Abstract
A pulse oxidation experimental facility was developed to examine the oxide nucleation behavior at different temperatures under a controlled oxygen atmosphere. An electromagnetic induction heater, a sample holder, and a controlled oxygen atmosphere are the key components of this facility. This experimental facility can also be used up to 1200°C and Po2 levels from 1.3 × 10-5 to 0.1Pa under isothermal conditions for times as short as 10s. The efficacy of the method was illustrated by a study of the oxidation behavior of Ni-30 wt. % Cr at 600°C for 45s at Po2 of 1.3 × 10-2Pa where the influence of grain orientation on oxidation behavior was highlighted by studying the nucleation rate on grains of known orientation. By using a single grain-orientation-mapped sample, pairs of grains each of known crystallographic orientation can be selected to be subjected to identical conditions. For example, new oxidation behavior was discovered where on a (111) oriented grain, corundum islands form with a nucleation density of 2.9 × 1011 islands/m2 and exhibited inward growth, whereas rock salt oxide islands formed on (100) grains at a density of 7 × 1012 islands/m2 and exhibited outward growth. The corundum oxide islands are in the range of 50-300nm, whereas rock salt oxide islands are in the range of 50-600nm and are well separated. The pulse oxidation facility with accurately controlled temperature and oxidation environment enables a new domain of study for the initial oxidation on bulk samples with a native oxide that represents realistic exposure conditions.
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