An investigation of surface damage using radioactive metals

Experiments have been carried out in which a radioactive metal hemisphere slides over a non-radioactive metal surface, and the amount and nature of the transferred material are examined autoradiographically. It is found that metal transfer takes place in the form of discrete fragments, and that well-lubricated surfaces give less transfer than clean surfaces by factors of 400 or more. On heating well-lubricated surfaces, both the coefficient of friction and the amount of metal transfer increase markedly at the melting point of the surface film. The metal transfer, however, in contrast to the friction, is sensitive also to temperature change below the surface film's melting point, and this is explained as due to the softening of the surface film near its melting point. In some cases, large non-radioactive fragments picked up on the radioactive slider prevent the transfer of radioactive fragments, and examples of this effect are shown.