Microstructural characterisation and corrosion behaviour of microwave-sintered magnesium alloy AZ61/fly ash microspheres syntactic foams

Magnesium alloy AZ61/fly ash microspheres (FAMs) syntactic composite foams were synthesised via powder metallurgy and microwave (MW) sintering techniques. MW sintering was rapidly completed in 20 min and minimized the formation of brittle interfacial products. Effect of FAMs on the density, microstructure, and corrosion resistance of the alloy were investigated. FAMs were intact and fairly distributed in the microstructure of the foams. Corrosion behaviour in 3 wt.% sodium chloride solution showed that Tafel polarization curves shifted to lower current densities as the volume fraction of FAMs increased. This indicated that FAMs generally enhanced the corrosion resistance of the foams due to minimal galvanic interaction and reduction in the surface area of the material exposed to the corrosion medium. These results are significant and outline the enhancement of corrosion resistance of magnesium alloy AZ61 foams by using FAMs

Bibliometric Mapping of Literature on High-Entropy/Multicomponent Alloys and Systematic Review of Emerging Applications

High-entropy/multicomponent alloy (HEA/MCA) has received significant research attention in the last decade. There is a dearth of data-driven works dedicated to assessing and visualizing the HEA/MCA literature from a global perspective. To this end, we present the first bibliometric literature analysis of more than 3500 HEA/MCA articles, published between 2004 and 2021, in the Scopus database. We identify the most prolific authors, their collaborators, institutions, and most prominent research outlet. Co-occurrence networks of keywords are mapped and analyzed. A steep rise in research outputs is observed from 2013, when the number of annual publications doubled the previous years. The top five preferred research outlets include Journal of Alloys and Compounds, Materials Science and Engineering A, Scripta Materialia, Intermetallics, and Acta Materialia. Most of these publications emanate from researchers and institutions within China, USA, and Germany, although international scientific collaboration among them is lacking. Research gaps and future research directions are proposed, based on co-occurrence frequencies of author keywords. Finally, a brief systematic review of emerging applications, covering hydrogen storage, additive manufacturing, catalysis, and superconductivity, is undertaken. This work provides an important comprehensive reference guide for researchers to deepen their knowledge of the field and pursue new research directions

Tunability of mechanical and biodegradation properties of zinc-based biomaterial with calcium Micronutrient alloying

Biodegradable metals are being investigated as temporary implants that dissolve safely in the body after bone regeneration. Zinc (Zn) has an intermediate biodegradation rate between magnesium and stainless steels, yet its degradation rate is too slow to function as a temporary orthopedic implant. Alloying with nutrient elements is considered a strategy to tune its mechanical properties and in vivo biodegradability. Zn/calcium (Zn/Ca) alloys (with 0.5, 1, and 2 wt% Ca) were processed by spark plasma sintering and their microstructure, mechanical, and biodegradation properties were investigated. Ca was distributed in the grain boundary regions of Zn due to its low miscibility in Zn. Furthermore, the corrosion rates of Zn/Ca alloys determined from linear polarization measurements (0.164–0.325 mm/yr) accelerated by at least 10% compared with pure sintered Zn (0.149 mm/yr) with simultaneous dissolution of Zn and Ca, as verified from X-ray diffraction analysis of the corrosion products. The alloy specimens exhibited hardness (52–58 HV) and compressive strength (93–119 MPa) comparable with those of human cortical and cancellous bones (49 HV; 90–209 MPa). This study demonstrated the tunability of the mechanical and biodegradation properties of Zn-based materials by alloying them with a nutrient element for potential application as temporary orthopedic implants.Validerad;2023;Nivå 2;2023-03-08 (joosat);Funder: National Natural Science Foundation of China (No.52020105011)Licens fulltext: CC BY License</p

The effect of weld geometry and post-weld heat treatment on the corrosion behaviour of austenitic stainless steel immersed in 1.0 M NaCl solution

