Influence of stainless steel surface roughness parameters on the degree of its blackening during femtosecond laser processing

The study is devoted to identifying the role of parameters characterizing the surface height distribution according to ISO 25178 when assessing the degree of surface blackening. The dependence of the correlation of parameters and the similarity of the color characteristics of the studied surfaces is also studied. The study was performed based on practical studies of the microstructure of surfaces obtained from processing the materials AiSi321 steel and AiSi304 steel with a femtosecond laser. The influence on the color characteristics and degree of surface blackening of such parameters as Smr1, Smr2, asymmetry (skewness) Ssk, and sharpness (kurtosis) Sku, as well as the presence of periodicity of the microstructure, has been established. The complex nature of the distribution of heights of the studied surfaces with periodic microstructures is described. • The periodicity of surface structures does not determine it's color characteristics. • A surface sharpness characteristic significant increase leads to surface blackening. • A change within 5% of the surface sharpness value does not change it's blackness. • The materials of the processed surfaces does not dictate their color similarity. • The predominance of surface's peak-shaped elements contributes to its blackening.