AlNiYCo Amorphous Matrix Composites Induced by Bismuth and Lead Additions
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INTRODUCTION
A series of investigations on the formation and fundamental properties of Al-based amorphous alloys were carried out with the aim of developing high specific strength materials.[1–3] Al-TM-RE (Al at. pct > 80, TM = transition metal, and RE = rare earth) systems with promising properties synthesized by direct quenching were intensively investigated. Among the Al-TM-RE systems, it was reported that Al-Ni-Y amorphous alloys exhibit better mechanical properties, and their glassforming ability can be enhanced substantially with the addition of small quantities of Co.[4] Recently, Yang et al.[5] successfully obtained bulk Al-rich amorphous alloy rods by casting the molten Al-Ni-Y alloys with small quantity additions of Co and La. The bulk Albased amorphous alloys exhibit ultrahigh specific strength but very limited plasticity. Because of brittleness at room temperature, the application of the amorphous alloys as structural materials may be restricted. To improve ductility, attempts have concentrated on developing composite materials consisting of crystalline reinforcement phases in amorphous matrix. Currently, three methods, such as nanocrystal precipitation upon annealing,[6–8] addition of high melting JIE HE, Associate Professor, is with the Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China, and also with IFW Dresden, Institute for Complex Materials, Dresden 01069, Germany. Contact e-mail: [email protected] HONGXIANG JIANG, M.Sc. Candidate, and JIUZHOU ZHAO, Professor, are with the Institute of Metal Research, Chinese Academy of Sciences. NORBERT MATTERN, Professor, is with IFW Dresden, Institute for Complex Materials. JU¨RGEN ECKERT, Professor, is with IFW Dresden, Institute for Complex Materials, and also with TU Dresden, Institute of Materials Science, Dresden 01062, Germany. Manuscript submitted March 26, 2011. Article published online August 3, 2011 4100—VOLUME 42A, DECEMBER 2011
crystalline particles or fibers prior to casting,[9, 10] and the in-situ formation of ductile dendrites,[11–13] were employed to prepare amorphous matrix composites. For the Al-Ni-Y systems, one of the most attractive characteristics is the precipitation of the a-Al nanocrystal phase thermally induced within the Al-based amorphous matrix. The Al-based amorphous matrix composites containing a high number density of a-Al nanocrystals exhibit better mechanical properties.[14–17] Nevertheless, investigations on the Al-based amorphous matrix ex-situ and in-situ composites are scarce.[18, 19] Al-Bi and Al-BiPb systems have a liquid miscibility gap owing to the positive heat of mixing. In this article, elements Bi and Pb are added to Al85Ni5Y8Co2 alloys. We report the AlNiYCo amorphous matrix in-situ composites induced by the additions Bi and Pb.
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EXPERIMENTAL
The nominal compositions of the alloys studied in this work are (Al85Ni5Y8Co2)98Bi2 and (Al85Ni5Y8Co2)98 (Bi50Pb50)2. For alloy preparation, the elemental pieces with a purity of 99.9 pct or higher were used as starting mate
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