Amorphous Phase Formation Analysis of Rapidly Solidified CoCr Droplets
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METALLIC glasses have many attractive intrinsic properties, for example, strength, corrosion resistance, soft magnetism, and high moldability in the supercooled region, because the atoms are disordered and there is no long-range periodicity. In general, glassy alloys combine both high elasticity and high strength. The very first amorphous alloy was discovered when a splat quenching-induced rapid solidification of small amounts of Au75Si25 (Au-25 at. pctSi) yielded an amorphous alloy.[1] Since this discovery, there has been an unprecedented interest in amorphous alloys among metallurgists and material scientists around the world that led to the development of numerous production methods.[2,3] The new materials named metallic glasses have remarkable properties including strength and corrosion resistance. However, the first generation of metallic glasses has some drawbacks that include the necessity of very high cooling rates (~105 K s1) limiting the production of these materials to thin foils (1 to 100 lm). A remarkable progress in the development of these newly found materials was made with the reported preparation of a 10-mm-diameter ingot of a fluxed Pd40Ni40P20 glass.[3]
ABDOUL-AZIZ BOGNO, Postdoctoral Fellow, CARLOS RIVEROS, Undergraduate Student, and HANI HENEIN, Professor, are with the Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, Canada. Contact e-mail: [email protected] DELIN LI, Research Scientist, is with Canmet MATERIALS, Natural Resources Canada, Hamilton, ON, Canada. Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2016. Manuscript submitted October 31, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
They discovered that the cooling rate could be highly reduced simultaneously with the increase of thickness of the metallic glass. Later on, Inoue et al.[4] reached an optimal metallic glass diameter of 72 mm by adding Cu to Pb-Ni-P alloy and varying the Ni and Cu concentrations. Metallic glasses with ingot diameters >1 mm are called bulk metallic glasses (BMGs). BMGs have a high potential as advanced engineered materials due to their strength and corrosion resistance properties and therefore represent a very dynamic research field in material science with wide application. Several hundreds of different BMG materials are known and commercially manufactured nowadays. Their production methods include centrifugal casting[5] or water quenching.[6] A key requirement for a BMG is that the material shall have a high glass forming ability (GFA). BMGs form in a variety of systems including Fe-and Co-based alloys.[7,8] Typically, these systems contain three to five constituents, with a large atomic size mismatch, a negative enthalpy of mixing among the main three elements and a composition close to a deep eutectic. The eutectic temperature of a BMG is significantly lower than the melting point of its individual constituents, which makes it easier to quench it into a glassy state. In addition, the alloy needs to be cooled from its li
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