NONEQUILIBRIUM SYNTHESIS OF NBAL3 AND NB-AL-V ALLOYS BY LASER CLADDING .1. MICROSTRUCTURE EVOLUTION

NbAl3, like many ordered intermetallic compounds, appears to have great potential for application as high-temperature structural material because of the high melting point and stability in high-temperature oxidizing environments. However, the D0(22) (tI8) lattice structure shows limited ductility at room temperature. Addition of group IVB, VB, and VIB elements to Al3X (D0(22) type of compounds) as partial replacement of X is a method being applied by various researchers to promote ductility in these materials by activation of numerous dislocations and ordered twinning. In this study, V was added in different amounts to improve the ductility of NbAl3. However, this has an adverse effect on the oxidation response of the system, as is explained in Part II of this article. This article deals with the microstructure evolution, phase identification, and characterization of laser-clad (rapidly solidified) nominal NbAl3 and also studies the effect of V additions on the final microstructure in this system. Laser cladding of nominal NbAl3 produces two metastable unreported phases [body-centered tetragonal (bct) and base-centered orthorhombic phases]. Addition of V suppresses the primary phase (NbAl3) in the Nb-Al-V system.