Oxidation Kinetics of Chromium Carbide Coating Produced on AISI 1040 Steel by Thermo-Reactive Deposition Method During High Temperature in Air

摘要

Oxidation of chromium carbide coating formed on AISI 1040 steel deposited by thermoreactive deposition method (TRD) has been realized by two stepped reactions. In the initial part of the reactions in the oxidation process, carbon atoms combined with chromium on the outer part of the coating layer react with the oxygen in air, effectively up to 120 min. After that, the chromium atoms react with oxygen in the air and produce Cr_2O_3 phase on the coating layer. The higher the temperature and the longer the treatment time, the more the Cr_2O_3 phases became. The kinetic study was realized for the reactions of carbon and chromium with oxygen, individually. The kinetic study of oxidation was calculated by weight changing of the coated samples at the temperatures of 973 K, 1073 K and 1273 K up to 720 min. We established that the chromium carbide coated steel are characterized by an insignificant increase in the mass in the oxidation period up to 3.5 h, after which the degree of oxidation increases somewhat. The nature of oxidation kinetics for chromium carbide coated steel varies from some mass degrease in the initial period (≈ 2 h) in connection with the formation of CO and CO_2 to later mass increase with in connection with the formation of Cr_2O_3 layer. The oxidation resistance of chromium carbide coated steel decrease with an increase in oxidation temperature. The growth rate constant of oxidation of chromium carbide coated steel ranged from 5.13×10~(-13) to -9.617×10~(-11) g~4·cm~(-2)s~(-1) in the initial period of oxidation (up to 120 min), while it ranged from 3,163×10~(-13) to 2.188×10~(-10) g~4·cm~(-2)s~(-1) in the second period of oxidation test (over 120 min). The activation energies of oxidation of the chromium carbide coated steel are 185 kJ/mol for the initial period and 215 kJ/mol for the second period.