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

• Published in: Physics of metals and metallography 2018-08, Vol.119 (8), p.780-788
• Main Authors: Illarionov, A. G., Korelin, A. V., Popov, A. A., Illarionova, S. M., Elkina, O. A.
• Format: Article
• Language: English
• Subjects: Aluminum; Chemical precipitation; Chemistry and Materials Science; Cooling; Decomposition; Deformation; Diffusion; High strength alloys; Impact strength; Isothermal treatment; Materials Science; Mechanical properties; Metallic Materials; Phase composition; Phase Transformations; Precipitates; Solid solutions; Structure; Thermomechanical treatment; Titanium alloys; Titanium base alloys; Transmission electron microscopy; Warm rolling; Warm working; X-ray diffraction
• ISSN: 0031-918X; 1555-6190
• DOI: 10.1134/S0031918X18080033

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 А 7 В-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.