Mechanical behaviour and constitutive models of ZDDP tribofilms on DLC coatings using nano-indentation data and finite element modelling

Abstract

The mechanical behaviour of zinc dialkyldithiophosphate (ZDDP) tribofilms on diamond-like carbon (DLC) coatings has been studied by combining the nano-indentation experimental data and finite-element modelling. Different constitutive models, whose analysis was performed using a global algorithm that consists of forward and inverse algorithms, were chosen to establish which of them more accurately predicts the actual mechanical behaviour of the ZDDP tribofilms. A non-homogeneous, dual structure, which was also verified by the local stiffness using the AFM force-modulation mode, was found. Based on the proposed algorithm, the mechanical properties of the ZDDP tribofilms were found, e.g. the elastic modulus E=26 GPa and the yield stress Y=1.55 GPa for the harder component and approximately E=1.65 GPa and Y=0.144 GPa for the softer component.

Sliding Evolution of the Mechanical Behaviour of Zinc Dialkyldithiophosphate Tribofilms on Diamond-Like Carbon Coatings

“…This complexity in structure has also been observed in molecular dynamics simulations of ZDDP tribofilms [9]. In our earlier work, we studied the behaviour for a specific testing time [10]. However, how the structure of ZDDP tribofilms and the mechanical behaviour of their components evolve during the sliding time has not been studied in depth.…”

“…The values of the independent variables that show the best correlation with the experimental data are chosen as a solution because the solution of the nano-indentation at moderate depths is unique according to Chen et al [20]. This algorithm is explained in more detail elsewhere [10].…”

“…Using this algorithm, the constitutive model that best fits the mechanical behaviour of the ZDDP tribofilms is obtained, as well as the mechanical properties of the ZDDP tribofilms. It is interesting that two different components are found for ZDDP tribofilms obtained after a short time [10], while long term results show up to three components.…”

A Study on the Tribofilm Growth and Tribological Properties of Tribofilms Formed from Zinc Dialkyl Dithiophosphate (ZDDP) and Molybdenum Dialkyl Dithiocarbamate (MoDTC)

“…Various techniques have been applied to study the tribofilms. Nanoindentation, nanoscratch and atomic force microscopic (AFM) phase-image measurements have been used to study the nanometer-scale mechanical/structural properties of the tribofilms [10][11][12]. X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption spectroscopy (XANES), Auger electron spectroscopy, and time-of-flight secondary ion mass spectrometer (TOF-SIMS) have been used to determine the chemical structure of the tribofilm layer [13][14][15][16][17].…”

Tribological performance of DLC/DLC and steel/DLC contacts in the presence of additivated oil

“…This study mainly focused the wear behaviour of DLC coating and therefore, the BO was additivated with an anti-wear additive. Zinc dialkyldithiophosphates (ZDDP) was used as the anti-wear additives which are well known for the reduction of wear of steel surfaces where they form a pad-like zinc phosphate tribolayer (Bartolomé et al, 2016). In this study, the ZDDP was chosen for the 'non-reactive' DLC surface.…”