The Effect of Argon as Atomization Gas on the Microstructure, Machine Hammer Peening Post-Treatment, and Corrosion Behavior of Twin Wire Arc Sprayed (TWAS) ZnAl4 Coatings

In the twin wire arc spraying (TWAS) process, it is common to use compressed air as atomizing gas. Nitrogen or argon also are used to reduce oxidation and improve coating performance. The heat required to melt the feedstock material depends on the electrical conductivity of the wires used and the ionization energy of both the feedstock material and atomization gas. In the case of ZnAl4, no phase changes were recorded in the obtained coatings by using either compressed air or argon as atomization gas. This fact has led to the assumption that the melting behavior of ZnAl4 with its low melting and evaporating temperature is different from materials with a higher melting point, such as Fe and Ni, which also explains the unexpected compressive residual stresses in the as-sprayed conditions. The heavier atomization gas, argon, led to slightly higher compressive stresses and oxide content. Compressed air as atomization gas led to lower porosity, decreased surface roughness, and better corrosion resistance. In the case of argon, Al precipitated in the form of small particles. The post-treatment machine hammer peening (MHP) has induced horizontal cracks in compressed air sprayed coatings. These cracks were mainly initiated in the oxidized Al phase.

Role of Coating Processes on the Corrosion Kinetics and Mechanism of Zinc in Artificial Seawater

Zinc (Zn) coating is being used to protect steel structures from corrosion. There are different processes to deposit the coating onto a steel substrate. Therefore, in the present study, a 100 µm thick Zn coating was deposited by arc and plasma arc thermal spray coating processes, and the corrosion resistance performance was evaluated in artificial seawater. Scanning electron microscopy (SEM) results showed that the arc thermal spray coating exhibited splats and inflight particles, whereas plasma arc spraying showed a uniform and dense morphology. When the exposure periods were extended up to 23 d, the corrosion resistance of the arc as well as the plasma arc thermal spray coating increased considerably. This is attributed to the blocking characteristics of the defects by the stable hydrozincite (Zn5(OH)6(CO3)2).

Investigation of the Chemical Composition of Films Obtained by Electric Arc Spraying of Graphite and Titanium from Two Sources

A promising material for cold cathodes creation are carbon films with both acceptable emission properties and satisfactory adhesion to the substrate. It is known that inclusions of metallic elements (chromium, titanium, etc.) improve the adhesion of the carbon film to the substrate. One of the methods for producing coatings based on carbon and titanium is electric arc spraying of a Ti/C composite cathode in an argon atmosphere. The disadvantage of this method is the presence in the total plasma flow of carbon microparticles, which are sources of structural defects in the growing film. Magnetic separation of carbon plasma solves the above problem. In this work, composite metal-carbon films were obtained by simultaneous electric arc spraying of graphite in a magnetic field and of titanium from two evaporators. The composition of the films was studied by Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS). It has been established that the samples obtained are composite films consisting of graphite nanoparticles, Ti14C13 nanoclusters or Ti8C12, titanium oxides, and titanium carbide TiCxN1–x compounds.

Thermodynamic Estimation of the Parameters for the C–H–O–N–Me-Systems as Operating Fluid Simulants for New Processes of Powder Thermal Spraying and Spheroidizing

Over the past few years, a group of new processes was developed for high-temperature, including plasma electric arc spraying (at ambient pressure) and spheroidizing of some ceramic and metal powder materials with the use of gaseous hydrocarbons in the heat carriers as well as with feeding of organic additions into a high-temperature jet, in particular, polymeric ones, to control porosity of sprayed metallic functional coatings. The paper considers the possibility to modify such technological processes by introducing solid fuel additions of a polymer type into the operating fluid of an apparatus for gasthermal (plasma or other) treatment, which provides melting of metal or oxide powders. For this, with the help of thermodynamic analysis, the processes have been evaluated at temperatures (300–3000) K for the set of such reacting five component systems as C–H–O–N–Me (at ambient pressure 0.101 MPa) with five variants of Ме – aluminum, titanium, chrome, copper, nickel. This makes it possible to consider these systems as simulants for potential technologies for the treatment of oxide powders (Al2O3, TiO2, Cr2O3) as well as metallic ones (Cu, Ni and their alloys). In order to obtain high exothermic contribution to the heating of powders, the combination “air + polymeric addition (polyethylene) of LDPE grade” was chosen as mixed heat carrier (operating fluid) for the basic version of simulated process. During the analysis of equilibria for the considered multicomponent systems (17 variants), a set of following parameters has been used to characterize the energy intensity of the target powder heating process: the equivalence ratio for reacting mixture and its adiabatic temperature; the energy efficiency of material heating with and without taking into account the effect of fuel addition; specific energy consumption for the powder melting; autothermicity degree of the process during the combined heating (electrothermal heating by the arc of plasma torch and heat flux from the “air + solid fuel additions” mixture) of refractory powders. As a result of the assessment, the preferred (from thermodynamic standpoint) regimes of the considered processes have been found and the possibility to realize an energy-efficient heating of these oxide and metal materials (without oxidation of the latter to CuOx, NiO) with a reduced part of the electric channel of energy transfer, resulted from the carrying out of appreciable effect of the fuel-initiated mechanism of heating in the analyzed C–H–O–N–Mesystems, has been shown in the paper.

