Dry sliding friction and wear behavior of HVOF sprayed FeCrMnCoNi high entropy coatings (HECs) at room and elevated temperatures

Abstract

Despite their extensive use in the aerospace industry Ni-, Ti- and Co-based alloys have shown some limitations when used in tribological interfaces under extreme environments, particularly in next-generation aero-engines where high temperatures are prevalent. To address these challenges, there is a growing demand for the development of wear-resistant coatings capable of operating efficiently under such harsh environments. High entropy alloys (HEAs) have emerged as potential candidates for high temperature tribological applications due to their superior combination of mechanical and thermal properties. However, their wear behavior over a wide range of temperatures has not been extensively studied. In this study, FeCrMnCoNi high entropy coatings (HECs) were developed using the high-velocity oxygen fuel (HVOF) process under three different spraying conditions: oxygen-rich (OR), fuel-rich (FR), and fuel-rich with high feed rate (H-FR). The tribological behavior of these HECs was evaluated under dry sliding conditions at room temperature (100 m sliding) and 350 °C (12 m and 100 m sliding) against alumina counterballs. The OR coatings demonstrated significantly improved wear performance at both temperatures compared to FR and H-FR coatings. A detailed characterization of the wear tracks using high-resolution electron microscopy and surface profilometry revealed that the enhanced wear performance of OR coatings at elevated temperatures could be attributed to their relative higher hardness, the formation of a smooth and compact tribofilm in the contact region, and subsurface strengthening through grain refinement. This research provides valuable insights into the wear mechanisms of HEA-based coatings, offering a pathway to develop more effective high-temperature tribological solutions for aerospace and other industrial applications.