RELATIONS BETWEEN SELECTIVE OXIDATION AND DIFFUSIONAL PHENOMENA IN FE-NI-CR TERNARY ALLOYS - EFFECT OF YTTRIUM ADDITIONS

For Fe Ni//4//5 Cr//2//5 alloys, the minimum chromium content necessary to form a continuous Cr//2O//3 layer is 15 at. %. For chromium contents below 15 at. %, oxidation kinetics is controlled by diffusion of alloy elements. Low additions of yttrium decrease the diffusivity of chromium and nickel yttrium may increase the value of the limit chromium content necessary to form a protective Cr//2O//3 layer and decrease the values of oxidation parabolic constants, this effect can be responsible for improvement of scale adherence.