The relationship between wear of semimetallic friction materials and pearlitic cast iron in dry sliding

Wear rate transitions for friction brake materials can be brought about by changes in the dominant wear mechanisms during operation. In order to investigate such effects, the relationship between the dry sliding wear rates of two commercial, semi-metallic friction materials, against a conventional cast iron counterface, have been investigated using a block-on-disc geometry. Applied load has been varied at a single, constant sliding velocity. Two distinct wear regions were recognized. The applied load for a transition in wear rate between these regions was 20% higher for one friction material than the other at contact temperatures in the range of 310-350 degrees C. The specific wear rates of the semimetallic friction materials and of the cast iron counterface depended on the operating wear mechanism. In the first region, wear was mainly by abrasion and the wear rates are correlated in an almost linear manner. In the second region, wear was by two thermally-activated processes (thermal degradation of the phenolic resin for the friction materials; tribo-oxydation for the cast iron). The specific wear rates were correlated by a power-law relationship. In summary, wear was controlled by the abrasivity of friction materials in the first region and by the contact temperature in the second region.