Temperature dependence of structural parameters and mechanical properties of Ti–45Nb alloy in ultrafine-grained state

The dependence of mechanical properties and structural peculiarities of the ultrafine-grained (UFG) Ti-45 wt.% Nb alloy on the heat treatment conditions was studied. The experiments revealed the stages of the evolution of the studied alloy’s UFG microstructure. The work performed showed that the annealing in the temperature range from 400 to 800 °C leads to significant changes in the state of the structure. The initial UFG structure is characterized by grains of the main β-phase, saturated with inclusions of the α-phase and nanosized particles of the ω-phase, providing dispersion strengthening of the alloy. It was shown that heat treatment at 400 and 500 °C leads to an increase in the content of the α-phase in the alloy. A further increasing the temperature up to 600 °C leads to the partial dissolution of this phase. It is noted that annealing at 500 °C is characterized by the transition of the structure from the UFG state to fine-grained and coarse-crystalline ones with the formation of dispersion-hardened grains of the β-phase. Subsequent increasing the temperature leads to the loss of strength of studied alloy, which is explained by the structure recrystallization, phase transformation, the presence of inclusions of α- and ω-phases, as well as decreasing their contribution to the dispersion hardening process.

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