600 ℃高温钛合金发展现状与展望

钛及钛合金具有比强度高、耐腐蚀性能和低温性能好、热强度高等优点,是航空航天工业中重要的结构材料。同时,相比于铝、镁轻合金,钛合金高温性能优异,因而在航空发动机耐高温部件中也有着相当大的应用潜力。1954年,美国研发出了第一种实用型高温钛合金Ti-6Al-4V,高温长时使用温度为300～350℃,综合性能良好,在之后的很长一段时间内被广泛使用。随着航空航天工业的不断发展,尤其是航空发动机的发展,其他各国也都相继研发出了一些使用温度更高的高温钛合金,直至1984年,英国开发出了世界上第一个使用温度达600℃的高温钛合金IMI834。IMI834的典型特点是在原有的近α型高温钛合金Ti-Al-SnZr-Mo-Si体系中加入了0.06%C,扩大了两相区的加工窗口,优化了组织。在此之后,美国于1988年在原有高温钛合金Ti-6542S的基础上通过调整一些合金元素的含量也获得了一种实用温度为600℃的高温钛合金Ti1100。1992年,俄罗斯在BT18Y的基础上用5%的高熔点W代替1%Nb也开发出了一种达600℃的高温钛合金BT36。而国内高温钛合金起步相对较晚,前期以仿制为主,后逐渐形成了以添加稀土元素为特色的高温钛合金体系,典型的有中科院金属研究所和宝钛集团研发的Ti60和西北有色金属研究院自主研发的Ti600,它们的实际使用温度均为600℃,综合性能优异。总体来说,目前高温钛合金的使用温度很难突破600℃,主要是由于使用温度高于600℃时合金的热强性与热稳定性难以匹配协调,并且合金的抗氧化性急剧下降,表面氧化严重,导致合金热稳定性以及疲劳性能下降,甚至可能使航空发动机高压压气机部位的零部件存在"钛火"的风险。本文综述了国内外600℃及600℃以上的高温钛合金的发展现状。重点介绍了美国的Ti1100、英国的IMI834、俄罗斯的BT36、中国的Ti60、TG6和Ti600(600℃高温钛合金)以及中国的Ti65和Ti750(600℃以上高温钛合金)。总结了各国发展高温钛合金的思路,指出了限制高温钛合金向更高使用温度发展的瓶颈并提出了可能的解决途径。从控制α2相大小、形态、含量以及改善热加工工艺的角度对未来高温钛合金的发展进行了展望,以期为进一步提高高温钛合金的使用温度、优化高温钛合金性能提供指导。

Present Situation and Prospect of 600℃ High-temperature Titanium Alloys

Titanium and titanium alloys which hold the advantages of high specific strength,favorable corrosion resistance and low-temperature performance,high thermal strength,etc.,have become a kind of critical structural materials in aerospace industry, and moreover,have displayed considerable application potential for aeroengine heat-enduring parts owing to superior high-tempera-ture performance compared with aluminum alloys and magnesium alloys.In 1954,the United States developed the first practical high-temperature titanium alloy Ti-6Al-4V which possesses a long-term use temperature range of 300—350 ℃ and a pleasurable comprehensive performance,and acquired extensive and long-lasting application.With the continuous progress of the aerospace indus-try,especially the advent of aeroengines,other countries successively developed some higher-working-temperature titanium alloys, among which IMI834,as the world’s first 600 ℃ high temperature titanium alloy,was created in 1984 by the United Kingdom.The typical feature of IMI834 is the addition of 0.06% C into the existing Ti-Al-Sn-Zr-Mo-Si titanium alloy system,expanding the pro-cessing window and optimizing the microstructure.After that,the United States obtained a high temperature titanium alloy Ti1100 in 1988,by adjusting the amount of some alloying elements in the original high-temperature titanium alloy Ti-6542S.In 1992,Russia also established its high temperature titanium alloy BT3 6 by substituting 5% W (a high-melting-point element)for 1% Nb within BT18Y.China’s research of high-temperature titanium alloy started relatively late,initially imitated foreign alloys,and later specia-lized in utilizing rare earth elements to design high-temperature titanium alloys.The Ti60 and Ti600 alloys,developed by IMR (CAS)/BaoTi Group and NIN respectively,both have the working temperature of 600 ℃ and favorable comprehensive performance. In general,the upper temperature limit of high-temperature titanium is difficult to exceed 600 ℃ at present.Sufficient studies have proved that the nearly ineliminable mismatch between thermal strength and thermal stability and the steep-oxidation-resistance-decay-induced severe surface oxidation at above 600 ℃ will result in the deterioration of thermal stability and fatigue properties,and even, the risk of "titanium fire"for those components serving in the high-pressure compressor section of an aeroengine. This review is concerned with the worldwide development status of 600 ℃ and above high-temperature titanium alloys.We give introductions for the 600 ℃ high-temperature titanium alloys including Ti1100 (US),IMI834 (UK),BT36 (Russia),and Ti60/TG6/Ti600 (China),as well as the 600 ℃-above ones including Ti65/Ti750 (China).The major nations’design schemes of high-temperature titanium alloys and the obstacles to raising the upper temperature limit are outlined,and some possible solutions are put forward.The paper ends with a prospective discussion over the future trends of high-temperature titanium alloys,from the perspec-tives of controlling the size,morphology and content ofα2 phase and adjusting the hot working process.