Investigation on the arc erosion behavior of new silver matrix composites: Part I. Reinforced by particles
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Static-gap, single-spark tests were used to investigate the arc erosion behavior of newly developed silicon carbide and alumina particle reinforced silver matrix composites (SiCp/Ag, Al2O3p/Ag). Craters and hills exist on the surfaces of eroded silver matrix composites, and their depths and sizes decrease as the particle content increases and the particle size decreases. Obvious melting, flow, severe splash of molten silver, and the segregation of particles are present on the surfaces of eroded composites containing low volume percents of large particles. Easier silver flow results in smooth surfaces and reduces the total surface areas of the eroded composites containing large particles. The flow and splash of silver decreased with increasing particle content and decreasing particle size, exhibiting a better erosion resistance to single-spark tests. The static-gap, single-spark erosion behavior of silver matrix composites is dominated by the flow and splash of molten composites. A high viscosity of the liquids provides the composites a good arc erosion resistance.
I. INTRODUCTION
During the short period of time when a switching contact supports a voltage difference or carries a current, an electrical arc occurs on the small contact surface area through which passes a large current density, which leads to high temperatures over the melting points of copper and silver.1,2 In an extreme case of a high-power switching contact, the load current even exceeds the order of several tens amperes.3–5 Associated with a strong electrical and magnetic turbulence, the arc severely damages the contact materials.6,7 According to previous researches, the failure of contact materials can be generally divided to the following types: (i) mass transfer, contact materials melt and splash out, leading to the loss of materials;8–11 (ii) oxidation, high temperatures result in the surface oxidation of contact materials, increasing contact resistance;8,12,13 (iii) welding, contact materials melt and weld with each other;8,9 (iv) bridging, contact materials splash and deposit to form needlelike precipitates, resulting in a short circuit.14–16 Conclusively, high strength and good wear resistance, high electrical and thermal conductivity, and good chemical stability are required properties for good contact materials.4,5,13,17 Silver-based materials have been used as electrical contacts for decades because of their high electrical and thermal conductivity and excellent oxidation resistance.13,18–20 However, they exhibit low strengths at elevated temperatures, leading to the low resistance to arc erosion. The most serious damage of arc erosion 804
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J. Mater. Res., Vol. 18, No. 4, Apr 2003 Downloaded: 21 Mar 2015
to contact materials results from mass transfer (i.e., splash and deposition).11,21,22 Solid-solution strengthening is applied to enhance the mechanical strength of silver by alloying copper, cadmium, gold, platinum, or palladium, etc.13 However, the electrical conductivity of the solid-solute alloys drast
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