Effects of Tantalum on the microstructure and properties of Ti-48Al-2Cr-2Nb alloy fabricated via laser additive manufacturing

Abstract

To improve the mechanical properties of Ti48Al2Cr2Nb (TiAl) alloys, Ti48Al2Cr2Nb-xTa alloy specimens without metallurgical defects were obtained by a laser additive manufacturing (LAM) technique using Ti48Al2Cr2Nb/Ta mixed powders as raw materials. The effects of different Ta contents on the microstructures, phase compositions, and tensile properties of the TiAl alloys were systematically investigated, and the relationship between these properties was established. The results showed that the lamellar structure was composed of α2 (Ti3Al), γ (TiAl), and β/B2 (β ordered to B2) phases. With the increase of Ta content, the thickness of the lamellar structure increased, and the lamellar length gradually shortened. The morphology of the α2 phase changed from an ultra-fine continuous lamellar structure to a short lamellar and an equiaxed structure. On the other hand, the morphology of the γ phase changed from lamellar to an equiaxed crystal structure, while the morphology of β/B2 phase changed from ellipsoid shape to fine block to coarse block structure. When the amount of Ta added to the TiAl powders was 0 at.%, 2 at.%, and 5 at.%, respectively, the tensile strength gradually decreased with the increase of temperature, while the elongation increased. When the amount of Ta was 8 at.%, the tensile strength at room temperature dropped to the minimum (393 MPa), and the elongation reached its maximum value (21.2%). Thus, it can be concluded that the 5 at.%Ta alloy had the best comprehensive tensile properties. The maximum tensile strength of the TiAl-5 at.%Ta alloy at room temperature, 750 °C and 850 °C, was 677 MPa, 651 MPa, and 538 MPa, respectively, and the elongation was 2.0%, 2.0%, and 13%, respectively. Compared with the TiAl-0 at.%Ta alloy, the tensile strength of TiAl-5 at.%Ta at room temperature, 750 °C, and 850 °C increased by 1.66, 2.08, and 1.9 times respectively, and the elongation increased by 1.43, 1.43, and 9.29 times, respectively.