RAPID SINTERING OF CERAMIC COMPOSITES BY HIGH TEMPERATURE EXOTHERMIC REACTION/DYNAMIC COMPACTION PROCESS

自蔓延高温合成（Self-propagatingHighTemperatureSynthesis，SHS）过程中至少有一种反应物是固体，即所谓的燃烧合成，已逐渐受到材料学家的关注。这些“固体火焰”的产物是具有重要技术意义的材料，如具有高熔化温度的结构陶瓷、金属间化合物和复合材料。固体燃烧反应一般都伴随着大量热量的释放。在充分放热的反应中，释放的热量足以通过燃烧前沿的快速传播来维持反应，而无需进一步添加能量。该方法的特征在于高的生成温度（例如，2000至4000 K），快速移动的燃烧波前（例如，0.1到25厘米/秒），和极高的加热（例如，10^4至10^6 K/sec）和冷却速率。自蔓延高温合成工艺具有产品纯度高、能耗低、反应时间短、工艺相对简单等优点 ...更多信息 过程的合法性。SHS产品通常是粉末状或多孔的。但是也可以使用该工艺和外部压力的组合技术来制造高密度形式，所述外部压力例如热压、热等静压（HIP）、伪HIP（P-HIP）、爆炸固结和高速锻造。本研究的目的是采用短时自蔓延高温合成（SHS）和砂介质准等静压致密化相结合的方法制备陶瓷/金属复合材料，如TiC/Ti-Al。Ti-C反应产生的SHS热很大，绝热燃烧温度可达3210 K，而Ti-Al反应是弱放热反应，不预热反应物不易引发。由于液相对复合材料的致密性至关重要，控制反应最高温度使Ti-Al合金熔化。采用准等静压（PIC）技术对高温半熔融试样进行致密化处理，研制了以砂子为传压介质的准等静压陶瓷/金属复合材料致密化工艺。该技术应类似于Merzharnov等人开发的技术。点火方法可能与俄罗斯SHS研究人员不同。在我们的PIC装置中，一片碳带作为仅用于点火的加热装置，与样品一起嵌入商业型砂中，型砂插入压力容器中。通过在SHS反应后立即快速压制含有样品的砂来进行压实。已知使用砂作为压力传递介质的PHIP的静压导致伪等静压。本文采用高速自动压砂机动态压砂的方法进行自蔓延高温合成后的粉末冶金。少

SELF-PROPAGATING HIGH TEMPERATURE SYN-THESIS (SHS) process in which at least one of the reactants is a solid, so-called combustion synthesis, has been gradually received attention from materials scientists. The products of these "solid flames" are technologically important materials such as structural ceramics with high melting temperature, intermetallics and the composites. Solid combustion reaction are generally accompanied by the release of a large amount of heat. In reactions that are sufficiently exothermic, the heat liberated is adequate to sustain the reactions by the rapid propagation of the combustion front without further addition of energy. The process are characterized by a high generated temperature (e.g., 2000 to 4000K), a fast-moving combustion wave front (e.g., 0.1 to 25 cm/sec), and extremely high heating (e.g., 10^4 to 10^6 K/sec) and cooling rates. The advantages of SHS process include high purity of products, low energy and short-time requirements, and relative simp … More licity of the process. SHS products are generally powdery or porous. But the highly dense form can be also fabricated using a combination technique of this process and an external pressure such as hot press, hot isostatic press (HIP), pseudo-HIP (P-HIP), explosive consolidation, and high-velocity forging. The objective of this research is to fabricate ceramics/metal composite, for example, TiC/Ti-Al by a combination technique of SHS for short time process and pseudo isostatic compaction through a sand medium for densification. A SHS heat generated by a Ti-C reaction is very large and the adiabatic combustion temperature reaches to 3210K.But a Ti-Al reaction is weak exothermic and is not easy to initiate without pre-heating the reactant. The reaction maximum temperature was contolled so that the Ti-Al alloy could be molten because a liquid phase is very important to make the composite dense well. The reason why Ti-Al alloy was chosen as a SHS sub-product was that the alloy is hard, light, and has received attention as structural materials in space materials.A pseudo isostatic compaction (PIC) was applied for densification of the hot and partially molten samples after the SHS.The PIC using sand as the pressure transmitting medium has been developed for the densification of the ceramics/metal composite. This technique should be similar to that developed by Merzharnov et al. An ignition method may be different from Russian SHS researchers. In our PIC apparatus, a sheet of carbon ribbon as the heat device only for ignition is embedded with a sample in commercial casting sand, which is inserted in a pressure vessel. The compaction was performed by quickly pressing the sand containing the sample just after the SHS reaction. A static pressing of PHIP using sand as the pressure transmitting medium is known to cause pseudo isostatic pressing. Herein, the sand-pressing by high speed auto-pressing machine was applied dynamically to perform the PIC after SHS. Less