High Temperature Oxidation of Cr-25Nb Alloy Synthesized by Mechanical Alloying and Hot Pressing

ABSTRACT

Cr-25Nb alloy was prepared by mechanical alloying (MA) and hot pressing (HP), and the influences of milling time on the density and oxidation property of samples were investigated. During the studying of the effect of different ball grinding time on oxidation resistance, we discover that the relative density of the Cr-25Nb alloy would increase with the ball grinding time increasing, but when it was oxidized at 1200°C for 5 h in the air, the gain weight rate of the oxidized samples does not only decreased with the ball milling time increasing. In the period of MA 0 to 20 h, the gain weight rate of the oxidized samples reduced with the ball milling time increasing. When the ball milling time further increased, the gain weight rate increased and the oxidation resistance of samples went down. Thus, the oxidation resistance of sample of MA 20 is best. The oxide layer appearance of MA 15 h, MA 20 h, MA 35 h were observed by SEM, respectively. It is found that the oxide layer thickness of specimen of MA 20 hour is thinnest. From the result of EDS and XRD, Cr₂O₃ was formed on the outer oxide layer. However, the oxides in the inner layer were mainly Cr₂O₃ and CrNbO₄.

Keywords: