Effects of material pair properties on the frictional behavior of metals

The objective of this work was to investigate the validity of the adhesion theory and the mechanical interaction view point in describing the frictional behavior of metals. Specifically, experimental work was conducted to investigate the relative importance of the material compatibility and hardness ratio on the friction and wear behavior of various metals in dry sliding condition in ordinary laboratory environment. Initial and steady state friction coefficients were measured using both pin-on-disk and pin-on-reciprocating testers for various metal pairs, which were strategically selected based on their compatibility and hardness ratio. The wear characteristics were also observed following the experiments. The experimental results showed that material compatibility had no significant correlation with either initial or steady state friction coefficient. As for the hardness ratio, material pairs with very large differences in initial hardness values resulted in high initial friction coefficient. Overall, it was observed that factors such as sliding motion, whether unidirectional or bi-directional, and wear particle dynamics were found to be more critical on frictional interaction than either material compatibility or initial hardness ratio. Furthermore, among several material properties analyzed, initial friction coefficient had the highest correlation with shear modulus while the steady state friction coefficient had the highest correlation with hardness.