The variation of welding parameters such as weld geometry and post-weld heat treatment on the corrosion behaviour of austenitic stainless steel in a saline environment of 1.0 M NaCl was investigated in this work. Rods of austenitic stainless steel of known chemical composition were prepared and welded using electric arc welding technique varying the aforementioned parameters. Thereafter, samples for the corrosion behaviour investigation were then cut out of the welded rods. The analysis of the experimental data revealed that the best weld geometry was chamfered and a post-weld heat treatment carried out at temperatures in excess of 700 °C followed by air cooling improves the quality of a weld

Compressive Characteristics of Aluminum-Fly Ash Syntactic Foams Processed by Microwave Sintering

Aluminum-fly ash (FA) syntactic foams were synthesized via powder metallurgy and hybrid microwave sintering for 30 minutes. This minimized the formation of unwanted brittle interfacial products. Sphericity of FA microspheres was preserved, and significant density reduction of about 36 pct was achieved. Compressive strength and energy-absorption characteristics of the samples reduced as the volume fraction (vol pct) of FA microspheres increased from 20 to 40 pct. These materials have potential applications as lightweight energy-absorption materials

Review of Novel High-Entropy Protective Materials: Wear, Irradiation, and Erosion Resistance Properties

By their unique compositions and microstructures, recently developed high-entropy materials (HEMs) exhibit outstanding properties and performance above the threshold of traditional materials. Wear- and erosion-resistant materials are of significant interest for different applications, such as industrial devices, aerospace materials, and military equipment, related to their capability to tolerate heavy loads during sliding, rolling, or impact events. The high-entropy effect and crystal lattice distortion are attributed to higher hardness and yield stress, promoting increased wear and erosion resistance in HEMs. In addition, HEMs have higher defect formation/migration energies that inhibit the formation of defect clusters, making them resistant to structural damage after radiation. Hence, they are sought after in the nuclear and aerospace industries. The concept of high-entropy, applied to protective materials, has enhanced the properties and performance of HEMs. Therefore, they are viable candidates for today&rsquo;s demanding protective materials for wear, erosion, and irradiation applications

A comprehensive review on the deformation behavior of refractory high entropy alloys at elevated temperatures

Thermo-mechanical processing of refractory high entropy alloys (RHEAs) at high temperatures is very important. It is an effective method of modifying the microstructure, properties, and shaping into final components after casting. Using the Scopus database, 57 articles relating to the hot deformation of refractory high entropy alloys were extracted from 2011 to 2022. Despite the limited number of articles on hot deformation of RHEAs, it is important to find out if the dominant softening mechanisms reported in other metallic alloys are evident. This is the main impetus for this study since the hot deformation behavior has not been comprehensively studied. All the probable mechanisms influencing deformation in metallic alloys, such as work hardening, dynamic recrystallization, and dynamic recovery, have also been observed in RHEAs. The bulging phenomenon, serrated grain boundaries, and necklace-like structures reported in metallic alloys have also been detected in hot deformed RHEAs. Unsafe deformation behavior such as cracks that have been reported in metallic alloys, have also been observed in RHEAs. This review has provided a comprehensive study on the hot working processes of RHEAs and highlighted critical gaps for future research direction with some suggested limitations

Synthesis and characterisation of floatable magnesium alloy syntactic foams with hybridised cell morphology

Powder metallurgy and rapid microwave (MW) sintering techniques were successfully applied to engineer a hybrid cell structure into magnesium alloy AZ61 syntactic foams. The hybrid cell structure, comprising open- and closed-cells, originated from leached carbamide granules and hollow microspheres of fly ash (HS), respectively. External MW susceptors accelerated the sintering process and greatly mitigated the formation of undesirable interfacial reactions. The cell hybridisation technique facilitated control over the density and strength of the syntactic foams. Accordingly, floatable syntactic foams with a density of about 0.79 g/cm3 and compressive strength of 16 MPa were synthesised without recourse to any surface modification or chemically-induced superhydrophobicity. The processing techniques were capable of mitigating damage to the HS microspheres as confirmed by microstructural examinations. Furthermore, potential applications of the floatable syntactic foam sample, as a microboat and chemical release agent, were demonstrated by using ethanol as a propellant. AZ61 syntactic foams synthesised in this study exhibited low density and adequate strength, suggesting their applicability as alternative materials to polymer composite foams