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An indentation method is used to study the variations in Young's modulus, hardness and fracture toughness of air plasma‐sprayed thermal barrier coatings at a high temperature. The coatings were exposed to 1100°C during 1700 h. A sudden increase in Young's modulus for the first 600 h was observed, while the hardness increased after 800 h as a consequence of sintering. Conversely, there was a reduction of 25% in fracture toughness after 1700 h, evidencing the thermal barrier coating degradation. The evolution of these mechanical properties was correlated with microstructural changes. After 1700 h, the thermally grown oxide thickness reached 6.8 μm, the volumetric percentage of porosity was reduced from 6.8% to 4.7% and the amount of monoclinic phase increased to 23.4 wt%. These characteristics are closely related to the stress distribution in the top coat, which promotes cracks nucleation and propagation, compromising the coating durability.

In this work, the effect of flame spraying parameters on physical, structural and microstructural characteristics of Al 2 O 3-13 wt.% TiO 2 (AT-13) coatings were studied. NiCrAl and AT-13 feedstock powders were used for spraying a bond coat (BC) and a top coat (TC), respectively, onto a 7075 aluminum alloy substrate. The effect of acetylene-to-oxygen ratio and the spraying distance on surface roughness, crystalline phases, porosity and thickness of top coat were analyzed. The results showed that for the evaluated spraying conditions, the volumetric oxy-fuel ratio had significant effects on roughness, porosity and crystalline phases of the coating. On the other hand, the spraying distance affected the thickness of the coating and did not influence the formation of Al 2 TiO 5 phase; no significant effect of spraying distance on roughness was observed. The results showed that an acetylene: oxygen volumetric ratio of 1:2.5 is preferable to obtain higher melting of the ceramic powders and therefore a denser coating with major content of γ-Al 2 O 3 crystalline phase.