Effect of yttrium near the interface on reaction and strength of sintered-SiC/Ni couple

Abstract

The effect of yttrium on reaction and bending strength of a pressureless-sintered SiC/Ni couple solid-state bonded in the range 923–1193 K was studied. The reaction between SiC and Ni is retarded by yttrium which was mixed into the SiC and Ni surfaces to a few micrometres depth by electric discharge machining. Si diffusion into Ni is retarded significantly by yttrium, but Ni diffusion into the SiC boundary phase is not. The four-point bending strength of the joined couple at room temperature is slightly improved by the treatment (maximum strength ∼110 MPa). Void or coalesced voids were observed at the reaction zone front, where fracture mainly initiated. Yttrium decreases the tendency of void formation. Void formation might be due to an imbalance of interdiffusable amounts between Si in the SiC boundary phase and the Ni bulk.