Title

Bimodal titanium alloys with ultrafine lamellar eutectic structure fabricated by semi-solid sintering

Document Type

Journal Article

School

School of Engineering

RAS ID

24011

Comments

Yang, C., Kang, L. M., Li, X. X., Zhang, W. W., Zhang, D. T., Fu, Z. Q., ... & Lavernia, E. J. (2017). Bimodal titanium alloys with ultrafine lamellar eutectic structure fabricated by semi-solid sintering. Acta Materialia, 132, 491-502.

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Abstract

We report on a novel approach to synthesize (Ti100-x-yFexCoy)82Nb12.2Al5.8 (at.%) bimodal alloys and provide fundamental insight into their underlying microstructural evolution and mechanical behavior. In our work, a bimodal microstructure is attained via selection of phases and composition in a eutectic reaction followed by semi-solid sintering. Specifically, if one selects an atomic ratio of Ti/Fe corresponding to the eutectic composition, the resultant (Ti63.5Fe26.5Co10)82Nb12.2Al5.8 alloy shows a bimodal microstructure of micron-sized fcc Ti2(Co, Fe) embedded in an ultrafine lamellar eutectic matrix containing ultrafine bcc β-Ti and bcc B2 superstructured Ti(Fe, Co) lamellae. This structure forms from the complete eutectic reaction between β-Ti and Ti(Fe, Co). The phase boundary of β-Ti and Ti(Fe, Co) lamellae consists of a coherent interface with the orientational relationships: (110)β-Ti//(110)Ti(Fe, Co), (200)β-Ti//(100)Ti(Fe, Co) and(11¯0)β-Ti//(11¯0)Ti(Fe,Co). Such bimodal alloy exhibits ultra-high compressive yield strength of 2050 MPa with a compressive plasticity of 19.7%, which exceed published values of equivalent materials. These unusual mechanical properties are attributed to a mechanism that involves blocking, branching and multiplication of β-Ti lamellae, dislocation interactions in Ti(Fe, Co) lamellae, and the stability of coherent interfaces. In addition, unusual phenomenon of introduced high-density dislocations in B2 superstructured Ti(Fe, Co) lamellae, other than β-Ti lamellae, can be rationalized based on the formation and decomposition of superlattice dislocations according to classic crystallographic strengthening theory.

DOI

10.1016/j.actamat.2017.04.062

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