Quantification of Mesoscale Deformation-Induced Surface Roughness in α-Titanium

The phenomenon of mesoscale deformation-induced surface roughening in titanium polycrystals is examined experimentally and numerically. The evolution of the surface morphology under uniaxial tension is analyzed in terms of the standard and ad hoc roughness parameters and the fractal dimension. The statistical estimates are compared to the grain-scale stress-strain fields in order to reveal an interrelation between the in-plane plastic strains and out-of-plane surface displacements. A strong correlation with a determination coefficient of 0.99 is revealed between the dimensionless roughness parameter Rd and the corresponding in-plane plastic strain. The standard roughness parameters Ra and RRMS are shown to correlate linearly with the in-plane strains, but only for moderate tensile deformation, which is due to filtering out low-frequency components in the surface profiles. The fractal dimension DF changes with the subsection strains in a sawtooth fashion, with an abrupt drop in the neck region. The descent portions of the DF dependences are supposedly related to the appearance of low-frequency components in the structure of the surface profiles.