Initial surface topography is an important variable affecting frictional contact states and material removal behavior. However, in water-lubricated WC–Ni/siliconized graphite contacts, the influence of initial surface morphology and its associated contact mechanisms on tribological behavior have not been fully clarified. In this study, siliconized graphite surfaces with five distinct surface morphologies were prepared by mechanical grinding. The two-dimensional surface roughness parameters increased from \(R_a\) = 0.02267 μm to 4.953 μm, while the composite three-dimensional roughness parameter \(S_{dq}\) increased from 0.0261 to 0.43928. A water-lubricated sliding friction test was conducted under boundary lubrication conditions. The results show that the effective friction–velocity parameter \((PV)_{eff}\), the central average separation distance, the liquid-film normal load ratio, and the liquid-film shear mechanical work ratio exhibit different evolutionary trends depending on the initial surface topography. The minimum friction coefficient values of the five surfaces were within the narrow range of 0.00714–0.00986, while the corresponding \((PV)_{eff}\) values decreased from 44.885 to 10.696 MPa·m/s. The friction transition window shifted significantly with changes in initial surface morphology and contact geometry evolution. The cumulative friction mechanical work of the complete test ranged from 20.220 to 27.613 kJ, with a maximum difference of only 1.366 times, whereas the macroscopic wear volume varied from 0.00688 mm³ to 0.29861 mm³, showing a difference of 43.40 times. This indicates a significant nonlinear relationship between macroscopic friction energy input and material removal.

By introducing a composite surface gradient model to quantify the influence of contact severity on frictional energy input, a positive correlation was established between severe-contact mechanical work and wear volume, following \(V_f = 1.933 \times 10^{-4} W_{sev}^{1.156}\) (\(R^2 = 0.9958\)). The sensitivity of material removal to localized micro-contact geometry was confirmed. Based on the worn surface morphology, the central average separation distance after wear was found to range from 0.187 to 2.190 μm under the minimum friction state, while the corresponding liquid-film load ratio was only 0.267%–3.312%. The proportions of liquid-film normal load-bearing work and cumulative liquid-film shear mechanical work throughout the entire process were 0.251%–2.466% and 0.382%–1.721%, respectively, and were higher on surfaces with larger roughness gradients than on smoother surfaces.

These results demonstrate that a larger central average separation distance does not necessarily correspond to stronger fluid dynamic load support. The occurrence of similar low-friction states does not imply identical material removal mechanisms. The findings provide theoretical guidance for controlling contact evolution in water-lubricated sliding contacts by considering surface morphology as a design variable, and highlight the importance of controlling local contact severity and coordinating the distribution of solid–liquid mechanical work during material removal.