Irradiation as a tool for studying solid-state amorphization phenomena
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I.
INTRODUCTION
M A N Y different processes have been developed to produce amorphous metallic alloys. They can be obtained from liquids, gases, or crystalline solids, and also from aqueous solutions by chemical or electrodeposition. When the initial state is gaseous, molten, or a liquid solution, the main procedure is to impose a quenching (or deposition) rate sufficiently high to prevent crystallization. When the initial state is crystalline, the long-range topological order must be destroyed. Solid-state amorphizing methods include particle irradiation, annealing of diffusion couples or multilayers, annealing of metastable solid solutions, plastic deformarion, mechanical alloying, and hydrogenation. [~j These methods are quite different, and it is therefore pertinent to inquire whether they reveal basically different physical mechanisms or whether the mechanisms involved have some common denominator. Any attempt to answer this question requires a comparative study of initial metallurgical conditions, microstructural evolution of the crystalline material, and mode of amorphization. Very severe conditions seem to be required to amorphize pure metals and semimetals. The case of gallium is perhaps the best known. An amorphous film can be produced by vapor condensation on a substrate maintained at 4 K. [2] Gallium has also been rendered amorphous by Ar + irradiation of the metastable fl phase at 4 K [21 and by pulsed-laser irradiation at similar temperatures, t31 There are reports in the literature of methods capable of producing amorphous films of pure metals,
D.F. PEDRAZA, Staff Scientist, is with the Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 378316376. This paper is based on a presentation made in the symposium "Irradiation-Enhanced Materials Science and Engineering" presented as part of the ASM INTERNATIONAL 75th Anniversary celebration at the 1988 World Materials Congress in Chicago, IL, September 25-29, 1988, under the auspices of the Nuclear Materials Committee of TMS-AIME and ASM-MSD. METALLURGICAL TRANSACTIONS A
e.g., nickel and molybdenum,t41 Contamination is, however, a serious possibility, particularly with gaseous impurities, t5,61 For metallic alloys or compounds, processing conditions necessary to produce an amorphous alloy are usually much less extreme. This fact suggests that perturbations to the interactions between different atomic species in the initial crystalline structure must play an important role in stabilizing the amorphous state. Indeed, the majority of amorphous metallic systems consists of concentrated alloys which include at least one transition metal. Glass-forming criteria have been developed to a great extent based on common trends for rapid solidification processing of metallic alloys. [71 These rules have been extended to apply to solid-state amorphization transitions as well, with additional considerations that are appropriate for the specific process. Amorphization criteria can be generally classified into three categories, viz., constitutive,
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