Surface force-induced bonding at metal multiasperity contacts

Abstract

Adhesion at multiasperity contacts of clean metal surfaces obtained by rupture in an ultrahigh vacuum and by vacuum deposition of thin metal films onto flat surfaces has been investigated. Indium and lead were chosen in this study because their high surface energy to hardness ratios allowed us to expect a marked surface force effect in adhesion. In the region of small applied loads, the adhesion coefficient varied from ~1 to ~200 while surface roughness R_a varied from ~120 to ~0.01 μm. In the case of smooth surfaces (R_a = 0.01-0.03 μm), complete bonding of the contacting surfaces at room temperature and under small applied loads (0.1-0.5 MPa, which is much smaller than the yield stress of metals in contact) occurred. This effect is considered to be evidence of a surface force contribution to adhesion. Such effect appeared to be useful in bonding non-metallic materials by the use of thin metal films as an adhesion-promoting interlayer.

Keywords:

• Adhesion
• surface forces
• metal films
• surface topography