Influences of milling and grinding on machined surface roughness and fatigue behavior of GH4169 superalloy workpieces

Surface topography of superalloy GH4169 workpieces machined by milling and grinding is different significantly. Meanwhile, surface roughness, as one of the main indicators of machined surface integrity, has a great influence on the fatigue behavior of workpieces. Based on analyzing the formation mechanism and characteristics of surface roughness utilizing different machining processes and parameters, the machined surface roughness curve can be decoupled into two parts utilizing frequency spectrum analysis, which are kinematic surface roughness curve and stochastic surface roughness curve. The kinematic surface roughness curve is influenced by machining process, parameters, geometry of the cutting tool or wheel, the maximum height of which is expressed as $R_{\text{z}}^{\prime }$. By subtracting the kinematic part from the measurement curve, the stochastic surface roughness curve and its maximum height $R_{\text{z}}^{″}$ can be obtained, which is influenced by the defects of cutting tool edge or abrasive grains, built-up edges (BUE), cracks, high frequency vibration and so on. On the other hand, the results of decoupling analysis of surface roughness curves indicate that R_a and R_z values of milling GH4169 are 2–5 times and 1–3 times as high as those of grinding, while $R_{\text{z}}^{″}$ value of milling is 13.85%–37.7% as high as that of grinding. According to the results of fatigue life tests of specimens machined by milling and grinding, it can be concluded that fatigue behavior of GH4169 decreases with the increase of $R_{\text{z}}^{″}$ monotonically, even utilizing different machining processes.