High temperature strength of Mo-Mo3Si-Mo5SiB2 molybdenum silicides

Ternary and quaternary intermetallic alloys consisting of the phases Mo3Si, Mo5SiB2 (T2) and alpha-Mo (Mo solid solution) were fabricated by melting and casting as well as powder-metallurgy (PM). A newly developed PM technique allowed the fabrication of microstructures with a nearly continuous alpha-Mo matrix. The creep strengths were determined by slow compression testing at an initial strain rate of 10(-5) s(-1) at temperatures ranging from 1200 to 140.6 degreesC. Alloying with niobium improved the creep strength much more than alloying with tungsten. This result is rationalized in terms of the atomic size difference between Mo and Nb. Not only the composition but also the topology and scale of the microstructure had a pronounced influence on the creep strength. As expected, coarse microstructures with isolated alpha-Mo particles resulted in higher creep strengths than microstructures with a continuous alpha-Mo matrix. (C) 2003 Published by Elsevier Science Ltd.