A new process for preparing Ti-Al alloys from low-valance titanium chlorides slurry by direct electrochemical reduction
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摘要: 针对低价氯化钛(LTC)浆料熔盐电解制备钛铝合金存在的电化学行为研究不系统、合金产品的高温抗氧化特性不明晰等问题,采用电化学工作站、示差热重分析仪等手段对LTC浆料在熔盐体系中电化学行为及合金产品的高温抗氧化特性进行研究。结果表明,LTC浆料在熔盐体系中可直接电化学还原制备Ti-Al合金,且为逐级还原的历程:Ti3+→Ti2+,Al3+→Al,Ti3+/Al3+→Ti-Al合金和Ti2+→Ti;随着熔盐体系中Ti3+离子浓度的增加,钛铝合金的组成变化规律为:Al/Al3Ti→Al3Ti2/Al5Ti2→AlTi/Al0.64Ti0.36→Al0.64Ti0.36/AlTi3→AlTi3→AlTi3/Ti→Ti,产品形貌变化规律为:粗枝晶→细枝晶→细球状结构→粗球状团聚体→细球状团聚体→细球多孔状→多孔状结构。钛铝合金中随着铝含量和产品致密性的增加,合金的抗高温氧化性能逐渐增强,Al0.64Ti0.36/AlTi3合金经高温熔炼后呈Al含量更高的α2/γ和γ组织,使其高温抗氧化性能优于商用Ti48Al2Cr2Nb。钛铝合金产品高温氧化历程为:Ti-Al合金→铝酸钛→金红石/氧化铝,并且形成的氧化物层可有效防止钛铝合金的进一步氧化。Abstract: Owing to the lack of systematic research on electrochemical behaviors and unclear high-temperature oxidation resistance characteristics of Ti-Al alloys prepared from low-valence titanium chlorides slurry by the electrochemical reduction in molten salt, the electrochemical workstation and differential 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 concentration 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 γ 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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表 1 电解质中[Ti]/([Ti]+[Al])比例对阴极产物组成及形貌的影响
Table 1. The effect of molar ratios of [Ti]/([Ti]+[Al]) in electrolytes on the compositions and morphology of cathodic products
电解质[Ti]/([Ti]+[Al]) 阴极产物[Ti]/([Ti]+[Al]) 物相组成 形貌特征 0.15 0.182 Al、Al3Ti 粗大枝晶 0.38 0.394 Al3Ti2,Al5Ti2 细枝晶 0.50 0.485 AlTi、Al0.64Ti0.36 细球状结构 0.69 0.725 Al0.64Ti0.36、AlTi3 粗状况团聚体 0.77 0.764 AlTi3 细球状团聚体 0.83 0.880 AlTi3、Ti 细球多孔状 1.00 1.000 Ti 多孔状 表 2 钛铝合金锭高温氧化后重量变化情况
Table 2. Weight changes of Ti-Al alloy ingot after high-temperature oxidation
合金类别 氧化前/g 氧化后/g 增重率/% 钛铝合金锭 3.018 3.059 1.36 Ti48Al2Cr2Nb 1.222 1.229 0.57 -
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