Microstructural characterization of high velocity oxy fuel coatings of Inconel 718 and iron aluminides

摘要

Thermal spray guns are used today to deposit metallic powders as homogeneous and durable coatings with low porosity onto metals. The objective is to improve their wear resistance and their corrosion resistance in order to withstand conditions such as abrasion and erosion. This can improve the life of turbines, generators and such devices in environments found in ultra-supercritical coal-fired (AUSC) boilers, steam turbines and gas turbines (Mohammed & Cabrera, 2014). Industries like manufacturing, automobile and especially in the sustainable energy area, have used this technique to improve component characteristics, extend product life, increase performance as well as reduce production and maintenance costs. To create the momentum necessary for the kinetic energy, High Velocity Oxy-Fuel guns (HVOF) use a converging-diverging nozzle, as the ones found in rocket engines, to accelerate the gas stream, with a lean mixture of methane-oxygen combustion, to propel the molten particles and create a coating onto the flat surface of an objective material. The HVOF technique has pike interest due to its lower production costs due to the fact that it does not require vacuum conditions (Mohammed & Cabrera, 2014). While the gun is in operation, particles of one powder metal, Inconel 718 (with a diameter that normally ranges from 5 ?m to 8 ?m) are injected into the flame and melt. The coating hits the surface of the substrate, carbon steel, and deposits there. With parameters such as different Mach numbers (the velocity at which the melted particles travel) and the distance that the substrate is from the barrel section, different coatings are to be evaluated to compare their properties and determine if they would sustain harsh environments. The substrates with the coatings will be analyze with a Nano Indenter where the tensile and compressive strength, there are to be tested at a three different temperatures 600 C, 700 C and 900C, which would then be compared to the un-oxidized sample to see the differences and determine if there was an improvement. Additionally, test with X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) will be performed to analyze the coating's microstructure at a nanometer scale and evaluate the phase distribution, grain size and shape along with an evaluation of the uniformity of the coating (porosity, surface roughness and segregation). Finally, the results will be compared to literature from previous investigations in order to validate the study, examine their methods and compare their findings.