PSI - Issue 2_A

Mikhail V. Bannikov et al. / Procedia Structural Integrity 2 (2016) 1071–1076 Author name / Structural Integrity Procedia 00 (2016) 000– 00

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Fig. 4. Results of fatigue tests of Armco iron in the air and in contact with the liquid metal In the case of ultrasonic loading of the sample interacting with liquid gallium, the fatigue crack was initiated at the sample surface as in the case of operation of the classical cycle fatigue mechanisms. The edges of the cracks indicate that liquid metal penetrates into the crack during fatigue tests. The main role in gigacycle fatigue durability of the material is played by the process of nucleation of the fatigue cracks by Bathias (2005), Mughrabi (2013), and the process of its propagation in the material takes only 2-5% of the "fatigue life". The fact that at the same level of the stress, fatigue fracture in the material being in contact with liquid metal occurs several orders of loading cycles earlier than in the air indicates that in general, changes in the mechanism of crack initiation occur under the influence of the surfactant.

(a) (b) Fig. 5. Center of fatigue crack initiation а) – optical microscope; б) – scanning electronic microscope

Fracture surfaces of the samples were uncovered after cooling by liquid nitrogen and studied by the optical profilometer and scanning electron microscope (Fig.5). The analysis of fractured surfaces revealed that the crack in the presence of liquid metal is initiated at the surface of the material. The analysis of the chemical elements using