Electron Beam Welding and Post Heat Treatment of a New Near-Beta High-Strength Ti-4Al-5Mo-5V-5Cr-1Nb Alloy

Abstract

Ti-4Al-5Mo-5V-5Cr-1Nb (wt.%) is a new type of high-strength (~1300 MPa) titanium (Ti) alloy developed for aerospace applications. Until now, the research on its welding and subsequent heat treatment is barren. Herein, we employed electron beam welding (EBW) to a solutionized Ti-4Al-5Mo-5V-5Cr-1Nb with a phase constituent of α + β and investigated its microstructure and mechanical properties in both as-welded (AW) and post-weld aging treated (PWAT) conditions. Results showed that due to the thermal input of the welding process, the α phase in the original microstructure of base material (BM) transformed into the β phase in the fusion zone (FZ). Similar microstructural evolution was observed for the heat-affected zone (HAZ) near the FZ (Near-HAZ), whereas the HAZ far away from FZ (Far-HAZ) contained a small amount of round α phase (ghost α) due to its slower cooling rate. Such a microstructural change resulted in poor tensile strength (~780 Mpa) for the as-welded joint. After PWAT, a large number of acicular α precipitated in the FZ and HAZ and its size (S) in different zones followed the order of SFar-HAZ < SFZ ≈ SNear-HAZ < SBM. The presence of αs precipitates remedied the tensile strength of the weld joint almost to the same as that of the BM. The present findings established the foundation of the application of this high-strength Ti alloy.