The oxidation of cobalt based alloys containing partially dissolved particles of Si3N4 at 1000°C |
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Authors: | G P Wagner G Simkovich |
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Affiliation: | (1) Metallurgy Program, The Pennsylvania State University, University Park, PA |
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Abstract: | The isothermal oxidation behavior of Co-Cr and Co-Cr-Si alloys with and without 5, 10, and 15 vol.% dispersions of unstable Si3N4 particles was studied in 1 atm of oxygen at 1000°C. The dispersion of Si3N4 which dissolved partially in the matrix, greatly reduced the oxidation rate of Co-Cr alloys. Silicon nitride was found to promote the formation of continuous Cr2O3 layers at low chromium concentrations. Furthermore, the unstable Si3N4 was more effective in reducing the oxidation rate than an alloy containing an equivalent amount of silicon. Additions of 15vol.% Si3N4 tended to increase the oxidation rate by forming nonprotective SiO2 particles which disrupted the protective Cr2O3 scale. The mechanism of oxidation was altered due to the Si3N4 additions. Marker experiments indicated oxygen diffusion inward via the CoO lattice, rather than a combination of both oxygen and metal ion motion which is encountered in Co-Cr alloys. |
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Keywords: | high temperature oxidation dispersion of Si3N4 cobalt base alloys Cr2O3 and SiO2 |
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