High‐temperature corrosion of NiCrAl alloy in oxygen‐chlorine mixtures

Abstract

AbstractIn order to decrease the attack of chlorine in O2Cl2N2 mixtures to NiCr alloys at high temperatures, the corrosion of a preoxidized Ni 20 Cr 4 Al alloy was investigated in N2O2 mixtures with 5 to 150 torr O2 and 20 torr Cl2 at 800°. For the generation of a protective layer of Al2O3 both the untreated and Al evaporated alloy sample was preoxidized in a H220 torr H2O atmosphere at 900° C. As was found, the catastrophic corrosion by Cl2 in a N2Cl2 gas mixture with 20 torr Cl2 could not be prevented by an Al2O3 layer. However, in the simultaneous presence of an oxygen content in the corroding gas mixture not lower than 10 torr, the attack of chlorine could be drastically decreased. The presence of 50 torr Cl2 postulates an oxygen pressure which is technically unrealistic. Since the formed oxide layer spalled off during the cooling period, the Ni 20 Cr 4 Al alloy cannot be used as material for cyclic oxidation. To what extent ThO2 particles dispersed in the alloy can prevent a spalling effect of the oxid film is at present an open question.