The Detonation Spray Coating (DSC) process is a unique variant among the wide choice of thermal spray processes. The typical functionalities of DSC coatings include wear and corrosion resistance, elevated temperature oxidation resistance, thermal barrier, insulative/conductive, abradable, lubricious surface, etc. Among the coatings for wear resistance, the cermet coatings based on WC–Co and Cr3C2–NiCr are the most popular materials of choice and contribute to bulk of the utilization by the industry towards wear resistance. Notwithstanding the above materials, alternative materials involving modifications in both hard and binder phases like TiMo (CN)–NiCo, WC-CrC-Ni, WC-Co-Cr, WC-Ni, Cr3C2-Ni, Cr3C2-Inconel, etc. exhibit great promise towards tribological applications under diverse wear modes. This chapter on the tribological characteristics of the detonation sprayed coatings provides a comprehensive overview on the characteristics of various cermet coatings generated at varied process conditions and its influence on the tribological properties under abrasive, sliding, and erosive wear modes.
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Surface modification approach has been attracting a great deal of attention as it presents a cost-effective way to combat degradation resulting from mechanisms such as wear, oxidation, corrosion, or failure under an excessive heat load without sacrificing the bulk properties of the component material. Various surfacing techniques are now available which offer a wide range of quality and cost. Since a vast majority of industrial components deteriorate, and eventually fail, due to one of several wear phenomena that may be experienced during normal operation, considerable attention has been devoted to the development of coating materials and processes specifically to combat the routinely confronted wear modes, viz. erosion, abrasion and sliding. Amongst all the currently available coating processes, the thermal spray technique has gradually emerged as the most useful method of developing a wide variety of coatings to enhance the performance and durability of engineering components exposed to the above forms of wear.
Of all the thermal spray variants, the detonation spray coating (DSC) technology is widely acknowledged to be the most superior by virtue of the very high particle velocities that it imparts, thereby leading to dense and well-bonded coatings which exhibit excellent tribological properties such as high abrasion and erosion resistance. Initially developed specifically for depositing wear-resistant coatings of tungsten carbide, which undergoes substantial decarburization during plasma spraying, the use of the DSC technology currently extends to all industry segments ranging from gas turbines to textile industries and from nuclear energy to data processing. The technique has grown substantially with a range of materials that can be sprayed, which includes metals, metal alloys, ceramics, cermets, composites and combinations of these.
Detonation spray coating (DSC) process is a unique thermal spray variant which relies upon the controlled explosive combustion of a measured mix of oxy-acetylene gases. The powder feedstock of the desired coating material is heated and accelerated by high-pressure, high-temperature gaseous products resulting from the detonation, to impact a substrate at very high velocities to yield a well-adherent layer (Sundararajan et al., 2013). The DSC process is cyclic in nature and operates at a firing frequency ranging between 2 to 10 shots per sec. The interesting aspect of DSC process is the versatility in depositing a wide variety of materials ranging from metals to ceramics, expect for few materials with very high melting points, which makes it worthwhile for many industrial applications. The schematic of the DSC process is shown in Figure 1, which is already described elsewhere in detail (Sundararajan et al., 2013).
Figure 1.
Schematic of detonation spray coating process (Sundararajan et al., 2013)
Like any other thermal spray variant, the velocity and the physical state of the powder particles at the time of impact are the most critical factors that influence the quality of detonation sprayed coatings (Sundararajan et al., 2001; Kharlamov, 1986). These factors are directly governed by the process parameters employed as well as the starting powder characteristics which eventually manipulate the resultant coating properties.