Effect of additional elements on fracture toughness of (Mo0.85Nb0.15)Si2 C40/C11b lamellar-structured crystals

Abstract

a b s t r a c tVariations in the fracture toughness of lamellar-structured C40/C11 b silicides as a function of the microstructure were examined by using Cr-, Zr-, and Ir-added (Mo 0.85 Nb 0.15 )Si 2 crystals. Fracture toughness variation showed strong orientation dependence, governed by the occurrence frequency of delamination and crack deflection. The refinement of the lamellar microstructure by Ir-addition led to an increase in fracture toughness when the lamella boundary was laid perpendicular to the loading axis, although it decreased at other orientations. The variation in fracture toughness when the alloyed crystal was loaded parallel to the lamellar boundary qualitatively showed good agreement with the predictions by firstprinciples calculations on the cohesive energy of the C40/C11 b interface.