Effect of the in-flight behavior of particles on the amorphous content of metallic coatings under thermal spray conditions

Amorphous metal alloys in the form of bulk materials or coatings exhibit generally high mechanical properties and high wear and corrosion resistance. Therefore, they have generated significant interest over the last three decades. Thermal spray processes that are characterized by rather high cooling rates (similar to 10(6) K/s) could be a possible route for the manufacturing of thick coatings (up to 1-2 mm) of glassy metal alloys and the first commercial product was developed in 1984. However, most of the "amorphous" thermal-spray coatings have a significant content of crystalline phase. The objective of this study is to investigate the relationship between the characteristics of particles (i.e. temperature, velocity and size) at impact and the degree of amorphisation of the as-sprayed coatings. Two thermal spray techniques (i.e. plasma and wire-arc) are used in order to get a large range of particle parameters and different heating histories before impact on the substrate.