Microstructure and microhardness of hydrogenated Ti-2Fe-0.1B alloy a subject to HPT in the solid solution state

Abstract

This paper presents the results of a study of the microstructure and mechanical properties of a hydrogenated Ti-2Fe-0.1B alloy (in wt. %), subjected to high-pressure torsion (HPT) in a solid-solution (SS) state. The hydrogenated samples with a uniform distribution of hydrogen were obtained by holding at a temperature of 700 °C for 2 hours in a high-purity hydrogen environment and naturally cooling together with a furnace to room temperature. To form the SS state, the samples were placed in a vacuum and subjected to heat treatment. SS state with a hydrogen content of 0.3 wt.% and 0.5 wt.% was formed by holding at temperatures of 720 °C and 640 °C, respectively, for 1 hour in a vacuum followed by cooling in water. The temperature was set 10 °C above the β → α phase transformation temperature. The phase composition after SS treatment was characterized by a predominance of the β-phase and a small volume of the α-phase. The HPT was carried out at a pressure of 6 GPa at room temperature with a different number of turns. The microstructure and microhardness of the hydrogenated samples that were SS and HPT treated were investigated. The results obtained were compared with similar results obtained for samples before HPT. Microstructural analysis showed that as a result of hydrogenation and SS treatment, a β-Ti(H) phase saturated with hydrogen was formed. HPT contributed to the formation of a dispersed ω-phase and the refinement of grains in both β- and α-phases. Precipitations in the form of whiskers of the TiB phase were also observed in the microstructure. The microhardness of the alloy has increased significantly as a result of the hydrogenation, SS treatment and HPT.