Microstructure, mechanical properties, and strengthening mechanism of high performance Ti-6Al-4V alloy by pressureless sintering and hot extrusion

Abstract

In this work, we fabricated a high-performance Ti-6Al-4V alloy from TiH2 and 60Al40V powder mixtures by powder metallurgy (PM) pressureless sintering and hot extrusion. The correlation among sintering temperature, hot extrusion microstructure, and mechanical properties was systematically investigated. The dehydrogenation of the mixed powder during sintering promotes the closure of pores and obtains a fine, fully dense microstructure. The billets sintered at 1200 °C possess a denser lamellar microstructure consisting of small (α + β) colonies, which provide more nucleation points during the later deformation. We made a detailed investigation into the deformation behavior and dislocation motion of the special lamellar structure in the fabricated Ti-6Al-4V via EBSD and TEM. The uniform α/β lamellar interface generated by continuous dynamic recrystallization is a good location for geometrically necessary dislocation generation and storage. The synergistic improvement of strength and ductility after extrusion is attributed to the homogeneous and fine recrystallized microstructure and the smooth appearance of deformation twins. The ultimate tensile strength of extruded rod is up to 1213 MPa and the elongation increases to 14 %. This work proposes a simplified method to achieve low-cost PM Ti alloys with excellent performance.