Harmonically structured Ti-6Al-4V alloy with ultrahigh strength fabricated by thermomechanical consolidation of mechanically milled TiH_2/Al_(60)V_(40) powder blend

摘要

Novel harmonically structured Ti-6Al-4V alloy samples consisting of ultrathin lamellar structured cores embedded in coarse-grained shells were fabricated through high energy mechanical milling of TiH_2/Al_(60)V_(40) powder blend and powder compact extrusion of the mechanically milled powder at 1000 and 1100 °C. Some samples extruded at 1100 °C were vacuum annealed subsequently at 700 °C for adjusting microstructural pa-rameters. The microstructure/mechanical properties correlations of the as-extruded and annealed samples were systematically investigated. It was proposed that the formation of the harmonic structure can be attributed to the stabilization effect of the residual hydrogen on β-Ti phase and the suppressed eutectoid transformation. In terms of the mechanical properties, the ultrahigh tensile fracture stress of harmonically structured samples was ascribed to the interface strengthening of ultrathin lamellar structured cores together with a relatively high content of oxygen. Thanks to the hetero-deformation induced hardening provide by coarse-grained shells, the strain localization was delayed. Specifically, by improving strain partitioning among heterogeneous domains, a better combination of strength and ductility was achieved. As a result, a tensile fracture strength of 1431 MPa and a uniform elongation of 4.5% were attained in an extruded and subsequently annealed Ti-6Al-4V alloy sample.