Thermal Spray Coatings for Erosion-Corrosion Protection

Thermal Spray Coatings for Erosion-Corrosion Protection

Keshavamurthy R. (Dayananda Sagar College of Engineering, India), Naveena B. E. (Dayananda Sagar College of Engineering, India) and Sekhar N. (Dayananda Sagar College of Engineering, India)
DOI: 10.4018/978-1-5225-4194-3.ch010

Abstract

This chapter discuss extensively on various thermal spray coatings for erosion-corrosion protection of industrial components, feedstock materials and their characteristics. Various coating removal mechanisms in thermal spray coatings have been presented. Influence of process variables, test parameters, coating thickness and working temperature on performance of thermal spray coatings for erosion-corrosion have been discussed comprehensively. Further, the concern of erodent's suspended in fluids, disintegrating and resulting in significant wear of the surfaces due to erosion-corrosion phenomenon also reported here.
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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).

Table 1.
Comparison of different thermal spray processes
Type of SystemTemperature of the Heat Source (0C)Particle Velocity (m/s)Oxide Content (%)Porosity (%)Adhesion (MPa)
Flame Spraying2500-300030-1804-610-158
Electric Wire Arc4000-6000100-2400.5-310-2012
Detonation Gun3000-4000800-12001-51-2>70
HVOF2500-3000500-8000.21-2>70
HVAF1400-2000600-12000.20-0.2>70
Plasma Spraying5500-12000200-6001-31.0 - 1010-70
Cold Spray200-1000300-10000<0.55->70

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

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