The Halogen Effect for Ni-Base Superalloys – A Thermodynamic Study
A new method for the oxidation protection of Ni-base superalloys with relatively low Al-content is proposed. By using the halogen effect the Al activity on the surface can be increased. Thus, the formation of a pure protective alumina scale becomes possible. The alloys IN738 and IN939 are considered in the present paper. Thermodynamic calculations for fluorine and chlorine predict the existence of the halogen effect for both alloys at temperatures between 900°C and 1200°C. The results also predict a change of the oxidation mechanism from internal alumina formation to external oxidation.
T. Chandra, N. Wanderka, W. Reimers , M. Ionescu
H. E. Zschau et al., "The Halogen Effect for Ni-Base Superalloys – A Thermodynamic Study", Materials Science Forum, Vols. 638-642, pp. 2375-2380, 2010