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Thermal spray coatings are used to improve the erosion resistance of boilers and turbine components for power plants and other industries. In this work, detonation gun spraying method is used to deposit WC-12Co, Stellite 6 and Stellite 21 coatings on SAE213-T12 boiler steel. The coatings were characterized using microhardness tester, scanning electron microscope (SEM), optical microscope and X-ray diffractometer (XRD). The solid particle erosion behaviours of the coatings were evaluated at 30°and 90°impact angles using an air jet erosion test rig. The erosion rates of Stellite 6 and Stellite 21 coatings are found approximately 60% and 50% respectively higher than WC-Co coating, which might be attributed to the respective hardness of the coatings. Cobalt content in the coatings played an important role on the erosion behaviour of the coatings. The erosion mechanisms of the coatings involved micro-ploughing, micro-cutting along with some micro-cracking and hard phase pull-outs.

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Pipeline materials used for the transportation of bottom ash slurry generally suffer from intense wear due to slurry erosion. In this work, High-Velocity Oxy-Fuel (HVOF) spray process was used for the deposition of WC-12Co coating on the Mild steel, SS 304 and SS 202. Slurry erosion pot tester was used for erosion tests of uncoated and coated materials. Effects of three factors namely slurry concentration, the speed of impacting particles and erosion test duration on erosion rate were investigated using the Taguchi approach. Influence of speed of impacting particles on the erosion rate of uncoated and all the coated materials was found to be maximum, which was followed by erosion test duration and then slurry concentration. WC-12Co coating showed significant improvement in erosion wear resistance of three substrate materials namely mild steel, SS 304 and SS 202. WC-12Co coating showed the brittle mechanism of erosion wear. After the Taguchi analysis slurry erosion results were further validated with analysis of variance (ANOVA). From both ANOVA and Taguchi analysis, it was observed that the influence of speed is maximum on the erosion wear of all the uncoated as well as WC-12Co coated specimens, followed by time and slurry concentration. K e y w o r d s : bottom ash, slurry erosion, pipeline steel, HVOF spray