Frictional Properties of Bearing Metals

Abstract

MOST bearing alloys consist of a matrix of a soft metal in which are distributed uniformly small crystals of a harder metal. Such a structure has been found by long experience to possess the most satisfactory mechanical, frictional, and low-wearing properties. It is usually supposed that the hard constituent carries the load, while the soft matrix serves to distribute the pressure uniformly and to embed abrasive particles in the lubricant¹. The hard phase also stands out in relief from the soft phase at room temperature, and such a surface of minute hills and valleys is often said to possess desirable lubricating qualities. On account of the higher thermal expansion of the softer constituent, Kyropoulos² states that the latter is able to take the load at higher temperatures, that is, under running conditions. On the other hand, the opinion has been expressed³ that a single soft metal constitutes as efficient a bearing as the conventional structure of hard crystals in a soft matrix. In actual practice, of course, a variety of different bearing alloys are used depending on the conditions of sliding. When the conditions are severe, as at high speeds and high and varying loads, only certain types of alloy structure can be used with success, and the homogeneous metal is unsatisfactory. It does therefore appear that a heterogeneous structure possesses definite advantages for bearing metals.