A gas-water atomization process for producing amorphous powders

Metallic glasses (MGs) are out-of-equilibrium metallic systems known for their unique structural and functional properties arising from structural long-range disorder. Despite their attractive properties, practical applications of MGs fabricated by traditional casting strategy face challenges due to size constraints (limited glass-forming ability) and shape complexity issues. Over the decades since the discovery of MGs in the 1960 s, significant progress has been made in overcoming these limitations by the manufacture strategy, enabling the fabrication of engineering components with desired sizes, tailored shapes, and intricate geometries. This paper presents a comprehensive assessment of the state-of-art for manufacturing techniques of large MG and MG parts. The advancements in subtractive, formative, and additive manufacturing of MGs, as well as their joining and welding processes, are reviewed. By consolidating the existing knowledge, this review aims to suggest the practical and promising approach to overcome the limited glass-forming ability and size restrictions in cast MGs through the manufacture strategy, offer insights for further advancements in MG manufacturing, address evolving nature of the field and promote a better understanding of the key scientific aspects of structures and properties in processed MG components.

Thermoplastic elastomers (TPEs) and metallic glasses (MGs), both lack of long-range ordering structure, have different physical and mechanical properties. To combine unique viscoelasticity of elastomers and excellent wear resistance of MGs, we propose to introduce a Pd₄₀Ni₄₀Si₄P₁₆ MG into a commercial styrene-butadiene-styrene (SBS) TPE to form MG/TPE composites. Serving as a hard and strong second phase dispersed in the SBS matrix, the micrometer-sized MG particles can effectively improve the wear resistance of the matrix due to a strengthening effect. In particular, the MG/TPE composite with an addition of 60 wt% MG shows significantly enhanced wear resistance up to about three times that of the SBS matrix. The present results provide a new way to enhance the wear resistance of the widely used TPEs, which may generate immense economic value by extending their service life.

Metallic glasses, first reported in 1960, are solid alloys that are not crystalline, having an atomic arrangement inherited directly from the liquid state. At first it was considered that a metallic glass could be obtained only by ultra-rapid quenching of the liquid, but now many compositions are known that can be cast fully glassy in bulk (i.e. with minimum cross-section of 1 mm to 1 cm) without the need for high cooling rates. The availability of such bulk metallic glasses has opened up possibilities for exploitation, and they are currently among the most intensively studied of all metallic materials. This chapter describes the thermodynamics and kinetics of the glassy state in metals. The wide range of possible compositions is surveyed. Their structures and the structural changes induced by thermal or mechanical treatments are covered. As metallic glasses can exhibit strengths and combinations of strength and toughness better than any other class of metallic material, their mechanical properties are of particular interest. The possibilities for exploiting these and other properties in functional and structural applications are briefly reviewed.

Iron-based metallic glass coatings (denoted as FeWCrNiMoBSiC) were prepared on 1Cr18Ni9Ti stainless steel cylinders by atmospheric plasma spraying at different parameters. The morphology, microstructure, and crystalline structure of as-prepared Fe-based metallic glass coatings were analyzed by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. A Pycnometer and a Vickers hardness tester were adopted to measure the porosity and microhardness of iron-based metallic glass coatings. Moreover, differential scanning calorimetry analysis was conducted to investigate the crystallization behavior of various iron-based metallic glass coatings, and a ball-on-disk tribometer was performed to evaluate the tribological properties of the coatings coupled with silicon nitride ceramic balls under unlubricated conditions. It has been found that the microhardness of iron-based metallic glass coatings increases with increasing plasma arc power, which is related to the degree of melting of feedstock powders and the compactness of as-prepared coatings. Besides, the phase compositions of as-sprayed coatings consist of amorphous structure and limited crystalline structure, and the contents of the amorphous structure and crystalline structure vary with plasma arc power. Moreover, iron-based metallic glass coatings deposited at different plasma arc powers show similar steady-state friction coefficients (0.8–0.9), but their wear rate varies with varying plasma arc power. Particularly, iron-based metallic glass coating with next to the highest hardness exhibits the best anti-wear ability, which is the outcome of the compromise between the hardness and brittle fracture as well as abrasive wear of the coatings during sliding process.

Spark plasma sintering (SPS) was used to sinter gas-atomized Zr₅₇Cu₂₀Al₁₀Ni₈Ti₅ amorphous powder. Systematic analyses were performed to study particle size and annealing time effects on the parts structure and properties. Partial devitrification and particles welding were observed and correlated to particle size and thermal conditions. Mechanical testing, through compression and micro-hardness, reveals that the sintered parts show strength similar to a quenched bulk metallic glass and damaging before failure. However, the pulsed current input does not seem the most relevant way to sinter amorphous powders: during the sintering initial stages (when necks are small), excessive over-heating is generated in the vicinity of particles necks, and is responsible for partial devitrification; further current input at large necks leads to complete densification. Effects of the stress, the thermo- and electro-transports on the sintering are evaluated to provide a better understanding of the SPS mechanisms of densification of metallic glasses.

A laboratory method of producing amorphous powder by fine gas jet impingement of molten Al–Mg–Zn alloy is described. The powder has been characterized by X-ray diffraction and differential thermal analysis (DTA) techniques. The grain size of the powder varied from 5 to 80 μm . The fine grains (size upto ∼20 μm) are completely amorphous. However, large grains are partly amorphous. Using the DTA technique, glassy–crystalline phase transition temperature T_g is found to be 473.6°C. Vickers hardness of the grains is in the range 215 to 255 kg/mm².