Relationships among crystallographic structure, mechanical properties and tribological behaviour of electroless Ni–P(9%)/B 4C films

Abstract

The tribological behaviour of electroless Ni–P composite coatings was investigated by dry sliding tests with a slider-on-cylinder tribometer. The tests were carried out in laboratory air at room temperature against a PVD-TiN coated HSS cylinder. Friction and wear data are discussed on the basis of the mechanical properties (microhardness, plasticity parameter, fracture toughness) of the coatings, that were derived by indentation measurements at low loads. The wear depths measured on unreinforced Ni–P were about one order of magnitude larger than those obtained on the corresponding composite coatings. Furthermore, wear depth proved to increase with increasing annealing time, for both pure matrix and composite layers. The wear volume Q was correlated to the mechanical properties using Archard-type equations. For composite coatings the plasticity parameter δ H was inserted into the equation for the estimation of Q, in order to take into the account the action of a B 4C-rich layer observed on the surface of the worn coatings.