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

Authors: Shubin I.Yu., Nikitin Ya.Yu., Puchkov Yu.A., Alekseev E.B., Davydova E.A. Published: 24.12.2020
Published in issue: #6(135)/2020  

DOI: 10.18698/0236-3941-2020-6-83-105

 
Category: Mechanical Engineering and Machine Science | Chapter: Machines, Units and Processes  
Keywords: heat-resistant alloys, ortho-rhombic intermetallic titanium alloys, high-temperature gase-ous and salt corrosion, destruction

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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