Study on the mechanism of chip forming and the microhardness of micro-grinding nickel-based single-crystal superalloy

Nickel-based single-crystal superalloy has no grain boundary, hence has excellent high-temperature mechanical properties and is the best option for the manufacturing of the blades of aero-engine and gas turbine. The removal mechanism of grinding traditional polycrystalline material is different from that of single-crystal material, but so far there are very few studies on grinding nickel-based single-crystal superalloy. To understand low-damage manufacturing of micro-grinding single-crystal parts, this paper first explored the chip-forming mechanism of micro-grinding nickel-based single-crystal superalloy; secondly, this paper analyzed the microstructure of micro-grinding sub-surface damage through the scanning electron microscope (SEM), then studied the microhardness on the sub-surface of grinding nickel-based single-crystal superalloy parts, and the surface-hardening phenomenon from the aspect of dislocation theory through the transmission electron microscope (TEM); finally, this paper investigated the microstructure of subsurface recrystallization and the influence of recrystallization on the microhardness of the micro-grinding workpiece through simulating the high-temperature application environment, and the measures for controlling or inhibiting recrystallization of single-crystal parts were also discussed. The experiment results showed that the chip shape of grinding nickel-based single-crystal superalloy had the typical serrated structure due to the occurring of adiabatic shearing slippage, while the shearing slippage and the distortion took place in the sub-surface plastic deformation layer; the sawtooth degree of chips increased gradually with the spindle speed increasing; the feeding rate and grinding depth also had some effect on the sawtooth degree of the chips; the dislocation cell substructure appeared on the sub-surface of micro-grinding single-crystal superalloy, which improved the surface hardness of single-crystal parts; cellular recrystallization occurred on the sub-surface of the single-crystal parts after high-temperature treatment, which decreased the surface hardness of the workpiece and affected the service life of the parts; when the workpieces were precisely grinded using the microgrinding tool electroplating 1000# abrasives at v(s) = 50,000 r/min, v(w) = 20 mu m/s, and a(p) = 2 mu m, followed by the annealing treatment at 760 degrees C for 4 h, the thickness of recrystallization layer significantly decreased, and the service life was improved. Therefore, these were good guidelines and references to the manufacturing of nickel-based single-crystal superalloy micro-workpiece.