Avaliação da relação oxigênio/combustível na microestrutura e propriedade de revestimentos depositados aspersão térmica de alta velocidade

Abstract

The main objective of this work is to study thermal spray coatings, varying the oxygen rate parameter during the fuel combustion process, on coatings made of 316L austenitic stainless steel, Hastelloy C276, and WC-17Co tungsten carbide. The highvelocity thermal spraying (HVOF) process aims to protect or modify the behavior of materials, such as for restoration and protection. The protection provided by the sprayed coating can have variations in material properties, such as porosity, hardness, coating thickness, toughness, and wear rate, according to variations in temperature and flame speed, temperature and particle speed, and oxidation rate. These parameters are altered according to the type of fuel, fuel state, and fuel and oxidizer injection rates. To evaluate the behavior of this parameter, thermal spraying is performed for each selected alloy, using liquid kerosene as fuel and with different oxygen fluxes, resulting in a coating with a stoichiometric oxygen/fuel ratio less than (carburizing flame), equal to (neutral flame), or greater than one (oxidizing flame). The influence of the oxygen rate on these samples is evaluated based on the velocities and temperatures of the particles during spraying, the stresses generated, the porosity of each coating, the microhardness, the coating thickness, and the rate of wear due to cavitation and erosion. In this work, it was observed that the oxidizing regime tends to produce particles with higher temperatures and lower velocities. The combustion regime generates higher particle velocity and a lower temperature, while preserving the unique characteristics of the material being coated. The coatings in the oxidizing regime showed less porous results. Resistance to cavitation and resistance to erosion depend on a combination of properties, such as toughness, hardness, and porosity, with samples from the oxidizing regime obtaining better results due to dense coatings. However, in general, the stoichiometric oxygen/fuel ratio does not follow a standard for all materials, it generates some particularity for each material.