Effect of Si on High Temperature Oxidation Characteristics of Laser Cladding 625 Alloy

Abstract:

The high temperature oxidation behavior of 625 alloy cladding layer with different Si contents was studied by cyclic oxidation method after 144 h oxidation at 700, 800 and 900 °C. The oxide phase was analyzed by XRD. The surface and cross section morphology, elemental composition and oxide film thickness were studied by SEM/EDS. The results show that the oxidation kinetics of the samples at different temperatures keep a parabolic law, and the oxidation mass gain increases gradually with the increase of temperature. The oxidation film of 0wt% Si 625 alloy cladding sample peels off in a large area at 900 °C, while the oxidation film of 3wt% Si alloy cladding sample remains intact. With the increase of Si content at 700 °C, the oxidation particles on the surface of the oxide film decrease in size and become denser, which promotes the formation of Cr₂O₃. At 700 °C, a large area of internal oxidation appears in 0wt% Si sample, there are two strip oxides containing Ni, Cr and Mo in the substrate of 1wt% Si sample, while the inner oxidation of 3wt% Si samples is prevented due to the formation of Si-rich inner oxidation layer. The combined effect of the outer layer of Cr₂O₃ oxide film and the inner layer of SiO₂ not only prevents the infiltration of O anions but also inhibits the diffusion of Fe and other metal ions, thus improving the oxidation resistance of the alloy cladding.

Key words:laser cladding;625 alloy;oxidation kinetics;oxidation film;diffusion