UC Berkeley

A numerical model of the interaction between liquids and rough solids is presented in this work. Partial-Transient-Liquid Phase (PTLP) bonding has proven an effective method of joining ceramic materials. The joining process is facilitated through the development of a thin-liquid layer between ceramic and metallic solids. Successful joining requires a liquid that will spread to fill interfacial voids, which can act as critical flaws that decrease the strength of the joined assembly. A full understanding of this method requires a model of the liquid behavior between dissimilar, rough solids. This work discusses the effect of wetting angle and surface roughness on the behavior of the liquid layer.

Numerical simulations are presented that test possible liquid configurations on rough surfaces, determining the preferred geometry based upon the total interfacial energy. Use of computational methods allows independent control of surface roughness, liquid volume, and interfacial energies. In this way, the effect of the liquid contact angle and the amplitude and wavelength of surface-roughness features on the liquid behavior is examined. Emphasis is placed upon surface-roughness parameters and the correlation with preferred liquid configurations. Models are presented and discussed for liquids in contact with one rough surface and for a liquid entrapped between two dissimilar surfaces. Comparison of the one-surface simulation to previous studies of liquid/roughness behavior is provided.

In liquid-based joining methods, the ability of the liquid layer to fill interfacial voids is strongly affected by surface roughness. Numerical simulations of a liquid flowing to fill an inter-solid gap are presented. The importance of dissimilar surface roughness, dissimilar contact angles, and inter-solid distance is discussed. It is found that increasing surface roughness can act to aid liquid-based joining in certain systems.