THE EFFECT OF THE PARTICLE SIZE FRACTION OF CR3C2-NICR POWDER ON THE STRUCTURE AND PROPERTIES OF COATINGS DEPOSITED BY THE HVOF METHOD

Abstract

Al-Cu-Fe quasicrystalline coatings were deposited onto AISI 321 stainless steel substrates using the high-velocity oxygen fuel (HVOF) spraying method at oxygen pressures of 3.0 and 3.5 bar. The effect of oxygen pressure on the phase composition, microstructure, porosity, corrosion behavior, and thermal stability of the coatings was investigated using X-ray diffraction (XRD), scanning electron microscopy combined with energy-dispersive spectroscopy (SEM/EDS), porosity analysis in ImageJ, electrochemical corrosion tests in a 3.5% NaCl solution, and simultaneous thermal analysis (TGA/DSC). XRD analysis revealed the formation of quasicrystalline intermetallic phases alongside phases of Al, Fe3Al13, FeAl, Fe3O4, CuFe2O4, Cu2O, and CuO. The coating deposited at a pressure of 3.5 bar exhibited the lowest porosity (5.37%), the most uniform microstructure, and the greatest residual coating thickness after corrosion testing. SEM and EDS analyses showed that corrosion predominantly initiated in pores, particle boundaries, and interphase boundaries, whereas the coating obtained at a pressure of 3.5 bar exhibited the most stable surface condition after exposure to a 3.5% NaCl solution. Thermal analysis showed that all coatings remained stable up to 900 °C. Sample (a) exhibited the lowest mass loss and the highest thermal stability, whereas sample (b) demonstrated the most favorable combination of structural integrity, phase order, coating density, corrosion resistance, and thermal stability. The results show that oxygen pressure is a critical parameter controlling the microstructure and functional properties of Al-Cu-Fe coatings deposited by the HVOF method, with 3.5 bar providing the most balanced set of properties.