The effect of HVOF spraying parameters on the tribological properties of the Al 65 Cu 20 Fe 15 coatings

This study investigates the effect of oxygen pressure during high-velocity oxygen fuel (HVOF) spraying on the microstructure, phase evolution, and tribological performance of Al 65 Cu 20 Fe 15 quasi-crystalline coatings deposited on American Iron and Steel Institute (AISI) 321 stainless steel. Oxygen pressure was varied between 3.0, 3.5, and 4.0 bar while all other processing parameters were kept constant. Microstructural analysis shows that oxygen pressure significantly influences particle deformation, splat formation, and coating densification. An intermediate pressure of 3.5 bar produces a dense and homogeneous microstructure with reduced porosity and improved inter-splat cohesion. X-ray diffraction confirms the coexistence of quasi-crystalline and intermetallic phases, with the highest quasi-crystalline phase fraction obtained at 3.5 bar. Tribological tests under dry sliding conditions reveal a strong correlation between microstructure and frictional behavior. The coating deposited at 3.5 bar exhibits stable tribological performance with a coefficient of friction of 0.55–0.60 and the lowest wear rate. The 3.0 bar coating shows higher friction and wear due to insufficient particle heating and weak cohesion, while the 4.0 bar coating exhibits lower average friction (0.48–0.52) but unstable behavior and increased wear due to oxidation-induced brittleness. All coatings demonstrate significantly enhanced hardness (>750 HV) compared to the substrate, while adhesion strength is maximized at 3.5 bar. Overall, 3.5 bar is identified as the optimal oxygen pressure for producing Al 65 Cu 20 Fe 15 quasi-crystalline coatings with balanced wear resistance, structural integrity, and tribological stability.