Effect of Ag-particulate addition on processing, microstructure, and properties of MgO-whisker-reinforced bulk BPSCCO hi
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Effect of Ag-particulate addition on processing, microstructure, and properties of MgO-whisker-reinforced bulk BPSCCO high-Tc superconductor composites Y. S. Yuan,a) M. S. Wong,b) and S. S. Wangc) Department of Mechanical Engineering and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204-4792 (Received 14 August 1995; accepted 29 January 1996)
In associated papers [Y. S. Yuan, M. S. Wong, and S. S. Wang, J. Mater. Res. 11, 8–17 (1996); J. Mater. Res. (1996, in press)] it has been shown that weak thermomechanical properties of a bulk monolithic high-Tc superconductor (HTS) can be improved by introducing strong ceramic whiskers into the HTS ceramic materials. In this paper, we report a further study of incorporating Ag particulates, (Ag)p , in a bulk monolithic BPSCCO and in the MgO-whisker reinforced BPSCCO composite. Effects of the (Ag)p addition on processing, microstructure, and superconducting and mechanical properties of the bulk monolithic BPSCCO and the (MgO)wyBPSCCO composite are investigated. The results indicate that the highly ductile Ag particulates promote densification of the BPSCCO matrix phase in the composite during hot pressing. The microstructure of the HTS composite with the (Ag)p addition is similar to that in the HTS material without the (Ag)p . The (MgO)wyBPSCCO composite with 10% (by weight) Ag particulates has been shown to possess excellent superconducting properties. The (Ag)p addition to both the monolithic BPSCCO and the (MgO)wyBPSCCO is found to increase appreciably their fracture toughnesses, but has little effects on mechanical strengths of the materials. Quantitative relationships have been established among solid-state processing variables, HTS phase developments, microstructures, and superconducting and mechanical properties of the (Ag)pyBPSCCO and the (MgO)wy(Ag)pyBPSCCO HTS composites.
I. INTRODUCTION
In applications of high-Tc bulk superconductors (HTS), such as flywheel energy storage systems,3 magnetic bearings,4 and current leads,5 the HTS materials are required to possess desirable, combined superconducting and thermomechanical properties. Despite their excellent superconducting properties, oxide-based monolithic HTS materials are generally very brittle with extremely low strengths.6,7 To improve their mechanical properties, attempts have been made to reinforce the HTS materials with strong ceramic fibers and whiskers.8–10 Recently, high-strength/high-modulus MgO whiskers have been successfully incorporated into a Pb-doped Bi-2223 (BPSCCO) HTS material.1,11 The HTS composite has been demonstrated to possess not only excellent superconducting properties,12 but also improved mechanical properties.2 However, it a)
Formerly, Graduate Research Assistant; currently with General Plastics & Rubber Co., Houston, Texas 77087. b) Senior Research Scientist, Mechanical Engineering Department, University of Houston, Houston, Texas 77204. c) Distinguished University Professor, Mechanical Engineering Department, U
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