Kinetics of Layers Produced on Niobium by Salt Bath Boriding

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Materials Performance and Characterization

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In this study, the growth kinetics of NbB2 (niobium boride) layers on pure niobium by boriding was described. The boronizing process was performed in a salt bath composed of borax (sodium borate) and aluminum (10 wt.%). The processing temperatures used were 1123, 1173, 1223, 1273, and 1323 K with residence times in the bath of 2, 4, and 6 h. The borided samples were characterized with respect to hardness and layer kinetics formation. Scanning electron microscopy (SEM), X-ray diffraction (XDR), and Vickers hardness tests were performed. The formation of niobium boride on the surface of pure niobium was confirmed by XRD analysis. The value of Vickers hardness of the layer was up to 2700 HV0.5. The growth kinetics were analyzed by measuring the depth of niobium boride layer as a function of time and temperature. The kinetics equation of the treatment has also been determined with Arrhenius equation K = K0 exp(−Q/RT). The results showed that the diffusion coefficient (K) of the process increased with treatment temperature. Activation energy (Q) for boriding treatment was calculated as 362 kJ/mol.



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