Corrosion Resistance Related to Eutectoid Orientation of Ti50Al48Mo2 Alloy by In-Situ Directional Solidification and Thermal Processing

The orientation of lamellar eutectoid (α₂ + γ) structure in the Ti₅₀Al₄₈Mo₂ alloy was controlled by in-situ directional solidification and thermal processing (DS-TP). The eutectoid orientation was parallel to the directional solidification direction by DS-TP, instead of 45 deg or being perpendicular during directional solidification. The spacing and orientation of lamellar eutectoid influenced corrosion resistance and the evolution of corrosion morphologies in both transverse and longitudinal sections. As the growth velocity decreased, temperature gradient increased, the lamellar spacing decreased and the directional orientation of eutectoid was significantly enhanced, the micro-galvanic effect between the γ and α₂ phases was weakened, the sensitivity to pitting corrosion decreased, the corrosion resistance of the alloy increased. The alloy by DS-TP exhibited improved anti-corrosion performance with the minimum lamellar spacing (1.02 μm) and the eutectoid orientation being parallel to the directional solidification direction. On account of directional solidification, the corrosion resistance of longitudinal section was better than that of transversal section in directionally solidified alloys. Owing to the existence of only one eutectoid growth orientation and similar lamellar spacing in the transverse and longitudinal sections of the alloy by DS-TP, consequently the corrosion resistance of both transverse and longitudinal sections was improved synergistically and showed isotropic.