Nonequilibrium synthesis of nbai3 and Nb-Ai-V Alloys by Laser Cladding: Part II. Oxidation Behavior

Abstract

In this study, the isothermal oxidation behavior of laser-clad NbAl3 has been investigated in the temperature range between 800 °C and 1400 °C in air. The effect on oxidation of vanadium microalloying, used to increase the ductility of the otherwise brittle NbAl3 and discussed in Part I, [1] has also been considered. Bulk and surface oxide chemistry has been investigated using X-ray diffraction and X-ray photoelectron spectroscopy (XPS), respectively. Oxidation kinetics have been determined from weight gain data. The XPS and X-ray diffraction data show that NbAl3 does not exclusively form a protective A12O3 layer when oxidized in air. The oxidation products at 800 °C are a mixture of Nb2O5 and A12O3, while at 1200 °C, a mixture of NbAlO4, Nb2O5, and Al2O3 is formed. At 1400 °C, a mixture of NbAlO4, A12O3, NbO2, NbO2.432, and Nb2O5 forms. Upon addition of vanadium, the oxidation rate is found to dramatically increase and may be related to the formation of (Nb, V)2O5 and VO2, which grows in favor of protective A12O3. Consequently, although vanadium may be a good additive in terms of its potential for improving ductility in NbAl3, it is not in terms of its deleterious effects on oxidation.