Oxidation of Cr-Ni coatings on diamond

Autor: I. M. Shalya, V. G. Chuprina, V. P. Umanskii
Rok vydání: 1993
Předmět:
Zdroj: Powder Metallurgy and Metal Ceramics. 32:613-617
ISSN: 1573-9066
1068-1302
DOI: 10.1007/bf00559946
Popis: The kinetics of the oxidation of chromium and chromium-nickel coated diamond powders in air at 750 and 850°C was studied by means of interrupted weighing. The coatings and metallized powders were subjected to x-ray phase analysis. Decrease of the powder mass confirms that permeation of the mass with volatile oxides predominates over the increment due to the weight of the absorbed oxygen in the oxides NiO and Cr2O3. The weight loss is caused by the burning away of both the coating (oxidation of chromium and its carbides to CrO with formation of CO and CO2) and the diamond. Carbon from the diamond is also removed with CO and CO2 as a result of successive reduction of chromium oxide by carbon, which diffuses to the oxidized layers, and further reduction of the carbides by the same mechanism. The higher the oxidation temperature and the thinner the coating, the greater the contribution of these reactions is to the processes responsible for the decrease in weight of the metallized diamonds. It is also encouraged by diffusion of carbon to the scale formed and by simultaneous diffusion of oxygen to the coating. The reactions of primary oxidation of chromium contained in the nickel solid solution, reduction of nickel by carbon and chromium, and dissolution of chromium in the reduced nickel contribute significantly to the oxidation of chromium-nickel coatings.
Databáze: OpenAIRE
Externí odkaz: