TOUGHENING MOSI2 WITH NIOBIUM METAL-EFFECTS OF MORPHOLOGY OF DUCTILE REINFORCEMENTS

摘要

Morphology effect of ductile reinforcements was evaluated using a four-point bend test on chevron-notched MoSi2 composites reinforced with 20 vol. % niobium. The niobium used had three different morphologies, i.e., fibre, foil and particle. The thickness of the foils was 250 mu m, while the fibres and particles had diameters of 250 and 200 mu m, respectively. Toughness of MoSi2 composites was increased from 3.3 MPam(1/2) for the matrix to 15 MPam(1/2) with the incorporation of the Nb fibres or foils. The particulate composites also exhibited an increase in toughness (similar to 7 MPa m(1/2)). The toughening achieved was mainly attributed to ductile phase bridging in all the composites tested. The relatively small toughness improvement in the particulate composites was ascribed to the embrittlement of the Nb particles. The results indicate that toughening by crack bridging depends mainly on the intrinsic properties of the ductile bridging ligaments rather than on their morphology, and that the embrittlement of the bridging ligament is detrimental to the toughening of the composites. [References: 40]