Functional ternary Fe-Co-Mo(W) coatings

Abstract

The researchers and technologists increased interest to multicomponent galvanic alloys of iron triad metals with refractory elements (W, Mo etc.) [1, 2] is caused by several reasons. The main is creation new technology of coatings with a unique set of functional properties such as wear and corrosion resistance, increased catalytic activity and microhardness, magnetic properties, and others [3, 4]. This allows replacing toxic chromium-plating, to create effective catalytic materials, more available compared to traditional platinum based systems [5] and to obtain new soft magnetic films for the production of magnetic head elements for recording and reproducing information [6]. In this connection, the electrochemical methods of deposition are considered to be a competitive alternative to the physical methods of production [7] due to the possibility of flexible process control and monitoring. This enables the formation of coatings of a varying composition and structure, which is a key factor for production of the materials with specified functional properties. Many scientific papers delve into the electrodeposition of binary [8, 9] and ternary [10] iron and cobalt alloys with refractory components. In [11], Fe-W and Fe-W-P coatings with high wear resistance and corrosion resistance were obtained from electrolytes of different composition. It is noted that friction coefficient of amorphous ternary Fe-W-P alloys is lower than that of binary Fe-W coatings. The authors of [12] emphasize the increased wear resistance of Fe-W, Ni-W and Co-W coatings obtained from citrate and citrate-ammonia electrolytes at low bulk current densities. The molybdenum incorporation into cobalt deposits leads to a significant decrease in the coercive force and an increase in the saturation magnetization of the materials [13]. It is shown [14] that the molybdenum content in the alloy increases as the potential shifts toward negative values. The structure of deposits varies from close-packed hexagonal to mixed crystalline and amorphous with increasing current density. depends on coatings thickness: thin films have an amorphous structure. The great practical interest for works [15, 16] are due to electrosynthesis of ternary Fe-Mo-W alloys with increased physic-mechanical and corrosion protective properties for hardening machine parts. Obviously, in each individual case the formation of the coating depends on the qualitative and quantitative composition of the electrolyte and on the synthesis conditions. It should be noted the modes and parameters of the electrolysis predetermine in a particular way the concentration ratio of the alloy components and phase composition of the coatings [17]. Accordingly, the functional properties of coatings depended on the composition and structure can be controlled by deposition conditions. It should be noted that most published results covers to binary alloys Fe (Ni, Co) -Mo (W). Thereby it is relevant to study the process of electrosynthesis of ternary alloys and to analyze their properties.