http://orcid.org/0000-0003-1801-7815
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Abstract
Fine particle peening (FPP) is a peening process using fine shots with an average diameter of less than 200 µm. Pairs of twin-disc specimens made of carburized and quenched 18CrNiMo7-6 gear steel were subjected to two different FPP processes and conventional shot peening (CSP) using big shots with an average diameter of 600 µm. Rolling–sliding tribology tests were carried out under oil lubrication, and comparisons of the friction coefficient were made between untreated, FPP-treated, and CSP-treated twin-disc specimens. To characterize the relationship between surface topography and friction coefficient, 3D surface parameters, including root mean square roughness (Sq), skewness (Ssk), kurtosis (Sku), core roughness depth (Sk), reduced peak height (Spk), and reduced valley depth (Svk) were measured before and after tribology tests. A linear regression method was applied to analyze the correlations between the surface parameters and the friction coefficient. It was found that FPP is effective in decreasing the friction coefficient during the lubricated rolling–sliding contact compared to untreated specimens. The friction coefficient has a higher correlation with Ssk and the ratio RSvk, which is defined as the ratio of Svk to the sum of Sk, Spk, and Svk. A lower friction coefficient was obtained when the topography had a more negative Ssk and a higher RSvk in the rolling–sliding condition. However, there was a weak linear correlation between the friction coefficient and surface parameters Sq, Sku, Sk, Spk, and Svk, and the relationship between the trend of friction coefficient and those surface parameters is not obvious.