T. P. Tolmachev, V. P. Pilyugin, A. M. Patselov, N. V. Nikolayeva, A. M. Vlasova

PRESSURE DEPENDENCE OF SHEAR STRESS DURING HIGH-PRESSURE TORSION OF Au-Co ALLOYS IN LIQUID NITROGEN

Measurements of shear stress were for the first time carried out during mechanical alloying by high-pressure torsion of a gold-cobalt powder mixture at cryogenic temperature under various pressures. The pressures were about 5, 8, 10, and 12 GPa. The Au-Co system is characterized by limited solubility and different properties of the constituents. It has been found that, in comparison with the data obtained for torsion at room temperature, the shear stress values are higher both at the stage of initial intensive growth and subsequently, upon reaching saturation. With an increase in the pressure of low-temperature torsion, a corresponding increase in resistance to shear strain is observed at all the stages of processing. In this case, the shape of the curves at each new pressure changes, as does the staging of the strain dependence. This reflects the extreme heterogeneity of the phase composition and structure formation in the non-equilibrium alloy. The most intense reflections in the X-ray diffractogram correspond to a supersaturated fcc solid solution of cobalt based on gold. Also as a result of mechanical alloying, the components of the system are evenly distributed on the fracture surface of the alloy.

Acknowledgments: The research was financially supported by the RFBR under project No. 19-32-60039 and partially under the state assignment from the Ministry of Education and Science of the Russian Federation (theme Pressure, No. AAAA-A18-118020190104-3). The materials were produced and processed at the IMP UB RAS, Ekaterinburg. The electron microscope investigations were made with the use of the equipment of the Testing Center of Nanotechnology and Advanced Materials shared access center at the IMP UB RAS, Ekaterinburg.

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