## 2 Materials and Methods
### Performance Testing of the Ceramic Material  
The ceramic material after hot pressing was cuboid with the size of 3 mm \(\times\) 4 mm \(\times\) 35 mm. The surface roughness Ra of the ceramic material was less than 0.1 \(\upmu\)m. The instrument used for the hardness test of the ceramic tool material was the Hv-120 Vickers hardness tester (Hv-120, Jinan, China), which measured with the Vickers indentation method. The indentation load was set to 196 N for 15 s. The indentation of the ceramic material was observed and measured by optical microscope. Then, the length of the diagonal of the two indentations was recorded. The hardness of the ceramic material could be calculated by the function:  
\[\mathrm{H_{V}}=\frac{1.8544\mathrm{P}}{\left(2\mathrm{a}\right)^{2}} \tag{1}\]  
Figure 1: The flow chart of the composite ceramic material preparation.  
where \(\rm{H_{V}}\) is the hardness value (GPa); P is the indentation load (N); and 2a is the arithmetic average value of the diagonal lengths of the two indentations produced.  
The flexural strength of the ceramic material was measured by the three-point bending method. The span value was 20 mm and the displacement loading speed was 0.5 mm/min. The flexural strength of the ceramic material could be calculated by the function:  
\[\rm{\sigma_{f}}=\frac{3 PL}{2 bh^{2}} \tag{2}\]  
where \(\rm{\sigma_{f}}\) is the flexural strength (MPa); P is the maximum load (N) value loaded when the sample is broken; L is the distance (mm) between the two supports supporting the sample; and b and h are the width (mm) and height (mm) of the sample, respectively.  
The fracture toughness was also measured by the indentation method. The instrument used for fracture toughness test of the ceramic material was the Hv-120 Vickers hardness tester (Hv-120, Jinan, China). The fracture toughness of the ceramic material could be calculated by the function:  
\[\rm{K_{IC}}=0.203H_{V}a^{\frac{1}{2}}\Big{(}\frac{c}{a}\Big{)}^{-\frac{2}{3}} \tag{3}\]  
where \(\rm{K_{IC}}\) is the fracture toughness (MPa-m\({}^{1/2}\)); \(\rm{H_{V}}\) is the hardness value (GPa) measured by the Vickers indentation method; a is the half length (mm) of the diagonal lengths; and c is the half length (mm) of the crack diagonal.  
Density test of the ceramic material was performed by the drainage method. The dry weight M\({}_{1}\), submerged weight M\({}_{2}\) and wet weight M\({}_{3}\) of the sample were weighed by a precision electronic balance (ME105 DU, Jinan, China). The density of the ceramic material could be calculated by the function:  
\[\rm{\rho_{s}}=\frac{M_{1}\rho_{0}}{M_{3}-M_{2}} \tag{4}\]  
where \(\rm{\rho_{s}}\) is the density (g/cm\({}^{3}\)) of the sample; \(\rm{\rho_{0}}\) is the density (g/cm\({}^{3}\)) of the distilled water; M\({}_{1}\) is the weight (g) when the sample is dried; M\({}_{2}\) is the submerged weight (g) in the liquid; and M\({}_{3}\) is the wet weight (g) measured in the air after the sample is sufficiently absorbed. The relative density of the ceramic material could be calculated by the function:  
\[\rm{\rho}=\frac{\rm{\rho_{s}}}{\rm{\rho_{t}}}\times 100\% \tag{5}\]  
where \(\rm{\rho}\) is the relative density of the ceramic material; \(\rm{\rho_{s}}\) is the density (g/cm\({}^{3}\)) of the sample; and \(\rm{\rho_{t}}\) is the theoretical density (g/cm\({}^{3}\)).  
To decrease the measurement error and ensure the accuracy of the measurement, every ceramic material was tested 5 times. The arithmetic average value was the measured value of the ceramic material.