Academician Guo Wanlin's team has made important progress in the strengthening and toughening mechanism of TiAl single crystal. Synergistic effects of twin boundary and phase boundary for enhancing ultimate strength and ductility of lamellar TiAl single crystals was published in the International Journal of Plasticity.

TiAl alloy, as a light superalloy, has great development potential in the aerospace field. Its low density and high temperature strength have attracted the attention of many researchers. In 2016, Academician Chen Guang's team invented the preparation technology of TiAl single crystal, overcoming the two problems of high brittleness at room temperature and low service temperature of TiAl alloy, and realizing the leap-forward improvement of strength, plasticity and creep resistance. In order to ensure the safe application of TiAl single crystal in practical engineering, it is necessary to deeply understand its mechanical behavior such as strengthening and toughening mechanism.

Fig. 1. Structures of TiAl boundaries (a) TB and (b) PB. (c) FCC, HCP, and Node regions are defined according to the geometry of the PB. (d) Schematic diagram of the PB with three stacking regions: FCC; HCP and Node. (e) The phase boundary is colored by their potential energy (PE) and the yellow lines are dislocation structures identified by the DXA algorithm.

Recently, Professor Wanlin Guo and his team found that the synergistic effects of twin and phase boundaries in TiAl single crystal make the material exhibit a strengthening and toughening mechanism different from that of existing materials. The synergistic effect of twin boundary and phase boundary increases the strength and ductility by 8.3% and 24.7%, respectively, compared with the pure phase boundary. This synergistic effect results from the multistage strain hardening of the stress-strain curve caused by dislocation retraction. At the same time, the synergistic effect can be significantly improved by increasing the ratio of twin boundary to phase boundary. The theoretical model shows that the dislocation retraction mechanism occurs when the lamellar thickness is less than 217 nm, which provides a feasible way to improve the strength and ductility of TiAl single crystal limit.

Fig. 2. Synergistic strengthening of twin boundary and phase interface to improve strength and toughness of TiAl single crystal.

These results reveal a new mechanism for strengthening and toughening TiAl single crystal, which opens up a new way to improve the mechanical properties of TiAl single crystal. The first author of this paper is Dr. Henggao Xiang from Nanjing University of Aeronautics and Astronautics, and the corresponding author is Academician Wanlin Guo.

Link:

https://www.sciencedirect.com/science/article/pii/S0749641921002631