In order to explore the structural transformation of superalloys for gas turbines in the service environment and their effects on the oxidation performance of the alloys

the microstructure of the Mar-M247 nickelbased superalloy after long-term aging at 900 ℃ was characterized by scanning electron microscope and energy dispersive spectroscopy

and the oxidation performances were investigated after different aging time.The results reveal that surface oxide phases of the alloy is changed fast and the oxide structure is complex at the initial stage of aging 1 000 h.The Al

2

O

3

film is incomplete with thickness increasing obviously.As the oxidation time increases

a large number of holes and discontinuous island-like WO

2

are generated in the W-rich film

Leading to the peeling of the inner Al

2

O

3

film interface.The structure of outer oxidation film is simplified and the inner Al

2

O

3

film grows and becomes uniform.After aging for 8 000 h

the thickness of whole oxidation film and rangeability of the inner Al

2

O

3

film are decreased significantly.The whole oxidation structure tends to be stable.Due to the thickening of the protective Al

2

O

3

film and homogeneous continuous structure

the oxidation performance of MarM247 superalloy is optimized.