properties were constant irrespective of laser processing, the overall mechanical properties of the PBF-processed BMGs samples are dominated by pore characteristics. While the densest printed BMG sample had a comparable macroscale hardness to the as-cast material, an increase in porosity of ~8% led to a decrease in HV5 hardness of ~17%. The presented results provide a detailed analysis of pore characteristics, and their impact on mechanical properties of PBF-processed BMGs, for further experimental and computational studies of structure-property relationships in this materials class.

Structural and Mechanical Characteristics of Cu50Zr43Al₇ Bulk Metallic Glass Fabricated by Selective Laser Melting.

In this work, the structural and mechanical characteristics of Cu50Zr43Al7 bulk metallic glass (BMG) fabricated by selective laser melting (SLM) are studied and the impacts from the SLM process are clarified. Cu50Zr43Al7 alloy specimens were manufactured by the SLM method from corresponding gas-atomized amorphous powders. The as-built specimens were examined in terms of phase structure, morphologies, thermal properties and mechanical behavior. The x-ray diffraction and differential scanning calorimetry results showed that structural relaxation and partial crystallization co-exist in the as-fabricated Cu50Zr43Al7 glassy samples. The nano- and micro- hardness and the elastic modulus of the SLM-fabricated Cu50Zr43Al7 BMG were higher than CuZrAl ternary BMGs with similar compositions prepared by conventional mold casting, which can be attributed to the structural relaxation in the former sample. However, the macro compressive strength of the SLM-fabricated Cu50Zr43Al7 BMG was only 1044 MPa mainly due to its porosity. This work suggests that the SLM process induced changes in structural and mechanical properties are significant and cannot be neglected in the fabrication of BMGs.

Additive Manufacturing of Advanced Multi‐Component Alloys: Bulk Metallic Glasses and High Entropy Alloys

Bulk metallic glasses (BMGs) and high entropy alloys (HEAs) are both important multi‐component alloys with novel microstructures and unique properties, which make them promising for applications in many industries. However, certain hindrances have been identified in the fabrication of BMGs and HEAs by conventional techniques due to the intrinsic requirements of BMGs and HEAs. With the advent of metal additive manufacturing, new opportunities have been perceived to fabricate geometrically complex BMGs and HEAs with tailorable microstructure theoretically at any site within the specimen, which are not achievable using conventional fabrication techniques. After providing some background and introducing the conventional fabrication techniques for BMGs and HEAs, this review will focus on the current status, development, and challenges in metal additive manufacturing of BMGs and HEAs including different additive manufacturing techniques being used, microstructure design and evolution, as well as properties of the fabricated BMGs and HEAs. A future outlook of metal additive manufacturing of BMGs and HEAs will also be provided at the end.

Cutting Characteristics of Zr-Based Bulk Metallic Glass

Cutting behavior exerts a considerable influence on the fabrication of bulk metallic glass (BMG) components. In this study, the influences of machining parameters (i.e., depth of cutting, feed rate, and spindle rate) on the turned surface of a Zr-based BMG after observing the 3D morphologies of this surface were characterized. The results showed that the influence of the spindle rate on the surface morphologies is more substantial as compared to the depth of cutting and the feed rate. Nanoscratch tests were conducted to further characterize the separation mechanism of the chips, which revealed that the chips are torn off the surface of a BMG because of inhomogeneous localized maximum shear stress.

Evaluation of thermoplastic formability of Zr-based bulk metallic glasses and its correlation with characteristic temperature parameters

Thermoplastic formability (TPFA) is a key factor in fabrication of bulk metallic glass (BMG) components by thermoplastic forming (TPF) technology. In this paper, the softness in the entire super-cooled liquid region (SCLR) is used to evaluate the TPFA of 18 Be-free Zr-based BMGs and the reliability is verified by mould forming experiments. The correlations between softness and thermo-dynamic characteristic temperature parameters are well explained under the assumption of linear SCLR in Angel plot. A parameter constructed by thermo-dynamic and thermal–mechanical characteristic temperatures is proposed, representing the best correlation with softness. These results help understand the TPFA of BMGs well.

