High temperature erosion of T22 steel coated by Cr–Ni electroplating, HVOF sprayed stellite–6 and WC–12Co

In present study, erosion behavior of ASTM–A213–T22 steel (T22 steel) coated by different coating processes was evaluated at high temperature. Cr–Ni electroplating and high–velocity oxy–fuel (HVOF) spraying using Stellite–6 and WC–12Co powders were chose as coating processes. Average coating thicknesses of the Cr–Ni electroplated coating and the HVOF sprayed Stellite–6 and WC–12Co coatings were 40 µm, 226 µm and 200 µm respectively. Oxide scale formation on an uncoated T22 steel specimen and coated specimens was done by covered the specimens with a synthetic coal ash and then annealed under a synthetic flue gas at temperatures of 700 °C with annealing times of 24 h 72 h and 123 h. After oxide scale formation process, the specimens were eroded in erosion tester at temperature of 700 °C using SiC erodent particle with average particle size of 60 µm at impingement velocity of 40 m s−1 and impingement angles of 30° and 90°. The experimental results showed that erosion rate of the specimens dramatically increased with increasing of exposure time at 700 °C. Erodent impingement angle was unaffected to erosion rate of the uncoated T22 steel, the Cr–Ni electroplated and the HVOF sprayed Stellite–6 and WC–12Co coatings. Microcracks, debonding of coating as well as deep cavities were observed on eroded surface of the uncoated T22 steel, the Cr–Ni electroplated and the HVOF sprayed Stellite–6 and WC–12Co coatings. Erosion resistance of the HVOF sprayed Stellite–6 coating was highest compared with that of the Cr–Ni electroplated and the HVOF sprayed WC–12Co coating. The superior erosion resistance of the HVOF sprayed Stellite–6 coating was due to high hardness, more thickness and low porosity of the deposited coating.