Development of a modified CVD coating process for the enhancement of the high temperature oxidation resistance of Cr2O3 and Al2O3 forming alloys

In this work, a new deposition method for coating Cr2O3 and Al2O3 forming alloys has been set up. This is a modified CVD deposition method based on the pyrolisis of an aerosol produced by an ultrasonic wave focussed on the surface of a solution containing a reactive element soluble salt that will later transform to an oxide. The deposition takes place in a reaction chamber maintained at 473 K. To test the efficiency of the deposition method, commercial AISI-304 stainless steel samples were coated directly on the mill finish surface and on a pre-formed oxide layer with lanthanum nitrate. Specimens were then oxidised at 1173 K in synthetic air atmosphere during 25 h in a thermobalance. Oxidation kinetics of coated samples was compared with that of untreated ones. The results show that coated samples improve their high temperature oxidation resistance by decreasing their parabolic rate constant by one order of magnitude. The deposition method developed proves to be an easy, cheap and efficient way of increasing the service temperature of conventional stainless steel.