Pressure dependence of shear stress during high-pressure torsion of the Au–Co alloys in liquid nitrogen

Abstract

Measurements of the shear stress were carried out during mechanical alloying by high-pressure torsion of gold-cobalt powder mixing under cryogenic temperature at various pressures for the first time. The pressures were about 5, 8, 10 and 12 GPa. The Au–Co system is characterized by restricted solubility and difference in properties of the constituents. It was found that, in compari-son with the data obtained at room torsion temperature, the values of the shear stress are higher both at the stage of the initial intensive growth and subsequently, upon reaching saturation. With an in-crease in pressure of low-temperature mechanical alloying, a corresponding increase in the resistance to shear strain is observed at all 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 heter-ogeneity of the structure formation and phase composition processes of the non-equilibrium alloy. The most intense reflections in the X-ray diffractogram correspond to supersaturated fcc solid solu-tion of cobalt based on gold-base matrix. Also as a result of mechanical alloying, the components of the system are evenly distributed on the fracture surface of the alloy.