IN-SITU FRACTURE MONITORING OF PLASMA-SPRAYED MOSI2-TA COMPOSITES

Initial work has shown that the ambient toughness of brittle silicide intermetallics such as MoSi2 have been toughened by incorporating irre gular pancake-shaped Ta phases via deposition of powders by plasma-spr ay processing techniques. The mechanisms of toughness enhancement were observed in situ by conducting fracture toughness tests in an instrum ented loading stage situated in a scanning electron microscope. It was observed that increases in toughness were obtained via ductile-phase toughening and the development of bridged-zones. The initiation and pe ak toughness of the composites varied with testing orientation, with t he highest values measured when the crack plane intersected the Ta par ticles perpendicular to their edge. The shape of the resistance curve, however, was independent of Ta orientation.