Effects of roughness on the wettability of high temperature wetting system

• The substrate roughness enhances the wettability of non-reactive high temperature wetting system such as AgCu/Cu.
• The substrate roughness detrimental to the wettability of reactive high temperature wetting system such as AgCuTi/alumina.
• The wettability of reactive system has strong relationship with the width of lateral growth of product layer.

The effects of substrate roughness on the wettability of non-reactive wetting and compound forming wetting systems were investigated by the sessile drop technique at high temperature. The AgCu eutectic alloy/copper and the AgCuTi/alumina wetting systems were selected. It is found that the substrate roughness has a great effect on both wetting systems. For the non-reactive wetting system, an additional capillary driving force exists when melt flows into the micro v-grooves of the rough surface, leading to a decrease in final contact angle (θf) and consequently a better wettability. For the compound forming metal/ceramic reactive wetting system, wetting on a rough surface exhibits a slow spreading kinetics and a short period of spreading time, and the retarding force of spreading increases because of overcoming the energy barriers due to asperities of the rough surface, resulting in an increase in θf. Thus, a rough substrate has negative effect on the wettability of the compound forming reactive wetting system.