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

Abstract

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 μm exhibits the highest relative density and fracture toughness of 98.8% and 5.51 ± 0.33 MPa·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·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 μm, the fracture toughness of 3YSZ/10 wt%Ni composites with a microsphere size of 0–50 μm is increased by 73.9%.