Influence of data processing decisions on ISO 25178 areal surface roughness parameters and their relevance to micro-Vickers hardness measurements

This study investigates how data-processing decisions influence ISO 25178 areal surface roughness parameters and examines which of those parameters most reliably characterise surfaces used in micro-Vickers hardness testing. Six processing variants — two form-removal polynomial degrees, two resampling densities, and two L-filter cut-off wavelengths — were applied independently to measurements of stainless steel and aluminium alloy surfaces prepared at three roughness levels (Sa = 0.014–0.42 µm). Parameter sensitivity to processing was found to depend strongly on surface roughness level, with smooth surfaces exhibiting deviations an order of magnitude larger than rough surfaces under identical processing changes. Among the processing variants examined, the L-filter cut-off wavelength was identified as the dominant source of parameter variation, followed by form-removal polynomial degree and resampling density. Sa, Sq, Sk, and Spk showed the strongest correlations with hardness values (r = 0.79–0.96), with Vmp providing supplementary correlation (r = 0.80–0.91). On smooth surfaces (Sa < 0.02 µm), no parameter remained within acceptable deviation bounds under any λc variation, identifying strict filter standardisation as an absolute requirement at this roughness level. Consistent documentation of processing methodology is essential for valid cross-study comparison of surface texture–hardness relationships.