Influence of Steel Surface Composition on ZDDP Tribofilm Growth Using Ion Implantation

Mao Ueda,Hugh Spikes,Amir Kadiric

doi:10.1007/s11249-021-01436-8

Abstract

This paper examines the influence of steel surface composition on antiwear tribofilm formation by ion-implanting typical steel alloying elements, Ni, Mo, Cr, V and W, into AISI 52100 bearing steel surfaces. Such implantation changes the chemical composition of the steel surface but has relatively little effect on its mechanical properties or topography. The behaviour of zinc dialkyldithiophosphate (ZDDP) antiwear additive was studied. The study employs a ball on disc tribometer with ability to monitor tribofilm development and a range of analytical tools including STEM-EDX, XPS and FIB-TEM to analyse the formed tribofilms. It was found that Ni implantation promotes ZDDP tribofilm formation while Mo and Cr implantation deters tribofilm growth. V and W implantation do not significantly change tribofilm formation. Results on the influence of ZDDP concentration on tribofilm formation rate with different implanted metals suggest that one important mechanism by which steel composition influences tribofilm formation may be by controlling the extent of ZDDP adsorption. This study shows the importance of steel surface composition on ZDDP response and also demonstrates a powerful way to study and potentially improve the tribological performance of machine components via a combination of lubricant formulation and surface modification.

Highlights

In recent years the role of lubricant antiwear additives, especially zinc dialkyldithiophosphate (ZDDP), has become increasingly important because of the introduction of very low viscosity oils to reduce power losses from hydrodynamic friction, churning and pumping, and increase machine efficiency
V and W implantations did not significantly affect ZDDP tribofilm growth. These results suggest that the chemical composition of steel can have a significant influence on ZDDP tribofilm growth
On Mo- and Cr-implanted steels, tribofilms grew faster and thicker as P concentration increased from 800 to 1600 ppm. These results show that the concentration of ZDDP above which tribofilm formation saturates varies with the presence of different elements in the surface, being no more than 800 ppm P for unimplanted steel, 400 ppm P for Niimplanted steel, and greater than 1600 ppm P with Mo- and Cr-implanted steels

Summary

Introduction

In recent years the role of lubricant antiwear additives, especially ZDDPs, has become increasingly important because of the introduction of very low viscosity oils to reduce power losses from hydrodynamic friction, churning and pumping, and increase machine efficiency. Such low viscosity oils can result in the machine components operating for long periods in thin film, mixed lubrication conditions. Previous investigations have shown that ZDDP tribofilm formation is affected by the solid surface properties, including hardness [1,2,3] and roughness [4,5,6], as well as chemical composition [7, 8]. The least well understood is the influence of chemical composition since it is quite difficult to vary this independently of hardness and roughness

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