Experimental evaluation of the curves of maximal ductility and fluidity for titanium alloys in hot torsion testing

Abstract

The purpose of this work is to clarify the temperature-deformation modes of extrusion pipes of titanium alloys (VT1-0, PT-7M, VT-14, VT-15, TS-5 and TS-6) and to determine the regression coefficients of the Hansel-Spittel equation by investigating plasticity and the deformation resistance during hot rotation of the specimens. This method using the torque, obtained at test procedures, makes it possible to get a complete picture of the metal flow developing in conditions of prevailing shear deformation. The shear strain, calculated from torque curves, is used as an indicator of transition to plastic area and consequent failure The hot-torsion tests were performed on a testing machine SMEG-10Т (torsion machine of the horizontal type with a maximum torque 100 Nm, equipped with a heating chamber). The temperature of the samples during the tests was in range of 800…1250 oС. Presented in this work results of hot-torsion experiments and its statistical processing are aimed to determine the regression coefficients of Hansel-Spittel equation which can be applied to calculation of parameters of seamless tubes extrusion for studied titanium alloys. Using specimens with a different ratio of radius to the length of the working part, were obtained the range of the strain rates from 6 to 25 s–1. The sensibility to strain rate at hot deformation was studied. It was found that it falls at temperatures of maximal duration of ductile behavior for majority of studied titanium alloys, excepting VT15 and PT7-M. The main results of the study should be considered experimentally determined curves of the torque dependence on the angle of rotation of the sample to change the resistance of deformation of the metal, which allowed to clarify the temperature interval of maximum ductility during pressure treatment for alloys VT1-0, PT-7M, VT-14, VT-15, TS-5 and TS-6.