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

Al-Cu-Cr quasicrystalline coatings were prepared by low power plasma spraying with axially-fed powder systerm. The Al65Cu20Cr15 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 Al65Cu24Cr11 and three minor crystalline phases, including a body-centered cubic alpha-Al69Cu18Cr13, a monoclinic theta-Al69Cu18Cr13 (i.e. Al83Cu4Cr13) and a hexagonal epsilon-Al2Cu3. A qualitative analysis on the XRD patterns indicated that the volume fraction of any crystalline phase (alpha, epsilon or theta) in the coatings increased, while the quasicrystalline I-phase decreased with increasing hydrogen content in the plasma gas. As H2JAr 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. Crown Copyright (c) 2008 Published by Elsevier B.V. All rights reserved.