Glass formation and sluggish nucleation: Growth in ternary eutectic Co-Hf-B system

Four rapidly quenched (RQ) ribbons of Co-Hf-B alloys with the ternary eutectic compositions were obtained by melt-spinning. The thermal stability and glass forming ability (GFA) were studied using high-temperature differential scanning calorimetry (DSC) measurements. Very high GFA was found for all the alloys studied, which are characterized by high values (above 0.64) of the reduced crystallization temperature (Trx = Tx/Tm). The supercooled liquid region (ΔTx = Tx − Tg = 45 K) was found for Co66Hf6.5B27.5 amorphous alloy with equilibrium microstructure composed of three intermetallic compounds (Co2B, Co21Hf2B6 and Co3HfB2). The high GFA was explained by the sluggish nucleation and slow growth of the complex structure intermetallic compounds in the ternary Co-Hf-B system. The Hf presence in the alloys studied plays an important role due to the slow diffusivity of relatively large atoms of this element.