Fabrication of Al-ZrO2-Y2O3 composite coating on SUS 304 stainless steel substrate using mechanical alloying method

Stainless steel is one of the most important materials used in aerospace due to its high strength and favorable corrosion resistance. However, the severe oxidation loss of stainless steel when utilized at the temperature higher than 1000 °C restricts its further applications. Thus research on the fabrication of protective coating on stainless steel is thought of an essential and effective work. In the present work, Al-ZrO₂-Y₂O₃ composite coatings were fabricated on 304 stainless steel substrate to improve its high temperature oxidation resistance. The coatings were prepared by means of mechanical alloying method at different milling durations. Microstructures and chemical compositions of as-synthesized coatings were analyzed by SEM and EDS. Phases of the coatings were identified by XRD. The results indicated that the milling time have an effect on the continuity and homogeneity of the coating. Short milling time resulted in the low density of coating and long milling duration led to the formation of microcracks. A proper extension of milling duration favored the thickening and densification of coating and promoted the interdiffusion between coating and substrate, which enhanced the adhesive behavior of the coating. Microhardness tests were conducted along the profile of the substrate from the coating to the inner substrate. The test results proved the substrate an improvement of the as-prepared coating. High temperature oxidation tests were carried out at 700 °C and 1000 °C, respectively. The test results indicate that the as-fabricated coatings could enhance the high temperature oxidation resistance of 304 stainless steel substrate. Taking into consideration the coating microstructure, microhardness and high temperature oxidation resistance, the optimal treating duration was 8h at the selected other mechanical alloying processing parameters.