Enhancing the Mechanical Properties Induced by Ta Microalloying in TIG-Welded Ti2AlNb-Based Intermetallic Alloy

Abstract

During the tungsten inert gas (TIG) welding process of Ti₂AlNb alloy, high heat input leads to the formation of coarse grains, which are detrimental to the mechanical properties of welded joints. To address this problem, Ta microalloyed welding wires were developed to enhance the strength of the welded joints. The Ta-modified fusion zone (FZ) exhibited a well-defined structure with a smooth, defect-free surface. Systematic analysis of the microstructure evolution and mechanical properties of the welded joints revealed that the Ta element completely dissolves into the FZ. During solidification, a significant constitutional undercooling effect occurs, promoting the columnar-to-equiaxed transition (CET) and reducing grain size from 187.42 to 133.49 μm. Mechanical properties tests indicated that with increased Ta content, the strength of the welded joints initially increased and then decreased. When the Ta content in the welding wire was 1 wt%, the joints showed the best performance, with a tensile strength of 909.36 MPa and an elongation of 1.21%. Compared to the welded samples without Ta, the tensile strength and elongation increased by 153.01 MPa and 0.53%, respectively. Grain refinement and increased dislocation density were the main reasons for the improved mechanical properties. However, excessive Ta content led to significant the intragrain misorientation, increasing the joint’s anisotropy and causing uneven deformation during tensile testing. Therefore, further addition of Ta did not substantially enhance the tensile properties of the joint. Additionally, the paper provides a detailed analysis of the low elongation observed in the joint. After welding, dislocations were neatly arranged in the FZ, forming numerous parallel dislocation walls, leading to local stress concentration and accelerating crack initiation and propagation. Consequently, the elongation at the weld was lower than that of the base metal (BM). This research offers a new approach to improve the mechanical properties of Ti₂AlNb alloy during welding.