Solid-state reaction to synthesize Ni-Mo metastable alloys

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Abstract
In the Ni‐Mo system, amorphous alloys and three metastable crystalline (MX) phases, i.e., an hcp (hcp‐I), an enlarged hcp (hcp‐II), and a fcc phase, were synthesized by solid‐state reaction in the Ni‐rich multilayers. An interesting point is that with increasing the annealing temperature, the hcp‐I phase was formed first in the Ni67Mo33 film and then turned amorphous, while in the Ni75Mo25 film, the amorphous phase was formed first and then changed into the hcp‐I phase. The compositions of three MX phases were determined experimentally. A free‐energy diagram of the Ni‐Mo system was established by calculating the free energies of the amorphous phase and the three MX phases, as well as those of the solid solutions and the related compounds on the basis of the model of Niessen et al. [CALPHAD 7, 51 (1981)] and Alonso’s method [Solid State Commun. 46, 765 (1983)]. The calculated free‐energy diagram can give relevant interpretation to the observed phase formation behaviors.