Ultrafine-grain formation and improved mechanical properties of novel extruded Ti-Fe-W alloys with complete solid solution of tungsten

Abstract

Thermomechanical processing and solid-solution strengthening are effective ways to improve the mechanical properties of Ti alloys with elements such as W and Fe. In this study, we present a novel extruded Ti-Fe-W alloys with improved mechanical properties. To analyze the effect of W on the mechanical properties and microstructure of the alloys, Ti-4Fe-xW (x = 0–3 wt%) alloys were prepared by spark plasma sintering followed by homogenization heat treatment and hot extrusion. The microstructure of the as-sintered specimens included undissolved W particles distributed in the acicular α + β matrix. However, heat treatment at 1300 °C for 1 h led to the complete dissolution of W. After hot extrusion at 850 °C, an ultrafine equiaxed (globular) microstructure was observed, in which Fe and W preferentially diffused into the β phase. The main effect of W on the microstructure was a remarkable grain refinement by activation of dynamic recrystallization and impediment of the grain boundary mobility in Ti-4Fe-(1–3)W (~1 µm) when compared to Ti-4Fe (~3 µm). Additionally, W increment resulted in a gradual decrease of the average size of α grains. The tensile yield strength increased as W content increased so that the Ti-4Fe-3W alloy exhibited a remarkably high tensile strength, yielding at ~1123 MPa with an elongation of ~26%. Finally, theoretical and experimental analyses suggested that grain refinement and solid-solution strengthening were the main mechanisms contributing to the strengthening phenomenon in W-containing alloys.