Physical and chemical properties of Ag–Cu composite electrical contacts prepared by cold-press and sintering of silver-coated copper powder

Abstract

Effects of silver content (5–35 wt %), sintering temperature (150–850 °C), sintering time (30–180 min), and compaction pressure (200, 300, and 400 MPa) were studied on characteristics of prepared contacts. XRD (X-Ray Diffraction), OM (Optical Microscope), SEM (Scanning Electron Microscope), and electrical resistance analyses were used to study the properties of the contacts. The Results showed that increasing the percentage of silver in the contacts as well as increasing the time and temperature of the sintering process increase the oxidation of copper. It was found that galvanic corrosion and the Kirkendall effect between Cu and Ag (especially in high silver content) resulted in the formation of microvoids around the copper particles facilitating the copper oxidation. Apparent bulk density remained almost constant as the sintering temperature increased from 150 to 700 °C, while it dropped sharply in a sintering temperature of 750 and 800 °C. It was determined that increasing the sintering time from 30 to 60 min increases the apparent bulk density, while increasing the sintering time to more than 60 min reduces it. Moreover, increasing the amount of compaction pressure in 200–400 MPa did not affect the apparent bulk density. The electrical resistance is almost independent of sintering temperature in 25 °C–700 °C. Further change in sintering temperature from 700 to 750 °C raised the electrical resistance from 0.2 Ω to 15 kΩ. A Study of the electrical resistance of the samples indicated that increasing the Ag content up to 25 wt% reduces the electrical resistance. The electrical resistance of the sample containing 35 wt% Ag was 14 kΩ that which was higher than that of the sample containing 25 wt% Ag (0.11 Ω).