Influence of the Combined Radial Shear Rolling and Rotary Forging on the Deformation Mode of the Small-Diameter Rod Billet Made of Titanium Alloys

Abstract

This work is devoted to the finite-element modeling of the deformation mode of a small-diameter rod billet during pressure hot treatment in the combination of radial shear rolling (RSR) and rotary forging (RF). Modeling is performed using a rheological model of the Ti–6Al–4V titanium alloy using the QForm VX program. The combination of RSR for one passage of a billet 15 mm in diameter to a rod 12 mm in diameter and subsequent RF in 1, 2, and 3 passages with the formation of rods 11, 10, and 8 mm in diameter is modeled. The operation-by-operation accumulation of the plastic deformation in nonuniformity conditions of its distribution is taken into account. Intermediate and final plastic deformation fields, deformation rates, and average stresses are found. It is shown that the distribution of the plastic deformation after RSR has the pronounced gradient character with a minimal value (3 and larger) at the cross-section periphery and a minimal value (about 1) in the center. Due to this, RF, even with small reductions, leads to a substantial increase in uniformity of the deformation mode when compared with the billet after the same diameter after radial shear rolling only. In addition, residual tensile stresses decrease due to compressing stresses during RF. The direct experimental approval of the combined deformation method is performed for the promising Ti–Zr–Nb shape memory alloy of medical prescription when fabricating rods 7–8 mm in diameter under pilot production conditions. The results of modeling are qualitatively confirmed by the metallographic analysis. The prospects of a combination of RSR and RF for the development of industrial fabrication technologies of small-diameter rods with a high uniformity of finely dispersed structure are shown.