Brazing vs. diffusion welding of graded Fe based matrix composite and yttria stabilized zirconia

Two graded Fe based matrix composite (MMC) – yttria stabilized zirconia (YSZ) joints were developed by brazing with Ticusil™ braze and by diffusion welding. The brazed joint was formed by solidification. During reactive brazing, some few micrometers thick continuous TiO2, Fe2Ti3O9 and FeTiO3 layers were developed at the interfaces of the braze with both YSZ and MMC. On MMC side, TiO2 was formed by reduction of FeO, stemming from MMC, by Ti. The formation of Fe2Ti3O9 and FeTiO3 compounds on YSZ side resulted from the combination of Fe and Ti which diffused through the braze, and O provided by YSZ and dissolved in the braze. The diffusion joint was developed by solid state sintering and YSZ-YSZ, YSZ-FeO and YSZ-Fe discontinuous bonds were created at the MMC-YSZ interface. During 3 points static bending tests, the diffusion joint showed a greater bending resistance compared to the brazed one. Some ways of optimization were finally proposed.