Influence of the Vacuum Heating Temperature on the Morphology of the Structural Constituents of a Preliminarily Hydrogen-Charged VT22 Titanium Alloy

Abstract—The possibility to control the structure formation in a VT22 titanium alloy of the transition class (Ti–5.5Al–4.3V–4.2Mo–0.8Cr–0.8Fe) using thermohydrogen treatment (reversible hydrogen alloying) is studied. A high volume fraction of the β phase, which is characteristic of α + β titanium alloys of the transition class (at least 40% in the alloy under study), is shown to suppress martensitic transformation even at 0.1 wt % hydrogen; at 0.3 wt % hydrogen, only the metastable β phase is retained in the structure of the alloy. Different types of structure, from a bimodal to a fine equilibrium structure, can be formed in the alloy during subsequent vacuum annealing by controlling the development of the β → α transformation. A fine α + β structure with an α-phase particle size of at most 0.5 μm forms only upon low-temperature (625–700°C) vacuum annealing.