Embrittlement mechanisms and magnetic properties optimization conditions in amorphous Co69Ge3.7Cr3.8Si12.5B11 alloy without ductile-brittle transition

Resumo

The influence of annealing time on the ductile-brittle transition temperature (embrittlement temperature) Т_f in amorphous Co-based alloy Со₆₉Fe_3.7Cr_3.8Si_12.5B₁₁ with extremely low saturation magnetostriction λ_s (λ_s < 10^–7) is investigated. It is revealed that the embrittlement temperature Т_f dependence on annealing time t_a can be described by the Arrhenius equation. Embrittlement at annealing temperatures higher and lower than 300°С can be described by different kinetic parameters owing to the different states of the amorphous phase. It is shown that, in the studied alloy, the embrittlement proceeds in a very narrow annealing temperature range, not exceeding 5°С. On the basis of experimental data on the evolution of hysteresis magnetic properties during isochronous annealing and isothermal exposure, the thermal treatment mode is investigated, providing rather high values of permeability μ₅ (Н = 5 mOe, f = 1 kHz) of about 50000, without transforming studied alloy into the brittle state.