Phase Transformation of High Velocity Air Fuel (HVAF)-Sprayed Al-Cu-Fe-Si Quasicrystalline Coating

Al-Cu-Fe-Si quasicrystalline coatings were prepared by high velocity air fuel spraying to study their phase transformation during the process. The feedstock powder and coating were phase characterized by scanning electron microscopy, X-ray diffractometry, differential scanning calorimetry, and transmission electron microscopy. Results show that Al(3)Cu(2)phase, a small amount of lambda-Al(13)Fe(4)phase, quasicrystalline phase (QC), amorphous phase, and beta-Al (Cu, Fe, Si) phase were present in the sprayed Al(50)Cu(20)Fe(15)Si(15)powder. For a typical flattened powder particle, the splat periphery was surrounded by a 1 mu m thick amorphous phase. The inside area of the splat was composed of the QC covered by the Al(3)Cu(2)and Si-rich beta-Al (Cu, Fe, Si) phases. Another kind of Cu- rich beta-Al (Cu, Fe, Si) phase can be found close to the amorphous area with a similar composition to the original beta-Al (Cu, Fe, Si) phase in the powder. Different phases were observed when the periphery and inside area of the splat were compared. This result was caused by the difference in the heating and cooling rates.