Electrical Insulation Properties of Alumina Coatings on SAE 52100 Bearing Steel 2022-01-0726

In recent years, bearing electrical failures have been a significant concern in electric cars, restricting electric engine life. This work aims to introduce a coating approach for preventing electrical erosion on 52100 alloy steel samples, the most common material used on manufacturing bearings. This paper discusses the causes of shaft voltage and bearing currents, and summarizes standard electrical bearing failure mechanisms, such as morphological damages and lubrication failures. Alumina coatings are suitable for insulating the 52100 alloy steel samples because alumina coatings provide excellent insulation, hardness, and corrosion resistance, among other characteristics. The common method to coat an insulated alumina coating on the bearing is thermal spraying, but overspray can cause environmental issues, and the coating procedures are costly and time-consuming. Based on the research, this article briefly discusses employing plasma electrolytic aluminating to coat 52100 alloy steel samples, an eco-friendly and high-efficiency coating process. Coating experiments were conducted over different coating periods to determine the most appropriate thin film for 52100 alloy steel samples. Scanning electronic microscopy observations indicated that pores reduced as their size and porosity rose with the increased treatment time. Longer treatment period resulted in thicker coating layers, but a rougher surface. The results indicated that extending the coating period increased the insulating characteristics of the ceramic coating on 52100 alloy steel samples. The single piece of 20-minute coated sample had the best insulation property, compared with other single pieces. Two 20-min coatings sample combinations provided the best resistance (121-143 MΩ) and the highest breaking voltage (914-935 V). Coatings remained in good condition after thermal shock tests.