Abstract
Amorphous metallic coatings are of high interest because of their good wear and corrosion resistance as well as their high hardness and toughness relative to the crystalline alloys with the same composition. Thermal spray that makes it possible to reach quenching rates in the order of 106-107 K/s, has the ability to deposit coatings with a high content of amorphous phase. However, very few studies dealt with the understanding of the spraying factors that affect the formation of the amorphous phase under thermal spray conditions. In this work, the relationship between temperature and velocity of the spray particles and coating characteristics is investigated. Special attention is given to the degree of amorphisation of the as-sprayed coatings. The latter were produced both by plasma and wire-arc spraying in order to get a larger range of particle parameters at impact and different particle heating history in the gas flow before impingement onto the substrate. A commercial iron-based alloy available both in powder and wire forms was used. Microstructural analyses show that the as-sprayed coatings are partially amorphous and that the proportion of the amorphous phases depends on the sizes of the sprayed particles as they control the heating and acceleration of particles in the gas flow and their cooling rate on the substrate.
