Mechanism Of Superfast Sintering Of Ceramic Composites By SHS/QP Process

Self-propagating High-temperature Synthesis/Quick Pressing or SHS/QP is a new processing technique with high efficiency and low cost. In the process, following the SHS reaction, when the sample is still in a red hot and soft state, a quick and high hydraulic force is applied on the sample, so that dense product can be obtained.The relative density of ceramic composites fabricate by SHS/QP in few minutes was nearly theoretical, which is hard to explain by traditional diffuse sintering theory and indicates a new sintering mechanism. In this paper, the TiB2 ceramic and TiB2-AI2O3 composites were processed by SHS/QP, and the microstructure and residual stress of the products under different relevant parameters were studied. A new mechanism of superfast sintering of ceramic composites by SHS/QP was firstly represented.The mechanism of sinter single-phase ceramic by SHS/QP is: after SHS the product is in a state of semi-solid because of the extra high combustion temperature. Once the reaction completes, and at a pre-established time delay, a quick and high hydraulic force is applied on the sample. The re-arrangement and plastic deformation of the grains under high temperature and pressure lead to the densification of the product. The gas impurities are excluded and finally the dense ceramic is obtained. The diffuse of the grains strengthens the neck of sintering. However, it has few contributions to the densification of materials due to the time limit.The mechanism of sinter diphase ceramic by SHS/QP is: after SHS the product is liquid-solid mixture because of the extra high combustion temperature. Once the reaction completes, and at a pre-established time delay, a quick and high hydraulic force is applied on the sample, which cause the re-arrangement by the gliding, turning of the grains following the channel of liquid and then the plastic deformation. At the same time thegrowth and diffuse of the solid grains are proceeding but limited by the extinction of liquid phase. The extinction of liquid phase accelerates the re-arrangement of the grains and enhances the densification by filling the clearance between solid grains. Since the time when the product is in high temperature is very short, the contribution of the diffuse is very limited to the densification of diphase composites, which is controlled by the re-arrangement and plastic deformation of the grains under high temperature and pressure.