【摘要】 具有低密度和高熔点特性的Nb-Si基超高温合金是下一代航空发动机热端部件的重要候选材料之一。但Nb-Si基超高温合金的低室温断裂韧性限制了其工业化应用,合金化和定向凝固是改善室温断裂韧性的有效方法,本文综述了这2个方面的研究进展。合金化方面重点介绍了合金元素通过位错增韧和相改变增韧实现铌基固溶体（Nbss）相的韧化,通过固溶强化和相变提高硅化物相的高温性能,促进硅化物以近"Y"型生长,改善两相的界面等影响,分析发现Ti、Hf、Zr、B和Mg等元素均可改善室温断裂韧性。定向凝固方面综述了Nb-Si基超高温合金的定向凝固方法及特点,不同定向凝固工艺对Nb-Si基合金的组成相、组织形貌、室温断裂韧性以及高温强度的影响,定向凝固过程的组织演变规律及强化机理,分析发现调控工艺可获得Nbss/Nb₅Si₃良好单向生长的组织。在保证Nbss/Nb₅Si₃共晶耦合单向生长的情况下,减小Nbss相的厚度,提升其连续性是提高室温断裂韧性的有效方法。还展望了Nb-Si合金化与定向凝固的未来发展趋势。更多还原

【Abstract】 The Nb-Si base ultrahigh temperature alloys with low density and high melting point is one of the candidate materials for the hot components of next-generation aero-engines. The insufficient of the Nb-Si based ultrahigh temperature alloy at 270-280 K is the bottleneck for its industrial application.Alloying and directional solidification are considered as effective methods for improving the roomtemperature fracture toughness. The research progress of the two methods for the Nb-Si-based ultrahigh temperature materials are reviewed herein. In the aspect of alloying, the toughening of the Niobium solid solution（Nbss） phase is mainly conducted by dislocation toughening and phase transformation toughening. The high-temperature performance of the silicide（Nb₅Si₃） phase can be improved by solid-solution strengthening and phase transformation, and the silicide phase would tend to grow in a near“Y”shape.The interface between the Nbss and silicide phases could be modified. In conclusion, Ti, HF, Zr, B, and Mg can improve the room-temperature fracture toughness of Nb-Si base ultrahigh temperature alloys.The methods and characteristics of the directional solidification of Nb-Si materials are introduced. Herein,the effects of different processing parameters on the phase composition, microstructure morphology,room-temperature fracture toughness, and high-temperature strength of Nb-Si base ultrahigh temperature alloys are summarized. The microstructure evolution and mechanical property strengthening mechanism during directional solidification are reviewed. The well-coupled Nbss/Nb₅Si₃ unidirectional growing eutectic structure can be obtained by controlling the process. In this condition, the room-temperature fracture toughness could be improved by reducing the Nbss phase thickness and increasing the eutectic structure continuity. The future development of Nb-Si alloying and directional solidification is prospected.更多还原