Influence of growth defects on the running-in behavior of an a-C:H:W coating under pure sliding contact conditions

Abstract

The mechanical and tribological behaviors of coated surfaces are affected by the presence of local variations on coating composition, morphology and microstructure. During the deposition process, irregular surface topography and/or process instabilities can produce regions with macroscale defects, including voids and macroparticles. The interface between those regions and other portions of the coating presents an irregular columnar structure, identified by discrepancies between two consecutive columns, which may lead to local lower mechanical properties. In this work, numerical and experimental analyses were conducted to explore the effect of growth defects with irregular columnar boundaries (GDICB) on the mechanical and tribological behavior of a Tungsten Carbide/Carbon (a-C:H:W) multilayer coating subjected to multiscale tribological tests, including macroscale reciprocating tests and microscale scratch tests. Samples consisted of a commercial a-C:H:W coating deposited onto polished AISI H13 discs and AISI 52100 steel balls. Mechanical properties and microscale surface topography were evaluated using a triboindenter capable of carring out instrumented indentation tests and scanning probe microscopy techniques, while the microstructure was observed by scanning electron microscopy analyses. Macroscale reciprocating tests revealed a variable GDICB mechanical behavior, including deformation and detachment of those regions inside the wear track in the beginning of the test. Microscale scratch test results indicated a load-dependent mechanical behavior of the GDICB, showing a transition from deformation to detachment mechanism with the increase in the normal load. The digital tribology package TriboCODE was applied to model a realistic representation of the microscale scratch test, allowing the identification of individual GDICB behavior dependence on the applied normal load and the local mechanical properties.