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 65Cu 20Cr 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 65Cu 24Cr 11 and three minor crystalline phases, including a body-centered cubic α-Al 69Cu 18Cr 13, a monoclinic θ-Al 13Cr 2 (i.e. Al 83Cu 4Cr 13) and a hexagonal ε-Al 2Cu 3. A qualitative analysis on the XRD patterns indicated that the volume fraction of any crystalline phase ( α, ε 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.