Investigation of the Wear Corrosion and Hot Corrosion Properties of Alumina Coating Applied on Steel Substrate via High Velocity Oxy-Fuel Method

In the present work, Alumina coating with an approximate thickness of 240 µm was applied via high velocity oxy-fuel (HVOF) method on a 4340 hot-work tool steel substrate. The morphology of the coating and the influences of the corrosive medium which contained hydro-chloric acid (5-15 vol.%) were studied using scanning electron microscope (SEM). Afterwards, the wear behavior of the coatings in dry and acidic wet environments were studied using a pin-on-disk wear apparatus and the wear mechanism was analyzed through SEM studies. The results of the wear tests showed that the wear rate in the 5% acidic medium was approximately the same as that of the dry test. Furthermore, the results showed that increasing the concentration of acid in the wear medium (up to 15%), leads to a continuous increase of the wear rate which was ascribed to increased corrosion rate. The dominant wear mechanism in all the tested situations was determined as sticking wear. As the wear rate increased, the wear surfaces showed increased roughness. Finally, hot corrosion experiments were carried on the coated specimens at the temperature of 880 ˚C. At this condition, the coating lasted for about 460 hours.