Critical free energy for nucleation from the congruent melt of MoSi2

As a potential candidate for high-temperature applications, the intermetallic compound molybdenum disilicide, MoSi2, has been the focus of many recent investigations. plasma spraying has been demonstrated as a viable technique for producing dense monolithic and composite forms of MoSi2. It has been reported that in the plasma spraying process, in which the melting of powders and the rapid solidification are involved, the metastable hexagonal structure of beta-MoSi2 is the major phase observed in the as-sprayed molybdenum disilicide deposit and/or coating. This study examines the formation of beta-MoSi2 in terms of the classical nucleation theory. It is concluded that the critical free energy for nucleation of beta-MoSi2 is lower than that of the stable phase of alpha-MoSi2 on solidification and thereby beta-MoSi2 will be the prevailing phase formed by the homogeneous nucleation mechanism from liquid droplets of a certain undercooling, resulting from the rapid solidification rate.