Enhancing the tensile properties of laser repairing Ti-6Al-4V alloys: Optimization of strain distribution based on composition fine-turning

Abstract

In the context of laser repairing damaged forging titanium (Ti) alloys, a common challenge is the significant reduction in elongation of the repaired samples compared to that of the substrate. In this work, directed energy deposition (DED) technology was employed to repair the TC4 (Ti-6Al-4V) forgings by manipulating the Al and V contents of the repaired zone (RZ). Subsequent evaluation encompassed the microstructure, microhardness, and tensile properties across the laser repair deposition samples (LRDs). The results revealed that despite the LRD TC4–0Ti's strength reaching 97.80% of the substrate, its elongation is only 43.93% of the substrate. Upon appropriately reducing the Al and V contents of RZ, the LRD TC4–5Ti demonstrates a strength of 935.04 MPa and an elongation of 14.59%, achieving 98.70% and 82.38% of the substrate, respectively. As the Al and V contents of RZ are further decreased, the strength of the LRDs gradually diminishes, falling below the forging standards. Utilizing digital image correlation (DIC) technology, the deformation behavior of different zones during the tensile process of these LDRs was investigated. The results indicated a concentration of strain distribution within either RZ or the substrate zone (SZ) of the LRDs during the tensile process, which signifies the mismatch of deformation capacity between these two zones. Consequently, the tensile properties of the LRDs were adversely affected. By judiciously adjusting the Al and V contents of RZ, the abovementioned mismatch phenomenon can be ameliorated, which facilitates a synergistic strain behavior between SZ and RZ during the tensile process, aiding in the homogenization of strain distribution and consequently enhancing the tensile properties of the LRDs.