Mechanism of high temperature oxidation of laser surface engineered TiC/Al alloy 'composite' coating on 6061 aluminium alloy

Structural, morphological, and kinetic investigations into the oxidation behaviour of a laser surface engineered TiC/Al alloy 'composite' coating on 6061 aluminium alloy are discussed in the present work. Specimens of 6061 alloy coated with TiC were oxidised at 473, 673, and 873 K in air for 50 h to study the effects of long duration exposure on the coating. Severe oxidation of the coating was observed above 673 K and delamination/separation of the coating occurred in the specimen exposed to 873 K. The oxidation kinetics were studied by thermogravimetric analysis (TGA) of pure TiC (coating material), 6061 alloy (substrate material), and the TiC/6061 aluminium alloy 'composite' coating in the temperature range 473-873 K. Oxidation and oxidation rate within the lower temperature range (473-573 K) were comparable for both TiC and 6061 alloy, whereas both oxidation and oxidation rate were several times greater for TiC compared with 6061 alloy above 573 K, which illustrates accordingly two different oxidation behaviours below and above 573 K for the 'composite' coating TiC/6061. These effects were further demonstrated for different TiC contents in the TiC/6061 'composite' coating by preparing specimens with various precursor thicknesses.