Erosion of hard material coating systems

The use of coating systems to protect structural metal surfaces from elevated temperature, small solid particle erosion and erosion-corrosion can extend component life and permit operation in more severe environments. The room and elevated temperature erosion behavior of several hard material coating systems, i.e. carbides, borides and nitrides, were determined over a range of test conditions. Particle velocities from 70 to 150 m s −1 and test temperatures from 25 to 540°C were used. Mechanisms of erosion were established and related to erosion rates in a manner that defined the requirements of composition, morphology and defect levels of coating systems for long-term performance. It was determined that small grain size, low porosity and absence of cracks were the microstructural features that enhanced erosion resistance. Hardness levels and the composition and distribution of second phase, hard particles had less effect on coating performance. Angular SiC particles were considerably more erosive than either Al 2O 3 or chromite-mixed oxide round-shaped particles and the rankings of the coatings' performance were different for each erodent and set of test conditions.