Increasing the hydroabrasive wear resistance of surfaces by combined methods based on electrospark alloying and laser treatment

Combined technologies based on electrospark alloying (ESA), such as sequential ESA followed by laser treatment (LT), are used to improve ESA and increase efficiency of the process. Вevelopment of integrated methods for synthesis of coatings is relevant because it allows the quality of the surface layers to be improved and the service life of critical machine parts to be extended. In the literature, combination of electrical impact on the surface with subsequent application of metal-polymer materials (MPM) is proposed. The ESA + MPM technology makes it possible to obtain the required height of micro-irregularities (roughness), and subsequent cutting allows different ratio of the areas of applied metal and MPM. However, this technology has disadvantages. To overcome them, a new method of surface treatment is proposed. The aim of this paper is to study the structure and properties of combined coatings on steel obtained by sequential ESA, MPM application reinforced with VK6 powder, followed by LT in different modes. After machining, specimens were subjected to surface roughness determination, metallographic studies, microhardness distribution and abrasive wear resistance tests. Special set-up was designed to determine the abrasive wear resistance. The metallographic analysis showed that samples after combined treatment have a layered structure. The surface layer has the highest hardness of 6100-7300 MPa and in some areas up to 10 GPa. The outer layer is up to 420 µm thick. The sub-surface layer (up to 260 µm) is poorly etched by the reagent and has maximum hardness of 7400 MPa. Tests on abrasive wear showed that the untreated specimens suffered the most wear. The coatings obtained by the combined technology demonstrated the highest resistance: sequential ESA with a hard alloy, MPM application and final LT, and has wear resistance that exceeds the same indicator of uncoated samples by 7.5 times. Therefore, the technology studied for obtaining combined coatings can be recommended to increase thickness of the wear resistant coating and to ensure abrasive wear resistance of surfaces.