Effects of Thermal Loading Conditions on the Mechanical Properties of S45C/Cu/Si3N4 Composites
Nobuhiro SETTSU, Manabu TAKAHASHI, Masafumi MATSUSHITA, Keiji OGI and Mitsuyoshi TSUTSUMI
Abstract:The effects of thermal loading conditions on the mechanical properties of S45C/Cu/Si3N4 composites with brazing filler metals of AgCu and AgCuTi are described. Thermal loading tests were conducted on test samples under various heat conditions, after which the joint parts of the samples were observed with a focus on the Cu interlayers using an optical microscope. Four-point bending tests were conducted on the samples to evaluate the residual strength and stress strain characteristics of the samples. In addition, fracture surfaces and the origins of the fractures were observed using an optical microscope. The results showed that thermal loading of the S45C/Cu/Si3N4 composites caused fatigue damage to the Cu interlayers and its amount increased with increases in the cycle number and temperature range of thermal loading. In the case of relatively-mild thermal loading conditions, fracture initiation regions were observed at the Cu/Si3N4 boundary. In contrast, fracture initiation regions were observed in the Cu interlayer for the samples subjected to relatively-extreme thermal loading conditions. The increases in the cycle number and temperature range of thermal loading promoted reductions of residual strength, resilient modulus and residual fracture ductility for the samples. The reductions of the mechanical properties of the S45C/Cu/Si3N4 composites were affected by the fatigue damage of the Cu interlayers. It was concluded that continuous operation (no start-stop system) is suitable for long-term use of ceramic/metal composites including interlayers in order to minimize reduction of their mechanical strength. Key Words:Thermal loading condition, Composite, Cu interlayer, Residual strength, Cycle number, Temperature range