Amorphization behavior of mechanical alloyed CoTa alloy powders prepared by ball milling

Amorphization behavior of Cox-Ta100-x powders by mechanically alloying mixtures of pure crystalline Co and Ta powder with a high-energy shaker ball mill was studied. The mechanically alloyed powders were amorphous for the composition range between Co10Ta90 and Co80Ta20. This range is larger than for amorphous alloys prepared by the r.f. sputtering process and equal to that of electron-gun-deposition method. A supersaturated cobalt solid solution formed for Co-rich composition. Moreover, the thermal stability was investigated by differential thermal analysis. The crystallization temperature of amorphous Co-Ta powders was found to be proportional to Ta content and higher than those of amorphous alloys produced by thin-film techniques. The high values of activation energy of amorphous Co-Ta powders were observed near the eutectic compositions. Experimental results indicated that the amorphization rate in the early stage of mechanical alloying was faster for the middle compositions than for Co- and Ta-rich compositions.