Strengthening Mechanisms of Ti17 Titanium with Ultrahigh Strength and Moderate Plasticity Fabricated by Laser Powder Bed Fusion

Abstract

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 α lamellae and related mechanical property trends. In the as-deposited LPBF-Ti17, α lamellae features extremely fine dimensions, with an average lamellar thickness of 45 nm, and comprises approximately 52.2% of total volume. This finely dispersed α lamellar microstructure provides numerous α/β 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 α-phase lamellar thickness. The rate of α lamellar thickness growth reaches its peak between 650°C and 700°C. The main dislocation distribution of LPBF-Ti17 lies at α lamellae edges, adjacent to β phase, and dislocation density diminishes with rising heat treatment temperature. Concurrently, the Termination migration mechanism causes α lamellae ends to become progressively rounded from sharp features with increasing heat treatment temperature. The increase in α lamellar thickness, reduction in dislocation density, and smoother ends collectively contribute to the effective enhancement of Ti17 plasticity.

Keywords: titanium alloys, additive manufacturing methods, phase transformations, plasticity