Phase Assemblage of Al-Cu-Cr Quasicrystalline Coatings Sprayed by Low Power Plasma

Abstract

Abstract Al-Cu-Cr quasicrystalline (QC) coatings were deposited onto mild steel Q235A substrate by low power plasma spraying. The plasma torch was designed such that the powders can be injected axially (parallel to the axis of the plasma arc) into the region between the anode and cathode, and the carrier gases were transferred to the plasma flame, so the heating efficiency of the powders is greatly increased and the velocity of particles is much higher than an externally-fed powder system. The Al-Cu-Cr QC coatings were sprayed via this new technique at different plasma power (3~7kW) by controlling the secondary plasma gases (H2 and N2) flow or changing the arc current. The results show that, the original powder was mainly composed of a dominant icosahedral quasicrystalline phase I-Al65Cu24Cr11 and a minor monoclinic θ-Al13Cr2. However, besides these two phases, body-centered cubic α- Al69Cu18Cr13, the approximant to quasicrystal I-Al65Cu24Cr11, has been detected in as-sprayed coatings. On the other hand, peak intensity of QC phase I-Al65Cu24Cr11 decreased and that of crystalline phases (θ-Al13Cr2 or α-Al69Cu18Cr13) increased as the plasma power was increased.