Microstructure evolution and mechanical properties of 3YSZ/Ni composites with uniform phase distribution prepared by core-shell structure microspheres

Yttrium-stabilized zirconia(3YSZ) microspheres with different size ranges were prepared by sol-gel method, followed by electroless Ni plating on their surfaces. The as-prepared core-shell structure 3YSZ/Ni microspheres were then spark plasma sintered (SPS) into 3YSZ/Ni composites, in which a uniform distribution of ceramic and metal phases was achieved. The underlying correlations among microsphere size, Ni concentration, microstructure, and resultant mechanical properties were experimentally analyzed. Results show that: continuous and smaller microsphere sizes can obtain relatively high-density samples with good mechanical properties, which can be proved by the Minimum Solid Area (MSA) model. 3YSZ sample prepared with the optimized microsphere size range of 0-50 mu m exhibits the highest relative density and fracture toughness of 98.8% and 5.51 +/- 0.33 MPa & sdot;m1/ 2, respectively. Furthermore, the core-shell structure 3YSZ/Ni microspheres with varying Ni contents exhibited a uniform composite of flakes and particles Ni metal after sintering, among which 3YSZ/10 wt%Ni composites have achieved better mechanical properties, with density, hardness and fracture toughness of 96.9%, 8.61 +/- 0.35 GPa, 7.92 +/- 0.71 MPa & sdot;m1/2, respectively. Firstly, the uniformly dispersed Ni metal flakes or particles provide multiple toughening effects, including crack bridging, pull-out, interfacial debonding, crack deflection, etc. Secondly, due to residual stress, cracks tend to deflect near Ni metal, extending the crack path. Thirdly, the 3YSZ matrix's transition from an intergranular to a transgranular fracture also increases fracture energy consumption. Compared to the pure 3YSZ sample with a wide microsphere size range of 0-100 mu m, the fracture toughness of 3YSZ/10 wt%Ni composites with a microsphere size of 0-50 mu m is increased by 73.9%.