Title

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

Document Type

Journal Article

School

School of Engineering

Comments

Originally published as:

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.

Original available here

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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