Experimental studies of high-temperature creep of titanium alloy VT6 under conditions of a complex stress state under the influence of an aggressive medium

The results of experimental studies of high-temperature creep and long-term strength under conditions of a uniaxial and complex stress-strain state are presented. Tests for uniaxial tension, torsion and their combined action.
The tests were carried out on laboratory tubular specimens made of VT6 material at a temperature of 600$^\circ$C as delivered and under conditions of exposure to an aggressive environment. An aggressive environment was created by preliminary hydrogenation of laboratory samples with different hydrogen-ion concentration by mass C$_{m}$ equal to 0.15 % and 0.3 %.
Experimental information for the construction of material parameters and scalar functions of a thermal creep model with isotropic-kinematic hardening is presented. This information is obtained from basic experiments to determine: the initial radius of the zero level creep surface; fans of creep curves at different levels of specified stresses, with obtaining the characteristics of the third section on the creep diagram, which precedes the failure of the sample at a fixed temperature at a given time interval; torsional creep curves up to the moment of loss of stability in the working part of the specimen. Based on the results of tests for uniaxial loading, two levels of stress intensity were selected, with different combinations of which experiments were carried out under conditions of complex loading.
The results of experimental studies of high-temperature creep and long-term strength under several different programs of isothermal loading under conditions of a complex stress-strain state are presented. Investigations are carried out for specimens made of VT6 alloy at delivery condition, under conditions of exposure to an aggressive environment. The obtained experimental information makes it possible to determine the necessary material parameters and to verify the used mathematical model of thermal creep.