Thermomechanical Powder Processing of Ti-6Al-2Sn-4Zr-2Mo-0.1Si: Influence of Powder Morphology, Oxygen Content, and Elemental Partitioning on Microstructure and Mechanical Performance

Abstract

This study investigates the thermomechanical powder metallurgy processing of Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242S) using two commercially available titanium powders: spherical powder produced by the plasma rotating electrode process (PREP) and irregular powder from the hydride–dehydride (HDH) method. Elemental powder blends were pre-consolidated under inert conditions and subsequently extruded in air to evaluate the feasibility of secondary processing without protective gas atmospheres. The powders differed in morphology, and the extruded alloys exhibited distinct oxygen contents (~0.21 wt.% for PREP-derived and ~0.52 wt.% for HDH-derived materials), enabling a controlled investigation of microstructure–property relationships under α+β (925 °C) and β-phase (1080 °C) extrusion regimes. HDH-derived alloys developed fine, uniform lamellar α/β microstructures with increased β-phase volume fractions, while PREP-based materials exhibited coarser α colonies and molybdenum-rich segregation. Mechanical testing showed that HDH alloys achieved higher strength (up to 1232 MPa) but reduced ductility (~4.8%) due to oxygen-induced embrittlement. In contrast, PREP alloys showed a better strength–ductility balance (1057 MPa, 7.6%) with finer lamellae and reduced β grain coarsening at elevated extrusion temperatures. Energy-dispersive X-ray spectroscopy and transmission electron microscopy confirmed phase-specific partitioning: aluminium and titanium enriched the α phase, while molybdenum stabilised the β phase and promoted α₂-Ti₃Al precipitation. Fracture analysis revealed a transition from ductile rupture in PREP alloys to brittle cleavage in HDH alloys. These findings demonstrate that air-based extrusion, when combined with suitable powder selection and thermal control, offers a practical and scalable route for producing high-performance near-α titanium alloys, potentially enabling more sustainable and cost-efficient component manufacturing in aerospace and related sectors.