THERMAL SPRAY COATINGS

THERMAL SPRAY COATINGS

Abstract 

Thermal sprayed coatings are used extensively for a wide range of industrial applications. The technique generally involves the spraying of molten powder or wire feedstock, the melting being achieved by oxy- fuel combustion or an electric arc (plasma). The molten particles are accelerated by the flame, Followed by impacting onto a properly prepared substrate, usually metallic. Solidification occurs at rates akin to those obtained in ÒRapid Solidification TechnologyÓ. Thus, the as-sprayed deposit is ultra-fine grained, having the properties associated with such microstructures. The materials which are sprayed include most metal alloys and ceramics. In fact, virtually any material can be thermal sprayed as long as it does not decompose prior to melting.
In this review, the various methods of thermal spray will be discussed. The feed materials characteristics will be briefly reviewed in reference to the properties of the deposit. The connection between the flame and the particles will be examined, together with the means of diagnosing key aspects of the flame- particle interaction. Solidification processes will be overviewed relative to the influence on microstructure and properties. The as-sprayed imperfection structure will be explored, from measurements of these defects to their influence on coating properties. Finally, applications and the possible future directions of thermal spray will be reviewed.