Effect of carbon addition on elevated temperature crack growth resistance in (Mo,W)Si₂-SiC_p composite

Abstract

Experimental results on subcritical crack growth behavior of hot-pressed MoSi₂-50 mol% Wsi₂ alloy reinforced with 30 vol% SiC particles in the temperature range 1200° -1300° C are presented. The effect of 2 wt% C addition on the stable crack growth resistance of this composite was investigated under both static and cyclic loading conditions. The results indicate that the addition of carbon to the composite improves the subcritical crack growth resistance under both static and cyclic loads and increases the elevated temperature capabilities of the (Mo,W)Si₂ composite. Increasing the temperature from 1200° to 1300°C is found to increase the crack growth velocities with a concomitant decrease in the crack growth initiation thresholds. Electron microscopy of the crack-tip region indicates that the stable crack growth process is influenced primarily by interfacial cavitation. At 1300°C, deformation processes such as twinning of the SiC particles and dislocation motion within the matrix grains appear to play an active role in determining the crack growth kinetics. The role of glassy phase in influencing the high-temperature fracture behavior and its implications for design of the microstructures of the brittle materials are discussed.