The hot corrosion behaviors and mechanisms of hot-dipped Ti-Al-Si coatings on TiBw/Ti6Al4V composite against NaCl and Na₂SO₄

The Ti-Al-Si coatings were prepared on TiBw/Ti6Al4V composites by a two-step method comprising hot dip and heat treatment processes to enhance the hot corrosion resistance. Results show that Ti-Al-3Si (wt%) and Ti-Al-20Si (wt%) coatings were mainly composed of the Ti(Al,Si)₃ and Ti₃AlSi₅ phase, respectively. Both of the coatings can protect the substrate against the deposited NaCl, 25 wt%NaCl+ 75 wt%Na₂SO₄, and Na₂SO₄ salts. In particular, the coatings exhibited superior hot corrosion resistance in the deposited Na₂SO₄ salts, which is attributed to the formation of dense and continuous Al₂O₃ oxide scales and the slow dissolution process of sulfate during the hot corrosion process. Moreover, the Ti-Al-Si coatings exhibited serious external oxidation when hot corroded in the deposited 25 wt% NaCl+ 75 wt%Na₂SO₄ and Na₂SO₄ salts, in which more corrosion products and pores were formed due to the autocatalytic reaction processes. Since the deposited NaCl salt would rapidly dissolve the oxide scale and destroy its compactness and continuity, which presented a more serious hot corrosion effect.