Lamellae Orientation Control and Mechanical Properties of Directionally Solidified Binary Ti-49Al Alloy in Oxide Ceramics Crucible

In this paper, the lamellar orientation control and mechanical properties of directionally solidified (DS) Ti-49Al (at%) alloy in oxide ceramic crucible were investigated. Based on the nucleation undercooling theory, the feasible solidification parameters for the lamellar orientation control of Ti-49Al (at%) alloy by the seeding technology were selected. The optimal solidification parameters were as follows: the growth rate (V) ranged from 10 to 25 μm/s, and temperature gradient (G) ranged from 10 to 20 K/mm. DS Ti-49Al (at%) alloy with paralleled lamellar orientation was successfully prepared according to the predication solidification parameters. The mechanical properties of DS Ti-49Al (at%) varied with the orientation of the lamellar structures. The specimen with paralleled lamellar orientation showed relatively higher tensile strength (450 MPa) and elongation (0.60%). The mechanical properties of specimens with paralleled lamellar orientation were greater than the specimens with equiaxed grain structures even though the specimens contaminated slightly by the interfacial reaction between the TiAl melt and the oxide ceramics crucible. Meanwhile, the fracture modes of DS Ti-49Al (at%) alloy were interlamellar mode, translamellar mode, or combined with the two modes, which also depended on the lamellar orientations.