The Effect of Thermal Treatment Modes on the Structure and Corrosion Resistance of Plasma Coatings Made of Alloys Based on Nickel and Iron

Resumo

The structural state and corrosion resistance of the plasma coatings based on iron (FBKh6-2 alloy) and nickel (RW 12496 alloy from Castolin Co.) in aqueous solutions of sodium hydroxide and nitric acid upon varied thermal treatment modes have been investigated. Structural and electrochemical characteristics of these coatings have been compared to those of their analogs in the as-cast state that underwent respective thermal pretreatment. The morphological heterogeneity of the coatings’ surface has been demonstrated to determine the formation of their corrosion-electrochemical characteristics. The specific character of the corrosion process evolution responsible for significant degradation of the coatings’ corrosion resistance as compared to the cast alloys has been described. It has been established that the effect of morphological defects of the coatings’ surface (cavities, microcracks, roughness, open pores, etc.) on the corrosion process evolution can be substantially reduced and, in some cases, completely excluded through impregnation by the hydrophobizing fluid Anakrol-2501 with high penetrating ability. Corrosion tests of the coatings have been performed. It has been demonstrated that impregnation results in a significant reduction of the corrosion rate that becomes compatible to that of the annealed cast samples.