Oxidation property of powder metallurgy EP741NP Ni based superalloy at elevated temperatures

摘要

The oxidation property of powder metallurgy (PM) EP741NP Ni based superalloy in the temperature range of 700-1100°C is investigated by isothermal oxidation test, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Results show that oxidation kinetics follows a square power law as the time extends. Oxidation layers are composed of Cr_2O_3 and TiO_2 as well as a small amount of NiAl_2O_4, NiCo_2O_4 and NiCr_2O_4. Surface morphologies exhibit that spallation starts to occur at 900°C and becomes severe at 1000 and 1100°C. Cross-sectional morphologies and elemental distributions indicate that the oxidation layer consists of Cr and Ti rich oxide layers. Oxidation kinetics and layer thicknesses confirm that the oxidation activation energy is 164.87 kJ mol~(-1) and the oxidation process is controlled by diffusions of oxygen, Cr and Ti. A diffusion controlled mechanism is confirmed to understand the oxidation property of PM EP741NP superalloy at elevated temperatures.