Improving the High-Temperature Oxidation Resistance of Nb4AlC3 by Silicon Pack Cementation

Niobium aluminum carbide (Nb4AlC3), as a member of the MAX phases, can retain its stiffness and strength up to over 1400 degrees C. However, its applications are limited due to its poor oxidation resistance at high temperatures. In this work, silicon pack cementation has been applied to improve the oxidation resistance of Nb4AlC3. After Si pack cementation at 1200 degrees C for 6h, a dense and uniform silicide coating which was mainly composed of NbSi2 and SiC and well bonded to the matrix was successfully formed on the surface of Nb4AlC3. The Si pack cemented Nb4AlC3 shows excellent oxidation resistance up to 1200 degrees C due to the formation of protective Al2O3 layer. The oxidation kinetics of the cemented Nb4AlC3 obey parabolic law all the way to up to 1200 degrees C, and the parabolic rate constants of cemented Nb4AlC3 are in the same order of magnitude as those of Ti3AlC2 in the temperature range 1000 degrees C-1200 degrees C. However, the oxidation of the cemented Nb4AlC3 was accelerated after oxidation at 1300 degrees C for about 15h due to the formation of NbAlO4.