Development of the erosion durability technique for thin coatings

Abstract

A novel method has been developed to assess the durability of thin coatings exposed to solid particle erosion. In this test a stream of particles travels from a parallel nozzle to strike a coated surface. The divergence of the stream leaving the nozzle can be described analytically and the flux of particles at any point may thus be predicted. By monitoring the growth in the diameter of the wear scar the critical dose Q c of particles required to remove the coating may be determined and used to describe the durability of the coating. The behaviour of a series of well-characterised titanium nitride PVD coatings on tool steel substrates has been studied. Q c depended on the erosion conditions (particle type, shape, size and velocity) and on the thickness of the coating. The effects of these parameters were systematically investigated and an analytical relationship determined which allows values of durability to be normalised. The work has provided an improved understanding of the properties determined by the erosion durability test and has also suggested methods for tailoring the technique to investigate different aspects of coating performance such as adhesion.