Ion Beam Manipulation to Fabricate Ordered Layered Structures and Amorphous Alloys in Some highly Immiscible Binary Meta
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Ion Beam Manipulation to Fabricate Ordered Layered Structures and Amorphous Alloys in Some highly Immiscible Binary Metal Systems X. Y. Li, R. F. Zhang, and B. X. Liu* Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, CHINA ABSTRACT We developed a new scheme, namely ion beam manipulation, i.e. interface-assisted ion beam mixing, for fabricating amorphous alloys and artificial solid-state microstructures in metal-metal multilayers, in which the individual layer thickness is down to about 2 nm, differing significantly from the typical thickness of 5-8 nm in conventional ion beam mixing. Employing the scheme, some interesting results were obtained in three highly immiscible systems. In the Ag-W system, which has the largest positive heat of formation among the transition metal alloys, amorphous alloys were obtained, for the first time, through a two-step structural transition, i.e. the initial polycrystalline Ag and W transformed into an intermediate bcc phase, which later transformed into an amorphous state. In the Ru-Pd system, the initial polycrystalline Pd and Ru first transformed into a single crystalline FCC phase, and then turned into a well-ordered structure, which showed an apparent tendency to transform back to the FCC phase upon over-irradiation. In the Ag-Co system, an ordered layered structure was observed and identified to consist of two overlapped FCC lattices, corresponding to a new magnetic state of Co atom with an average magnetic moment measured to be 2.84 µB, which was about twice the equilibrium datum and was the largest value ever observed. We present, in this paper, a brief review concerning the scheme of ion beam manipulation in fabricating the metastable alloys, the structural evolution upon ion irradiation and the associated magnetic properties of some ordered structures obtained by the scheme. I. INTRODUCTION In developing new materials of high performance, a powerful way is to fabricate novel artificial solid-state microstructures or atomic configurations frequently by applying some nonequilibrium and even far-from-equilibrium processes, which could provide excess energy to help reaching highly energetic states, enabling one to obtain the corresponding nonequilibrium phases/structures in the materials systems of interest [1]. For instance, a scheme of ion beam mixing (IBM) of multiple metal layers was introduced in early 1980s and has been employed to produce a great number of nonequilibrium solid phases in the binary metal systems, such as amorphous, metastable crystalline and quasicrystalline phases [2,3,4]. In recent years, the experimental scheme of IBM has been significantly advanced, i.e. the individual layer thickness of the multilayers was intentionally designed to be 2-3 nanometers. Under such circumstance, the interfacial free energy could contribute importantly in elevating the initial state of the multilayers up to a highly energetic level, corresponding to an existing nonequilibrium state. Meanwhile, the atomic migration length require
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