Effect of LaB6 on the microstructure evolution and mechanical properties of Ti-45Al-8Nb alloy

High-Nb-containing TiAl alloys have been considered an excellent candidate for demanding high-tem-perature structural components due to their attractive mechanical properties and low density. However, the intrinsic brittleness at room temperature remains a great barrier limiting its processability. Here a novel alloy design strategy was introduced to improve its ductility from the perspective of grain refinement and removal of oxygen within the matrix. A minor content of LaB6 was introduced into Ti-45Al-8Nb alloy prepared by vacuum arc melting. La2O3 and TiB ceramic phases were in-situ synthesized owing to the decomposition of LaB6 additive. The effect of LaB6 addition on the microstructure and compressive prop-erties of TiAl-based alloys was investigated. The LaB6 inoculation not only refines the lamellar colonies but also promotes the generation of single gamma phases, contributing to the transformation from coarse full-la-mellar to refined near-lamellar and even dual-phase colonies. The major fracture mode transformed from inter-lamellar to trans-lamellar to inter-granular with LaB6 addition increasing. With 0.4 wt% LaB6 addition, both the ultimate compress strength and fracture strain increased from 1065 MPa and 17.1 % to 1503MPa and 26.98 % respectively.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

High-Nb-containing TiAl alloys are promising for high-temperature structural components but suffer from brittleness at room temperature. A novel alloy design strategy involving LaB6 addition was proposed to improve ductility through grain refinement and oxygen removal. LaB6 decomposition generated La2O3 and TiB ceramic phases, leading to the transformation of microstructure and enhancement of compressive properties. The addition of 0.4 wt% LaB6 increased ultimate compressive strength from 1065 MPa to 1503 MPa and fracture strain from 17.1% to 26.98%.