Effect of the reaction layer formed at the bonding interface on the tensile strength of Si₃N₄-molybdenum joints using copper-base active insert metals was examined in order to discuss the governing factors of the bonding strength and to improve the bonding strength by controlling the reaction layer thickness. The bonding joints were completed in vacuum (6 mPa) at 1573 K for 0-4.8 ks to vary the reaction layer thickness. The tensile strength of joints was, risen up to about 100 MPa, 90 MPa and 120 MPa (at R.T.) by maintaining the reaction layer thickness at around 40 μm, 2 μm and 4 μm with Cu-5%Cr, Cu-1%Nb and Cu-3%V insert metals, respectively. The fractured modes shifted from the interfacial fracture to the brittle fracture in reaction layer with increase in the reaction layer thickness. In case of the optimum reaction layer thickness, the fractured surfaces were comprised of the regions fractured in the reaction layer and at the interface between Si₃N₄ and the reaction layer. The elevated temperature tensile strength of joints bonded using Cu-5%Cr insert metal increased to the maximum value approx. 125 MPa (at 473 K), as the testing temperature was increased from R.T. to 473 K, and then fell down contrarily with rising the testing temperature.

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