A novel near-α high temperature titanium alloy with trimodal microstructure and submicron-nanosilicides for superior mechanical properties at both room and elevated temperatures

Abstract

To address the persistent challenge of balancing room and elevated temperature mechanical properties in conventional near α titanium alloys, this study proposes an innovative approach through compositional design and thermomechanical treatment process optimization. A high Zr/Si containing near-α titanium alloy is developed by decreasing-temperature multidirectional forging (DMDF) and subsequent heat treatment, yielding a trimodal microstructure consisting of lamellar primary α-phase (α_l), equiaxed primary α-phase (α_e) and transformed β-phase (β_t). This microstructure features a hierarchical dispersion of dual-scale silicides, where submicron-scale silicides are preferentially distributed along grain/phase boundaries, while nanoscale silicides are uniformly dispersed within grains. After DMDF followed by solution treatment at 950 °C/40min (HT2), the alloy achieves superior room-temperature mechanical properties (UTS = 1306.6 MPa, EL = 7.5 %), primarily attributed to synergistic strengthening effects involving multiscale precipitates (α_S and dual-scale silicides), dislocation networks and activated slip systems. The alloy maintains excellent strength at elevated temperature up to 650 °C, demonstrating a UTS of 799.8 MPa paired with an elongation of 16.2 %. This sustained strength originates from strain gradient formation at α/β interfaces combined with dual-scale silicides pinning mechanisms. Additionally, the enhanced ductility at 650 °C arises from the slip bands within the α-phase and additional <c+a> dislocation activation. This design strategy of trimodal microstructure with hierarchical dispersion of dual-scale silicides provides a new perspective for tailoring high-temperature titanium alloys with balanced mechanical properties at both room and elevated temperatures.