Special Orientation Relationships of CuZr 2 in the Annealed Zr 64.5 Cu 35.5 Metallic Glass
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INTRODUCTION
SINCE metallic glasses (MGs) were invented, crystallization has been an important issue for amorphous alloys. The crystallization phase results in the generation of multiple shear bands in Cu-Zr, containing bulk amorphous alloys, which, in turn, leads to enhanced plasticity.[1,2] Different methods could lead to crystallization, such as deformation, irradiation, and annealing. Chen et al.[3] first reported crystallization in a bent amorphous alloy ribbon by transmission electron microscopy (TEM). Irradiation by electron or ion resulted in the formation of nanocrystalline structures, which was rarely realized by thermal annealing.[4,5] Thermal annealing is the most common way to induce crystallization in MGs. In the Zr-Cu amorphous alloy, the most probable crystallization products are CuZr2, Cu10Zr7, Cu8Zr3, and CuZr.[6] Crystallization is related to the cooling rate of MG and the heating rate.[7] The formation of quasicrystal phases in Zr-Cu alloys is favored by the addition of oxygen;[8] noble metals, such as Ag, Pd, Pt, and Au;[9–13] and the transition metals Nb, Ta, V, and Ti.[14–16] Wang et al.[17] reveal that, prior to nanocrystallization, there exists a metastable state prone to forming icosahedra-like atomic clusters, which impede
PENGFEI YU, Ph.D. Candidate, LIJUN ZHANG, HU CHENG, and HUAN ZHANG, Master Students, QIN JING, MINGZHEN MA, and RIPING LIU, Professors, are with the State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, P.R. China. Contact e-mail: [email protected] PETER K. LIAW, Professor, is with the Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996. GONG LI, Professor, is with the State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, and also with the Department of Materials Science and Engineering, The University of Tennessee. Contact e-mail: [email protected] Manuscript submitted October 28, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
subsequent crystallization and, hence, stabilize the supercooled liquid. The atom structure in MGs is still a subject for further studies. Many models have been proposed for MG formation in the past, such as the model of dense random packing of hard spheres,[18] the topological model,[19,20] and the particular types of clusters (such as Kasper polyhedra).[21] The atomic structure of MGs could be studied by amorphous crystallization for being closely related to the structure of MGs. Devitrification is an efficient approach to connect the medium-range order[22] and long-range order.[23] Binary MG Zr-Cu amorphous alloys are appropriate candidates for studying crystallization. Therefore, in the present work, we select the Zr64.5Cu35.5 MG as the model material and focus on its crystallization process and phases orientation relationship in order to reveal the atomic structure. In particular, we report the observation of a special orientation relationship of the crystallization phase CuZr2 during annealing of the ZrCu amorp
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