Surface Roughness, Areal Topographic Measurement, and Correlation to LCF Behavior in a Nickel-Based Superalloy

Surface roughness often determines fatigue performance of advanced engineering components making definition of this parameter essential subsequent to manufacture. Traditionally, topography measurements employ an average amplitude parameter, R (a), obtained from a two-dimensional contact measurement. This parameter, however, is highly localised making it relatively unreliable. This study attempts to correlate areal (3D) topographic, measurements with the low cycle fatigue (LCF) performance defined for a nickel-based superalloy (Waspaloy). Three different surface finishes, namely longitudinal polished, circumferential ground, and longitudinal ground were applied to fatigue specimens. The height and orientation of the topographic features with respect to the loading axis were found to affect LCF performance. Results indicate a close correlation between cycles to failure and the maximum height (S (z)) and ten-point height (S (5z)) parameters. A power fit to account for the topographic effect was generated based on the experimental data.