目的 DZ125定向凝固高温合金作为航空发动机高压叶片的核心材料,其表面性能直接影响发动机的服役寿命。因此,针对DZ125加工表面损伤与摩擦学性能关联机制不明的问题,研究电火花线切割（WEDM）多次走刀加工表面及亚表面损伤的演变规律,进而揭示表层损伤与摩擦学性能之间的内在关联机制。方法 以DZ125为研究对象,利用WEDM的多次走刀去除工艺制备一次走刀到五次走刀5组对比样件。通过往复式摩擦磨损试验,分析不同样件的抗摩擦磨损性能。并结合3D光学轮廓仪、SEM、EDS、XRD等,系统地表征不同走刀次数下的表面特征。结果 随着走刀次数从一次增加到五次,表面算术平均高度Sa从4.46 μm降至1.26 μm,表面偏斜度Ssk在三次走刀时由正转负。表明表面质量逐渐优化但存在边际效益递减规律。热影响区厚度变化趋势与残余应力并未随走刀次数线性减小。从一次走刀的38.27 μm降至三次走刀的最低点7.5 μm,随后反升至五次走刀的12.92 μm,残余应力同样在三次走刀时达到最小值33.1 MPa,这主要归因于热损伤的“去除效应”与“累积效应”之间的竞争与平衡。摩擦试验结果显示,三次走刀样件因具备优化的表面形貌与最小的亚表面损伤,表现出最优的减摩抗磨性能。五次走刀样件虽然表面最光洁,但因表面硬度下降及热损伤累积,耐磨性反而下降。结论 多次走刀能够有效改善表面完整性,但过度加工会加剧内部热损伤,进而降低其服役性能。因此,三次走刀是平衡加工效率、加工质量和工件性能的最佳加工策略。
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 (Sa) 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 (Ssk) 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.
关键词
电火花线切割 /
DZ125高温合金 /
表面完整性 /
摩擦学性能
Key words
WEDM /
DZ125 superalloy /
surface integrity /
tribological property
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基金
国家自然科学基金（U22A20197）; 浙江省“尖兵领雁+X”科技计划项目（2025C02031）
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