Effect of hardness and morphology of potassium titanate on frictional wear characteristics of brake pads

Abstract

We investigated the effects of the properties of potassium titanate (PT), a raw material used in automobile brake pads, on the resulting frictional characteristics. Potassium hexatitanate, K2Ti6O13 (PT6), with a non-fibrous shape, was synthesised by acid leaching and subsequent thermal treatment of potassium tetratitanate, K2Ti4O9 (PT4), with the layered crystal structure. Comparing frictional characteristics, the brake pads including the largest sized PT6 (b, mean size ~72 μm, 980 Hv) with high mechanical hardness exhibits much higher coefficient of friction (COF) values and wear amounts of both the friction material and counter disc than the others. Our PT6 particles (a, mean size ~15 μm, hardness ~674 Hv) with the higher mechanical hardness than commercial PT6 (c, mean size ~24 μm, hardness ~310 Hv), show almost the same COF value and pad wear amount as PT6, c, despite reduced mean particle size. On the other hand, wear amounts and roughness of counter disc were found to be increased by ~30% for PT6, a, with higher mechanical hardness. This result shows mechanical hardness influences frictional wear of the disc, on the other hand, pad wear is proportional to COF, which is complicatedly affected by hardness and mean size. The area of secondary plateaus for commercial PT6 (c), with lower hardness and larger mean size than a, was larger than those of our PT6 (a); this finding indicates that the formation of the secondary plateau (contact area) is related to mean particle size of PT6 rather than hardness. As a result, our PT6 particles (a) with the higher hardness and smaller size than commercial PT6 exhibit almost the same COF values because the effects of mean size and hardness compensate each other.