In friction experiments material is exchanged between the sliding surfaces. A study of this transfer of material was made possible by the development of a radioactive tracer method by means of which one could detect quantities of metal as small as 10−4 microgram. Spherical or hemispherical specimens were slid over an activated base surface. After the friction experiments, the riders were tested for the presence of radioactive material, and the quantity of metal deposited on the rider was determined as a function of various parameters. A copper‐beryllium base surface was used for all measurements reported here. For the materials investigated it was found that the amount of base metal adhering to the rider was proportional to the load and increased with the distance of travel. Under otherwise identical conditions the amount of base metal deposited on the rider depended on surface finish and hardness of the rider. If the rider was harder than the base, the transferred material increased with surface roughness. If, on the other hand, the rider was softer than the base, surface finish was found to be of secondary importance. Measurements made with steel specimens showed that the amount of metal deposited on them was inversely proportional to their Brinell hardness. For riders of different materials, but having the same hardness and surface finish, the amount of transferred metal increased with the solid solubility of the base metal in that of the rider. Lubrication decreased the transfer; the reduction depended on load and, for the same load, on the material of the rider. The influence of lubrication was greater for smaller loads.

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