Microstructure evolution and mechanical properties of a novel ultrastrong and ductile PM Ti6Al4V composite

Novel in-situ polycarbosilane (PCS)-derived TiC particles reinforced Ti6Al4V composites with ultrahigh strength and good ductility were fabricated by powder extrusion. The grain microstructure, dynamic recrystallization (DRX), texture orientation, mechanical properties and strengthening mechanisms were systematically investigated. The pyrolysis of PCS and in-situ reaction with Ti6Al4V matrix promote the formation of TiC particles and Si atoms solid-solution. TiC particles provide many heterogeneous nucleation sites for DRX and restrict grain growth by pinning effect, forming many fine equiaxed α grains. The average grain size of α-Ti is refined from 50.17 μm in as-sintered Ti6Al4V alloy to 3.17 μm in as-extruded Ti6Al4V-3PCS composite. The basal texture with {0001}<11 2‾ 0> orientation is dominant in the as-extruded microstructures, originating from the deformed α grains during β single-phase extrusion. The incorporation of PCS activates the occurrence of DRX and weakens the {0001}<11 2‾ 0> basal texture. Benefiting from the in situ formed TiC particles, solid solution Si atoms and low interstitial oxygen (O) contamination, the as-extruded Ti6Al4V-3PCS composite achieves the best combination of room-temperature strength and ductility, with 1307 ± 18 MPa in ultimate tensile strength (UTS), 1178 ± 25 MPa in yield strength (YS) and 10.0 ± 0.8% in elongation (EL), much higher than those of wrought Ti6Al4V alloy (ASTM B381). This work offers a feasible route for fabricating novel ultrastrong and ductile Ti6Al4V composites.