Investigation of calcium phosphate (CaP) tribofilms from commercial automatic transmission fluids (ATFs) and their correlation with antishudder performance

Abstract

The friction properties of wet clutches are highly dependent on the surface tribofilms formed by automatic transmission fluids (ATFs). Here, four commercial ATFs were evaluated with a disc-on-disc tribometer to study tribofilm formation on steel surfaces and the effects of tribofilms on the friction properties. The chemical composition, stoichiometry, structure, and thickness of the tribofilms were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS). Calcium phosphate (CaP) tribofilms form on the friction surface with all ATFs, which contributes to their antishudder characteristics. The thickness and surface coverage of CaP tribofilms are positively correlated with their antishudder properties.

Non-destructive depth analysis of acidic phosphate ester boundary layers by hard X-ray photoelectron spectroscopy

“…Conventional methods for analyzing the vertical structure and thickness of boundary layers include ion sputtering (Briggs and Seah, 1990;Watts and Wolstenholme, 2003) with X-ray photoelectron spectroscopy (XPS) (Momose et al, 2018;Ohmiya et al, 2021;Di et al, 2020) and Auger electron spectroscopy (AES) (Hofmanna et al, 2019;Yan et al, 2017). However, these methods have the potential to alter the elemental composition and chemical state of the material due to selective sputtering, in which light elements constituting organic materials are selectively sputtered, and atomic mixing, in which irradiated ions agitate atoms in the sample (Malherbe et al, 1986;Hashimoto et al, 1991;Suzuki and Takimoto, 1995).…”