Influence of Fe micro-alloying and TiB₂ reinforcement on the corrosion behavior of high Nb-containing TiAl alloys

To investigate the corrosion behavior of high Nb-containing TiAl alloys, samples of Ti-45Al-8Nb, Ti-45Al-8Nb-0.5 wt% Fe, and Ti-45Al-8Nb-0.5 wt% Fe-2wt% TiB₂ were fabricated via hot isostatic pressing (HIP). The effects of Fe micro-alloying and the combination of Fe micro-alloying with TiB₂ reinforcement on the corrosion properties of TiAl alloys were explored. The results revealed that the introduction of Fe caused significant lattice distortion in the γ-TiAl phase, while the presence of TiB₂ particles hindered the formation of a dense passive film on the sample surface. However, both Fe micro-alloying and TiB₂ reinforcement led to a notable reduction in the size of lamellar colony and the width of lamellar layers. The surface of TiAl and TiAl-Fe samples after corrosion was affected by the layered morphology formed by the difference in corrosion resistance between TiAl and Ti₃Al phases. The addition of Fe element reduced the number of corrosion pits, while TiAl-Fe-TiB₂ was subjected to micro-galvanic corrosion near TiB₂. The preferential corrosion area appeared, and there were flocculent and granular oxides. As a result, the corrosion current density of the sample decreased progressively from 1.42 × 10⁻⁷ A/cm² to 1.05 × 10⁻⁷ A/cm², and further to 9.86 × 10⁻⁸ A/cm². Additionally, the corrosion potential exhibited an anodic shift, increasing from −0.27 V to −0.11 V, and further to −0.09 V, indicating a significant enhancement in the corrosion resistance of the material. This combined effect of lattice distortion and grain refinement was found to impede the diffusion of Cl^- ions, significantly enhancing the formation rate of the passive film.