Synthesis, Wear and Corrosion of Novel Electrospark and Electrospark–Electrochemical Hybrid Coatings Based on Carbon Steels

Abstract

The electrospark deposition (ESD) technique is a low-heat-input process that has great potential for coating applications and the restoration of damaged high-value parts. Carbon steels are commonly used as a substrate material for ESD coatings. However, we demonstrated that carbon steels could be used successfully as the electrode tool for the ESD process. Furthermore, ESD coatings commonly have a high as–deposited roughness. In view of this, in order to reduce the roughness of the ESD coatings, electrodeposition as a tool to alter surface morphology was investigated. Hence, the micro-leveling power of several electrolytes for Ni, Fe-W, Fe, and Cr electrodeposition were evaluated. The maximum leveling effect was detected for Ni electroplated from the Watts electrolyte. Thus, the novel hybrid coatings based on an ESD layer and a subsequent layer of electrodeposited Ni were obtained. ESD layers were obtained by using the following electrode tools as anodes: several types of carbon steels (St20, St30, and St45), alloys T15K6 (WC + TiC + Co), CuNiZn; and NiCr. The morphology and structure of the obtained hybrid coatings with an electrodeposited Ni top-layer was analyzed and compared to ESD coatings from the point of view of their wear and corrosion behavior. The wear rate of the novel ESD coatings based on carbon steels was comparable with coatings obtained using the NiCr electrode tool. Moreover, for all the studied cases, the corrosion resistance of the hybrid coatings was higher than for their ESD counterparts and close to electrolytic chromium.

The Effect of Plasma–Electrolytic Nitrocarburizing of a Medium Carbon Steel Surface on Friction and Wear in Pair with Tin–Lead Bronze

“…Based on the XRD analysis, the surface layer of samples after PENC contains mainly iron oxides Fe3O4, Fe2O3, and FeO (Figure 27a-e), which is typical for this kind of processing [3,7,10,11]. It has been shown that, with an increase in the PENC temperature, the relative amount of oxide Fe3O4 decreases, while FeO increases.…”

“…The tribological tests were performed according to the "shaft-block" scheme (Figure 6) [11,13]. The sample was mounted on a shaft driven by an electric motor.…”

“…Substituting the expressions for the absolute approach (11) and the specific load (2) into (1) allows one to obtain an estimate of the contact stiffness in the form (12):…”

“…The values of topographic characteristics, obtained experimentally after processing the surface profilograms, make it possible to determine another important parameter characterizing the type of stress state of a tribological contact. Expressions (10) and (11) allow one to calculate the relative penetration of the roughness of the compressed surfaces:…”

“…The emission of electrolyte components into the vapor-gas envelope makes diffusion saturation of the part surface possible. Meanwhile, the high heating rate, up to hundreds of degrees per second, contributes to an austenite grain size reduction, increasing diffusion capacity [10,11]. Moreover, simultaneous diffusion saturation with nitrogen and carbon provides an increase in the hardness, wear resistance, fatigue strength, ductility, and impact strength of steel products [12,13].…”