Oxidation or Nitridation Behavior of Pure Chromium and Chromium Alloys Containing 10 mass%Ni or Fe in Atmospheric Heating
The oxidation or nitridation behavior of pure chromium and chromium alloys containing 10 mass%Ni or 10 mass%Fe in atmospheric heating was investigated in the temperature range of 1073 to 1373 K. The formation behavior of the outer oxide phase of Cr2O3 and its growth kinetics in both chromium alloys was very similar to that of pure chromium. The nitride layer with the Cr2N phase was formed beneath the oxide phase at temperatures above 1273 K in pure chromium. Marked internal nitridation with the formation of the Cr2N phase was observed in the Cr-10 mass%Fe alloy, while the formation of Cr2N was negligible in the Cr-10 mass%Ni alloy. Neither Ni nor Fe were detected inside the Cr2O3 phase, and was enriched in the subsurface layer between the oxide layer and the base alloy in a respective alloy. The Ni-enriched layer in Cr-10 mass%Ni alloy had a relatively narrow width, but a very high concentration of Ni compared with the Fe-enriched layer formed in the Cr-10 mass%Fe alloy. [doi:10.2320/matertrans.47.2540]
On the Oxidation and Nitridation of Chromium at 1300 °C
Chromium can be a candidate of interest as a base component for refractory alloys for high temperature applications. Few data are available about oxidation kinetic of chromium in air for temperature as high as 1300 °C. Moreover, rare papers take the nitridation of chromium into account in the description of the oxidation process or in the calculation of the kinetic constants. In the present study, global methods like thermogravimetry were linked to thickness measurements and microstructural characterisation to evaluate oxidation and nitridation contribution to weight gain. High stress levels were induced in the oxide layer during its formation. The kinetic constant associated to the nitridation, at this temperature, was one order of magnitude higher than the parabolic oxidation constant. Experiments demonstrated that the presence of nitrogen in the substrate is always a precursor to breakdown of the oxide layer and does not result from diffusion through the Cr2O3 layer.
The oxidation of Cr and an Fe-50% Cr alloy
Abstract A study of the oxidation of Cr and an Fe-50%Cr alloy has been carried out using micro-gravimetry, microscopy and electron probe microanalysis. High purity oxygen was used together with isothermal conditions in the range 650 to 1000 °C for periods of up to 1200h. The importance of the technique of commencing an oxidation experiment has been considered together with the significance of the extensive blistering of the scale which took place. In the early stages a uniform scale forms, probably by a cation vacancy diffusion mechanism. The Cr 2 O 3 scale on the alloy contained Fe in substitutional solid solution, the concentration decreasing with duration of oxidation. After some 2–5h oxidation at all temperatures the oxidation rate decreases below that indicated by the initial parabola and extensive blistering and occasional cracking of the scale are observed. Factors leading to the inferred compressive oxide stress, such as anion vacancy diffusion, are considered.