MICROSTRUCTURES AND PROPERTIES OF THE REFRACTORY COMPOUNDS TISI2 AND ZRSI2

Physical and mechanical properties of polycrystalline high melting point TiSi2 and ZrSi2 intermetallics have been investigated with special emphasis on their complex orthorhombic structures. The thermal expansion and the elastic stiffness are correlated to the compression moduli as well as to the lattice energies and the interatomic distances of the metal-metal and metal-silicon bond. The anomalous high flow stresses at medium temperatures are caused by sessile (a over arrow pointing right + b over arrow pointing right)/2 superdislocations of the hexagonal silicon ring structures, which will be thermally activated at temperatures above 800-degrees-C. This leads to an exponential decrease of the flow stress vs. temperature curves. The steady state creep exhibits stress exponents of about n = 3 and the mechanisms are discussed on the base of the viscous dislocation glide model, developed by Wertman, and the jogged screw dislocation model, proposed by Barrett and Nix. The high activation energies of (330 +/- 20) kJ/mole (TiSi2) and (405 +/- 20) kJ/mole (ZrSi2) are attributed to the diffusion of silicon in the complex C 54 and C 49 lattices of the ordered disilicides.