Microstructure globularization of high oxygen concentration dual-phase extruded Ti alloys via powder metallurgy route

Research related to the substitution of ubiquitous elements for high-cost rare elements during the fabrication of high-performance Ti alloys has attracted significant attention. The microstructure evolution is, however, challenging when several elements with different properties are used. This research aims to study the effect of Si addition on the microstructure formation of the dual-phase Ti alloys in the presence of solid solution-forming elements such as Fe and Cu, and a high oxygen concentration. Ti-4Fe-0.5O-3Cu (TFOC) alloys with different Si contents (0.2, 0.4, and 0.6 wt%) were fabricated from the elemental powders using spark plasma sintering, followed by hot extrusion. The TFOC sintered alloys with 0.2 and 0.4% Si showed very similar microstructures in the lamellae alpha+beta dual-phase. The coarsening of alpha colonies and primary beta grains was remarkable when Si content increased to 0.6%. The obtained primary beta grains were, however, significantly smaller than those in previous studies. In contrast, the refined globular alpha grains (respective grain sizes = 2.6 and 2.2 mu m) embedded in the beta matrix were observed in the hot extruded TFOC-0.2Si and TFOC-0.4Si alloys due to dynamic globularization. Additionally, EBSD analysis clarified that the hot extruded alloys had the strong fiber textures of (10 (1) over bar0) and (101) for alpha and beta phases respectively, which were consistent with the XRD results. High-resolution TEM examination demonstrated that Ti2Cu and Ti3Cu intermetallics of a length of 100-400 nm could form preferentially at alpha/beta interfaces. The experimental results showed that 0.4 wt% Si added to TFOC alloys formed fine globular microstructures in the presence of hot plastic deformation.