Towards new formulations for journal bearing alloys

For the last half century, the literature on journal bearing alloys has been limited, with some exceptions, to technological papers describing small improvements in existing alloys and textbook descriptions repeating in one way or another the few reviews available on this topic. Several of the comments in these reviews are now outdated, some contained incorrect statements and no evolution is visible in the formulation of commonly used journal bearing alloys. The absence of new solutions in this area imposes restrictions on the improvement of the efficiency of combustion engines. It will be seen that the classical terms used to describe the optimal properties for these alloys are mostly qualitative. Based on present-day knowledge on the wear mechanisms of ductile alloys, the paper shows that these criteria can be substituted with a smaller set of quantitative parameters, with yield strength and strain hardening capability as the most important ones. Others, like the concept of tribological compatibility remains as enigmatic as it was 50 years ago, although possible lines of exploration will be highlighted based on current understanding of friction and adhesion. To illustrate the former points, two sets of experimental results will be summarised in the text. The first set relates to an extensive study of classical Al-Sn alloys, illustrating that even in this system, improvement is still possible. The second one describes an attempt to use the concept of compatibility, as described by Rabinowicz, to define a new formulation for copper based triboalloys, in the form of the Cu-Mg-Sn system. These examples, together with the general principles derived from modern literature, indicate that there is no theoretical or practical reason why journal bearing alloys should be limited to the existing classes.