Thermal expansion behavior of silver matrix composites

Abstract

Silver matrix composites containing 10 to 40 vol pct ceramic reinforcements of different types, shapes, and sizes were processed by electroless silver plating and hot pressing. The thermal expansion behavior of the silver matrix composites has been studied from room temperature to 300 °C. The coefficients of thermal expansion (CTEs) of the composites are effectively lowered to below 10 × 10⁻⁶/°C by the addition of 40 vol pct reinforcements. The CTEs of composites decrease as the content of reinforcements increases due to the constraint effect provided by the ceramic reinforcements with low CTEs; this effect is more pronounced with the addition of whiskers and fibrous reinforcements. At the beginning of measurements, large residual thermal stresses existing in the water-quenched composites restrict the expansion of the silver matrix, resulting in lower CTEs than those of furnance-cooled composites. As the temperature increases, the residual thermal stresses are gradually released, and the CTEs of composites reach higher and stable values. At temperatures above 250 °C, the CTEs of composites increase at a higher rate due to the matrix yielding and interfacial debonding.