Formation mechanism of ultrafine α lamellae with high-density dislocations in Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy fabricated by laser powder bed fusion

This study employed laser powder bed fusion (LPBF) to fabricate Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti17) alloy, and the microstructural characteristics and mechanism of α phase formation were investigated. Results revealed that the as-deposited sample, after undergoing stress relief annealing, exhibited a microstructure characterized by a high volume fraction of ultrafine nanoscale α phases dispersed throughout. Abundant edge dislocations and dislocation loops were observed within the α phase, while dislocations were scarcely detected in the β phase. The formation of ultrafine nanoscale α phases occurs during the subsequent low-temperature stress relief annealing process following additive manufacturing. After stress relieving, the Ti17 sample exhibited a superhigh tensile strength of nearly 1500 MPa.