Nb-Si基超高温合金及其定向凝固工艺的研究进展

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 room-temperature 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.