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

自传播高温合成（SHS）过程中至少有一种反应物是固体，即燃烧合成，已逐渐受到材料科学家的关注。这些“固体火焰”的产物是高熔点结构陶瓷、金属间化合物和复合材料等技术上重要的材料。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锋面的快速传播来维持反应，而无需进一步增加能量。该工艺的特点是产生温度高（例如，2000至4000K），快速移动的燃烧波前（例如，0.1至25厘米/秒），以及极高的加热（例如，10^4至10^6 K/秒）和冷却速率。SHS工艺具有产品纯度高、能耗低、时间短、工艺相对简单等优点。SHS产品一般为粉末状或多孔状。但高密度的形式也可以使用该工艺和外部压力的组合技术，如热压，热等静压（HIP），伪HIP (P-HIP)，爆炸固结和高速锻造。本研究的目的是利用SHS短时间工艺和砂介质致密化伪等静压相结合的方法制备TiC/Ti-Al等陶瓷/金属复合材料。Ti-C反应产生的SHS热量很大，绝热燃烧温度可达3210K。但Ti-Al反应是弱放热反应，不预热反应物不易引发反应。控制反应的最高温度，使钛铝合金能够熔融，因为液相是使复合材料致密的重要因素。之所以选择Ti-Al合金作为SHS子产品，是因为该合金硬度高，重量轻，在空间材料中作为结构材料受到关注。采用伪等静压实（PIC）方法对高温和部分熔融试样进行了致密化处理。开发了以砂为传压介质的陶瓷/金属复合材料致密化PIC。这项技术应该类似于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，将一片碳带作为仅用于点火的加热装置与样品嵌入商业铸造砂中，并将其插入压力容器中。压实是通过在SHS反应后快速压紧含有样品的沙子来完成的。使用砂作为压力传递介质的PHIP静压已知会引起伪等静压。本文将高速自动压砂机的压砂动态应用于SHS后的PIC。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