| Summary: | 博士 === 國立臺灣大學 === 材料科學與工程學研究所 === 103 === Ceramics exhibit excellent ballistic performance. However, many large cracks are formed after being hit by bullet for their brittle nature. The multi-impact protection ability of ceramics is thus limited. In the present study, a liquid-phase sintered silicon carbide (LSC) was prepared for the applications as ceramic armor. Its microstructure-ballistic performance relationships are established. The controlling factors for ballistic performance under single-hit and multi-hit are investigated. The design principles for ceramic armor are then proposed. More importantly, the factor controlling multi-impact performance is determined; direct experimental evidence is provided.
In the present study, the SiC specimens doped with Al2O3 and Y2O3 is prepared by pressureless sintering. The microstructure is characterized and the ballistic performance is evaluated. For comparison purpose, the SiC specimens prepared by solid-state sintering were also prepared.
For single-impact resistant, the kinetic energy from bullet correlates strongly to the hardness of ceramic armor. The hardness of solid-state sintered SiC (SSC) is higher; its performance against single impact is better than that of LSC. It can be related to the presence of two second phases, Y3Al5O12 (YAG) and Y4Al2O9 (YAM) after sintering at 1875 °C. Due to the formation of YAG and YAM, the hardness of LSC decreases from 23.2 GPa to 15.6 GPa. Compared with SSC specimens, the single-impact resistance of LSC specimen is 5-40% lower than that of SSC specimen.
Due to the difference of CTE between the second phase and SiC matrix, residual stresses are generated. The presence of residual stresses encourages more crack deflection. The KIC value with the second phase increases from 2.7 MPa．m0.5 to 4.6 MPa．m0.5. The toughened LSC specimen disperses the shock wave energy from bullet impacts through intergranular fracture. The trauma area in LSC specimens is 25-60% smaller than that in SSC specimen. The liquid-phase sintered SiC thus exhibit better resistance against multiple impacts.
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