Physical Analysis of Worn Surfaces Formed Under Extreme Pressure Lubrication Conditions

Abstract

A considerable amount of work, over the last 20 years, has elucidated some of the reactions that take place on the surfaces of steel worn against steel under extreme pressure lubrication conditions. However, in most studies of the worn surfaces only one or two physical analytical techniques have been used. In this study a comprehensive examination of the surfaces has been attempted using a wide selection of physical techniques. The surface topography of worn specimens has been examined using both optical and scanning electron microscopy. The distribution of the elements in the wear scars in conjunction with the surface topography has been observed with an electron probe microanalyser. The chemical environment of these elements in the wear scars has been studied with an electron spectrometer for chemical analysis and the crystalline structures formed using glancing angle X-ray diffraction. Metallographic techniques havebeen used on taper sections (micro-indentation hardness tests and etching)to observe the structures formed below the wear scars in the base metal. These techniques have been applied to specimens worn under varying loads with two groups of additives (three disulphides and two zine dithiophosphates) and two base oils. The role of these additives has been studied under antiwear and extreme pressure conditions using the above techniques of physical analysis and the mechanisms of their action have been explained on the basis of the results obtained in this research.