Investigation on the arc erosion behavior of new silver matrix composites: Part II. Reinforced by short fibers
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An electroless plating and hot-pressing process was developed to fabricate silver matrix composites reinforced with uniformly distributed graphite and Saffil short fibers (Graphitesf and Saffilsf). The hardness of the composites increases as the content of short fibers increase. Static-gap, single-spark erosion and repeated-collision, multiple-arc erosion tests were used to investigate the arc erosion behavior of the composites. The composites exhibited better arc erosion resistance when the contents of short fibers were increased in a static-gap, single-spark erosion test. However, the weight loss of the composites after 10,000 times repeated-collision, multiple-arc erosion operation shows that the composites with low volume percents of short fibers have a good arc erosion resistance. The Saffilsf /Ag composites show a better arc erosion resistance than Graphitesf /Ag because of the greater strengthening effect of the finer Saffil short fibers. The erosion behavior of the composites is dominated by the viscosity of composites in single-spark tests, while it depends on the competition of viscosity and thermal properties in multiple-arc tests.
I. INTRODUCTION
Silver-based electrical contact materials have been well developed and widely applied in the electronic industry, including control systems, electric instruments, and so on.1–3 They are subjected to severe arc erosion and contact wear resulting in material damage.3–9 Among them, particulate-reinforced silver matrix composites with good properties at only a small expense of electrical and thermal conductivity are mainly used as upgraded electrical contact materials.2–4,10–12 It was previously reported in “Investigation on the arc erosion behavior of new silver matrix composites. Part I: Reinforced by particles” that the molten composites with a high viscosity provided by particulate reinforcements exhibit a high resistance to flow and splash during arc formation.13 However, for high-power make-break contacts or brushes, contact materials must withstand much stronger mechanical collision than arc erosion under sustained high temperatures during continuous arc formation.5,6 Therefore, composites with different types of reinforcements need to be developed to provide a higher strengthening effect and viscosity. Composites reinforced by short fibers of large aspect ratios exhibit different properties from particulate-reinforced ones,12 so Graphitesf / Ag and Saffilsf /Ag composites were chosen and tested in this research for the investigation of their arc erosion resistance. J. Mater. Res., Vol. 18, No. 4, Apr 2003
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Traditional oxide-reinforced silver matrix electrical contact materials are processed by internal oxidation, which is expensive and requires long process times.3,11 Besides, internal oxidation has never been proposed for processing short fiber reinforced composites. An alternative is a simple process using electroless plating and hot pressing to fabricate silver matrix composites with uniformly dis
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