Effects of Particle Size on the Microstructure and Mechanical Properties of HVAF-Sprayed Al-Based Quasicrystalline Coatings

To obtain dense Al-based quasicrystalline (QC) coatings with high content of quasicrystal phase, the QCs were deposited by the high-velocity air fuel spray process with different feedstock powder sizes. The phase composition, microstructure, chemical composition, tribological, and mechanical properties of the coatings were analyzed using x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, a pin-on-disk wear tester, and a nanohardness tester. The results indicated that smaller particle sizes produced denser structures with lower coating porosities, while the coarser powder helped maintain the desired quasicrystalline phase. In addition, the coatings sprayed with coarser powders exhibited a lower sensitivity to the sliding velocity due to a stronger bonding strength between the splats and a lower oxidation degree. The coating first exhibited abrasive wear coupled with oxidative wear, which was then converted to delamination, abrasive wear, and intensified oxidative wear.