The influence of Si on NbAl coatings

Although high-strength intermetallics are intrinsically suitable for high-temperature applications because of their ordered structure, producing structural parts with ordered alloys represents a major challenge. Intermetallics can also be processed as coatings. However, further research is required to identify chemical compositions that yield high-performance ordered alloys. The impact of Si and the diffusion of elements from the substrate on NbAl coatings is addressed in this study. In situ synthesis procedures were used to process coatings. Coatings in the as-deposited condition and after exposure to temperatures of up to 1000 °C were systematically characterized. Differential thermal analysis was also used. The presence of Si in the deposited powder mixtures resulted in coatings with a dendritic solidification structure. The primary solidification products were Nb5Si3 and Nb2Al for powder mixtures with and without Si, respectively. Regardless of the composition of the deposited mixture, the coating interacted with the substrate to form Fe3Al compounds and Laves-phase Cr2Nb. Enhanced oxidation performance was observed in coatings containing Si and can be attributed to inhibition of the formation of Nb2O5 by Si.