Synergistically enhanced strength and ductility in TiAl/Nb composites via core-shell structure design

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2024-12, Vol.918, p.147417, Article 147417
• Main Authors: Shen, Jingyuan, Wang, Luting, Cao, Zhuohan, Hu, Lianxi
• Format: Article
• Language: English
• Subjects: Core-shell structure; Powder metallurgy; Strength-ductility synergy; TiAl/Nb composites
• ISSN: 0921-5093
• DOI: 10.1016/j.msea.2024.147417

In view of the long-standing dilemma of low ductility of TiAl alloys at room temperature, the TiAl/Nb composites with core-shell structure were developed and prepared by powder metallurgy. The results show that insufficient and excessive milling are not conducive to the formation of core-shell composite powders, the former leads to low adhesion rate of β-Nb particles while the latter aggravates the fragmentation of γ-TiAl powders and the segregation of free β-Nb particles. The γ-TiAl matrix powders can be encapsulated by ductile Nb shell after ball milling at 180 rpm for 168 h. The core-shell structured TiAl/Nb composites can be obtained by hot pressing sintering of 1200°C/40 MPa/1 h. During this process, the strong metallurgical bonding of core/shell and shell/shell interfaces is the result of atomic diffusion in accordance with vacancy-mediated displacement pattern. A series of intermetallics are produced between γ-TiAl matrix and β-Nb plasticizer. The phase transformation on the matrix side was studied from the perspective of crystal structure, i.e., L10→HCP→D019 (γ→α→α2) and HCP→BCC→B2 (α→βd→B2). Moreover, the prepared composites show a promising strength-plasticity combination, with 32.9 % fracture strain and 2.4 GPa compressive strength. The high strength is attributed to the unremitting increase of back stress induced by non-synchronous deformation of core-shell structure, while the high plasticity is closely associated with the honeycomb shell which can not only coordinate the relative sliding between matrix colonies in the early stage of deformation, but also alleviates the stress concentration and retards the crack propagation at the middle and late stage of deformation due to the hierarchical multi-constituent phases. •The preparation of core-shell structured TiAl/Nb composites was systematically studied.•The mechanism of high strength-ductility synergy of the prepared composites was elucidated.•The transformation process of γ.→α2→B2 was understood from the perspective of crystal structure evolution.