High temperature oxidation behavior of a multi-element Nb-Si system in situ composite

A multi-element Nb-Si-X system in situ composite with composition of Nb-16Si-24Ti-6Cr-6Al-2Hf (at%) is prepared by arc metlting method. The high temperature oxidation behavior of the alloy is investigated by scanning electron microscopy (SEM), energy dispersive spectrum (EDS) and X-ray diffraction (XRD). The as-cast composite consistes of Nb_ss phase and β-Nb₅Si₃ phase, and after oxidation test at 1250°C for 100 h, the composite formes a thick scale being mainly composed of CrNbO₄ and TiNb₂O₇, below which severe inner oxidation occurres. The morphological investigation also showes that the internal oxidation of Nb_ss phase is faster than that of Nb₅Si₃ phase, because of the faster diffusion of oxygen in Nb_ss phase than in Nb₅Si₃ phase. It is suggested that the dispersion of the silicide phase has a beneficial effect on reducing the internal oxidation of the composite and releasing the compression stress in oxide scale.