Forming and Transforming of by-Product Phases in Reactive Flame Sprayed Al<sub>2</sub>O<sub>3</sub>-Based Coatings

Abstract

The multiphase coatings with major phases Al2O3-AlxCuy were prepared by the reactive flame spray technology. The melting and reactive behavior of the Al-CuO agglomerated particles and the forming process of the coatings were studied by means of water-quenching experiments and the methods of XRD and SEM. It was shown that during the spray distance between 60 and 150 millimeters, CuO in the agglomerated particles was heated to decompose into Cu2O, Cu and O2. During the flying course, a little of Al reacted with Cu2O and produced Al2O3 and Cu. The reduced Cu mutually dissolved with Al and formed liquid Al-Cu alloy. After the spray particles bumped into the substrate, Cu2O reacted with Al richly, then lots of Al2O3 was produced and Cu was reduced at the same time. These products were wallowed up by the liquid Al-Cu alloy soon. When the temperature of the system dropped quickly, the structure transforming process began. The intermetallics of Cu9Al4 and Al2Cu3 were deposited from the liquid Al-Cu alloy via complicated eutectic reaction and eutectoid reaction.