Influence Mechanism of Multi-pass WEDM on Surface-subsurface Damage and Tribological Properties of DZ125 Superalloy

NI Jing; ZHOU Boli; ZHANG Haohan; MENG Zhen; LIU Guozhen

doi:10.16490/j.cnki.issn.1001-3660.2026.15.001

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Surface Technology ›› 2026, Vol. 55 ›› Issue (15) : 1-15. DOI: 10.16490/j.cnki.issn.1001-3660.2026.15.001

Precision and Ultra-precision Machining

Influence Mechanism of Multi-pass WEDM on Surface-subsurface Damage and Tribological Properties of DZ125 Superalloy

NI Jing, ZHOU Boli, ZHANG Haohan^*, MENG Zhen, LIU Guozhen

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Abstract

Directionally solidified superalloy DZ125 features outstanding high-temperature strength and corrosion resistance, making it a key material for aerospace turbine blades. However, it is precisely these characteristics that endow it with excellent performance, yet also make its processing extremely difficult for traditional methods, with severe tool wear and surface defects being very common. Wire-cut electrical discharge machining (WEDM) offers a solution for processing complex structures, but it also introduces a new problem: the recast layer formed by high-temperature discharge will shorten the service life of the component. Is there a method that can balance processing quality and tribological properties? To answer this question, this paper studies the asynchronous evolution of surface and subsurface damage during multi-pass WEDM machining and its influence on wear mechanics.
DZ125 superalloy is utilized as the base material. Using the number of tool passes ranging from 1 to 5, five different experimental groups are established: NOC-1 to NOC-5 (Number of Cuts). The surface morphology evolution of these samples is observed by 3D optical profiler and scanning electron microscope (SEM). The elemental migration map is plotted using an energy dispersive spectrometer (EDS), especially the enrichment and oxidation of carbon. In addition to surface features, the thickness of the heat-affected zone (HAZ) and the distribution of residual stress are also measured. Finally, reciprocating sliding friction tests are conducted using GCr15 steel balls to reveal the tribological properties.
The data indicates that there are different changing trends between surface damage and internal thermal damage. In surface damage, this trend is monotonous and positive. The rough surface gradually transitions to a smooth one as the number of tools passes increases. The arithmetic mean height (S_a) decreases from 4.46 μm to 1.74 μm of NOC-3, and ultimately reaches 1.26 μm at NOC-5. Furthermore, the surface skewness (S_sk) changes from positive to negative at NOC-3. This inversion transforms the surface from a peak form to a valley form, creating concave areas that are conducive to the retention of wear debris.
However, beneath the surface, the situation is different. The thickness of the heat-affected zone (HAZ) shows a distinct U-shaped change in the chart. It decreases from 38.27 μm of NOC-1 to 7.5 μm of NOC-3. However, by NOC-5, the thickness of the damage layer increases to 12.92 μm again. This non-linear phenomenon is governed by a dynamic competition between two opposite forces: the "removal effect" and the "accumulation effect". In the initial stage, removing the damaged layer plays a leading role. After three cuts, the "cumulative effect" begins to take the lead. Repeated thermal pulses have a tempering effect, reducing hardness and regenerating the heat-affected zone.
Tribological tests confirm the criticality of this thermal damage. The samples of NOC-1 fail severely due to the brittle and carbon-rich recast layer. The tribological properties of NOC-3 reach the optimum. This group of samples features the shallowest elliptical wear marks and the most stable coefficient of friction, which is attributed to the elimination of surface microcracks and the reduction of thermal damage. On the other hand, excessive finishing is detrimental to tribological properties. The NOC-5 samples will be affected by the softening and subsurface defect regeneration, leading to accelerated fatigue wear. Therefore, to achieve the best balance between efficiency and performance, it is recommended to stop further processing after three tool passes. Tribological experiments prove that in WEDM of superalloys, a smoother surface is not the decisive factor for tribological properties. We should pay more attention to the thermal damage inside the material.

Key words

WEDM / DZ125 superalloy / surface integrity / tribological property

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NI Jing, ZHOU Boli, ZHANG Haohan, MENG Zhen, LIU Guozhen. Influence Mechanism of Multi-pass WEDM on Surface-subsurface Damage and Tribological Properties of DZ125 Superalloy[J]. Surface Technology. 2026, 55(15): 1-15

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