Features of the Formation of Surface Layers on Metals

Abstract

The practical application of metal alloys, in particular amorphous ones, often necessitates the creation of multifunctional coatings of various nature and purpose on their surfaces. The main requirements for obtaining optimal results of applying such coatings are as follows: 1. Understanding of the morphology of the surface before coating. 2. Information on the physical and mechanical properties of the metal-coating composition. 3. Testing of the adhesion strength immediately after coating. 4. The use of different methods of control of the application and functionality of the coating, depending on the operating conditions of the product. The reliability of functional coatings also depends on the preparation of the surface of the material, as well as the choice of appropriate conditions for its formation. However, regardless of the purpose, a general requirement that all coatings must meet is a good adhesion to the surface of the substrate material. It is also important to ensure the uniform thickness in different areas (protrusions and depressions), because the thickness of the coating determines the longevity of its protective effect. Also, the coatings should have very low rate of dissolution even in the most aggressive environments in which they work. Therefore, the problem of creating optimal coatings is complex and requires a comprehensive study in each specific case. In the case of industrial use of amorphous metal alloys (AMA) based on transition metals with different alloying elements, special attention must be paid to the elemental composition of the surface of the finished products, which can differ significantly from the quantitative composition of the initial charge, which depends on the nature of the components and the applied protocol of ultra-fast cooling of the melt. The difference in the elemental composition on the surface and in the volume of the amorphous alloy is also due to the possible formation of surface chemical compound i.e. metal oxides. The protective properties are evaluated by the speed of metal oxidation, the formation of a layer and the duration of its action. Comparative assessment of the reactivity of amorphous alloys Al87.0Y5.0Ni8.0, Fe73.6Cu1.0Nb2.4Si15.8B1.2, Fe78.5Ni1.0Mo0.5Si6.0B14.0, Co75.5Fe4.6Si6,B16.7 in an aqueous solution of sodium chloride was carried out using electrochemical studies. The main requirements for obtaining optimal results of applying protective coatings on crystalline and amorphous surfaces have been analyzed.