材料期刊网

The sulfidation behavior of three two-phase Fe-Cu alloys containing 25, 50, and 75 wt.% copper has been investigated in H-2-H2S mixtures at 500-700 degrees C under gas-phase sulfur pressures, which is significantly above those for the dissociation of both FeS and Cu2S. In all cases, the three alloys sulfidized more slowly than both pure metals under the same conditions. At all temperatures, Fe-25Cu showed the slowest growth rates, whereas Fe-50Cu sulfidized more rapidly than the other two alloys. However, the kinetics curves for the three alloys tended to over lap, particularly at the higher temperatures. The scales were complex and contained an outer layer composed of a mixture of two different Cu-Fe double sulfides, Cu5FeS4 and CuFeS2, plus an inner zone containing a mixture of metallic iron with the double sulfide Cu5FeS4 formed by complete sulfidation of the copper-rich phase anti partial sulfidation of the iron-rick phase. This region also contained large voids, possibly because of outward diffusion of metal cations, whereas the iron-rich islands were mainly unattacked. The depth of intrenal attack increased with increasing temperature and/or iron content. Finally, particles of almost pure copper metal, probably formed during cooling from the reaction temperature,,were present at the scale-subscale interface, as inclusions in the scale and as whiskers producing out of the external scale surface.