The Effect Of Cr, Si And B On The Oxidation Behavior On Three Nb-Based Alloys

Nb-based alloys are of particular interest to replace the current Ni-based superalloys for high-temperature structural applications. One important limitation to improve the efficiency of gas-turbine engines is the temperature limit of current materials being used. By allowing the temperature to increase, the efficiency will increase. Nb-based alloys have high melting points and adequate mechanical properties but the oxidation resistance is still inadequate. This research focuses on the oxidation behavior of three Nb-based alloys to study the effect of Cr and Si variation and look at the effect of Boron. Boron can form a glassy borosilicate which is viscous at high temperatures and serves as an oxygen barrier and this improves the oxidation resistance. Compositions of the alloys were Nb-20Cr-20Si-5Al, Nb-25Cr-15Si-5Al and Nb-25Cr-15Si-5Al-5B. The alloys were oxidized from 700oC to 1400oC in air for 24 hours. Thermogravimetric data was collected and plotted against temperature. The Nb-20Cr-20Si-5Al had better oxidation resistance at lower temperatures while the Nb-25Cr-15Si-5Al-5B perform slightly better at higher temperatures when compared to the other two alloys. Better oxide layer adhesion was observed when boron is added. Specimens and oxide products were characterized by SEM, EDS, BSE and XRD