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.

中文翻译：

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放电钻孔在DD5单晶镍基高温合金中制备微孔的实验研究

单晶高温合金由于在高温使用条件下具有出色的综合物理和化学性能，因此得到了迅速的发展，并广泛用于高级热结构部件中。然而，常规的微孔加工导致诸如边缘断裂和毛刺的缺陷。在这项研究中，首先采用放电钻孔（EDD）与螺旋微电极相结合来制造DD5单晶镍基高温合金。详细研究了刀具几何形状和加工参数对表面损伤层，微孔锥度，表面形态，表面粗糙度和加工时间的影响。实验结果表明，与圆柱状微电极相比，螺旋状微电极可获得较光滑的表面，且无碎屑沉积，且次生损伤层深度较薄，没有微裂纹。此外，还建立了计算流体动力学模型，以分析工作流体的运动并揭示螺旋微电极的有效除屑机制。旋涡将在微孔和螺旋微电极之间的横向间隙流体中产生，并具有一定的延迟时间。与圆柱形微电极相比，螺旋微电极制造的微孔的表面粗糙度和尺寸精度大大提高，加工效率也提高了30.94％。