The effect of the gas atmosphere on the response of the Al86Ni6Y4.5Co2La1.5 metallic glass powder to heating

The response of nitrogen gas-atomised fully amorphous Al86Ni6Y4.5Co2La1.5 powder (<25 μm) to heating in nitrogen and argon from 5 K/min to 40 K/min was investigated using differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and nano-indentation. The powder showed noticeably lower glass transition temperature, crystallization onset temperature, and peak crystallization temperatures in nitrogen than in argon, particularly at heating rates of ≥30 K/min. The activation energy for the onset of crystallisation of the powder was determined to be 301.58 ± 42.47 kJ/mol in nitrogen compared to 418.18 ± 7.20 kJ/mol in argon. Experimental evidence confirmed the reaction between the amorphous Al86Ni6Y4.5Co2La1.5 powder and nitrogen at ≥360 °C or even from ∼280 °C. The powder that crystallized in nitrogen exhibited slightly but consistently higher hardness and elastic modulus. These results are necessary to inform the selection of the sintering atmosphere and parameters for the fabrication of bulk metallic glass of Al86Ni6Y4.5Co2La1.5 from powder.

ChemInform Abstract: Bulk Metallic Glass: The Smaller the Better

AbstractReview: 113 refs.

Fabrication of bulk metallic glasses at the region of multiple quasi-peritectic reactions

We report that Ca-Cu-Mg bulk metallic glasses (BMGs) can be fabricated at the region of multiple quasi-peritectic reactions by a conventional copper mold casting method, demonstrating that finding a deep eutectic composition is not the sole solution for the fabrication of BMGs. Unusual relationship between the glass transition temperature and the elastic constants of these BMGs were discussed in comparison with other BMGs. These results have implications for exploring new BMGs and understanding the glass formation mechanism.

Bulk Metallic Glass: The Smaller the Better

Bulk metallic glasses (BMGs) are strong, highly elastic, and resistant to wear but still find limited utility due to their macroscopic brittle nature, high costs, and difficulty of processing, particularly when complex shapes are desired. These drawbacks can be mitigated when BMGs are used in miniature parts (< 1 cm), an application which takes advantage of BMGs' enhanced plasticity at small length scales as well the insignificant material cost associated with such parts. As an alternative to traditional metal processing techniques, thermoplastic forming (TPF)-based microfabrication methods have been developed which can process some BMGs like plastics. In this article, we discuss the properties and fabrication of BMGs on minuscule length scales to explore their prospective application in small-scale devices.

Y effects on magnetic and mechanical properties of Fe-based Fe–Nb–Hf–Y–B bulk glassy alloys with high glass-forming ability

The effects of partial substitution of Y for Fe on the glass-forming ability (GFA), mechanical, thermal and magnetic properties of quinary Fe 73− x Nb 4Hf 3Y x B 20 ( x = 0–3 at.%) alloys were investigated. The replacement of 1–3 at.% Fe by Y increased thermal stability of the supercooled liquid in the Fe–Nb–Hf–Y–B alloys, enabling the fabrication of bulk metallic glasses (BMGs) with diameters up to 4 mm from the original 2 mm. Properties of Fe 73− x Nb 4Hf 3Y x B 20 BMGs were measured, yielding a rather high saturation magnetization of 1.05–1.22 T, low coercive force of 1.6–3.6 A/m, high compressive fracture strength of 3200–3490 MPa, Yong's modulus ( E) of 177–190 GPa and compressive strain before failure ∼2%. Furthermore, the role of Y addition on the GFA as well as mechanical and magnetic properties is also discussed.

Effect of Y addition on thermal stability and the glass forming ability in Fe–Nb–B–Si bulk glassy alloy

The effect of Y addition on the thermal stability and glass forming ability (GFA) has been investigated in (Fe 72Nb 4B 20Si 4) 100− x Y x ( x = 0–5) alloys. Addition of 3–5 at.% Y improves the GFA. With increasing the Y content, glass transition temperature ( T g) and crystallization temperature ( T x ) shifted to the higher temperature region. The (Fe 72Nb 4B 20Si 4) 97Y 3 alloy shows a high thermal stability, with T g of 859 K and the supercooled liquid regions reached maximum value of 56 K. The (Fe 72Nb 4B 20Si 4) 97Y 3 alloy exhibits the largest γ (=0.402) value among the alloy investigated, enabling fabrication of bulk metallic glass (BMG) sample with the diameter of 4 mm.

