In Situ Temperature Measurements of Sliding Surface by Raman Spectroscopy

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ORIGINAL PAPER

In Situ Temperature Measurements of Sliding Surface by Raman Spectroscopy Makoto Miyajima1,2   · Kazuyuki Kitamura1 · Keishi Matsumoto3 · Kazuyuki Yagi4,5 Received: 24 December 2019 / Accepted: 14 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract In the current study, surface temperature in sliding contacts was in situ measured by Raman spectroscopy. The contact area comprised a stationary sapphire hemisphere and a rotating carbon steel disk. The surface temperature was estimated from the Raman spectrum of sapphire. Three estimation methods of temperature were compared, which were obtained from the peak shift, full width at half maximum (FWHM), and intensity ratio of Stokes/anti-Stokes scattering. The estimated temperature from the peak shift exhibited the least fluctuations among the three methods. However, the peak shift varied with stress and temperature. The estimated temperature from the FWHM was highly accurate, although the fluctuation was greater than that from the peak shift. The estimated temperature from the intensity ratio of Stokes/anti-Stokes scattering was unaffected by pressure and crystallinity, although this estimated temperature exhibited a significant fluctuation because the signal-to-noise ratio of the anti-Stokes scattering was small. This in situ measurement technique using Raman spectroscopy can simultaneously acquire the temperature and chemical state of the sliding surface. Namely, the temperature of a tribofilm and the temperature during scuffing can be measured directly and the mechanism can be analyzed effectively. Graphical Abstract

Keywords  Surface temperature · Raman spectroscopy · In situ · Steel * Makoto Miyajima [email protected] Extended author information available on the last page of the article

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1 Introduction Temperature increase in sliding contacts is an important factor related to the formation of tribofilms and the scuffing phenomenon. Two aspects are involved in the friction surface temperature: the mean temperature and flash temperature [1–4]. The mean temperature is the average temperature increase over a contact area with low time resolution, while the flash temperature is an instantaneous and local temperature increase occurring on a surface. The target tribological phenomenon determines which temperature is important. The surface temperature is crucial in phenomena where the contact area in a wide range of lubrication conditions. In hydrodynamic lubrication, the surface temperature significantly affects the flow of viscous films, thereby reducing the film thickness [5, 6]. In boundary lubrication, the structures of tribofilms derived from additives [7, 8] are well known to change with temperature. When tribofilms break and cause the appearance of nascent surfaces, a macro plastic flow of the steel surface results in a high temperature increase, which causes a transformation from martensite to austenite [9–12]. The rapid temperature increase an