Investigating High-Temperature Gaseous and Salt Corrosion Resistance of a Heat-Resistant Intermetallic Titanium Alloy VTI-4 (ВТИ-4)

We investigated high-temperature gaseous and salt corrosion resistance of heat-resistant intermetallic titanium VTI-4 (ВТИ-4) alloy samples by conducting accelerated cyclic laboratory testing in air, in a NaCl environment, and in a mixture of Na₂SO₄ and NaCl. While testing the VTI-4 (ВТИ-4) alloy in air, we observed corrosion of a chemical nature and pseudo-parabolic specific mass variation kinetics. After cyclic testing in a NaCl environment at 700 °C the surface of the VTI-4 (ВТИ-4) alloy was covered by a film consisting of two layers: a mixture of Al₂O₃ and (Ti, Nb)O₂ oxides, and a (Ti, Nb)O₂ layer. In a NaCl + Na₂SO₄ environment at temperatures of 650 and 700 °C a liquid ion conductor film may manifest on the alloy surface alongside the oxides, while corrosion becomes predominantly electrochemical, of the pitting type. Globular orthorhombic phase particles initiate the pitting process. We detected that the pit depth in the alloy after testing in a Na₂SO₄ + NaCl environment at 650 and 700 °C is twice that obtained in NaCl at 700 °C. At the temperatures of 650 °C in Na₂SO₄ + NaCl and 700 °C in NaCl and Na₂SO₄ + NaCl environments the specific mass variation becomes negative, which is due to the oxide film peeling and shedding as temperatures change. The corrosion rate for the VTI-4 (ВТИ-4) alloy in the Na₂SO₄ + NaCl environment at 650 °C is lower than those for the nickel alloys VV751P (ВВ751П) and VZh175-ID (ВЖ175-ИД)

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