  The brittleness of an aluminide diffusion coating protecting a Ren\'e 125
Ni-based polycrystalline superalloy was investigated over a wide range of
temperatures in its as-received and thermally aged form. Isothermal and thermal
cycled aging were performed on the coated system at a maximum temperature of
1100 {\deg}C. Microstructure evolutions and damage initiation within the
coating were characterized. Interrupted tensile tests and thermomechanical
fatigue tests were conducted to document critical stress-strain conditions
leading to the coating cracking and lifetime for the case of thermo-mechanical
fatigue loading. Advanced digital image correlation and acoustic emission
techniques were used to detect coating cracking. Isothermal oxidation or cyclic
oxidation led to improved strain-to-failure due to metallurgical evolutions and
also longer fatigue life under thermomechanical fatigue conditions.
