Formation Of Multilayer Coatings Research Articles

Electrochemical technology for the formation of heterogeneous metal structures with increased corrosion resistance

Research into corrosion resistance of multilayer materials obtained by the method of potentiostatic pulse electrolysis was conducted. The purpose of the work was to select materials for the creation of multilayer steel coatings with high corrosion resistance, as well as to develop technology for their formation. The formation of galvanic coatings was carried out in stationary and potentiostatic pulse electrolysis modes. The study of corrosion resistance was carried out by accelerated methods in solutions simulating the marine environment. Corrosion resistance of samples made of St3 steel coated with nickel and zinc-nickel alloys of different compositions when using various electrolysis modes was studied. It has been experimentally proved that the potentiostatic mode of pulse electrolysis allows the formation of galvanic coatings with a zinc-nickel alloy of various compositions from one electrolyte. Based on the study of electrode potentials of coatings in various media, the composition of the outer and inner layers of a multilayer heterogeneous structure was substantiated. It was experimentally proved that the formation of multilayer coatings on the surface of steel could significantly increase the protective properties of these coatings. It was theoretically justified that the materials of the layers should have different values of electrode potentials, and the inner layer should have a more negative value of the potential than the outer one has.

Multilayered Zn-Ni alloy coatings for better corrosion protection of mild steel

A simple aqueous electrolyte for the deposition of anti-corrosive Zn-Ni alloy coatings was optimized using conventional Hull cell method. The corrosion protection value of the electrodeposited coatings at a current density (c.d.) range of 2.0–5.0Adm−2 has been testified in 5wt% NaCl solution, as representative corrosion medium. The electrochemical behavior of the coatings towards corrosion was related to its surface topography, elemental composition and phase structure using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses, respectively. Among the monolithic coatings developed at different c.d.’s, the coating obtained at 3.0Adm−2 was found to be the best with least corrosion current (icorr) value. Further, the corrosion protection efficacy of the monolayer coatings were improved to many folds through multilayer coating approach, by modulating the cyclic cathode current densities (CCCD’s). The composition modulated multilayer (CMM) Zn-Ni alloy coating with 60 layers, developed from the combination of CCCD’s 3.0 and 5.0Adm−2 was found to be the best with 3 fold enhancement in corrosion protection efficiency. The formation of multilayer coatings was confirmed using cross-sectional SEM, and the experimental results are discussed with tables and figures.

Structurization and High-Temperature Oxidation Resistance of U8A Steel with Ti–Cr–Al Multi-Component Diffusion Coatings

The phase and chemical composition, structure, and microhardness of multi-component coatings produced by tetanizing (titanium) and titanaluminizing (titanium–aluminum) chemical vapor deposition (CVD) of U8A chromium steel are examined. Both titanizing and titanaluminizing were carried out in powder mixtures of titanium, aluminum, inert additive, and activators at 1050°C for 4 h. It is demonstrated that using the proposed saturation methods results in the formation of multilayer coatings of: (i) chromium and titanium carbides after titanizing; (ii) chromium and titanium carbides; titanium, aluminum, chromium, and iron intermetallides after titanaluminizing. A high concentration of iron, chromium, titanium, and aluminum is discovered on the external surface of the titanaluminized coatings. Both Fe and Cr can be provided by a chromium layer based on chrome carbides. It is demonstrated that the microhardness of multilayer coatings based on chromium and titanium carbides is 16–31.5 GPa and that based on chromium and titanium carbides and intermetallides is 5.8–36 GPa. It is established that, at a temperature of 900°C, the hightemperature oxidation resistance of titanium–chromium–aluminum coatings on U8A steel exceeds that of titanium, titanium–chromium, and chromium coatings.

Evaluation of the friction of WC/DLC solid lubricating films in vacuum

The accuracy of nanopositioning is to a large extent limited by the friction-caused errors, particularly in vacuum environments. An investigation of the friction behaviour of sp 2-bonds dominating diamond like carbon (DLC) coatings and WC 1− x /DLC, WC(N)/DLC multilayer coatings, which are considered to be used in nanopositioning in vacuum, have been performed by a vacuum microtribometer. By using an atomically smooth Si sphere as a counterface, the reciprocating sliding friction was measured at a normal load <5 mN, and running speed at a 1–100 μm/s in ambient air and in ultra high vacuum (UHV) at 10 −7 Pa, and correlated with microstructures and properties of the coatings. When tested in UHV, the coefficient of friction (COF) for pure DLC coatings (thickness: 700 nm) changes significantly between 0.2 and 0.4. Once the thickness of DLC layers is limited to 5 nm by formation of multilayer coatings, the COF in UHV decreases by nearly one order to 0.02–0.05. We suggest that the deformation of DLC films and the transfer films determines COF. Thick DLC coatings can induce more plastic deformation and consumes more energy in sliding resulting in a high COF. Thickening of the transfer film in running leads to a continuous decrease of COF since the deformation of the transfer films turns easier. The low COF of multilayer coatings is mainly due to their confinement of the thickness of DLC films. A consistent velocity-strengthening frictional behaviour of both WC 1− x /DLC and WC(N)/DLC coatings in UHV indicates that the transfer films acting as a thin layer of granular material. Further study of the friction behaviour with the presence of such granular materials might be interesting for the further development of tribological coatings for vacuum applications.