Processing , microstructure , and elevated temperature mechanical properties of MoSi 2 containing Er 2 M 03 Si 4 and Er 20 3 particles

Powders of MoSi 2 containing ErzMo3Si 4 and Er203 particles were produced by ball milling arc-melted buttons of MoSi 2 containing 20 vol.% Er2Mo3Si 4. Two composites with grain diameters of 9 and 16/zm were produced by hot pressing the powders to 98% of theoretical density at 1565 °C and 1650 °C respectively. Some evidence of mechanical alloying was observed, but the majority of the Er2Mo3Si 4 and Er203 particles were situated on grain boundaries. Compressive decremental step-strain rate tests were performed in the homologous temperature range of 0.54 T m to 0.7 T,, / ( 1100-1400 °C) for strain rates ranging from 5 x 10-4 s~ to 1 x 10 -6 s 1. Nominal values for the stress exponent, n, and the activation energy for creep, Q, were determined using a constitutive equation for power-law creep. Below 1200 °C, creep was controlled by dislocation climb and glide mechanisms with n = 4.5 and Q = 425 _+ 15 kJ mol~. At 1300 °C and above, the creep resistance was shown to be grain size dependent with creep resistance increasing with larger grain size.