STM study of topographical changes on gold contact surfaces caused by loading

The topographical changes to the asperities of a flat cobalt-hardened gold electroplated surface that occur as a result of being contacted with a ruby sphere are studied by means of scanning tunneling microscopy and software developed to allow computer image registration and subtraction. A range of normal, force loads and sphere sizes are utilized. Quantitative information is obtained for each plastically deformed asperity in the contact region concerning the volume of material displaced during the contact process and the area of the contact spot resulting from the flattened asperity. Three-dimensional images are presented that show the location and size of the portions the asperities that were displaced in the contact process. Two-dimensional maps are generated to show the location and size of the asperity contacting spots in the contact region, Data from contact conditions of 10 to 100 grams normal force and from 1/16 inch to 1/4 inch contacting sphere diameter are used to show trends concerning the number of deformed asperities, total contacting area, total deformed volume, maximum area of the largest deformed asperity, force/total contacting area, and total deformed volume/total contacting area as a function of normal force and sphere diameter.