Study on Oxidation Behavior of Co-20Re-25Cr-7Al Alloy at Low Oxygen Pressure of 3.0×10^-5Pa

Abstract

In order to investigate whether adding a small amount of Al in a low oxygen pressure and high temperature environment has a synergistic effect ontheformationof aprotective Cr2O3oxidefilm on Co-Rebased hightemperature alloys，the isothermaloxidation behaviorofthe Co-20Re-25Cr-7Al alloy was studied under 3.0×10-5Pa O2at 1100～1 300 ℃for24h.Resultsshowed thattheoxidation kinetics curve of the alloy conformed to parabolic law quite well，with the value of oxidation activation energy of 242.3 kJ/mol.The oxidation film formed at 1 100～1 300 ℃were very similar and mainly composed of continuous and dense Cr2O3 layer，covered by a small amount of CoO and CoCr2O4 spinelle.The protective Cr2O3 layer could prevent the evaporation of Re element of alloy in the form of ReO3during the oxidation process，and thus provided better protection for the Co-20Re-25Cr-7Al quaternary alloy，as compared with the corresponding Co-20Re-25Cr ternary alloy，thus providing better protection for the alloy.The addition of 7% Al was not enough to result in the selective external oxidation of Al in Co-20Re-25Cr-7Al alloy，thus forming an internal oxidation zone of Al below the outer oxidation film.However，the addition of Al promoted the formation of continuous and dense Cr2O3 layer，and improved the high temperature oxidation resistance of the alloy greatly.The addition of Al and low oxygen pressure showed a synergistic effect on the formation of a protective Cr2O3 layer.

Keywords

• co-20re-25cr-7al alloy|high temperature oxidation|low oxygen pressure|al effect