Investigation of Ti2AlNb-Added TiAl Composite Prepared by Direct Laser Deposition

Abstract

Ti₂AlNb/TiAl composite columnar specimens without defects were fabricated by using direct laser deposition (DLD) process. In this study, the microstructure and mechanical properties were comprehensively investigated. Results revealed that each deposited layer contains two microstructure bands: the equiaxed grain band and the lamellar colony band. These two bands appeared as γ/α₂ lamellar with random lath orientation under high magnification, with different lamellar spacing of 210 and 380 μm, respectively. Unmelted Ti₂AlNb particles could be found in the lamellar colony band, which could decrease the dislocation density further to increase the strength. The tensile strength at room temperature reaches 541-543 MPa, with a corresponding elongation of 0.6-0.8%, while the fracture occurs mainly in the equiaxed grain bands with a translocation fracture mechanism. Hardness tests also showed higher hardness values in the lamellar colony bands than in the equiaxial grain bands. CT characterization tests did not reveal that fracture cracks started or passed through the Ti₂AlNb grains. These results demonstrate an in-depth understanding of the microstructure and properties of Ti₂AlNb/TiAl composites prepared by DLD, and provide a pioneering reference for further investigations of the strengthening effect of Ti₂AlNb on TiAl-based alloys.