Many studies on the friction and adhesion phenomena under a high-vacuum condition have been done and being continued steadily since the advanced development followed the improvement of the research method. At present studies many types of metal alloys such as bearing steel, stainless steel and phosphor bronze chosen as the test pieces with a few single metals like nickel and tin. Though in the ultra high vacuum condition a lot experiments have been done on friction phenomena, the wear phenomena have not been enough clarified in such condition because of being in itself complicated. As it is most desirable that the change of the worn surface during wear process can be limited within certain extents, the ultra high-vacuum condition are most suitable to clarify the wear mechanism on which a clear explanation has not been made. The experimental results under such condition can clarify the effect of the compatibility among the material combinations, and of difference of the contact shape, furthermore can make clear also experimentally the larger adhesive force than the ploughing term
