Effect of sizing on friction and wear properties of copper-iron based sintered composites

Sizing, also known as coining, is a post sintering near net shape metal forming operation performed on automobile brake and clutch liners to achieve improved physical and mechanical properties and close dimensional tolerances. Cu-15% Fe based composite pins were processed in the present investigation by powder metallurgy route with and without addition of mullite and graphite and both. Sizing of sintered pins was performed and tribological properties, such as; coefficient of friction (COF) and specific wear rate were studies under dry sliding conditions. Physical properties were also evaluated, which were found improved after sizing for all the compositions studied. Tribological properties, in particular specific wear rate, were found significantly deteriorated for the sized materials containing either mullite or graphite alone. However, composites that contained both mullite and graphite, showed slightly reduced, but more stabilized COF upon sizing. Specific wear rate of these sized pins was found minimal and exceptionally low compared to materials containing either mullite or graphite alone. There was little increase in the wear rate of sized pins compared to the as sintered pins containing both mullite and graphite, which was due to the development of microcracks after sizing. The tendency of microcracking could be minimized by optimization of the sizing pressure, so as to achieve both improved physical properties as well as tribological performance