Abstract
An investigation of cold and hot deformation and the subsequent heat treatment including the annealing at the (α+β)- field temperature and ageing of VST55531 alloy showed that the material after the cold drawing without the heat treatment has the extremely low values of uniform elongation and during the tensile test the strain becomes localized at a neck upon 0.2 % strain. The ageing of coldworked material improves the strength and increases a limit of uniform deformation and generally has a beneficial effect on a strengthto-ductility ratio of alloy probably due to achieving a special morphology of secondary α-phase. The obtained values of the combination of strength and ductility in the cold-worked material at 50% strain reduction degree are 1 625 MPa for UTS, 8% - El, 36% - RA, that exceed significantly the values obtained for the hot-worked and as-annealed material, and are attractive for application in products that require the increased strength and ductile characteristics.
Highlights
Due to capability of achieving the high strength and ductile characteristics the near β- titanium alloys are advanced materials for manufacturing of wide range of products beginning with large-sized die forgings and ending with miniature fasteners [1]
In the material after ageing along the slip bands the elongated precipitations of secondary α- phase are observed which form typical banding (Fig.2b see arrows)
A secondary alpha phase has an atypical morphology, in which there are no pronounced colonies of the secondary α- phase, while the particles enframe areas resembling cells, that have sizes about 20-30 nm
Summary
Due to capability of achieving the high strength and ductile characteristics the near β- titanium alloys are advanced materials for manufacturing of wide range of products beginning with large-sized die forgings and ending with miniature fasteners [1]. The hot deformation (~0.5 Тmelt) is a main method for manufacturing of stocks of titanium alloys, and mechanisms of its effect on the structure formation are sufficiently studied. For example, as for Ti-55531 alloy to study the influence of temperature – rate conditions the work for elaboration of processing map for deformation within the temperature range of β- & α+β- fields was conducted [2]–[4]. A typical picture for ageing of cold-worked β- titanium alloy is a growth of strength and a fall of ductility because of precipitation hardening process [5], [6]
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