Corrosion of 15 Cr—35 Ni—50 Fe Doped with Niobium, Titanium, or Molybdenum in High Temperature Reactor Helium

A ternary 15 Cr—35 Ni—50 Fe alloy and three versions of the same base doped with niobium, titanium, or molybdenum were exposed in the temperature range from 700 to 1000°C to simulated high temperature reactor helium in two corrosion experiments that differed mainly in moisture content at the High Temperature Materials Programme in Wimborne, United Kingdom. The water level in Run B was about ten times higher than in the dryer Run A. As expected, oxides that formed during exposure in the oxidizing atmosphere of Run B were generally thicker. Thickness and structural appearance of the oxides varied between the four alloys in both runs. In electron probe microanalysis studies the oxides were found to be virtually pure chromium oxides containing no significant amounts of the additives. It is inferred that variations in thickness and structural appearance of the oxides are caused by differences in kinetics of chromium oxidation, depending on the additives.