Morphology and Nanomechanical Properties of ZDDP Antiwear Films as a Function of Tribological Contact Time

We have employed scanning force microscopy (SFM) and nanoindentation analysis to track the evolution of tribologically generated antiwear films derived from zinc dialkyldithiophosphate (ZDDP) as a function of rubbing time. The SFM images reveal that film morphology evolves with time through a growth mechanism consisting of three stages. In the first stage nucleation on active sites at the steel surface leads to the growth of distinct segregated islands. In the second stage the islands coalesce causing the film to spread over a larger fraction of the surface. In the final stage continuous rubbing induces the large islands to divide into smaller, densely packed structures. In contrast to the observed morphological changes, rubbing time does not strongly influence the nanomechanical properties of the films. This highlights the importance of film morphology in determining the effectiveness of ZDDP antiwear films. We also observe large variation in both the morphology and nanomechanical properties that are likely due to the heterogeneity in contact pressure at the pin-sample interface of the wear rig.

[1]  An examination of the reactivity of zinc di-alkyl-di-thiophosphate in relation to its use as an anti-wear and anti-corrosion additive in lubricating oils , 1998 .

[2]  P. A. Willermet,et al.  The Composition of Surface Layers Formed in a Lubricated Cam/Tappet Contact , 1991 .

[3]  P. Harrison,et al.  External reflection FTIR, 31P MAS NMR and SEM study of the thermal decomposition of zinc(II) bis(O,O'-dialkyldithiophosphates) on 316 stainless steel , 1991 .

[4]  M. McDermott,et al.  Morphological evolution of films formed from thermooxidative decomposition of ZDDP , 2001 .

[5]  G. Bancroft,et al.  The chemistry of antiwear films generated by the combination of ZDDP and MoDTC examined by X-ray absorption spectroscopy , 1998 .

[6]  Graham C. Smith,et al.  Scanning probe microscopy of automotive anti-wear films , 1997 .

[7]  S. Jahanmir.  Wear Reduction and Surface Layer Formation by a ZDDP Additive , 1987 .

[8]  R. J. Bird,et al.  The application of photoelectron spectroscopy to the study of e. p. films on lubricated surfaces , 1976 .

[9]  M. S. Fuller,et al.  Mechanisms of tribochemical film formation: stabilityof tribo- and thermally-generated ZDDP films , 1997 .

[10]  John E. Hillier,et al.  Automotive Lubricants Reference Book , 1996 .

[11]  K. Ludema,et al.  Dynamics of dual film formation in boundary lubrication of steels part I. Functional nature and mechanical properties , 1991 .

[12]  P. A. Willermet,et al.  Lubricant-derived tribochemical films: an infra-red spectroscopic study , 1992 .

[13]  T. Michalske,et al.  Nanomechanical properties of films derived from zinc dialkyldithiophosphate , 1998 .

[14]  E. Ferrari,et al.  A multi-edge X-ray absorption spectroscopy study of the reactivity of zinc di-alkyl-di-thiophosphates anti-wear additives: 2. In situ studies of steel/oil interfaces , 1999 .

[15]  Kishore K. Kar,et al.  A model of the dynamics of boundary film formation , 1994 .

[16]  P. A. Willermet,et al.  The composition of lubricant-derived surface layers formed in a lubricated cam/tappet contact II. Effects of adding overbased detergent and dispersant to a simple ZDTP solution , 1995 .

[17]  M. S. Fuller,et al.  Application of soft X-ray absorption spectroscopy in chemical characterization of antiwear films generated by ZDDP Part I: the effects of physical parameters , 1997 .

[18]  Masoud Kasrai,et al.  Chemical characterization of antiwear films generated on steel by zinc dialkyl dithiophosphate using X-ray absorption spectroscopy , 1993 .

[19]  William D. Callister,et al.  Materials Science and Engineering: An Introduction , 1985 .

[20]  M. S. Fuller,et al.  Solution decomposition of zinc dialkyl dithiophosphate and its effect on antiwear and thermal film formation studied by X-ray absorption spectroscopy , 1998 .

[21]  W. Glaeser.  Materials for Tribology , 1992 .