FORMATION OF METASTABLE PHASES IN NI-43.5 AT.PERCENT MO POWDER MIXTURES DURING MECHANICAL ALLOYING AND AFTER HEAT-TREATMENT

Mechanical alloying of Ni-43.5 at.% Mo powder was performed with three different types of ball mill: high-energy vibrating-frame grinder, me dium-energy vibrational mill and low-energy rotational mill. In all ca ses, the synthesized alloys exhibited an amorphous structure with some unreacted crystalline Mo. Additionally, a new phase has been formed a fter milling in vibrational and rotational devices. This phase has bee n described as bcc, with a lattice parameter a = 3.43 Angstrom. The di fferential scanning calorimetry (DSC) for these amorphous alloys exhib ited two exothermic features. The low-temperature effect has been attr ibuted to the crystallization process of the amorphous phase. The seco nd DSC thermal effect found at higher temperatures has been attributed to subsequent phase transformations resulting in a new phase defined as fee with a lattice parameter in the range 10.954-11.098 Angstrom, d epending on the mill employed. The existence of a supersaturated Ni(Mo ) solid solution in the structure of the heated samples has also been confirmed.