Study on milling material removal mechanism and surface integrity of nickel-based single crystal superalloy DD5

Nickel-based single crystal superalloy, which has better comprehensive mechanical properties than polycrystalline superalloy due to the prevention of microcrack generating from grain boundaries, has been widely applied in the hottest components of aeroengine. However, the mechanical machining of nickel-based single crystal superalloy is rarely studied due to the low thermal coefficient, high hardness, and high strength. In order to explore the surface quality of nickel-based single crystal superalloy after milling, surface characteristics and effects of processing parameters of nickel-based single crystal superalloy DD5 after end milling were systematically investigated in this paper. In addition, the effect of milling on the special microstructure composed of matrix phase gamma and ordered precipitated phase gamma ' in DD5 was studied by observing the subsurface after milling. The results show that the microstructure gamma and gamma ' phases distorted to a certain extent, and deducing a plastic deformation layer. In the region close to the machined surface, gamma and gamma ' phases were severely deformed and difficult to distinguish, forming a hardened layer. For revealing the material removal mechanism of DD5, chip morphology formed during milling were observed. The lamellar structure was found on the chip surface due to the adiabatic shear, illustrating the plastic removal is the dominant removal mechanism of DD5. This work provides a basis for analyzing the milling ability of nickel-based single crystal superalloy and provides technical supports for improving the machining quality.