Novel Approach In Search Research Articles

A Centimeter-Size High Toughness Zr-Cu-Al-Nb Bulk Metallic Glass with Nano-Crystallization and Phase Separation

In this paper, a centimeter-size Zr-Cu-Al-Nb bulk metallic glass (BMG) with high notch toughness of 107±13 MPa∙m0.5 was designed and fabricated by copper mold casting. With 1% Nb substitution for Zr in Zr48Cu45Al7 glass forming alloy, the glass forming ability (GFA) and toughness of the BMG were enhanced significantly. The coexistence of nano-crystallization and phase separation in the glassy matrix was observed in Zr47Cu45Al7Nb1, which would possibly lead to the high toughness of this alloy due to the easy and populous nucleation of shear bands and the increasing resistance of shear band propagation. The influences of nano-crystallization and phase separation on the toughness of BMGs are discussed in detail. The strategy utilized in this study provides a novel approach in search for new BMGs with high toughness and good GFA.

Microstructure and mechanical properties of Al20−xCr20+0.5xFe20Co20Ni20+0.5x high entropy alloys

In this paper, a series of Al20−xCr20+0.5xFe20Co20Ni20+0.5x (x = 2, 4.5, 7, 9.5 at.%) HEAs were fabricated by arc-melting, and their microstructures and mechanical properties (tensile properties, hardness and toughness) were investigated. It was found that the HEAs in the present study could form solid solution with FCC, BCC or FCC + BCC structures. With the decrease in Al content and the increase in Cr and Ni contents, the microstructure of the HEAs evolves from single phase with inconspicuous compositional fluctuation to dual phases with significant difference in element concentration. By adjusting the composition to x = 7, the HEA displays lamella structures and exhibits high tensile strength and fracture toughness as compared to the alloys with x = 2 and 4.5. Dendrite structure emerges in the HEA with x = 9.5, which displays good plasticity and impact toughness. The correlation between composition, microstructure and mechanical properties of these alloys is discussed in detail. This study provides a novel approach in search for new non-equimolar HEAs with outstanding comprehensive mechanical properties.

A centimeter-size Zr40Hf10Ti4Y1Al10Cu25Ni7Co2Fe1 bulk metallic glass with high mixing entropy designed by multi-substitution

In this paper, a Zr40Hf10Ti4Y1Al10Cu25Ni7Co2Fe1 (at.%) bulk metallic glass (BMG) with high mixing entropy was synthesized. Designed by (Hf, Ti, Y) multi-substitution for Zr and (Ni, Co, Fe) for Cu in Zr55Al10Cu35 BMG with low mixing entropy, this new BMG exhibits significant improvement in glass forming ability (GFA) and good plasticity among TiZrCuNi-containing BMGs with high mixing entropy. In addition, thermal properties, crystallization behaviors and mechanical properties of Zr40Hf10Ti4Y1Al10Cu25Ni7Co2Fe1 BMG are discussed in detail. Successful formation of Zr40Hf10Ti4Y1Al10Cu25Ni7Co2Fe1 BMG with high mixing entropy provides a novel approach in search for new high entropy alloys with non-equal atomic ratios.

High-Entropy Metallic Glasses

The high-entropy alloys are defined as solid-solution alloys containing five or more than five principal elements in equal or near-equal atomic percent. The concept of high mixing entropy introduces a new way for developing advanced metallic materials with unique physical and mechanical properties that cannot be achieved by the conventional microalloying approach based on only a single base element. The metallic glass (MG) is the metallic alloy rapidly quenched from the liquid state, and at room temperature it still shows an amorphous liquid-like structure. Bulk MGs represent a particular class of amorphous alloys usually with three or more than three components but based on a single principal element such as Zr, Cu, Ce, and Fe. These materials are very attractive for applications because of their excellent mechanical properties such as ultrahigh (near theoretical) strength, wear resistance, and hardness, and physical properties such as soft magnetic properties. In this article, we review the formation and properties of a series of high-mixing-entropy bulk MGs based on multiple major elements. It is found that the strategy and route for development of the high-entropy alloys can be applied to the development of the MGs with excellent glass-forming ability. The high-mixing-entropy bulk MGs are then loosely defined as metallic glassy alloys containing five or more than five elements in equal or near-equal atomic percent, which have relatively high mixing entropy compared with the conventional MGs based on a single principal element. The formation mechanism, especially the role of the mixing entropy in the formation of the high-entropy MGs, is discussed. The unique physical, mechanical, chemical, and biomedical properties of the high-entropy MGs in comparison with the conventional metallic alloys are introduced. We show that the high-mixing-entropy MGs, along the formation idea and strategy of the high-entropy alloys and based on multiple major elements, might provide a novel approach in search for new MG-forming systems with significances in scientific studies and potential applications.

High mixing entropy bulk metallic glasses

Bulk metallic glasses (BMGs) are usually based on a single principal element such as Zr, Cu, Mg and Fe. In this work, we report the formation of a series of high mixing entropy BMGs based on multiple major elements, which have unique characteristics of excellent glass-forming ability and mechanical properties compared with conventional BMGs. The high mixing entropy BMGs based on multiple major elements might be of significance in scientific studies, potential applications, and providing a novel approach in search for new metallic glass-forming systems.

A comprehensive analysis of hyper-heuristics

Meta-heuristics such as simulated annealing, genetic algorithms and tabu search have been successfully applied to many difficult optimization problems for which no satisfactory problem specific solution exists. However, expertise is required to adopt a meta-heuristic for solving a problem in a certain domain. Hyper-heuristics introduce a novel approach for search and optimization. A hyper-heuristic method operates on top of a set of heuristics. The most appropriate heuristic is determined and applied automatically by the technique at each step to solve a given problem. Hyper-heuristics are therefore assumed to be problem independent and can be easily utilized by non-experts as well. In this study, a comprehensive analysis is carried out on hyper-heuristics. The best method is tested against genetic and memetic algorithms on fourteen benchmark functions. Additionally, new hyper-heuristic frameworks are evaluated for questioning the notion of problem independence.