Thermal Stability of Titanium Alloy VT8M-1 with Ultrafine-Grained Structure

Abstract

The paper considers the effect of a long-duration heating at a service temperature of 450oC on VT8M-1 with a coarse-grained (CG) and ultrafine-grained (UFG) microstructure. A duplex ultrafine-grained microstructure, composed of equiaxed grains of primary α-phase and an ultrafine constituent of α- and β-phases, was processed by thermal treatment and further rotary swaging. This type of a microstructure demonstrates a best combination of strength and ductility at room temperature in comparison with the CG structure. A thermal stability of an UFG state was studied at 450°C for 50, 100, 200, 300, 400, and 500 hours. The evolution of the alloy microstructure against the duration of heating was considered by transmission electronic microscopy (TEM), scanning electronic microscopy (SEM). No increase in the alloy structural elements and strength decrease resulting from a long-term annealing (up to 500 hours) at T=450°C have been observed. This proves a high thermal stability of the UFG structure and mechanical properties of VT8M-1 processed via rotary swaging.

Investigation of the Role of Intermetallic Phases in Microstructure of UFG Titanium VT8M-1 Alloy

“…1b). The average size of grains/subgrains of the secondary α and βphases was 0.3 µm [6]. The electro-microscopic studies of the microstructure of the VT8M-1 alloy after rotary swaging showed the presence of fine particles mainly located on the inter-phase α/β-boundaries (Fig.…”