ON THE CREEP OF DIRECTIONALLY SOLIDIFIED MOSI2-MO5SI3 EUTECTICS

The high temperature deformation behaviour of MoSi2-Mo5Si3 eutectics has been investigated as a function of lamellar spacing over the temperature range 1100-1400 degrees C and strain rates (epsilon) of 1 x 10(-4) to 1 x 10(-6)s(-1) Specimens with lamellar morphologies were produced by directional solidification using the Czochralski method at pull rates of 25-210 mm/h giving lamellar spacings (lambda) of 2.6 to 1.09 mu m. The measured flow stress was found to increase as the lamellar spacing decreased for a given strain rate. A constitutive model for creep that incorporates reinforcement spacing for creeping fibers in a creeping matrix was found to describe the creep behaviour of the eutectic, i.e. epsilon alpha lambda(m) with m = 1. Creep deformation of the eutectic was controlled by 1/2[110](001) partial dislocations in the Mo5Si3 phase. The creep behaviour of a [314] oriented Mo5Si3 single crystal was also investigated.