Mechanism of the Oxidation of the Fe-C-Si-Al-Zr Alloys

Mechanism of the oxidation of the thermal-resistant Fe-C-Si-Al-Zr alloys was investigated at high temperatures. For the analysis three series samples: L1, L2 and L3, had been annealed at 1100 °C, were cast. After annealing the samples were investigated on the oxide thickness increase. They were observed and analysed by optical and electron microscopes. In case of the small zirconium content in the L1 sample, the graphite lamellae and only a significant amount of zirconium carbide in the ferrite matrix have been observed. At higher zirconium content (the L2 and L3 samples) graphite lamellae and particles of ZrC have been observed. During annealing an oxidation of graphite and ZrC took place. The oxidation of ZrC into ZrO2 is direct and progressive. Evolving CO gas formed the pores around ZrO2. Under sufficient amount of the dissolved oxygen the oxidation of aluminium was taking place too. Al2O3 was precipitating in the CO-ferrite interface filling up the formed pores. Finally the interaction between ZrO2 and Al2O3 were taking place and formation the compound of ZrO2·Al2O3 retarded further oxidation.
Ispitivao se mehanizam oksidacije termički otpornih legura Fe-C-Si-Al-Zr na visokim temperaturama. Za analizu su izlivena tri serijska uzorka L1, L2 i L3, i žarena na 1100 °C. Nakon žarenja uzoraka ispitivana je debljina oksidnog sloja. Promatrani su i analizirani optičkim i elektronskim mikroskopom. Kad je količina cirkonija bila mala u uzorku L1 uočene su grafitne lamele i čestice ZrC. Tijekom žarenja došlo je do oksidacije grafita i ZrC. Oksidacija ZrC u ZrO2 je vanjska i progresivna. Razvija se plin CO, koji oko ZrO2 formira pore. Kad je količina rastopljenog kisika postala dovoljno velika došlo je također do oksidacije aluminija. Al2O3 se istaložio u CO-feritnom međuprostoru i popunio postojeće pore. Konačno je došlo do interakcije između ZrO2 i Al2O3 te se stvorio spoj ZrO2·Al2O3 koji je usporio daljnju oksidaciju.