Diffusion in molybdenum disilicide

Abstract

Diffusion in molybdenum disilicideThe diffusion behaviour of the high-temperature material molybdenum disilicide (MoSi 2 ) was completely unknown until recently. In this paper we present studies of Mo selfdiffusion and compare our present results with our already published studies of Si and Ge diffusion in MoSi 2 .Self-diffusion of molybdenum in monocrystalline MoSi 2 was studied by the radiotracer technique using the radioisotope 99 Mo. Deposition of the radiotracer and serial sectioning after the diffusion anneals to determine the concentration-depth profiles was performed using a sputtering device.Diffusion of Mo is a very slow process. In the entire temperature region investigated (1437 to 2173 K), the 99 Mo diffusivities in both principal directions of the tetragonal MoSi 2 crystals obey Arrhenius laws, where the diffusion perpendicular to the tetragonal axis is faster by two to three orders of magnitude than parallel to it. The activation enthalpies for diffusion perpendicular and parallel to the tetragonal axis are Q ? ¼ 468 kJ mol À1 (4.85 eV) and Q k ¼ 586 kJ mol À1 (6.07 eV), respectively. Diffusion of Si and its homologous element Ge is fast and is mediated by thermal vacancies of the Si sublattice of MoSi 2 . The diffusion of Mo is by several orders of magnitude slower than the diffusion of Si and Ge. This large difference suggests that Si and Mo diffusion are decoupled and that the diffusion of Mo likely takes place via vacancies on the Mo sublattice.

Effects of solute and vacancy segregation on migration of a/4〈1 1 1〉 and a/2〈1 0 0〉 antiphase boundaries in Fe3Al

“…Kinetic data for diffusion [26][27][28] and ordering [31] used in the present study are listed in Table 1. Since various mobilities are employed in the present study, the mobilities are classified in Table 2 for clarity.…”

Internal friction in Fe–Al–Si alloys at elevated temperatures

“…As the next step, the computer analysis was carried out assuming two IF peaks (AleAl and SieSi) with unknown peak temperatures, approximately known activation energies of the AleAl and SieSi reorientations (from diffusion data [22,23]), and a broadening parameter b ¼ 0, i.e. each process has one relaxation time.…”

Mechanisms of lamellar structure formation and Cr interfacial segregation in C11b-MoSi2/C40-NbSi2 dual phase silicide verified by a phase-field simulation incorporating elastic inhomogeneity

“…The diffusion coefficient terms of M are assumed to be same as that for Mo self-diffusion along the a-axis in C11 b -MoSi 2 obtained experimentally [37]. We employed a relatively low value for a which in order to avoid the C11 b /C40 interface migration without being associated with solute diffusion.…”