Multicomponent bulk metallic glasses with elevated-temperature resistance

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oduction Most of the common metals have a simple crystal structure, body-centered-cubic (bcc), face-centered-cubic (fcc), or hexagonal closed-packed (hcp), though their alloys may include compounds with more complex structures. It is of interest to synthesize novel alloys with different structures that may be expected to give unique and useful properties. One effective method to change structures is by alloying with more metallic elements. This can change the structure from crystalline to glassy even in a cast bulk form.1–3 The formation of bulk metallic glass (BMG) is associated with alloys in which the selection of components follows three rules, namely: (1) at least three elemental components, (2) significant atomic size mismatches above 12% among the main three elements, and (3) negative heats of mixing among the three elements.1,4 In addition, such multicomponent alloys have deep eutectic valleys and permit access to a highly supercooled liquid state, resulting in the formation of BMGs, which have an atomic configuration that is disordered at long range and ordered at a medium range of 1.7–2.0 nm.5 These BMGs exhibit unique combinations of properties that cannot be obtained

for crystalline alloys (e.g., ultrahigh strength, large elastic strain, high corrosion resistance, high wear resistance, surface smoothness, viscous flowability, net castability, and precise formability).1,4 In addition, Fe- and Co-based BMGs exhibit good soft magnetic properties with low coercivity, high permeability, and low core loss since their atomic configuration is uniform on the scale of the magnetic domains.1,4 To exploit these advantages, BMGs have been used in many fields and applications such as structural, soft magnetic, coatings, ornamental, casing, springs, sensors, mirrors, gears, hinges, bolts, and cutlery.1,4 In general, BMGs have compositions selected to optimize their glass-forming ability ([GFA], which is used to describe the tendency for materials to form glassy phase). An equiatomic multicomponent BMG was synthesized for Ti20Zr20Hf20Ni20Cu20 in 2002.6 Two years later, equiatomic multicomponent crystalline alloys with fcc and bcc structures were also formed for Fe20Co20Ni20Cr20Mn207 and AlxFeCoNiCrCu (x = 0–3),8 respectively. The latter was named as a high-entropy (HE) alloy in the paper. Since these syntheses, much attention has also been paid to equiatomic and near-equiatomic multicomponent alloys since

A. Inoue, International Institute of Green Materials, Josai International University, Japan; [email protected] F.L. Kong, International Institute of Green Materials, Josai International University, Japan; [email protected] S.L. Zhu, School of Materials Science and Engineering, Tianjin University, China; [email protected] A.L. Greer, Department of Materials Science & Metallurgy, University of Cambridge, UK; [email protected] doi:10.1557/mrs.2019.253

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