Journal of Materials Research and Technology (Jul 2022)
Molecular dynamics study of nano-cutting mechanical properties and microstructural evolution behavior of Ni/Ni3Al phase structure
Abstract
Ni/Ni3Al (γ/γ′) phase interface structure in nickel-based single crystal alloys determines its excellent mechanical properties, which is widely used in aeroengine turbine blades. Because the deformation behavior of the γ/γ′ phase interface under external force is very different from that of a single crystal without an interface, it is necessary to study the influence of the γ/γ′ phase interface structure on nano-cutting performance. In this paper, molecular dynamics simulation is used to study the nano-cutting performance and mechanism of the γ/γ′ phase interface structure. We found that the γ/γ′ phase interface has a significant effect on the magnitude of cutting force and cutting stability. The cutting force of the γ phase is greater than that of the γ′ phase, but the cutting stability is reversed. Surprisingly, the cutting force gradually decreases when the tool moves from the γ phase to the γ′ phase; and when the tool moves from the γ′ phase to the γ phase, the cutting force gradually increases. When cutting processes are performed entirely in γ phase and alternately in γ and γ′ phases, respectively, nano-cutting deformation mechanisms are dominated by dislocation slip at lower speeds. The nano-cutting deformation mechanism transitions from dislocation slip to disordered atoms leading to unstable cutting forces when the cutting process is completely performed in the γ phase at a cutting speed of 200 m/s. However, when the cutting process occurs alternately in the γ and γ′ phases, the cutting deformation mechanisms of the γ′ and γ phases are twins, point dislocations and stacking faults, respectively. Moreover, we found that the stacking defects of the γ phase are absorbed by the γ/γ′ interface when the tool moves from the γ phase into the γ′ phase. But the dislocations are activated again when the tool moves from the γ phase into the γ′ phase. Finally, we found that the surface roughness of the workpiece is the smallest at cutting speed of 100 m/s, which is manifested as pits and surface steps. This study will provide theoretical guidance for the nano-cutting scheme of nickel-based single crystal alloy.