Fabrication of bulk metallic glasses in the alloy system Fe–C–Si–B–P–Cr–Mo–Al using hot metal and industrial ferro-alloys

Fe-base bulk metallic glasses in the alloy system Fe–C–Si–B–P–Cr–Mo–Al have been developed using hot metal and industrial ferro-alloys. The amorphous alloys can be cast into fully amorphous rods with diameters of up to 4 mm, demonstrating high glass-forming ability and high strength (>3 GPa). Thermal stability and crystallization behavior of the Fe–C–Si–B–P–Cr–Mo–Al bulk metallic glasses are also investigated. The Fe-base bulk metallic glasses can be produced cost-effectively and massively for extensive structural applications.

Synthesis of ferromagnetic Fe-based bulk glassy alloys in the Fe–Nb–B–Y system

The effect of substitution of Y for Fe on the glass forming ability (GFA), magnetic and mechanical property has been studied in Fe 77 − x Nb 6B 17Y x ( x = 0–4) alloys. Replacement of 1–4 at.% Fe by Y increased the thermal stability of the glass and liquid phase in the Fe–Nb–B–Y alloys. It was found that the Fe 74Nb 6B 17Y 3 alloy exhibited the largest T rg (0.60) and γ (= T x /[ T g + T L]) (0.396) values enabling the fabrication of bulk metallic glass (BMG) with a diameter of up to 2 mm. The BMG alloy (≥74 at.% Fe) exhibited high compressive fracture strength and hardness of about 3 GPa and 1060 Hv, respectively. The partial replacement of 3 at.% Fe by Y in Fe–Nb–Y–B improved the alloy magnetization saturation by about 10%.

Bulk Glass Formation in Mg-Cu-Ag-Y-Gd Alloy

The effect of partial substitution of Y for Gd on the glass forming ability of Mg 6 5 Cu 1 5 Ag 1 0 Y 1 0 alloy has been studied using X-ray diffraction and differential thermal calorimetry. Partial substitution of Y by Gd improves the glass forming ability. The Mg 6 5 Cu 1 5 Ag 1 0 Y 2 Gd 8 alloy shows the highest glass forming ability among the alloys investigated, enabling the fabrication of bulk metallic glass with the diameter of 9mm by conventional Cu-mold casting method in air atmosphere. The compressive fracture strength and fracture elongation of the Mg 6 5 Cu 1 5 Ag 1 0 Y 2 Gd 8 bulk metallic glass are 956MPa and 1.6% respectively.

Consolidation of amorphous copper based powder by equal channel angular extrusion

Cu 50Ti 32Zr 12Ni 5Si 1 gas-atomized powder was consolidated by equal channel angular extrusion (ECAE). Powder was vacuum encapsulated in copper cans and extruded at a temperature above the glass transition temperature ( T g), but below the crystallization temperature ( T x ). Five samples were subjected to one extrusion pass, each with a different temperature and extrusion rate. Microstructure, thermal stability, X-ray diffraction measurements and hardness of the ECAE consolidates were examined and compared with those of the initial powder and with a conventional extrusion (CE) consolidate. All consolidates exhibit a supercooled liquid region slightly narrower than that of the starting powder. No significant crystallization peaks are observed in XRD measurements; however, changes in peak shape and the total enthalpy of crystallization in differential scanning calorimetry measurements are attributed to nanocrystallization that is not easily detected by these methods. Greater microhardness values in ECAE consolidates in comparison with the starting powder also support the probability of nanocrystallization. The brittle behavior exhibited by all consolidates is attributed to an initial high oxygen contamination of the powder (∼2000 ppm) and the possibility of crystallization due to long exposure to temperatures above T g during consolidation. Microstructural examination of the ECAE consolidates shows significant shear deformation of the particles with one ECAE pass. The results of the present study encourage further work on the fabrication of bulk metallic glass from powder by ECAE consolidation.