Comparing friction behavior and mechanism of three generation bearing steel (GCr15, M50, CSS-42L) paired silicon nitride under ester oil lubrication from room temperature to 350 °C

The different generations of bearing steel are designed to withstand high temperatures, quick speeds, and heavy loads and meet the requirements of aviation, aerospace, and advanced equipment production. In this study, three generation bearing systems (Si3N4/GCr15, Si3N4/M50, and Si3N4/CSS-42L) with pentaerythritol ester lubricants were selected to investigate their friction behavior and evolutionary mechanisms from room temperature to 350 °C. The results indicate that the coefficient of friction (COF) values for all three systems initially decreased and then increased as the temperature increased. The COF of Si3N4/GCr15 was not more than 0.170 when the temperature did not exceed 150 °C. Furthermore, the wear rate of Si3N4/M50 and Si3N4/CSS-42L are 2.67 × 10−4 mm3·N−1·m−1 and 2.04 × 10−4 mm3·N−1·m−1 at 260 °C, which are only 15.4% and 11.8% of Si3N4/GCr15. This discrepancy can be attributed to the formation of metal oxides on the worn surface of Si3N4/M50 and Si3N4/CSS-42L, and was easier to form on the worn surface of CSS-42L. Therefore, the applicable temperature range for GCr15 usually below 150 °C and for Si3N4/M50 and Si3N4/CSS-42L, it was from 150 to 260 °C. These results disclose the friction behavior and mechanism of these three generation bearing steel are different, and can be a guideline to choose proper bearing steel in future situation.