ELECTROLYTIC-PLASMA PROCESSING OF HIGH-TEMPERATURE NICKEL ALLOY CHS88U-VI AT ION-IMPLANT SURFACE LAYER MODIFICATION

Abstract

The reliability and service life of gas pumping units (GPU) are largely determined by the presence, composition and quality of protective coat- ings created on the surface of the parts, especially on the most loaded ones - turbine blades. However, the service life of coatings containing mainly a complex of components of the Ni-Cr-Al-Y type is limited. The method of ion modification can significantly change the physical and chemical state of the surface and, as a result, increase the operating properties of the blade as a whole. Purposefully choosing atoms of dop- ing admixture and modes of irradiation using the ion implantation method, it is possible to provide high strength of the surface or subsur- face layer, change the concentration and spatial distribution of disloca- tions and other structural defects, ensure the formation of fine high- strength precipitates. Compared with traditional methods of chemical and thermal treatment, ion implantation can reduce the processing time by dozens of times and dramatically reduce the processing temperature. An important advantage of the method is the absence of an explicit phase boundary, a noticeable change in the size of the part. This circumstance allows to exclude the problems that have to be solved in the development of coating technol- ogy, such as providing adhesive strength, minimal impact on the strength properties of the part, compatibility with the base. The surface quality has a significant impact on the endurance limit and corrosion resistance of the GPU blades. The most promising method of surface treatment is electrolyte-plasma polishing (EPP) in neutral aqueous solutions of low concentration salts. As a result, the EPP from the surface removes several micrometers of the most rich in foreign inclusions and a polluted layer of metal, disappears directional anisotropy acquired during machining. The use of this meth- od before the hardening of ion implantation and the application of vacu- um ion-plasma coatings allows to combine in one operation degreasing, etching and activation of the surface, which in turn improves the effi- ciency of ion implantation, as well as improve the properties and adhe- sion of the coating to the base metal. The article presents the results of theoretical and experimental studies of the effect of EPP on ion-implantation modification of heat-resistant Nickel alloy CHS88U-VI by lanthanum ions. It is shown that the com- plex processing of the alloy, including EPP, ion implantation of lantha- num ions, post-implantation annealing can improve such characteristics of the alloy as microhardness, fatigue and long-term strength. Investigations of the modes of complex hardening treatment of alloy CHS88U-VI. The optimal modes of EPP, ion implantation, post-implan- tation annealing were selected. The results of the research are planned for the introduction of the production and repair of parts of the GPU.