Influence of temperature and hot corrosion on the micro–nanomechanical behavior of protective mullite EBCs

• Mullite coatings with different Al2O3:SiO2 ratios have been deposited by CVD.
• Thermal treatments, thermal shock and hot corrosion have been performed.
• Mechanical properties have been evaluated by nanoindentation and nanoscratch.
• Coatings retrain their structural integrity after thermal attack.

Materials for components installed in the hot section of gas turbines must endure highly aggressive conditions, such as elevated temperatures and corrosive environments. Under these scenarios, CVD mullite coatings enriched in alumina in the outer surface have demonstrated excellent thermal stability and protection to SiC against corrosion and recession. It is essential that, in addition to the excellent protective behavior exhibited by Al-rich mullite coatings, their structural integrity and mechanical properties can be retained after their exposure to such aggressive conditions. This investigation is devoted to the study of the effect of temperature and hot-corrosion on the main micro–nanomechanical properties and performance of mullite-based EBCs. Nanoindentation was conducted to determine coatings' hardness, stiffness and fracture toughness whereas nanoscratch tests allowed evaluating their intrinsic structural integrity. Temperature and corrosion were found to have a minor effect on the mechanical behavior of the studied coatings. Hardness and Young's modulus remained comparable after thermal treatments, and scratch tests show similar damage features. From these results it can be concluded that mullite-based coatings present a satisfactory structural integrity and reliability to be used as environmental barrier coatings for hot environments.