Designing ultrafine lamellar eutectic structure in bimodal titanium alloys by semi-solid sintering

• Published in: Journal of alloys and compounds Vol. 702; pp. 51 - 59
• Main Authors: Kang, L.M., Yang, C., Wang, F., Li, X.X., Zhu, D.Z., Zhang, W.W., Chen, W.P., Huan, Y.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 25-04-2017; Elsevier BV
• Subjects: Alloys; Aluminum base alloys; Bimodal titanium alloys; Body centered cubic lattice; Cobalt base alloys; Compressive strength; Eutectic; Eutectic composition; Eutectic reactions; Face centered cubic lattice; Ferrous alloys; Lamellar structure; Liquid phase sintering; Microstructure; Niobium; Phase composition; Semi-solid; Semisolids; Sintering; Spark plasma sintering; Studies; Titanium base alloys; Yield stress; Bimodal titanium alloys; Spark plasma sintering; Liquid phase sintering; Semi-solid; Eutectic
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2017.01.257

We report on a novel approach to design typical ultrafine lamellar eutectic structure in bimodal alloys fabricated by semi-solid sintering (SSS) of a eutectic mixture. In our work, ultrafine lamellar eutectic structure was implemented by controlling the phase composition of eutectic reaction, and consequently by regulating the structure of eutectic reaction-induced liquid phase through varying component number. Microstructure analysis indicate that although all SSSed alloys have the same three phase constitutions of bcc β-Ti, bcc Ti(Fe, Co), and fcc Ti2(Co, Fe), the morphology and distribution of the eutectic structure transforms from limited length and minor quantity, to partial fine alternating bcc β-Ti and bcc Ti(Fe, Co) lamellae, and further to typical complete ultrafine alternating continuous lamellae in the SSSed ternary Ti-Fe-Co, quaternary Ti-Fe-Co-Nb, and quinary Ti-Fe-Co-Nb-Al alloys. Interestingly, the SSSed Ti-Fe-Co-Nb-Al alloy presents a novel bimodal microstructure of coarse fcc Ti2(Co, Fe) surrounded by an ultrafine lamellar eutectic matrix containing ultrafine bcc β-Ti and bcc Ti(Fe, Co) lamellae. This bimodal microstructure exhibits ultra-high yield strength of 2050 MPa with plasticity in compression of 19.7%, which exceed published values of equivalent materials. Our results provide a novel pathway for fabricating new-structure metallic alloys for high-performance structural applications.
•A novel way was introduced to design ultrafine lamellar eutectic structure.•A new bimodal structure was fabricated by semi-solid sintering.•It contains coarse Ti2(Co, Fe) embedded in ultrafine lamellar eutectic matrix.•Its balanced strength and ductility exceeds reported values of similar alloys.•Our results provide a novel pathway for fabricating new-structure alloys.