Technology of obtaining composite conglomerate powders for plasma spraying of high-temperature protective coatings

OBRABOTKAMETALLOV Vol. 23 No. 1 2021 TECHNOLOGY Fig. 5. Appearance of conglomerated powders for spraying Ni-22Cr-16Al-1Y composition powder with grain size 0...100 μ m was deposited in the two side pipes. The coarse powder was sent to the head of the process. The fraction content of 0...100 μ m in the “dry” powder was taken as the optimization parameter ( Y ). Table 1 shows the values of the factors in absolute and encoded form, and the results of the study are also presented here. Taking into account the signi fi cance of the coef fi cients, the regression equation has the following form (the factors are presented in the encoded form): Y = 66.4 + 11.6 X + 10.2 VX , %. (2) The analysis of the regression equation shows that obtaining the maximum amount of powder with a grain size of 0...40 μ m requires increasing X and V . The pressure in the suspension feeder within the studied interval practically does not affect the composition of the dispersed powder. The increase in the yield of the fraction 0...100 μ m, depending on X and V , is explained by the fact that the increased solvent content in the suspension reduces its viscosity and surface tension, thus contributing to the jet fragmentation into smaller particles at spraying. When the solvent and the sprayed suspension are used excessively, the powder adheres to the walls of the spray chamber. A high value of the size X leads to additional jet fragmentation inside the nozzle, resulting in an increased number of smaller particles. According to Table 1, the maximum powder yield of 0...100 μ m is obtained under the following conditions: V = 380 ml of solvent /1 kg of powder; X = 2.0 mm; P = 1.32 atm. The study of the spraying air temperature effect on the quality of the sprayed powder showed that at temperatures of 363...523 K, the stability of the spraying process sharply decreases, and the process is interrupted in 1...2 minutes after the start due to the drying of the suspension in the nozzle feed channel. The binder (PVA) was distilled at a temperature of 573...773 K for half an hour, then the temperature was increased to the values of the subparticles sintering inside the conglomerates. An exothermic reaction of Al and Ni interaction with a large release of heat begins at the temperature of 903...923 K. The temperature of the crucible with the powder brie fl y rose to 1023...1273 K. To prevent sintering of conglomerates among themselves, they were diluted with a sintered powder of the same composition in an amount of 25 ... 35 %. After the solid-phase interaction, isothermal annealing was carried out at 1073 K for 30 min.