Effect of Mo and W interlayers on microstructure and mechanical properties of Si ₃ N ₄ –nickel‐base superalloy joints

Abstract Si ₃ N ₄ /nickel‐base superalloy (Inconel‐625) and Si ₃ N ₄ /Si ₃ N ₄ joints with refractory metal (W and Mo) interlayers were vacuum brazed using a Ti‐active braze Cu‐ABA (92.75Cu–3Si–2Al–2.25Ti) at 1317 K for 30 min with the following interlayered arrangements: Si ₃ N ₄ /Mo/W/Inconel and Si ₃ N ₄ /Mo/W/Si ₃ N ₄ . The joints exhibited Ti segregation at the Si ₃ N ₄ /Cu‐ABA interface, elemental interdiffusion across the joint interfaces, and sound metallurgical bonding. Knoop microhardness profiles revealed hardness gradients across the joints that mimicked the interlayered arrangement. The compressive shear strength of Si ₃ N ₄ /Si ₃ N ₄ joints both with and without W and Mo layers was ∼142 MPa but the strength of Si ₃ N ₄ /Inconel joints increased from ∼9 MPa for directly bonded joints without interlayers to 53.5 MPa for joints with Mo and W interlayers.