Hello, everyone, and this is the week 4 of our online course, theme 1. Gas-thermal spraying, different gas thermal spraying methods, flame, detonation, plasma, spraying, wire arc spray are characterized by the presence of dispersed spray material, accelerated by the jet of a gas. The surface of the part on which the coating is applied remains in solid state. As the result of this special feature, low thermal deformations and in many cases no structural changes in the part are typical for GGS processes. In addition, there are a few restrictions on the composition of the applied materials. All these determines the attractiveness of GTS to improve the performance characteristics of products. This method has no worthy alternatives for obtaining heat resistant coatings from oxides, aluminum, chromium, zirconium, etc, in the manufacture of the gas turbines and jet engines. In addition, it is traditionally used for other industries such as steel production, oil and gas industry, chemical industry, etc. Thermal spraying is a process in which the material for a semi-finished surface is heated to a plastic or molded state inside or outside the spray gun. Then it is accelerated and applied to the prepared surface substrate which remains in a melted state. Methods of GTS are classified according to the following characteristics. Energy source, influencing on atomized material, electric combustion, heat of liquid gaseous fuel. Kinetic under the influence of high pressure gas without its combustion and the radiation. Type of material to be atomized, powder, wire, liquid metal from the crucible. Degree of the motion, manual, mechanized, and automated spraying. Let us consider the distinctive features of GTS models. Flame spraying, the atomized material in the form of powder, wire, or cork is melted in the oxygen acetylene flame and accelerated by means of gaseous combustion products. High velocity oxygen fuel spraying, HVOF, compared to conventional gas flame spraying. The term high-velocity oxygen fuel spraying is used when the spray fuel gas reaches supersonic speeds. Under atmospheric pressure these conditions can be recognized when there are shock waves in the gas jet. As a rule powder is used as a starting material. Its typical sizes range from 10 to 70 micrometers. Heat source in high velocity oxygen fuel spraying, as in the case of flame spraying is the heat generated by combustion of various fuels. The principal differences are, Injection of the atomized material into the gas mixture before its combustion with subsequent heating and acceleration in the supersonic nozzle. Gas consumption is 57 times higher than the flame spraying which drastically increases the power of the flame. Plasma spraying, in the plasmatron, due to the forced compression of the arc, its temperature increases to 15,000K. The inlet gas argon, hydrogen, helium, nitrogen or the mixtures is transformed into an ionized state which is called plasma. When the gas dissociates with ions and electrons, and energy is released, which is enough to melt any material. For spraying powders and wires, plasmatrons with independent arc are used. Wire arc spray, during arc metallization the coating is formed from liquid metal droplets moving in a stream of the carrier gas. Heating and melting of the atomized material occurs due to the heat of the arc burning between the consumed wires, the electrodes from which the atomized material is formed. Liquid metal is blown off the ends of the electrodes, crushed by gas and electromagnetic forces, and in the form of droplets, moves in the direction of the resulting action. The scheme of the process determines the intensive combustion of alloying elements from the metal and saturation of the applied layer by atmospheric gases. This leads to a change in the chemical composition, a decrease in the concentration of following elements and an excess of oxides in the coating. Cold spraying, in the cold spraying or gas dynamic cold spraying method, the kinetic energy of the sprayed particles is used as an energy source. The cold spraying method is based on the effect of fixation of solid particles moving at supersonic speed on the surface when they collide with it. Erosion turns into coating information of their critical particle velocity of 300 to 500 meters per second. The productivity increases with the heating and gas pressurized. Detonation spraying. During detonation thermal spraying process, a mixture of acetylene, oxygen and powder is fed into the chamber and exploded by Spark. The shock wave in the nozzle tube accelerates the sprayed particles. After each explosion, the combustion chamber and the pipe are blown with nitrogen. Under conditions of detonation, the temperature of combustion products reaches 4000 degrees of Celsius. With free combustion the temperature of oxygen acetylene mixture is 30,100 degrees of Celsius. This increases the pressure in the nozzle pipe and accelerates the particles to high speeds. Detonation coatings have the highest adhesion and lower porosity among GTS coatings. The process is very successful in spraying materials that are sensitive to decomposition during heating.