MECHANICAL-PROPERTIES AND MICROSTRUCTURE OF SPUTTER-DEPOSITED NB5SI3 NB MICROLAMINATES/

Crystalline Nb5Si3/Nb microlaminates were fabricated to a thickness of 20 mu m by depositing the materials onto elevated temperature (750 de grees C) substrates. Modulation wavelengths of the microlaminates were varied (lambda = 40 and 200 nm) while holding their silicide volume f raction constant to assess the effect of layer thickness on the compos ite properties. X-ray and selected area diffraction confirmed that bot h the metal and silicide layers exhibited a polycrystalline structure in the as-deposited microlaminates. Nanoindentation measurements of bo th microlaminates indicated that calculated elastic modulus values wer e similar to the values obtained by the rule-of-mixtures (ROM). Nanoha rdness values of the microlaminates increased with decreasing waveleng th in a manner described by the Hall-Fetch relationship. Vickers hardn ess (Hv) measurements were also found to be a function of the modulati on wavelength, decreasing from 7.32 GPa at lambda = 40 nm to 3.04 GPa at lambda = 200 nm. Even with a Nb volume fraction of 50%, the lambda = 40 nm microlaminate and the monolithic Nb5Si3 film exhibited similar Vickers hardness values of 7.5 GPa. These results show the significan t role of modulation wavelength on the hardness, compressive strength, and toughness characteristics of a microlaminate composite.