X-RAY-DIFFRACTION STUDY OF SOLID-STATE FORMATION OF METASTABLE MOSI2 AND TISI2 DURING MECHANICAL ALLOYING

The formation of metastable C40-MoSi2 and C49-TiSi2 during the mechani cal alloying of metal/silicon powder mixtures has been investigated by x-ray diffraction. The mechanical alloying of a Si-rich Mo/Si powder mixture results in the formation of both C11(b)-MoSi2 and C40-MoSi2. T he C40-MoSi2 phase is metastable and transforms to C11(b)-MoSi2 after annealing at 850 degrees C. The mechanical alloying of a stoichiometri c Ti/Si powder mixture leads to the incipient formation of C49-TiSi2 a nd the subsequent polymorphic transformation to C54-TiSi2. The lattice parameters of C49-TiSi2, as determined from a mechanically alloyed Ti /Si powder sample that has been annealed at 700 degrees C, are as foll ows: a(0) = 3.56 Angstrom, b(0) = 13.57 Angstrom, and c(0) = 3.55 Angs trom. (C) 1997 American Institute of Physics.