超声辅助电火花粉末沉积WC-Ni金属陶瓷涂层的微观结构及摩擦学性能

针对传统电火花沉积工艺中工具电极预制成本高、工艺复杂、材料选择范围受限等问题，提出了一种超声辅助电火花粉末沉积（Ultrasonic-assisted electro-spark powder deposition，UEPD）的新方法。利用UEPD工艺成功地在316L不锈钢基材上制备了WC-Ni金属陶瓷涂层。所制备的WC-Ni金属陶瓷涂层的厚度为89~159 μm，表面粗糙度约为3.672 μm，并且与基材呈现良好的冶金结合。超声振动的引入能够有效改善涂层的成形质量。涂层的微观组织主要由亚微米级细小枝晶组成，主要物相包括FeNi、Cr₃Ni、WC、W₂C、Cr₂₃C₆和Cr₃C₂等。这些细小的晶粒和强化相使金属陶瓷涂层的硬度明显增加，平均硬度达到980.68 HV，约为基材的4.1倍。摩擦磨损性能测试表明，金属陶瓷涂层的磨损率相比基材和不含WC的Ni基合金涂层分别降低了50.7%和37.7%，并且还表现出明显低于二者的摩擦因数。WC-Ni金属陶瓷涂层的主要磨损机理为疲劳磨损和磨粒磨损，其中高硬度表面和具有颗粒流润滑效果的磨屑层是金属陶瓷涂层实现高耐磨、低摩擦的主要原因。UEPD工艺相比于传统的电火花沉积工艺省却了复杂的工具电极预制过程，其工艺更简单，成本更低廉、材料选择更广泛，并且所制备的涂层也表现出良好的成形质量和性能。这为电火花沉积技术的发展提供了一种新的思路。

Microstructure and Tribological Properties of WC-Ni Cermet Coatings Prepared by Ultrasonic-assisted Electro-spark Powder Deposition

To improve some problem of tool electrode prefabrication in traditional electro-spark deposition (ESD) technology, such as high cost, complex process and limited material selection, a novel ultrasonic-assisted electro-spark powder deposition (UEPD) process is developed. By using this UEPD process, a WC-Ni cermet coating is successfully fabricated on 316 L stainless steel. The cermet coating has an average thickness of approximately 89-159 μm and surface roughness of approximately 3.672 μm, which also exhibits good metallurgical bonding with the substrate. The introduction of ultrasonic vibration can effectively improve the forming quality of coatings. The microstructure in the coating mainly presents submicron-dendrites, which mainly contain FeNi、Cr₃Ni、WC、W₂C、Cr₂₃C₆ and Cr₃C₂. These refined grains and hard reinforcements significantly increase the hardness of the cermet coating. As a result, the average hardness of cermet coating reached 980.68 HV, which is about 4.1 times of the substrate. The friction and wear test shows that the wear rate of cermet coating decreases by 50.7% and 37.7%, respectively, compared to the substrate and Ni-bases alloy coating without WC addition. Moreover, the friction coefficient of cermet coating is also significantly lower than that of other two specimens. The wear mechanism of WC-Ni cermet coating is mainly fatigue wear and abrasive wear. The high hardness surface and the wear debris layer with granular flow lubrication are the main reasons for achieving the high wear resistance and low friction of cermet coating. Compared to the traditional ESD process, the UEPD process saves the complicated prefabrication process of tool electrode, which has a simpler process, lower cost, wider material selection and a good preparation quality and properties of coating. Therefore, the proposed of UEPD process provides a new idea for the development of ESD technology.