Abstract
In this experimental study, chromium oxide powder was sprayed on a low-carbon steel substrate using the atmospheric plasma spray process. The current and standoff distances (SODs) were varied to study their effect on the fracture toughness of the coatings. Theoretically, as the arc current increases, the melting of the ceramic oxide should increase and this in turn should lead to the formation of a dense coating. However, it was observed that if the arc power is too high and because the particle size of the powder is small (approximately 30 μm), the particles tend to fly away from the plasma core. Similarly, an appropriate SOD should provide the particles with more melting time, thus resulting in a dense coating. On the other hand, a larger SOD leads to the solidification of the molten particles before the droplets can reach the substrate. All these effects may lead to substantial variation in the fracture toughness of the coating. The present paper attempts to correlate the plasma spraying parameters and microstructure of the coating with the fracture toughness and other primary coating properties.
Highlights
Surface engineering includes the study of wear, erosion, corrosion processes on the component surface, and the various methodologies to prevent them
It reveals that for a low critical plasma spray parameter (CPSP), the porosity is high and the partially melted region (PMR) is small; at a recommended value of the CPSP, these defects are diminished; and at higher values of the CPSP, the PMR grows while the porosity decreases
On increasing the arc current, higher values of the CPSP lead to an increase in the partially melted regions while low values of the CPSP lead to high porosity
Summary
Surface engineering includes the study of wear, erosion, corrosion processes on the component surface, and the various methodologies to prevent them. With the help of thermal and thermo-chemical processes, surfaces can be modified to become wear and corrosion resistant while retaining the toughness and ductility of the bulk component [1]. One such example of surface engineering is a plasma sprayed chromia coating. It is extensively used as a corrosion and wear resistance coating [2, 3]. The fracture toughness (KIC), is a measure of a material’s resistance to brittle fracture when a crack is present [7, 8]. Evan and Charles (1976) have formulated a mathematical expression to evaluate the fracture toughness using the fracture length and Vickers indentation diagonal length as shown [9]: KIC c a
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