Microstructure and interfacial stability of diffusion bonded HfB2-SiC and ZrB2-SiC based composites

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Manufacturing of complex-shaped UHTCs occasionally requires joining of dissimilar materials. Herein diffusion bonded (1800 °C and 40 MPa) two dissimilar composites, ZrB 2 -20vol%SiC (ZS) and HfB 2 -20vol% SiC (HS), are compared with similar ones i.e., ZS-ZS. The ZS-ZS joints exhibit a seamless interface with uniform hardness (∼20 GPa) and Young’s Modulus (∼366 GPa). For ZS-HS, diffusion and reactivity between Hf and Zr created an interface with (Zr, Hf)B 2 solid solution , thus, decreasing interfacial hardness and Young’s modulus (by ∼17 %, ∼3 %) from HS sides, but were similar to that of ZS side. Under compressive stresses, both joints exhibited interfacial stability and comparable bending and shear strength , i.e., (∼259 MPa, ∼87 MPa for ZS-HS, and ∼296 MPa, ∼113 MPa for ZS-ZS). Though good thermal stability of joints is observed when oxidized at 1400 °C, 60 min, ZS-ZS joints with uniform mechanical properties and good structural and thermal stability are more promising for complex shape applications. • Successful spark plasma joining of similar and dissimilar ZrB 2 -SiC and HfB 2 -SiC composites without filler layer. • Uniform mechanical properties and interfacial strength (∼300 MPa) comparable to the base materials for ZS-ZS joints. • Despite non-uniform hardness and elastic modulus, good interfacial strength (∼259 MPa) obtained for ZS-HS joints. • Good structural stability of joints without any defects, after oxidation at 1400 °C, for 60 mins.