Formation of the Structure, Phase Composition, and Properties in High-Strength Titanium Alloy upon Isothermal and Thermomechanical Treatment

Abstract

Transmission electron microscopy, X-ray diffraction analysis, durometry, and mechanical tensile and impact toughness tests were used to study changes in the structure, phase composition, and mechanical properties in a high-strength VT22I titanium alloy (Ti–3Al–5Mo–5V–1Cr–1Fe) upon isothermal and thermomechanical treatments, including warm rolling and aging. It has been found that the decomposition of the β solid solution in an alloy preliminarily heated in the β region (Т_pt + 50°C) after isothermal treatment at 650°C for 1 and 4 min is accompanied by the formation of an intermediate α'' phase; upon holding for 20 min, an equilibrium α phase precipitates. The А₇В-type ordering processes, where β stabilizers and aluminum can serve as a B element, are possible and, upon final cooling, in water, the formation of an athermal ω phase can take place at the initial stages of decomposition. It has been shown that the warm rolling of the alloy at 650°C accelerates the processes of the decomposition of the metastable β solid solution, contributes to the refinement of the arising α precipitates, and suppresses the formation of the athermal ω phase upon cooling compared to the similar isothermal treatment without deformation. A regime of a thermomechanical treatment that provides the high mechanical properties required to fabricate elastic structural components has been proposed for this alloy.