Evaluation of the resistance to oxidation of niobium treated by high temperature nitrogen Plasma Based Ion Implantation

Niobium is a technological material used in very distinct applications. Most of them as an alloying element, making part of superconducting radio frequency cavities, nuclear reactor components, missiles, rockets, aviation and space-system engineering. Nevertheless, although refractory, pure niobium presents as the main drawback the poor oxidation resistance in moderate and high temperatures. Different treatment methods have been used to mitigate this issue, as is the case of cementation, conventional nitridation, CVD and PVD processes. The evaluation of the resistance to oxidation of Nb treated by high temperature nitrogen plasma based ion implantation (HTPBII) has been described herein. The implanted nitrogen in this case easily diffuses to inner layers of niobium heated up to 1250 °C during treatment, reaching depths of about 7 μm, while its atomic concentration of about 25% remains stable for almost the whole treated surface. This allows the formation of thick nitride layers. The produced interstitial nitrides have outstanding properties as the high hardness and strength, like ceramics, and high thermal and electrical conductivities, like metals. In addition, these refractory nitrides also present good chemical resistance and superior resistance against oxidation. The investigation performed herein includes a series of characterization performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), glow discharge optical emission spectroscopy (GDOES), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The oxidation of the ion-implanted niobium was retarded in comparison with the untreated counterpart in about 130 °C. Isothermal analysis revealed reduced oxidation rate when treatment time was extended from 4 h to 8 h.