AbstractTo investigate phase evolution of β-(Ni,Pt)Al/γ-(Ni3Al) in thermal barrier coating bond coat systems, specimens were subjected to 1200°C cyclic and isothermal heating. By removing the thermally grown oxide (TGO) after every 10 hours of heating, aluminum (Al) depletion from the bond coat was accelerated. Non-accelerated and accelerated Al-depletion samples were examined with scanning electron microscopy after every 10 hours of cyclic and isothermal heating. Observations from after the first 10 hours of thermal exposure show distinct microstructural differences. After 50 hours of heating, cyclic accelerated Al-depletion samples show more distinct grain boundaries and a higher proportion of-(Ni3Al) phase than isothermalaccelerated Al-depletion samples. Through instrumented micro-indentation, trends in elastic modulus were determined for isothermal and cyclic accelerated Al-depletion specimens.