Microstructural and phase evolution of Ti-6Al-4V alloy produced by laser powder bed fusion (LPBF) under electron irradiation

Abstract

In this paper, the microstructural, chemical, and phase evolution of a Ti-6Al-4V alloy fabricated by Laser Powder Bed Fusion (LPBF) and subsequently subjected to electron irradiation was investigated. The LPBF process results in the formation of a nonequilibrium microstructure under rapid solidification conditions (≈10⁵–10⁶ K/s), including acicular α′-martensite, oriented prior β grains, and microporosity (≈0.2–1.0 μm). Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) were employed to characterize the material before and after irradiation. SEM observations revealed that electron irradiation increased the agglomerate size from approximately 50–100 μm to 70–150 μm, while reducing pore size from 0.2–1.0 μm to 0.05–0.6 μm. EDS analysis indicated a decrease in Ti content accompanied by an increase in oxygen and carbon concentrations, suggesting surface oxidation and chemical modification. XRD analysis confirmed the transformation of the initial Al–Ti intermetallic phases and the predominance of the hexagonal Ti phase after irradiation. Changes in lattice parameters (a: 2.927→2.936 Å; c: 4.663→4.676 Å) indicate lattice expansion and redistribution of internal stresses. The obtained results demonstrate that electron irradiation significantly affects the structural state of LPBF-fabricated Ti-6Al-4V alloy and can be considered an effective approach for tailoring the process–structure–property relationship in additively manufactured titanium alloys.