2007 Volume 47 Issue 9 Pages 1245-1254
This study investigates effects of silicon on copper- and nickel-rich phases during the oxidation of iron-based alloys containing 0.3 wt% copper and 0.3 wt% copper +0.15 wt% nickel in addition to steel samples containing various amounts of copper (0.17–0.41 wt%), nickel (0.03–0.13 wt%), and silicon (0.03–0.12 wt%). Samples were exposed to air at 1 150°C for 60, 300, and 600 s. A low-carbon steel sample (0.02 wt% silicon) without copper and nickel was subjected to the same conditions for comparison.
The oxidation rates of copper- and nickel-containing steels decreased with time and were consistently lower than the rate of the residual-free low-carbon steel. An internal oxide layer was observed only in the copper- and nickel-containing steels. The number of internal oxides in this layer increased with oxidation time and larger internal oxides in this layer were characterized to be rich in iron and silicon. Compared to the iron–copper–nickel alloy, steels containing copper, nickel, and silicon, had more copper-, nickel-rich material found as particles entrapped in the oxide.
It is proposed that the population of internal silica particles increases due to increasing oxygen content near the oxide/metal interface. The rise in oxygen content results from increased oxygen solubility caused by copper and nickel enrichment. These internal oxides decrease oxidation rate and assist occlusion. An increase by a factor of 10 in amount of occluded material was measured in material containing copper, nickel and silicon compared to copper and nickel.