Structure, strength, and plasticity of semifinished products of VT22 titanium alloy
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STRUCTURE, STRENGTH, AND PLASTICITY OF SEMIFINISHED PRODUCTS OF VT22 TITANIUM ALLOY O. V. Abolikhina,1 S. L. Antonyuk,1 and O. H. Molyar 2
UDC 669.295
It is shown that the mechanical properties and structure of semifinished products of VT22 alloy are formed in the stage of hot deformation and depend on the kinetics and morphology of formation of the structure. It is shown that the α-edge and α-precipitates affect the properties of semifinished products of VT22 alloy, especially in the case of massive products, which means that the indicated structural inhomogeneities should be regulated by the technical specifications for supply and inspection.
The thermomechanical treatment of semifinished products of titanium alloys can be used for the purposeful modification of their structure and mechanical properties in broad ranges. The high-strength (α + β )-titanium alloys of the transition class with the maximum number of different phases are especially sensitive to structural changes. The VT22 alloy is a typical representative of these alloys [1, 2]. Unlike plasticity (very sensitive to the structure of semifinished products) which, as a rule, decreases with the formation of large grains and a rough lamellar intragranular structure, the strength of titanium alloys sometimes remains invariable or even increases. The influence of the structure on impact toughness is also ambiguous, although it is known that this characteristic is sensitive to admixtures and especially to hydrogen, which sharply decreases its value [3]. The most extensively used technology of production of semifinished titanium products is rolling. By using rolling, it is possible to make sheets, plates, and sometimes rods. To produce rods and thick-walled pipes, it is customary to use the procedure of pressing or extrusion. The semifinished products of titanium alloys with masses of several tons are manufactured by the method of free forging or by using stamps. The VT22 alloy is subjected to hot deformation in the one-phase β-region or two-phase (α + β )-region depending on the technological possibilities of guaranteeing the required geometric shape of a semifinished product. As far as the required properties are concerned, it is reasonable to deform the alloy in the (α + β )-region. At the same time, it is easier to get complex geometric shapes as a result of deformation in the one-phase region. In the present work, by analyzing commercial batches of semifinished products of VT22 alloy, we study the influence of the technology of manufacturing, phase composition, and structural state on their mechanical properties and establish possible ways of enhancement of the strength of titanium alloys preserving the admissible level of their plasticity. Method of Investigation In the mechanical tensile and impact-toughness tests, we use standard specimens cut out from 15 commercial semifinished products of VT22 alloy produced according to different technologies (Table 1). The structure 1 Antonov Aviation Scientific-Technical Complex, Kyiv, Ukraine. 2 Kurdyumov Ins
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