Topography and nanomechanical properties of tribochemical films derived from zinc dialkyl and diaryl dithiophosphates

In this paper we present recent results from an on-going effort to characte rize the nanomechanical properties of a variety of tribochemical, antiwear films through the use of modern scanning probe techniques. The two types of antiwear wear films studied, derived from zinc dialkyl dithiophosphate (al kyl ZDDP) and zinc diaryl dithiophosphate (aryl ZDDP), were chosen because they possess significantly different wear characteristics. High resolution AFM topographic images showed significant differences between the two types of films. More interestingly, high resolution imaging and quantitative mec hanical properties testing using the interfacial force microscope (IFM), re vealed different elastic and plastic properties between the two types of fi lms; in addition each type of film possessed several distinct regions with respect to mechanical properties. The maximum values for elastic modulus an d hardness were located on the highly loaded regions of the alkyl ZDDP film s which exhibited the best tribological performance. In contrast, the aryl ZDDP films, which exhibited poorer antiwear behaviour, were devoid of such resilient regions. Our results correlate the macroscopic wear behavior of t he tribochemical films to differences in the mechanical properties on a nan ometer scale.