Experimental study on fabricating micro-holes in DD5 single-crystal nickel-based superalloy using electrical discharge drilling

Abstract

The single-crystal superalloy materials have been rapidly developed and widely used in advanced thermal structural components due to their excellent comprehensive physical and chemical properties under high-temperature service conditions. However, conventional micro-hole making results in defects such as edge breakage and burr. In this study, the electrical discharge drilling (EDD) combined with helical microelectrode is first adopted to fabricate DD5 single-crystal nickel-based superalloy. The effects of tool geometry and machining parameters on subsurface damage layer, micro-hole taper, surface morphology, surface roughness and machining time were investigated in detail. Experimental results indicated that helical microelectrode can obtained smoother surface without debris deposition and thinner subsurface damage layer depth lack of micro-cracks compared with cylindrical microelectrodes. Additionally, the computational fluid dynamics model was developed to analyze working fluid movement and reveal effective debris removal mechanism of helical microelectrode. The vortices will be generated in lateral gap fluid between micro-hole and helical microelectrode and have a certain delay time. The surface roughness and dimensional precision of micro-holes fabricated by helical micro-electrodes are greatly improved and machining efficiency is also improved by 30.94% compared to cylindrical microelectrodes. This work could provide theoretical and process guidance to assist in realizing high surface quality and low subsurface damage of micro-holes obtained with EDD process.

Anodic Dissolution Characteristics of GH4169 Alloy in NaNO3 Solutions by Roll-Print Mask Electrochemical Machining Using the Linear Cathode

“…However, EDM also has defects that cannot be eradicated, such as edge fracture, burr and surface recast layer. Sun et al [ 9 ] proposed and studied the discharge drilling method using the spiral micro-electrode, and completed the processing and preparation of high-precision micro-porous structures on the surface of nickel-based alloy. In addition, Zhang et al [ 10 ] proposed a laser processing with high-temperature chemical etching method to complete the high-quality surface micro-porous structures processing of Inconel 718 under different processing media.…”

Studies on the Oxidation Behavior of a Designed Nanocrystalline Coating on K38 Alloy at 1050 °C

“…Nickel-based superalloys have been developed specifically for high-temperature applications for use in industrial gas turbines, aircraft and jet engines [1,2]. As the inlet temperature continuous to rise, improve the organization structure and element component content of superalloy has attracted increasing attention due to its influence on the performance by solution strengthen, coherence strengthening with γ/γ and forging process upgrading [3][4][5][6]. However, the requirement for improving the mechanical properties leads to a trend of higher refractory elements addition, such as Mo, W, Re and Ta, which results in a decreasing in the oxidation resistance [7,8].…”