Al-Cu-Cr quasicrystalline coatings prepared by low power plasma spraying

Abstract Al–Cu–Cr quasicrystalline coatings were prepared by low power plasma spraying with axially-fed powder systerm. The Al 65 Cu 20 Cr 15 powders were deposited on AISI 1045 steel substrate at the power ranged from 4.0 to 6.0 kW. The effects of H 2 /Ar flow ratio on the phase composition, microstructure and microhardness properties of the as-sprayed coatings were investigated. The XRD results showed that the original powders and as-sprayed coatings contained a predominant icosahedral quasicrystalline phase I -Al 65 Cu 24 Cr 11 and three minor crystalline phases, including a body-centered cubic α -Al 69 Cu 18 Cr 13 , a monoclinic θ -Al 13 Cr 2 (i.e. Al 83 Cu 4 Cr 13 ) and a hexagonal e -Al 2 Cu 3 . A qualitative analysis on the XRD patterns indicated that the volume fraction of any crystalline phase ( α , e or θ ) in the coatings increased, while the quasicrystalline I -phase decreased with increasing hydrogen content in the plasma gas. As H 2 /Ar flow ratio increased from 4.8% to 18.8%, the coating hardness increased whilst its porosity decreased, and they reached the maximum (4.98 Gpa) and the minimum (8%) respectively. However, with increasing H 2 content further, the hardness of the coating slightly decreased and its porosity increased because of the excessive vaporization of aluminum at higher plasma energy.