Effect of silicon on the formation of protective scale on Fe-10Ni-10Cr-4Al alloy pre-oxidized at low oxygen pressure

The effects of Si on the high temperature oxidation of Fe-10Ni-10Cr-4Al-xSi (x = 0, 1, 2, 3 wt%) austenitic alloys were examined at 1000 & DEG;C by pre-oxidation under low oxygen pressure. The results showed that when Fe-10Ni-10Cr-4Al-xSi alloys were oxidized at 1000 & DEG;C under oxygen pressure of 10-20 atm for 5 h, without Si element, the oxidation products formed were continuous outer M2O3 (M: Al and Cr) scale and a small amount of inner dendritic Al2O3. When Si was added, inner Al2O3 increased obviously and SiO2 formed between M2O3 and Al2O3, and Cr2O3 decreased and Al2O3 increased in the external M2O3 oxide layer. When 3 wt% Si was added, the oxide was only external Al2O3 scale. The oxidation resistance of the alloys was improved with an increase in the Si content. Only external Al2O3 scale on Fe-10Ni-10Cr-4Al-2Si alloy pre-oxidized at 1000 & DEG;C for 5 h under low oxygen pressure of 10-30 atm. The addition of Si promoted the diffusion coefficient and activity of Al, increased the driving force of Al2O3 formation and reduced the critical concentration for the transition from internal oxidation to external oxidation of Al2O3.