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Yttria (Y2O3) is the most popular lining material for the inner walls of plasma chambers, owing to its well-known resistance against corrosion by reactive fluorinated plasma. Yttria has a relatively lower toughness and strength compared to alumina (Al2O3) and zirconia (ZrO2). The present work aims to explore the strengthening and toughening of yttria by doping with zirconia, while retaining its good corrosion resistance. Ceramics with zirconia to yttria molar ratios of 2:8 and 5:5 (named 20ZY and 50ZY, respectively) were fabricated by pressure sintering in Ar atmosphere. The corrosion of the prepared ceramics in reactive fluorinated plasma (C4F8/CHF3/Ar) was investigated and compared with that of yttria as a control. The results indicated that 20ZY exhibited excellent corrosion resistance, comparable to that of yttria, while the fracture toughness and flexural strength showed increases of 87% and 44%, respectively. 50ZY exhibited a further improvement in fracture toughness and flexural strength, but at the price of a much lower resistance against plasma corrosion. A percolation model was proposed to interpret the observed plasma corrosion behaviors.

To improve the thermal and mechanical properties of Al2O3/AlN composite ceramics, a novel heterogeneous precipitation coating (HPC) approach was introduced into the fabrication of Al2O3/AlN ceramics. For this approach, Al2O3 and AlN powders were coated with a layer of amorphous Y2O3, with the coated Al2O3 and AlN powders found to favor the formation of an interconnected YAG second phase along the grain boundaries. The interconnected YAG phase was designed to act as a diffusion barrier layer to minimize the detrimental interdiffusion between Al2O3 and AlN particles. Compared with samples prepared by a conventional ball-milling method, the HPC Al2O3/AlN composites exhibited less AlON formation, a higher relative density, a smaller grain size and a more homogeneous microstructure. The thermal conductivity, bending strength, fracture toughness and Weibull modulus of the HPC Al2O3/AlN composite ceramics were found to reach 34.21 ± 0.34 W m−1 K−1, 475.61 ± 21.56 MPa, 5.53 ± 0.29 MPa m1/2 and 25.61, respectively, which are much higher than those for the Al2O3 and Al2O3/AlN samples prepared by the conventional ball-milling method. These results suggest that HPC is a more effective technique for preparing Al2O3/AlN composites with enhanced thermal and mechanical properties, and is probably applicable to other composite material systems as well.

In-situ SiAlON reinforced BN-matrix ceramics were prepared by hot pressing sintering, and the effects of different rare earth oxides on the thermal shock resistance of the materials were investigated. The effects of rare earth oxides on the phase composition, microstructure, bending strength, thermal properties and thermal shock resistance of the composites were studied. The results show that the phase composition and bending strength of ceramics with different rare earth oxides had no obvious change. However, the influence on the thermal expansion coefficient of the material was notable. The thermal expansion coefficient of the ceramics with CeO2 increased by 24.6% compared with Sm2O3 in the test temperature range. After 50 cycles of thermal shock at Δt = 1150 °C, the residual strength of ceramics with CeO2 was down to 157.1 MPa, decreased by 40.6% compared with the one tested in room temperature. And the Sm2O3-added ceramics reduced by 34.7%–167.1 MPa after thermal shock. The decrease of the residual strength of ceramics is mainly caused by the internal stress generated by the mismatch between the growth of quartz and SiAlON phase in the matrix and the thermal expansion coefficient of the matrix. However, no macro cracks were observed on the surface of the samples after thermal shock.

To meet the ultrahigh temperature requirements of a thermal protection system, an ultrahigh temperature phase of ZrB 2 was introduced into a SiBCN matrix that was fabricated using a reactive spark plasma sintering method. The thermal ablation behavior of SiBCN-Zr composites was investigated using an oxyacetylene flame test. The test results indicated that the ablation behavior of the modified ceramic composites was significantly improved over that of a monolithic SiBCN ceramic. The linear and mass ablation rates of the SiBCN-Zr material were found to be 0.004 mm/s and 4.75×10 −4 g/s, which was indicative of excellent ablation resistance. Analysis of the material after thermal ablation testing showed that ablation products mainly consisted of the ZrSiO 4 , SiO 2 and ZrO 2 phases. A reaction occurred between the SiO 2 and ZrO 2 phases in the central region of the ceramic forming ZrSiO 4 that protected the material from further thermal damage. A loose and porous oxidation layer was found from the matrix based on analysis of a cross-section image.

Ablation mechanism and properties of in-situ SiAlON reinforced BN–SiO 2 ceramic composites have been carefully studied under different ablation time. Results showed that the ablation properties depend on the ablation time. When the ablation time increases from 10 s to 60 s, the mass ablation rate increases from 0.20 mg/s to 6.24 mg/s and the linear ablation rate increases from 9.0 μm/s to 28.1 μm/s. The phases of ablation products mainly consist of amorphous SiO 2 , Mullite, Corundum and B 2 O. Four time-dependent ablation behaviors contributed to the various ablation regions: oxidation of matrix which includes BN and Si 2 Al 3 O 7 N; evaporation of B 2 O 3 ( l ) and softening of SiO 2 ( s ); scouring away of SiO 2 ( l ) and Al 2 O 3 ( l ) by high-speed gas stream; evaporation of SiO 2 ( l ) and Al 2 O 3 ( l ).