The oxidation and carbon transfer behaviour of Ni-27Cr-5Mo-5W based alloys in an impure helium atmosphere at high temperature

The corrosion behaviour of a series of Ni-27Cr-5Mo-5W alloys with various element additions in an impure helium atmosphere at 1273 K has been studied. Although the extent of oxidation was small, significant amounts of carbon transfer occurred. The carbon transfer behaviour was influenced by alloy composition with the effects of chromium and aluminium being particularly marked. The effect of Cr was interpreted by the carbon activity-oxygen potential equilibrium diagram for Cr and a Ni-Cr alloy and that of Al was interpreted by consideration of possible deterioration of surface scales due to the volume increase expected in the internal oxide zone where Al2O3 stringers precipitate. (author)