ISSN:
1573-4889
Keywords:
oxidation
;
chromium coating
;
laser
;
oxygen diffusion
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The oxidation of a chromium PVD coating on pure iron by a continuous 5-kW CO2 laser beam in pure oxygen at 700°C for 20 min was compared with classical furnace oxidation. Laser oxidation induces faster oxidation kinetics, especially at the beginning of oxidation, without modifying the oxide nature (Cr2O3) and morphology. Oxygen-isotopic-exchange tests show that oxygen grain-boundary diffusion does not depend on the oxidation conditions, at least after 12 min oxidation. The effec of the laser treatment is discussed with respect to oxide nucleation, metastable-oxide formation, and oxide-formation-entropy evolution. The oxidation kinetics follow a parabolic law, and the oxide-growth mechanism was attributed to countercurrent oxygen and chromium diffusion along grain boundaries. Oxygen diffusion occurred by oxygen interstitials. The oxidation constant calculated from grain-boundary diffusion in the chromia scale is smaller than the experimental oxidation constant, suggesting the presence of particular short circuits (e.g., microcracks).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01047031
Permalink