Characterization of microstructures and oxidation behaviour of Nb–20Si–20Cr–5Al alloy

Static oxidation in air was performed on Nb–20Cr–20Si–5Al alloy at high temperatures ranging from 700 to 1400 °C. Pesting occurred at 700 °C while internal oxidation took place at 1300 and 1400 °C where Al2O3 initiated at the interface between NbCr2 and Nb9Cr3Si2 phases. Phases present were Nb5Si3, NbCr2, Nb solid solution and Nb9Cr3Si2 depending on the temperature. The aluminium content on each of the phases was analyzed. Al content in Nb9Si2Cr3 has been found to be as high as 5–6 atomic percent. SEM, EDS and XRD techniques were utilized in order to characterize the specimens.

► Static oxidation was performed from 700 to 1400 °C on Nb–20Cr–20Si–5Al alloy.
► Internal oxidation occurred on the alloy at high temperatures.
► Aluminum content was analyzed in each of the phases.
► The presence of Nb9Si2Cr3 was detected.
► Swollen oxide formed at 1000 °C due to presence of the 3 polymorphs of Nb2O5.