PSI - Issue 40

Vladlen Nazarov et al. / Procedia Structural Integrity 40 (2022) 325–333 Vladlen Nazarov / Structural Integrity Procedia 00 (2022) 000 – 000

329

5

(2012) of photographs with structures for the VT5 titanium alloy after creep rupture tests that hydrogen saturation to a concentration of 0.1% by weight leads to a 3− fold decrease in porosity near the area of the fracture. Since the initial goal was to study the effect of hydrogen on the mechanical creep characteristics of a   titanium alloy the photographs (Fig. 5) have showed an undesirable presence of a   phase in specimens with a hydrogen concentration of 0.1% by weight.

a

b

c

d

Fig. 5. Structures Nazarov (2012) of the VT5 titanium alloy at the concentration of embedded hydrogen 0.1% by weight:   grain boundaries, where the   grains has a bright field (a); uneven content of the   phase in the layers of the   grains, where the   phase has a dark field (b, c);   phase in the form of streaks and curves in the form of dislocation output indicates one of two mechanisms of deformation: by moving dislocations (mechanism 1) and by moving grain boundaries (mechanism 2) (d). Thus, the concentration of hydrogen 0.1% by weight leads to a noticeable hardening of the titanium alloy VT5 under the influence of a stationary tensile force (for fatigue, the opposite effect is possible, in which the non stationary tensile force will lead to accelerated rupture). The effect of hydrogen on the mechanical characteristics and properties of titanium alloys at lower concentrations has long been investigated and is used in the technological processes of precipitation and stamping of large sized structural elements, when the preliminary introduction of hydrogen to small concentration values leads to an increase in the yield strength, and after the completion of the technological process, hydrogen is extracted back from the titanium alloy. 4. Torsion and tension at high temperature Tests at uniaxial tension are performed to determine the mechanical characteristics of the material under specified conditions. The need for complex stress tests occurs when it is necessary to take into account either the strength anisotropy or to recreate the real stress state from the structural element on the specimen in the laboratory.