APPLICATION OF COMBINED TECHNOLOGY FOR RENOVATION AND INCREASED RESOURCE DETAILS OF MEANS OF TRANSPORT

It presents various combinations of primary hardfacing technology for the renovation and improvement of the resource details of ship machinery. Currently, promising are integrated or combined methods hard facing (hybrid technology) coating in conjunction with the modification, the application of multi-layer, multi-functional coatings; development of integrated multioperational technologies. In all conditions, increasing scarcity of expensive alloying materials included in the composition of steels requiring high strength properties of the complex, are promising hybrid technology peening (restore) the surfaces of mild steel Combinations of various primary technologies of application of multipurpose coverings for restoration and increase of a resource of details of knots and units of vehicles are presented. Currently promising are combined methods of application of multifunctional coatings (integrated, hybrid technologies), methods of coating in combination with methods of modification, application of multilayer, multifunctional coatings; development of combined (integrated, hybrid) multioperational technologies. In the conditions of growing shortage of expensive alloying materials which are a part of the steels demanding a high complex of properties of durability, the combined methods of restoration of surfaces are perspective.At present, a methodology for the synthesis of combined multi-operational technologies has not been developed. An empirical-intuitive approach prevails in the combination of multifunctional coating restoration methods. The optimal choice of restoration methods and their sequence is determined by the increase of hardness, complex of mechanical properties, wear resistance, as well as the roughness of the restored surface and the accuracy of the dimensions of the restored part. In the first-best case of combined (hybrid) methods of recovery, the criterion of choice is the comparison of costs and increase the set of mechanical properties of the recoverable parts of components and units of vehicles [13-14]. Each method of recovery has its niche of optimal conditions of use, including even the technological traditions that have developed in a particular enterprise. The decisive factor in the choice of primary methods of applying multifunctional coatings in the combined restoration process is the presence of certain types of equipment at the enterprise and the ability to integrate them intoa single technological cycle. In order to restore vehicle parts with multifunctional coatings with high adhesion strength, hardness and wear resistance, we have proposed a combined (integrated) technology that includes electric arc spraying, electrospark doping and pulsed ion nitriding.

A Review on the Wear, Corrosion and High-Temperature Resistant Properties of Wire Arc-Sprayed Fe-Based Coatings

Among different thermal spraying methods, arc-spraying has been widely used due to its low operating costs and high deposition efficiency. The rapid progress of cored wire technology in arc-spraying has increased possibilities for the preparation of new Fe-based coating materials with enhanced properties by adding reinforcement particles and alloying elements to suit the different applications. Fe-based coatings have been extensively used because of their high strength, toughness, lower production costs, and availability of raw materials. This makes them suitable replacements for Ni-based coatings in ambient and high-temperature applications. This review discusses the research status and developments of the arc-sprayed Fe-based coatings. The study specifically reviews the wear behavior, corrosion analysis, and high-temperature resistant properties of arc-sprayed Fe-based coatings, aiming to develop an understanding of the protection mechanisms for Fe-based coatings. The performance of the Fe-based coatings depends on the integrity of the coating structure. Optimizing arc-spraying parameters minimizes defects (pores, grain boundaries, unmelted particles, oxides, and microcracks) that deteriorate the coating properties. High amorphous phase content, ceramic reinforcement particles and alloying elements enhance the corrosion, tribological, and high-temperature resistant properties of Fe-based coatings. In high-temperature applications, Fe-based coatings form oxide scales that protect the coating from further oxidation; thus, it is important to select the optimum composition for the alloying elements.

Airflow Dynamics and Aluminum Coating Oxidation Behavior under Electric-Arc Spraying with Airflow Pulsations

The paper aims to investigate the airflow dynamics of electric-arc spraying (EAS) with airflow pulsation. The study is focused on the dynamic structure of the airflow with an obstacle in the form of crossed electrodes at the steady and the pulsating air supply (with a frequency up to 120 Hz). The work was fulfilled using a computer simulation, the airflow “shadow” photo visualization, and the microstructure characterization of the coatings formed. It was found that when air flows along the crossed electrodes with a gap of 2 mm, a depression zone appears in the flow with a pressure drop from 0.56 MPa to 0.01 MPa. The air pulsation resulted in a change in a flow’s dynamic structure towards an increase in the length of the depression zone, which covers most of the arc, affecting the liquid metal oxidation. It is established that the frequency of a droplet formation should match the frequency of the airflow pulsation to minimize the metal oxidation. With the air pulsating at about 65 Hz, the oxide volume fraction in the aluminum coating was reduced by 3.6 times compared to the steady airflow. EAS with airflow pulsation has the potential for technological cost reduction.