Compositional dependence of amorphization of M–C–Si (M=Fe, Co or Ni) materials by mechanical alloying

Mechanical alloying (MA) of elemental powder mixtures of Mx(C,Si)100−x (M=Fe, Co or Ni) with x=65–85 at.% was carried out in an argon atmosphere by use of a planetary ball mill. In the MA processing, the addition of silicon to M–C materials highly enhanced amorphization of the MA materials. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) results of MA-processed materials showed that after 720 ks of processing, Cox(C,Si)100−x samples can be amorphized in the compositional range of x=65–80 at.%, whereas the amorphous range of Mx(C,Si)100−x (M=Fe or Ni) accessible under the same milling condition lies in the range of x=70–75 at.%. This seems to be associated with the difference in crystal plasticity of the host metals M, in view of the fact that the metals Co, Fe, and Ni have hexagonal close-packed (h.c.p.), body-centered cubic (b.c.c.), and face-centered cubic (f.c.c.) structures at ambient temperature, respectively. Prolonged MA processing made it possible to amorphize Fe80(C, Si)20 materials whose amorphization were not attained by liquid quenching process [Metall. Trans. A 18 (1987) 715]. The crystallization temperature Tx and Curie point Tc of MA-processed amorphous Fe70(C, Si)30 samples, measured by DSC, raised with increasing Si content. For instance, the values of Tx and Tc of the Fe70C10Si20 sample were 761 and 624 K, respectively.