The Wear of Steel Non Steel Systems in the Presence of Aviation Kerosene

Abstract

The introduction of new refining techniques designed to improve thermal stability of modern jet aircraft fuel has resulted in the removal of heterocyclic compounds and other polar impurities. This leads to a reduction in the fuel's lubricating ability and hence premature failure can result in aircraft fuel systems. Failures may be alleviated by the use of corrosion inhibitors which also act as boundary lubricating additives. In this investigation, a Denton pin-on-disc machine was used to measure friction and wear for aluminium-bronze sliding against steel in the presence of fuel alone and with the addition of one of the new generation of additives. The experiments were conducted in the load range from 24N to 200N inclusive at sliding speeds of 0.6, 2 and 4 ms-1 respectively and wear rates of between 10-15 and 10-13 m3 m-1 were found. Compared with experiments conducted when using fuel alone as a lubricant, the presence of the additive produced an increase in wear rates under mild boundary conditions. As the condition became more severe, however, the wear rates were lower than with fuel alone and the system showed a reduced tendency to seize. Metallographic techniques of taper sectioning and etching were employed to give a better understanding of the structural changes involved at the sub-surface layer of the worn pins. The results obtained showed that at least five different structures of aluminium-bronze have been used by various investigators. On the sub-surface layer of worn pins, aluminium-bronze was found to undergo superplastic deformation, with the formation of cavities, and this was related to the enhanced strain-rate sensitivity of the material at elevated temperatures. The super plasticity of aluminium-bronze material has an effect of reducing wear. Based on the results of analyses using Auger Electron Spectroscopy (AES), Electron Probe Microanalysis (EPMA), Scanning Electron Microscopy (SEM) and X-ray Powder Diffraction, possible wear mechanisms are suggested to explain the wear of this material combination in the presence of fuel alone and of fuel with additive. Finally, a new theory of oxidational wear under boundary lubricated condition has been proposed to predict wear rates.