Improved tribology performances of copper graphite (Cu/C) using a phosphorized oxidization surface obtained with tricresyl phosphate (TCP)

Abstract

Purpose

Copper-graphite (Cu/C) is a type of seal material that has been widely used in liquid rocket engines and with normal metal pairs, has a high wear rate under liquid oxygen lubrication. In this study, bearing steel disks were subjected to a high-temperature oxidization and phosphating progress to create an oxidized tricresyl phosphating film (OTCP) film, using tricresyl phosphate (TCP) as the phosphating solvent. It is hoped that the surface wear rate and friction coefficient can be reduced by this method.

Design/methodology/approach

This study aim to form an anti-wear film on the surface of bearing steel, which can significantly improve the lubrication performance of Cu/C and bearing steel. The surfaces of bearing steel disks were dried to remove surface water and then put on a heating plate with a magnetic stirrer and a blue glazed oxide film obtained by heating the disks in the air at 200°C for 1 h. To create the OTCP film, bearing steel disks with a blue glazed oxide film were cleaned ultrasonically three times in ethanol and then placed in baths of TCP. After heating for 2 h at 120°C, excess TCP liquid was removed from the disks using ethanol, leaving an OTCP film on the disk surface.

Findings

It was found that steel coated with an OTCP film demonstrated better tribological performance (lower coefficient of fiction and wear rate) when pairing with Cu/C than either oxidized or untreated bearing steel. Additional chemical reactions occur when the oxide disk is immersed in TCP and the FePO₄ film is formed after heating. Additionally, the OTCP film coated steel displayed good corrosion resistance, as confirmed by electrochemical corrosion tests. This finding demonstrates the potential for this process in the aerospace industry.

Originality/value

The preparation of OTCP films via high-temperature oxidization and phosphating of bearing steel was demonstrated, with the tribological properties of the OTCP film being investigated alongside those of the original surface and an oxidized film surface. The fabrication of OTCP films is easily scaled up and exhibits significant advantages as a new technology for applications in mechanical contact seal lubrication.

Citation

Lu, H., Hu, F., Liu, Q. and Li, Y. (2021), "Improved tribology performances of copper graphite (Cu/C) using a phosphorized oxidization surface obtained with tricresyl phosphate (TCP)", Industrial Lubrication and Tribology, Vol. 73 No. 7, pp. 1028-1036. https://doi.org/10.1108/ILT-05-2021-0181