Fabrication and microstructure of a ZrO2–Ni functionally graded bonding interlayer using the airbrush spraying method

A Ni–ZrO2 (stabilised with 3 mol% Y2O3) functionally graded (FG) layer of around 150 μm thick was prepared by airbrush spraying of diluted organic suspensions. Five layers including the two pure end compounds were sequentially sprayed onto Y2O3-doped tetragonal zirconia substrates, in 25 vol.% compositional steps. Two ZrO2 bulk samples were joined by this FG interlayer when heated in a high-vacuum furnace at temperatures of 1100–1200 °C. Neither cracking nor delaminating occurred within the FG interlayer or at the interfaces with the bulk material. For the 1200 °C treatment, some reaction at the ZrO2 bulk/Ni interface and also a small amount of nucleation of m-ZrO2 within the interlayer occurred. The porosity in each layer was estimated from microhardness tests.