Controlling the Stress State of the Coating during Plasma Spraying

Coatings obtained by spraying materials with a high-temperature gas jet onto a substrate followed by thermal treatment of the deposited materials (thermal gas coatings) are increasingly being used. The practical experience of using thermal spray coatings, accumulated over the past 20–30 years in industries, shows that in this way it is possible, as a rule, to reduce the wear of machine parts operating under various conditions by a factor of 2–5. The effectiveness of the technology has also been proven in the protection of products from corrosion and thermal damage. The efficiency of the applied materials is determined by their structure, which largely depends on the choice of the composition of the material, the method, and modes of application. A comprehensive solution to these issues with the study of the mechanism of the processes of formation of thermal gas coatings will create a scientific basis for the technology for its successful implementation in production. At the same time, the importance of studying the processes and optimizing the technological parameters of spraying and subsequent coating treatment increases. Optimization is carried out, as a rule, according to the results of experiments. Let us consider the study on the example of the development of wear-resistant composite coatings with solid lubricant inclusions with the substantiation of the technique and criteria for optimizing technological parameters taking into account the most important properties of sprayed protective coatings.

Theoretical and technological aspects of production mechani‑cally alloyed powders for the production of coatings and products by additive methods

The established regularities of the formation of powders based on iron and nickel, obtained by the method of mechanical alloying and intended for the deposition of thermal spraying coatings, as well as the manufacture of products by layer‑by‑layer synthesis. The structure, phase composition and properties of materials are investigated. Powders consist of particles with a size of 20–70 microns, differ in the submicrocrystalline type structures, and nonequilibrium phase composition. Thermal spray coatings made of them have a set of properties that significantly exceed the properties of coatings made of commercially available materials. The diameter of the grains of the material obtained by the SLМ method from the synthesized powder is 1.5–2.0 times smaller than that produced from the powder of 316L steel, and the heat resistance is higher.

Increasing the wear resistance of the pump-controlled hydraulic drive units

Due to the lack of 63.5 mm balloons in Ukraine in the first layout of Hop-900 hydraulic transmission sample, the balls of the PBG company (Precision Ball and Gauge Co., England) were used. However, the trials of hydraulic transmission showed increased wear and cracks on the surface of the balls. Goal. The purpose of the work is to increase the wear resistance of the units of a pump-controlled hydraulic drive. Methodology. The coating on the TICRN ball was carried out at the Bu-Lat-3T installation. The coating modes were chosen using a methodology for mathematical planning of an experiment by evaluating microhardness of molded coating and the material use factor. Metallographic studies of the structure of the materials studied and sprayed coatings were performed on the digestive and non-digestive grinds on the MIM-8M microscope. The phase composition of the spray coatings was determined on a Don-1.5 diffractometer in monochromatic CUKα radiation. Results. Following the wear resistance of all investigated materials showed the largest wear resistance of the balls with ion-plasma coating on the surface. Originality. The tests of the samples of radial ball-piston hydraulic transmission of GOP-900 type allowed to conclude that their reliability and further improvement is largely due to the reliability of the piston ball, to which there are high requirements for wear resistance, minimum volume of force and temperature deformation. Practical value. Taking into account the negative experience of using imported steel balls from chrome steel, positive experience of using balloons from Steel SH-15CG, mastered by the production of OJSC HARP, and at the same time, the need to increase the heat resistance and wear resistance of balls should be considered as promising research when using beads from powder, rapid steels of type P6M5F3-MP, ceramic balls having high strength properties.

Study and comparison of wear behaviour of Ni-Al2O3 coatings deposited by hot and cold spray

The sliding wear of hot and cold spray nickel-alumina coatings on SA 213-T 91 boiler steel has been evaluated and compared. The investigation was conducted with pin-on-disc apparatus. The wear testing was done by varying normal loads of 30, 40, and 50N at a constant sliding velocity of 1 ms-1. Then another set of experimentation was done at different sliding velocities of 0.5, 1, and 2 ms-1 at a constant normal load of 30 N. This experimentation was designed to study the effect of varying normal loads and sliding velocities on the wear performance of coatings developed with hot and cold spray techniques. The variation of friction coefficient and wear rate with variation in normal loads and sliding velocities were plotted and analyzed. The evaluation of wear mechanisms and characteristics of Ni-Al2O3 coatings is done with the help of weight change measurements and FE-SEM analysis. The wear resistance of hot spray coatings was found better at high normal loads and sliding velocities in comparison to cold sprayed coatings.

Mitigating CO2 Corrosion of Natural Gas Steel Pipelines by Thermal Spray Aluminum Coatings

Internal pipeline corrosion due to CO2 is a major challenge facing the oil and gas industry. To protect the pipelines and equipment from the ravages of CO2 corrosion, novel sacrificial coatings can be used. The objective of this study was to investigate the corrosion behavior of Al-based alloys as sacrificial coatings to protect pipelines in a CO2-saturated aqueous electrolyte (3.5 wt.% NaCl) at 4 bar CO2 partial pressure (3 barg) and 40 oC. The corrosion resistance of Al-based alloys and thermal spray coatings was evaluated in an electrochemical reaction autoclave using electrochemical methods (potentiodynamic polarization, linear polarization resistance, and electrochemical impedance spectroscopy). Post-corrosion surface characterization was performed by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. The obtained data show Al-based alloys demonstrated promising protection against CO2 corrosion with no breakaway degradation issues.

Measuring Residual Strain and Stress in Thermal Spray Coatings Using Neutron Diffractometers

Background During thermal spray coating, residual strain is formed within the coating and substrates due to thermo-mechanical processes and microstructural phase changes. Objective This paper provides a comprehensive guide to researchers planning to use neutron diffraction technique for thermal spray coatings, and reviews some of these studies. Methods ENGIN-X at the ISIS spallation source is a neutron diffractometer (time-of-flight) dedicated to materials science and engineering with high resolution testing. The focus is on the procedure of using ENGIN-X diffractometer for thermal spray coatings with a view that it can potentially be translated to other diffractometers. Results Number of studies involving neutron diffraction analysis in thermal spray coatings remain limited, partly due to limited number of such strain measurement facilities globally, and partly due to difficulty is applying neutron diffraction analysis to measure residual strain in the thermal spray coating microstructure. Conclusions This technique can provide a non-destructive through-thickness residual strain analysis in thermally sprayed components with a level of detail not normally achievable by other techniques. Neutron sources have been used to measure strains in thermal spray coatings, and here, we present examples where such coatings have been characterised at various neutron sources worldwide, to study residual strains and microstructures. Graphic Abstract