Study on hole quality and surface quality of micro-drilling nickel-based single-crystal superalloy

Abstract

Nickel-based single-crystal superalloy has no grain boundary. This makes the traditional cutting mechanism of shearing and slipping along grain boundary of polycrystalline material based on the theory of elastic-plastic deformation not suitable for drilling single-crystal parts. To achieve high-quality and low-damage micro-drilling of nickel-based single-crystal superalloy, the micro-drilling surface/subsurface quality of the (001) crystal plane of nickel-based single-crystal superalloy was studied in this paper. Firstly, the influence rules of the cutting speed (v s) and the feed rate (v w) on the micro-drilling hole size, surface morphology, surface roughness and subsurface damage depth were studied. Then, the micro-hardness on micro-drilling subsurface was analyzed. Finally, the subsurface recrystallization was explored. The results show that with the increase in v s , the hole diameter error and the surface roughness decrease, and the depth of subsurface plastic deformation layer decreases first and then increases; with the increase in v w , the error of hole diameter and the surface roughness increase, and the depth of the deformation layer decreases first and then increases. When v w > 0.33 μm/r, there are severe scratches on the surface of the hole wall, and the hole wall appears undulating stripes; white layer structure and severe plastic deformation layer appeared on the micro-drilling subsurface; the γ and γ' phases' deformation is severe; the micro-hardness at the subsurface white layer is small, and the micro-hardness value at the plastic deformation zone is large; after the hightemperature treatment, γ phase dissolves on the subsurface of micro-drilling parts, and the cellular recrystallization and the complete recrystallization occur. The minimum thickness of recrystallization layer obtained is 1.43 μm at v s = 141 m/min and v w = 0.105 μm/r. This study provides a good guidance and reference for the machining of nickel-based single-crystal superalloy micro-hole parts.

Influence of Size Effect in Milling of a Single-Crystal Nickel-Based Superalloy

“…Polycrystalline metallic alloys with grain sizes comparable to the undeformed chip thickness generally require higher specific energies for material removal, as shear and slippage do not necessarily progress along the weaker grain boundaries. Instead, material deformation upon engagement with the cutting tool predominantly occurs within the grain, inducing higher mechanical stresses [ 7 , 29 ]. For single-crystal alloys, the mechanism of grain boundary sliding does not arise [ 29 ].…”

“…Instead, material deformation upon engagement with the cutting tool predominantly occurs within the grain, inducing higher mechanical stresses [ 7 , 29 ]. For single-crystal alloys, the mechanism of grain boundary sliding does not arise [ 29 ]. Here, the motion of dislocations within the material is directly dependent on the lattice structure (unit cell) of the alloy [ 30 ], which can influence the onset of the size effect.…”

“…Here, the motion of dislocations within the material is directly dependent on the lattice structure (unit cell) of the alloy [ 30 ], which can influence the onset of the size effect. However, research pertaining to the micromachining of single-crystal Ni-based superalloys has hitherto mainly focused on aspects such as the optimisation of cutting parameters and conditions for improving hole quality in microdrilling [ 29 , 31 ], as well as the assessment of cutting forces [ 32 ], tool wear mechanisms [ 33 ] and surface quality [ 34 ] following micromilling operations. Therefore, the present work aims to investigate the influence of the size effect on chip formation, tool wear, cutting forces and surface quality when slot-milling a single-crystal Ni-based superalloy using micro- (Ø 1 mm) and conventional/macro-sized (Ø 4 mm) end-mills, with the results subsequently analysed to estimate the h min value.…”

Influence of Cutting Tool and Drilling Process on the Machinability of Inconel 718

“…Drilling is a usual hole-making technology, but it is also a semi-closed cutting process and its performances of chipbreaking and cooling are far less than those of turning and milling. Therefore, the precision drilling of nickel-based superalloy has always been a key technical problem in the field of advanced machining [12]. Imran et al [13][14] researched the surface integrity of drilling Inconel 718 and found that a metamorphic layer with nanostructure was formed on the machined surface because of the combined action of cutting heat and cutting force, the lubrication condition and cutting parameters were important influencing factors of the thickness of the metamorphic layer.…”