Hertzian stress contribution to low friction behavior of thin MoS2 coatings

Abstract
Friction coefficients were measured for bearing materials slid in dry air against sputter‐deposited MoS2‐coated substrates. Ball versus flat tests were performed over a wide range of initial Hertzian pressures (200–1500 MPa) by varying loads (1–50 N), elastic moduli (70–615 GPa), and ball diameters (1.6–12.7 mm). The friction coefficient μ decreased as load L increased according to μ∝ L(−0.32), in agreement with the Hertzian contact model. Regression analysis of over 600 data points for friction coefficient versus Hertzian pressure (PH), fitted to μ=(S0/PH)+α, gave mean values of the shear strength S0=24.8 MPa±0.5 and α= 0.001±0.001, with S0 in good agreement with values in the literature.

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