Analysis of the creep and long-term strength of VT6 titanium alloy with preliminarily injected hydrogen
- PDF / 3,796,410 Bytes
- 8 Pages / 595.276 x 793.701 pts Page_size
- 42 Downloads / 161 Views
ANALYSIS OF THE CREEP AND LONG-TERM STRENGTH OF VT6 TITANIUM ALLOY WITH PRELIMINARILY INJECTED HYDROGEN A. M. Lokoshchenko,1 A. A. Il’in,2 A. M. Mamonov,2 and V. V. Nazarov 1
UDC 539.376:539.42:620.193.01
We describe the results of experimental and theoretical investigation of the influence of the concentration of preliminarily injected hydrogen on the creep and long-term strength of VT6 titanium alloy under the action of tensile stresses equal to 47–217 MPa. The tests carried out at a temperature of 600°C show that hydrogen (up to 0.3 wt.%) strongly decreases the steady-state creep rate of this alloy, increases the time to fracture, and lowers (severalfold) its ultimate fracture strain. The obtained results are interpreted on the basis of the analysis of changes in the structural state of the alloy. The proposed version of the kinetic theory of creep gives good agreement between the experimental and theoretical values of the principal characteristics of creep and long-term strength.
Statement of the Problem From the positions of physical metallurgy, the effect of hydrogen on the resistance of titanium alloys to plastic deformation is studied fairly comprehensively [1, 2]. However, little attention is given to the problem of creep at temperatures exceeding the temperatures of traditional applications of titanium alloys, including refractory alloys (i.e., at temperatures higher than 500°C). Furthermore, the data on the regularities of the deformation behavior of hydrogen-containing titanium alloys is fairly contradictory, especially for heterophase alloys. This is explained by the strong influence of hydrogen not only on the processes of irreversible deformation of the α- and β-phases but also on the changes in the volume fractions of the phases in alloys, sizes and morphology of the phases, the concentrations of alloying elements (Al, V, etc.) in the phases, strength, etc. The collection of all these factors (that can be called structural) also substantially affects the irreversible deformation of alloys [2]. Hence, to study the action of dissolved hydrogen on the high-temperature creep of hydrogen-containing heterophase titanium alloys, get sufficiently reliable results, and perform their correct analysis, it is necessary to apply special methodological approaches guaranteeing the possibility of the maximum possible weakening of the effect of the indicated structural factors on the mechanism and parameters of creep. Preparation of the Specimens An approach of this sort realized in the present work can be described as follows: Specimens of two-phase VT6 ( α + β )-titanium alloy (Ti – 6Al – 4V) are saturated with hydrogen by the thermodiffusion method in the Siewert’s installation. This installation enables one to get high-purity gaseous hydrogen and perform hydrogenation in a high vacuum at 600–900°C, which excludes the possibility of oxidation of the specimen surfaces [2]. 1 Scientific-Research Institute of Mechanics, Lomonosov Moscow State University, Moscow, Russia. 2 Tsiolkovskii “MATI” Russian State Technol
Data Loading...
