OXIDATION OF MULTICOMPONENT 2-PHASE ALLOYS

The high-temperature corrosion behavior of two-phase alloys presents a number of differences compared to that of single-phase alloys. These differences are mainly a consequence of the limitations that the prese nce of two phases impose on the diffusion of the alloy components. In this review, it is shown that the exclusive scale formation of the mor e stable, slow-growing oxide is move difficult on a two-phase alloy, r equiring a higher concentration of the more reactive alloy component t han for a corresponding single-phase alloy. The main types of corrosio n behavior for binary two-phase alloys are also considered, showing th at if diffusion in the alloy is slow the scale structure will closely reflect that of the starting material. When diffusion in the alloy is not negligible, the scale structure becomes similar to what forms on s ingle-phase alloys. The oxidation of two-phase ternary alloys is shown to be even more complex than the two-phase binary alloys. The princip al added complexity compared to the binary alloys is that diffusion in the ternary alloys may also occur in the presence of two metal phases , as a result of an extra degree of freedom in the ternary system. The oxidation behavior of two-phase ternary alloys is discussed in the co ntext of a number of recent experimental results.