Oxide properties of deformed Alloy 690TT in caustic solution at high temperature

•The oxide film included surface oxide layer formed by precipitation and the inner oxide layer formed by diffusion.•The surface oxide layer was a bi-layer with semi-coherent Ni-rich phases and Fe-rich phase.•The inner oxide layer exhibited a tri-layered structure with various oxides.•Preferential oxidation channels were formed along GB & slip band underneath oxide film.