The GH4169 superalloy has high strength at high temperatures. Cooling conditions have a major impact on the machined surface integrity, which further affects the fatigue properties of specimens of the GH4169 superalloy. The influence of cooling conditions on the surface integrity of the GH4169 superalloy is first studied during the side milling. Then, the effect of surface integrity under different cooling conditions on the fatigue behavior of specimens of the GH4169 superalloy is investigated by a standard tensile and tensile–mode fatigue testing. The results obtained show that surface roughness and the depth of the plastic deformation layer in wet milling and dry milling makes little difference, the surface microhardness rate in dry milling is slightly lower than that in wet milling, the surface tensile residual stress in dry milling is significantly higher than that in wet milling, and the fatigue behavior in dry milling is only about 50% of that in wet milling. In addition, the crack initiation of specimens of the GH4169 superalloy utilizing wet milling is on the subsurface, while that from dry milling is on the surface. Thus, cooling conditions have an important impact on the fatigue behavior of specimens of the GH4169 superalloy, and micro defects in dry milling are the main factors of decreasing of fatigue behavior of specimens of the GH4169 superalloy.

In addition to the micro-topography of machined surfaces, plastic deformation is an important factor affecting the machined surface integrity and the fatigue performance of specimens. For 20Cr and TC17 materials, the effect law of milling surface plastic deformation on high- and low-cycle fatigue performance of specimens was studied. Experimental results show that the effect law of milling surface plastic deformation on high- and low-cycle fatigue performance of specimens is different. When the high-cycle fatigue life is about 2 × 10⁵ cycles, severe surface plastic deformation can increase the maximum stress suffered by TC17 specimens from 1060 MPa to 1080 MPa; when the low-cycle fatigue life is about 6 × 10⁴ cycles, severe surface plastic deformation can reduce the maximum stress suffered by 20Cr specimens from 680 MPa to 660 MPa. Therefore, severe surface plastic deformation can improve the high-cycle fatigue performance and, on the contrary, it has a negative effect on the low-cycle fatigue performance. Combined with the analysis of the surface integrity index and the fatigue fracture topography of specimens, it is concluded that the machined surface plastic deformation significantly reduces the plastic deformation capacity of surface layer material and enhances the stress concentration phenomenon caused by the surface micro-topography, so that when a specimen is subjected to a large load, it is very easy to make microcracks appear on the machined surface and form the “over-plastic deformation” phenomenon, resulting in a sharp decrease in the low-cycle fatigue performance of specimens. This suggests that the plastic deformation degree of machined surfaces needs to be optimized depending on the magnitude of the working load and the micro-topography.