Improvement of the tribological and high-temperature oxidation behavior of mild steel by alumina coating

In this study, the surface characteristics of mild steel are modified using aluminum oxide (alumina) coating using the microwave-assisted solution combustion synthesis (mSCS) and physical vapor deposition (PVD) technique. The deposited coatings are subjected to microstructural, X-ray diffraction (XRD), micro-hardness, surface roughness, high-temperature oxidation, and wear tests. The XRD results confirmed the formation of alpha-alumina coating on the mild steel surface. An average thickness of coatings is approximately 125 +/- 5 mu m in mSCS and around 1 +/- .3 mu m in PVD. The coating demonstrated good adherence and significantly improved surface hardness, wear resistance, and high-temperature oxidation resistance. The surface hardness of coatings increased to 12.2 and 9.4 GPa from mSCS and PVD, respectively, while it is 1.57 GPa for the uncoated mild steel. The PVD-coated alumina surface exhibited a smooth surface (Ra = .076 mu m) compared to the mSCS coating (Ra = .344 mu m). The specific wear rate of the alumina-coated sample decreased to 2.5 times, and the high-temperature oxidation rate decreased about 1.7 times at 500 degrees C.