Microstructure and magnetic properties of Co82-(x+y)Zr13V5BxSiy melt-spun ribbons

The combined addition of Boron (B) and Silicon (Si) to the rapidly quenched Zr-Co ribbons on improvement of hard magnetic properties was investigated in Co82-(x+y)Zr13V5BxSiy alloy compositions which were annealed at various temperatures. The ribbons mainly contain rhombohedral Co5Zr phase and small amount of Zr2Co11, fcc-Co and cubic Zr6Co23 phases. The addition of small amounts of Boron (B) reduces the grain size effectively of the magnetic phases, and thus significantly increases coercivity. The introduction of Silicon (Si) into Zr-Co alloys contributes to an increase in the coercivity but results in slight decreases in the magnetization. It has been observed that with increase in annealing temperature beyond 650 degrees C, the amount of the soft magnetic phases (Co23Zr6 and fcc-Co) have increased, while the amount of hard magnetic Co5Zr phase is decreased. It has been observed that with increase in annealing temperature beyond 650 degrees C, the amount of the soft magnetic phases (Co23Zr6 and fcc-Co) have increased. High coercivity values were observed in all the ribbons annealed at 650 degrees C. Among all the ribbons prepared, the maximum coercivity of 6.14 kOe was observed in Co79Zr13V5B1Si2 ribbons annealed at 650 degrees C due to the formation of a high volume fraction of hard magnetic phase (Co5Zr) and homo-geneous finer grains throughout the matrix. The achieved high BHmax value of 6.14 MGOe was measured for same composition annealed at 600 degrees C. Microstructural analysis have shown fine grains with average grain size of 140-180 nm in Co79Zr13V5B1Si2 ribbons annealed at 650 degrees C.