Effects of Boron on Microstructure and Mechanical Properties of High-Nb TiAl Alloy Fabricated via Laser Melting Deposition

The high-Nb TiAl alloy is an excellent lightweight alloy used in aerospace applications. However, its poor room-temperature plasticity and hot workability significantly hinder its engineering application prospects. In this study, high-Nb TiAl alloy powder with uniformly dispersed boron particles was prepared via the synchronous ultrasonic dispersion mechanical stirring method; and, a crack-free Ti-45Al-8Nb-xB (x = 0, 0.5 at.%) alloy was obtained through laser melting deposition. The microstructures and mechanical properties of the deposited alloys were observed and examined via optical microscopy, scanning electron microscopy, electron backscatter diffraction and extensometer. The boride type and its influence mechanism were investigated using transmission electron microscopy. The results indicated that after the addition of 0.5 at.% boron, the primary TiB phase formed from the liquid phase prevented the rapid growth of beta crystals, significantly refining the lamellar structure from 75 to 45 mu m and weakening the phase transformation texture from 58 to 20. In addition, the TiB adjusted dislocations and hindered their movement. The TiB inoculation treatment significantly increased the room-temperature plasticity (51%) of the deposited high-Nb TiAl alloy, which was considerably better than that of high-Nb TiAl alloys prepared via conventional casting techniques.