Improving ductility in coaxial electron beam wire additive manufacturing of Ti48Al2V-based alloy with Cu element introducing globular γ-grains

Abstract

TiAlV-based alloys are ideal for designing lightweight materials; however, the addition of V does not mitigate the inherent brittleness of TiAl-based alloys. This paper presents a novel alloying strategy to enhance the room temperature ductility of TiAlV-based alloys produced via coaxial electron beam wire additive manufacturing. By leveraging the unique characteristics of the cold-cathode electron beam heat source, Cu was introduced into TiAlV-based alloys through in-situ dual-wire alloying process. The resulting Ti48Al2V alloy and Ti48Al2V1.27Cu alloy samples exhibited good appearance, free from microcracks and porosity, due to the stable dual-wire transition state, real-time layer height control, and closed-loop temperature control. A comprehensive comparison between the Ti48Al2V alloy and the Ti48Al2V1.27Cu alloy was conducted, focusing on grain morphology, chemical composition homogeneity, phase constitution, and mechanical properties. A multiphysics numerical model was developed to elucidate the feeding, melting, and mixing of dissimilar wires, as well as melt pool convection and the influence of phase transformations on the solidification behavior of TiAl-based alloys. The strengthening mechanism of the alloy's room temperature ductility was thoroughly explained. Results indicate that the selection of Cu, with its face-centered cubic structure, for the composition design of TiAlV-based alloys is justified based on thermodynamic calculations. A near-lamellar (NL) microstructure and enhanced room temperature ductility was achieved through precise process parameter control. The tensile strength at room temperature and 650°C improved by 5.6% and 4.5%, respectively, while the elongation at room temperature and 650°C increased by 39.3% and 36.2%, respectively. This study provides valuable insight for further low-cost in-situ alloying methods to regulate the microstructure and enhance the room temperature ductility of TiAlV-based alloys.