The effect of Nb and W alloying additions to the thermal expansion anisotropy and elastic properties of Mo5Si3

The directional thermal expansion and elastic properties of Mo5Si3, (Mo0.8Nb0.2)5Si3, and (Mo0.85W0.15)5Si3 have been studied as a function of temperature through the use of single crystals. Thermal expansion anisotropy was reduced by Nb and W alloying. The decrease in thermal expansion anisotropy by Nb alloying was only found to occur at low temperatures, and thermal expansion anisotropy of (Mo0.8Nb0.2)5Si3 was similar to that for the other two compounds at 800 °C. Values for the polycrystalline Young’s, bulk, and shear moduli calculated from the measured single-crystal elastic constants are reduced by Nb alloying, and increased by W alloying at all temperatures studied. The elastic modulus E was calculated for the orientations between [100]-[001] and [100]-[010]. In contrast to the effects of Nb on thermal expansion anisotropy, Nb alloying increased the E[001]/E[100] elastic anisotropy.