Microstructure evolution of Ti17 titanium with ultrahigh strength and moderate plasticity fabricated by laser powder bed fusion

This study utilized laser powder bed fusion (LPBF) to fabricate Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti17) specimens, exploring their ultrahigh strength microstructural strengthening mechanisms and examining heat treatment effects on alpha lamellae and related mechanical property trends. In the as-deposited LPBF-Ti17, alpha lamellae features extremely fine dimensions, with an average lamellar thickness of 45 nm, and comprises approximately 52.2% of total volume. This finely dispersed alpha lamellar microstructure provides numerous alpha/beta phase interfaces, enabling LPBF-Ti17 mechanical properties to reach ultra-high strengths close to 1500 MPa. During heat treatment, the Ostwald ripening mechanism primarily drives growth in alpha-phase lamellar thickness. The rate of alpha lamellar thickness growth reaches its peak between 650 degrees C and 700 degrees C. The main dislocation distribution of LPBF-Ti17 lies at alpha lamellae edges, adjacent to beta phase, and dislocation density diminishes with rising heat treatment temperature. Concurrently, the Termination migration mechanism causes alpha lamellae ends to become progressively rounded from sharp features with increasing heat treatment temperature. The increase in alpha lamellar thickness and reduction in dislocation density collectively contribute to the effective enhancement of Ti17 plasticity.