Wear study of metallic interfaces for air-conditioning compressors under submerged lubrication in the presence of carbon dioxide

The implementation of carbon dioxide (CO2) as an alternative refrigerant for air-conditioning compressors has gained significant attention recently. The main interest in CO2 is related to its zero ozone depletion potential (ODP) and low global warming potential (GWP) compared to commonly used hydroflurocarbon (HFCs) refrigerants such as R-134a. Friction and wear studies on tribological contacts commonly used in air-conditioning compressors under the presence of CO2 are scarce in the literature. The present study focuses on the tribological behavior of Al390-T6, gray cast iron, and Mn-Si-brass (UNS C67300). These materials were tested against 52100 steel shoes using a pin-on-disk configuration. The tests were performed under submerged lubrication conditions using polyalkylene glycol (PAG) lubricant in the presence of CO2. Results showed that the wear resistance of gray cast iron and Mn-Si-brass was higher compared to Al390-T6. In spite of the fact that Al390-T6 and Mn-Si-brass had similar hardness, Al390-T6 showed higher wear after testing. X-Ray Fluorescence (XRF) analysis of the lubricant after testing of Al390-T6 showed the presence of eutectic silicon particles. Also, Auger Electron Spectroscopy (AES) of Al390-T6 showed an atomic concentration decreased in silicon content after testing. Decreased in silicon content was attributed to the depletion of eutectic silicon particles, leading to a decrease in hardness and a subsequent increase in wear during the test.