Viscosity of melts of the ternary Co – B – Si system with cobalt content of more than 60 at. %: Experiment and calculation

The article presents the results of experimental studies and viscosity calculations of the Co – B – Si system for five quasi-binary sections: Co 89 B 11 – Co 89 Si 11 , Co 81 B 19 – Co 81 Si 19 , Co 75 B 25 – Co 75 Si 25 , Co 66.7 B 33.3 – Co 66.7 Si 33.3 , Co 60 B 40 – Co 60 Si 40 . For three of them (Co 89 B 11 – Co 89 Si 11 , Co 66.7 B 33.3 – Co 66.7 Si 33.3 , Co 60 B 40 – Co 60 Si 40 ), the studies were carried out for the first time and are original. Our previously obtained results for the sections Co 81 B 19 – Co 81 Si 19 and Co 75 B 25 – Co 75 Si 25 are presented in order to compare and generalize the data for the ternary Co – B – Si system. Viscosity measurements were performed using the oscillation-cup method while heating the melt to 1700 °C and then cooling it to solidification. For all the liquid alloys studied, the temperature dependences of viscosity exhibit a monotonic exponential form similar to the Arrhenius equation. The polytherms obtained during heating and subsequent cooling are identical. In the studied concentration range, the viscosity and activation energies of viscous flow in quasi-binary sections depend weakly on the boron-to-silicon ratio in the alloy, and their concentration dependences are linear. This behavior of the viscosity isotherms is explained by the preservation of strong interatomic bonds in pairs of Co – Si and Co – B atoms in ternary melts, while no bonds are present between boron and silicon atoms. In calculating viscosity, seven equations for predicting viscosity isotherms were tested. These equations are based on the data on thermodynamic properties of the melt and/or physical properties (viscosity, density, etc.) of its components (Kozlov-Romanov-Petrov; Kaptay; Chhabra; Sato; Hirai; Budai-Benkö-Kaptay and Živković-(Budai-Benkö-Kaptay) equations). For all five quasi-binary sections, the general picture of the obtained results is preserved. The Kozlov-Romanov-Petrov equation demonstrates the best agreement with the experimental data, with a relative deviation of no more than 15 %.