IMPRESSION CREEP-BEHAVIOR OF SIC PARTICLE MOSI2 COMPOSITES

Using a cylindrical indenter (or punch), the impression creep behavior of MoSi2-SiC composites containing 0-40% SiC by volume, was character ized at 1000-1200 degrees C, 258-362 MPa punch pressure. Through finit e element modeling, an equation that depends on the material stress ex ponent was derived that converts the stress distribution beneath the p unch to an effective compressive stress. Using this relationship, dire ct comparisons were made between impression and compressive creep stud ies. Under certain conditions, compressive creep and impression creep measurements yield comparable results after correcting for effective s tresses and strain rates beneath the punch. However, rate-controlling mechanisms may be quite different under the two stressing conditions, in which case impression creep data should not be used to predict comp ressive creep behavior. The addition of SiC affects the impression cre ep behavior of MoSi2 in a complex manner by pinning grain boundaries d uring pressing, thus leading to smaller MoSi2 grains and by obstructin g or altering both dislocation motion and grain boundary sliding.