A new process for preparing Ti-Al alloys from low-valance titanium chlorides slurry by direct electrochemical reduction
Owing to the lack of systematic research on electrochemical behaviors and unclear high-tem-perature oxidation resistance characteristics of Ti-Al alloys prepared from low-valence titanium chlor-ides slurry by the electrochemical reduction in molten salt,the electrochemical workstation and differ-ential thermal gravimetric analyzer were used to study the electrochemical behavior of LTC slurry in the molten salt system and the high-temperature oxidation resistance characteristics of alloy products.The results show that LTC slurry can be directly electrochemically reduced to Ti-Al alloys,following a step-by-step reduction process:Ti3+→Ti2+,Al3+→Al,Ti3+/Al3+→Ti-Al alloys,and Ti2+→Ti.As the concentra-tion of Ti3+ions in molten salts increases,the composition of Ti-Al alloys changes as follows:Al/Al3Ti→Al3Ti2/Al5Ti2→AlTi/Al0.64Ti0.36→Al0.64Ti0.36/AlTi3→AlTi3→AlTi3/Ti→Ti.The variation law of product morphology is as follows:coarse dendrite→fine dendrite→fine spherical structure→coarse spherical aggregate→fine spherical aggregate→fine spherical porous structure→porous structure.With the increase of aluminum content and product density in Ti-Al alloys,the high-temperature oxidation resistance gradually enhances.After high-temperature melting,Al0.64Ti0.36/AlTi3 alloy shows α2 and y phase structures with a higher Al content,and its high-temperature oxidation resistance is superior to commercial Ti48Al2Cr2Nb.The high-temperature oxidation process of Ti-Al alloys is as follows:Ti-Al alloys→titanium aluminate→rutile/alumina,and the formed oxide layer can effectively prevent further oxidation.
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