Thermal Spray Coatings for Erosion-Corrosion Protection

Introduction

Friction, wear, corrosion, erosion, fatigue, oxidation are all surface phenomenon. Hence, it is of utmost importance that one focuses on improving the surface properties of the materials. This involves surface modification to tailor make the surface properties. The various industrial techniques of surface modifications mainly used are hot dipping, thermal spraying, heat treatment, electro less plating, electro plating, chemical/physical vapour depositions and weld overlaying. Among these techniques, thermal spray methods have been gaining widespread importance in order to produce products which will meet requirements of all surface phenomena and to ensure competitiveness in the market (Fauchais et al, 2014; Sidhu, 2005).

In this technique, the coating is formed in layers by accelerating fine molten, semi-molten or softened particles towards the component surface, where they rapidly flatten and solidify on impact. Upon impact, a mechanical interlocking takes place with the target surface. With succeeding striking particles, depositing platelets called splats. With various layers of these splats forming the thickness of coating. Figure 1 presents the principle of a thermal spray process.

Figure 1.

Scheme of thermal spraying process

Feedstock material is usually introduced in powder, wire or rod form. The actual material can be anything between low melting plastics and refractory materials, e.g., oxide ceramics, as long as the material has a melting point, a stable molten state, and does not evaporate or excessively react with the surrounding atmosphere. The material is melted with the heat produced by an electric arc, fuel combustion or an ionized gas, i.e. plasma, and particles are accelerated towards target surface by the high velocity stream of process gases (Pawlowski, 2008; Saber-Samandari & Berndt, 2010).

Talib et al., 2003; Vuoristo, 2014; Matikainen et al., 2015.