Study on surface quality and subsurface recrystallization of nickel-based single-crystal superalloy in micro-grinding

Abstract

Nickel-based single-crystal superalloy is a typical kind of difficult-to-machine material, which has no grain boundary and has excellent high temperature mechanical properties, making it the best choice for the manufacturing of hot end components of aviation engine and gas turbine. Micro-grinding which uses tool with a diameter of less than 1 mm to remove material is the final procedure of machining micro-parts, and its machined surface quality directly affects the service life of workpiece. In this paper, micro-grinding experiments of nickel-based single-crystal superalloy with only one grain were carried out, which considered the influence of crystal anisotropy. Firstly, the reasons for the anisotropy of single-crystal material were analyzed theoretically. Secondly, the influence of different crystal planes and different crystal orientations in the same crystal plane on micro-grinding surface quality was analyzed. Then, the influence of micro-grinding parameters and micro-grinding tool-wear on micro-grinding surface quality was analyzed. Finally, a preliminary exploration and research on the generation and restraint process of the subsurface recrystallization of micro-grinding workpiece was conducted through simulating the high-temperature application environment of nickel-based single-crystal superalloy. The experimental results show that the grinding surface roughness along (100) crystal plane is higher than that along (110) crystal plane and (111) crystal plane, and the grinding surface roughness along (110) crystal plane is higher than that along (111) crystal plane. When grinding in the (001) crystal plane, the grinding surface roughness along [110], \( \left[\overline{1}10\right] \), \( \left[\overline{1}10\right] \), \( \left[1\overline{1}0\right] \) crystal orientations is the lowest, and that along [100], [010], \( \left[\overline{1}00\right] \), \( \left[0\overline{1}0\right] \) crystal orientations is the highest. The subsurface recrystallization layer thickness of the workpiece grinding along the [110], \( \left[\overline{1}10\right] \), \( \left[\overline{1}10\right] \), \( \left[1\overline{1}0\right] \) crystal orientations and under high temperature is larger, and that along the [100], [010], \( \left[\overline{1}00\right] \), \( \left[0\overline{1}0\right] \) crystal orientations is smaller. With the decreases of spindle speed (vs), and the increase of feed rate (v w ), grinding depth (a p ) and degree of grinding wheel wear, micro-grinding surface quality becomes worse gradually. It is appropriate when the extended length of micro-grinding tool is 18 mm. When the micro-grinding workpiece of nickel-based single-crystal superalloy was insulated at 760 °C for 4 h and the furnace cooling was used, the thickness of recrystallization layer is smaller, which is nearly 1.6 μm. The service life of single-crystal components can be improved. So this is a good guide and reference to the machining of nickel-based single-crystal superalloy micro components.