Surface performance degradation mechanisms and fatigue enhancement strategies of Inconel 718 workpiece after milling with ceramic tools

Inconel 718, known for its excellent high-temperature mechanical properties, is widely used in crucial aircraft engine components. Due to its poor machinability, ceramic tools are often employed to enhance cutting efficiency, but they suffer from severe wear, which deteriorates surface integrity and shortens component service life. This limits their application in finishing processes and key structural parts. This study conducted machining experiments on Inconel 718 using ceramic and cemented carbide tools to analyze the effects of different tool wear levels on the workpiece surface integrity. The relationship between surface integrity and fatigue life was further investigated. Based on the observation that ceramic tool machining led to the formation of a surface metamorphic layer, a machining strategy was proposed to improve fatigue life by removing the affected layer (RAL) using cemented carbide tools. The effectiveness of this strategy was experimentally compared with laser shock peening (LSP) and ultrasonic cavitation peening (USCP). The results showed that machining with ceramic tools produced a surface metamorphic layer, increased surface roughness and microhardness, and introduced tensile residual stress. These adverse factors intensified with increasing tool wear, ultimately reducing the fatigue life to ∼0.41 times that of components machined by cemented carbide tools. Using RAL, the fatigue life was improved by 2.36, 1.75, and 2.78 times compared to ceramic tool machining only, LSP, and USCP, respectively. The optimal removal depth was determined to be 120 μm. This strategy effectively expanded the applicability of ceramic tools in machining critical aerospace components.