Trade-off Balancing between Strength and Toughness of Multi-Phase alloys containing Brittle Phases

在韧性基体中具有脆性金属间相或脆性金属间相的合金中，已经系统地研究了强度和韧性之间的平衡。所研究的体系包括Nb-Si基合金、fe基铁素体合金、奥氏体Fe-Mn-Al-C合金、cu合金和Al-Fe合金。Nb- si合金由脆性Nb_5Si_3和韧性Nb固溶相组成，呈混合层状形貌，是燃气涡轮发动机部件等超高温应用的候选材料。合金的高温强度和室温韧性取决于层状组织的形貌和间距。本文成功地提出了一种考虑脆性基体中韧性相增韧机理的权衡性能优化方法。对以Laves相为强化剂的Fe-Cr基铁素体合金和通过析出e2_1型金属间化合物实现强化的Fe-Mn-Al-C合金也进行了类似的研究。在这两种情况下，脆性相的形态变化与晶体取向有关，两相之间的失配控制着合金的强度和韧性或延展性。本工作成功地为先进金属材料的显微组织和力学性能提供了许多有价值的基础信息，有助于设计用于各种结构应用的合金。

Trade-off balancing between strength and toughness has been systematically investigated in alloys having brittle an intermetallic phase in a ductile matrix or having a ductile phase within the brittle intermetallic matrix. The systems investigated include Nb-Si base alloy, Fe-base ferritic alloys, an austenitic Fe-Mn-Al-C alloys, Cu-alloys and an Al-Fe alloy. The Nb-Si alloys consist of brittle Nb_5Si_3 and a ductile Nb solid solution phase in a mixed lamellar morphology, which is a candidate material for ultra-high temperature application such as components in gas-turbine engines. Both high temperature strength and room temperature toughness of the alloy depend on the morphology and spacings of the lamellar microstructure. A method for optimization of trade-off properties has been successfully suggested with a consideration on the toughening mechanism by the ductile phase in a brittle matrix.Similar investigation was made in the Fe-Cr base ferritic alloys in which the Laves phase is the strengthening agent, and also in Fe-Mn-Al-C in which the strengthening is achieved by the precipitation of E2_1-type intermetallic compound. In both cases change in morphology of the brittle phase in relation to the crystallographic orientation and misfit between two-phases control the strength and toughness, or ductility of the alloys.The present work successfully provides many valuable basic information on the microstructure-mechanical properties of advance metallic materials that helps in designing the alloys for various structural applications.