Oxidation behavior of Ni-20W and Ni-20W-20Cr heterogeneous seeds under different vacuum conditions

Since the oxide film on the surface of the heterogeneous seeds would usually cause the failure of the orientation control, the oxidation behavior of Ni-20 W and Ni-20 W-20Cr (wt. %) heterogeneous seeds under the different pressure was investigated in this work. The results showed that the thickness of the oxide layer thickness of the Ni-20 W heterogeneous seed in the atmospheric environment (1250 °C for 1 h) was about 133.1 μm, while that of the Ni-20 W-20Cr heterogeneous seed was near the 95.1 μm. The Cr element had greatly inhibited the penetration of the O₂, and reduced the thickness of the oxides. However, the experiments conducted under low-vacuum conditions demonstrated that the surface of the Ni-20 W heterogeneous seed exhibited no significant oxides, while a layer of Cr₂O₃ was observed on the surface of the Ni-20 W-20Cr heterogeneous seed. Therefore, the oxidation thermodynamics for different elements was further calculated, and a different controlling factor of the oxidation under different environments was proposed.