Erosion is caused by particulate in gases or liquids striking the surface of a component. The severity of the wear is strongly dependent on the velocity and hardness of the particles, as well as the angle of impact. It is of crucial importance to consider all of these conditions for a properly designed surface solution. For high-angle attack, a somewhat compliant coating or a very thick coating applied by welding or thermal spray should be selected. For low-angle attack, very hard coatings are preferred.