## 2 Materials and Methods  
The laminated ceramics were prepared by tape-casting followed by hot-press sintering. The ceramic slurry was prepared by ball-milling \(\alpha\)-SiC (average particle size of 0.5 \(\upmu\)m, North High-tech Industry Co., Ltd., Ningxia, China), Y\({}_{2}\)O\({}_{3}\) (purity > 99%, average particle size of 1 \(\upmu\)m, Shanghai Shuitian technology Co., Ltd., Shanghai, China), Al\({}_{2}\)O\({}_{3}\) (purity > 99.8%, average particle size of 1 \(\upmu\)m, Shanghai Shuitian technology Co., Ltd., Shanghai, China), BN (purity > 99.9%, average particle size of 0.2 \(\upmu\)m, Shanghai Shuitian technology Co., Ltd., Shanghai, China), triethylphosphate, and ethanol for 24 h. The polyvinyl butyl, dioctyl phthalate, and glycerol were then added to the slurry and ball-milled for another 24 h. After de-gassing for 30 min, the slurry was tape-casted to tapes with the desired thickness. Two types of ceramic green tapes, the matrix tapes and the interface tapes were prepared for the lamination. The matrix tape consisted of a 92 wt.% \(\alpha\)-SiC and 8 wt.% Al\({}_{2}\)O\({}_{3}\)/Y\({}_{2}\)O\({}_{3}\) mixture (the molar ratio of Al\({}_{2}\)O\({}_{3}\) to Y\({}_{2}\)O\({}_{3}\) was 3:2) of total ceramic powder. The interface tape consisted of a 46 wt.% \(\alpha\)-SiC, 46 wt.% h-BN and 8 wt.% Al\({}_{2}\)O\({}_{3}\)/Y\({}_{2}\)O\({}_{3}\) mixture of total ceramic powder. The thickness of the matrix tape and interface tape was approximately 0.25 mm and 0.05 mm, respectively. The green tapes were then cut into 130 \(\times\) 130 pieces and stacked as designed. The uniform-layered sample had a uniformly layered structure. In each repeating unit, the number of the matrix layer to the number of the interface layer was 10 to 1. The gradual-layered sample was designed as a gradually layered structure, i.e., the number of the matrix layer between two interface layers was gradually changed. The number of the matrix layers using the following sequence from strike face to the back: 10, 10, 5, 2, and 2. The layer structure for different sample types is listed in Table 1.  
The ceramic green bodies were then prepared by pressing the stacked tapes under the pressure of 80 MPa. Before sintering, the green bodies were de-binded at 850 \({}^{\circ}\)C for 4 h in nitrogen. The de-binded samples were then sintered at temperature ranging from 1840 \({}^{\circ}\)C to 1900 \({}^{\circ}\)C for 1 h under the pressure of 40 MPa in argon. After firing, the sintered ceramic plates were cut and polished into the dimension of 120 \(\times\) 120 \(\times\) 5.5 mm, as shown in Figure 1.  
The ballistic performance was carried out following the Chinese national military standard, GJB4300-2002. The 5.8 mm \(\times\) 42 mm type-87 steel core bullet was used in this study. The bullet had a full metal jacket and the mass of the bullet was 4.15 g. The velocity of the bullet was measured using an infrared tachometer. The infrared tachometer had two consecutive screens so that it could record the time for the bullet that passed through it and to calculate the velocity of the bullet. The gunpowder for the bullet was adjusted based on the velocity measured several times to guarantee that the velocity of the bullet was within the range of 900 to 920 m/s. The armor or armor system was mounted on the \begin{table}
\begin{tabular}{c c} \hline
**Sample Type** & **Layer Structure** \\ \hline Uniform-layered & 10 matrix layers followed by 1 interface layer \\ Gradual-layered & Gradually layered, the number of the matrix layer \\  & followed by 1 interface layer was 10, 10, 5, 2, 2 \\ Pure-matrix & Matrix layers without any interface layers \\ \hline \end{tabular}
\end{table} 
Table 1: The layer structure for different sample types. Figure 1: The image of the 120 \(\times\) 120 \(\times\) 5.5 mm laminated ceramic prepared in this study (gradual layered). armor carrier. The armor carrier was filled with clay as the backface signature (BFS). The configuration for the ballistic testing is shown in Figure 1(a).