| The effect of melt temperatures on the thermal stability of amorphous Co_(75)B_(25) alloys was studied by DTA, tensile test, X-ray diffraction and electrical resistance measurement. The melt of Co_(75)B_(25) alloy were quenched from 1300, 1350, 1400 and 1500℃, respectively. The pre-existing crystallites were increased with increasing melt temperature. This can be explained by the increased superheating. The crystallization temperature of the first step reaction were increased as the melt temperature increase and the reaction of the first step is believed to be a peritectoid type reaction having the equation "amorphous +Co₂B- Co₃B". The transformation mechanism of Co_(75)B_(25) alloy can be explained by the diffusion controlled growth of discs of constant thickness. The apparent diffusion activation energy for amorphous Co_75B_25 alloy is found to be 59 ㎉/㏖for 1300℃, 61 ㎉/㏖ for 1350℃, 65 ㎉/㏖ for 1400℃, 72 ㎉/㏖ for 1500℃, respectively. |
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