Influence of Air Heat Treatment on Bonding Strength and Microstructure of Al2O3-13wt%TiO2/NiCrAl Coating

Owing to typical weaknesses of Al 2 O 3 -13wt%TiO 2 /NiCrAl coating (AT13), appropriate air heat treatment is an effective method in improving the bonding strength and microstructure of AT13. AT13 was air heat-treated with varying holding times and cooling methods. The aims are not only to ascertain the changes of the bonding strength and micro-structure of AT13 under various conditions, but also to understand the influence of holding time and cooling method on the bonding strength and microstructure of the coating. The experimental results showed that the best bonding strength and lowest porosity of AT13 were obtained using proper heat treatment of heating up to 560°C for 6 h along with two-step cooling. The two-step cooling is better than normal furnace cooling in improving properties of the coating, which is attributed to the densification of AT13 and release of residual stress.