Nb-Ti-Al基超高温合金研究进展

Progress in Investigation of Nb-Ti-Al Based Ultrahigh-Temperature Alloys

Nb-Ti-Al基超高温合金熔点高、密度低,其综合力学性能具有潜在的优势,是未来先进航空发动机涡轮热端部件的重要备选材料。NbTi-Al基合金主要组成相为铌固溶体β相和金属间化合物δ相,β相改善合金室温塑性,δ相提供优良的高温强度和较低的蠕变速率。近年来,Nb-Ti-Al合金体系相图不断完善,β→δ相变以及β相有序化转变获得了广泛的研究。分析了Nb-Ti-Al合金的3种主要制备方法:电弧熔炼铸锭、粉末冶金和激光成形技术及工艺对组织和力学性能的影响。热等静压、热压烧结等先进粉末冶金技术适用于熔点高、反应活性强的Nb-Ti-Al基合金制备。激光成形技术应用于制备铌基超高温合金空心叶片等复杂结构部件,具有巨大的潜力。为提高Nb-Ti-Al基合金抗氧化性,可综合利用合金化防护、第二相防护、涂层防护等技术。随δ相含量增加,合金高温强度提高,而室温断裂韧性则降低,因此需平衡合金高低温力学性能,引入弥散强化。进一步优化合金体系,推进激光成形等方法的应用和改进抗氧化涂层,是Nb-Ti-Al合金的重要发展方向。

Nb-Ti-Al based ultrahigh-temperature alloys are significant candidate materials for manufacturing hot-section components of advanced aero turbine engines,due to high melting point,low density and potential advantages in comprehensive mechanical properties. Nb-Ti-Al based alloys mainly consist of solid solution β phase and intermetallic δ phase. The β phase improves room-temperature ductility while the δ phase provides admirable high-temperature strength and low creep rate. In the past several years,the Nb-Ti-Al phase diagrams were modified gradually,and β→δ phase transformation and ordering transformation of β phase received much attention. Three main preparation methods,arc melting,powder metallurgy and laser forming process,and their influences on the microstructure and mechanical properties of Nb-Ti-Al alloys were analyzed. Advanced powder metallurgy techniques such as hot isostatic pressing and hot pressed sintering were suitable for manufacturing Nb-Ti-Al alloys,which were characterized by high melting point and high reactivity. Laser forming had large potential in manufacturing niobium based ultrahigh-temperature hollow blades and other sophisticated structural components. To improve the oxidation resistance,alloying protection,the second phase protection and coating protection should be utilized comprehensively. As the proportion of δ phase increased,the high-temperature strength increased while the room-temperature fracture toughness decreased,thus the high and low temperature mechanical properties should be balanced,and the dispersion strengthening should be investigated. Optimizing the alloy system,promoting the applications laser forming and developing oxidation resistant coating were key developing orientations of Nb-Ti-Al based alloys.