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Functionally graded materials (FGMs) are a promising engineering material, which is highly desirable in extreme environments of aerospace, nuclear, and bio-implants. Although the surface accuracy and quality of 3D-printed Ni–Fe FGMs can meet most application scenarios, it still requires post-cutting treatment especially in nuclear industry. The FGMs, with the gradient of mechanical property, are a new type of difficult-to-cut material. However, no ready-made post milling process can be referred. The poor-machined surface quality induced by excessive tool wear still cannot be handled even with textured tool under minimum quantity lubrication (MQL). In this paper, the mechanical properties and machinability of the Ni–Fe FGMs as well as its 5 isotropic component 304LxIN625y were firstly studied and correlated. Then, two milling parameter selection strategies were proposed by minimum milling force and by minimum surface roughness, corresponding to strategy I and strategy II. The results show that tool breakage occurs in bottom cutting edge when strategy I is adopted. On the contrary, strategy II can reduce tool major flank wear 40.1% by forming an elastohydrodynamic lubrication between bottom cutting edge and the machined surface, which is a prospective method to solve the tool failure during milling of 3D-printed Ni–Fe FGMs. [ABSTRACT FROM AUTHOR]