Study of the fracture mechanism of NbSS/Nb5Si3 in situ composite: Based on a mechanical characterization of interfacial strength

The reinforcement/matrix interfaces in Nb-Si based in situ composites play a crucial role as the medium of load transfer in determining the overall mechanical performance. Especially during the fracture process, whether the interfaces are stronger or weaker than the matrix or reinforcement phase usually dominates the fracture behavior. In this work, the mechanical properties of NbSS/Nb5Si3 interface in Nb-15Si-24Ti-4Cr-2Al-2Hf (at%) alloy were characterized by a hybrid method of nanoindentations and finite element analysis. As a consequence, the interfacial shear strength tau 0, interfacial normal strength sigma 0 and the interfacial fracture energy Gamma n of NbSS/Nb5Si3 interfaces between the (002) alpha -Nb5Si3//(002)NbSS and [310] alpha -Nb5Si3//[110]NbSS have been evaluated to be 300 plus or minus 20MPa, 800 plus or minus 50MPa and 3 plus or minus 0.5Jm-2 respectively. According to the characterized interfacial properties, the fracture behavior of this alloy was further discussed. By comparing the fracture morphology of the composite with the characterized interfacial strength, the possible fracture process can be deduced and described as the sequence of phase boundary, brittle Nb5Si3 and ductile NbSS.