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

摘要

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 beta solid solution in an alloy preliminarily heated in the beta region (T-pt + 50 degrees C) after isothermal treatment at 650 degrees C for 1 and 4 min is accompanied by the formation of an intermediate alpha '' phase; upon holding for 20 min, an equilibrium alpha phase precipitates. The A(7)B-type ordering processes, where beta stabilizers and aluminum can serve as a B element, are possible and, upon final cooling, in water, the formation of an athermal omega phase can take place at the initial stages of decomposition. It has been shown that the warm rolling of the alloy at 650 degrees C accelerates the processes of the decomposition of the metastable beta solid solution, contributes to the refinement of the arising alpha precipitates, and suppresses the formation of the athermal. 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.