Effect of Mo and W interlayers on microstructure and mechanical properties of Si₃N₄–nickel‐base superalloy joints

Abstract

Si3N4/nickel‐base superalloy (Inconel‐625) and Si3N4/Si3N4 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: Si3N4/Mo/W/Inconel and Si3N4/Mo/W/Si3N4. The joints exhibited Ti segregation at the Si3N4/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 Si3N4/Si3N4 joints both with and without W and Mo layers was ∼142 MPa but the strength of Si3N4/Inconel joints increased from ∼9 MPa for directly bonded joints without interlayers to 53.5 MPa for joints with Mo and W interlayers.

Microstructure and Mechanical Properties of the Joint between Si3N4 and Mo Brazed by Near‐Eutectic Ag–Cu–In–Ti Filler Alloy

“…At 720 °C, the concentrated and highly brittle Cu 2 InTi and CuTi intermetallic compounds in the joint lead to residual stress accumulation, leading to crack initiation and propagation. As a result, a fracture [12,22,[29][30][31][32][33][34][35] occurred in the middle of the brazing seam (Figure 9a). When the temperature increased from 720 to 830 °C (Figure 9b-e), the reaction layer on the Si 3 N 4 ceramic side gradually became thicker and could transfer the load.…”

“…Figure 8. Comparison of mechanical properties of various brazed joints [12,22,[29][30][31][32][33][34][35]. …”