Creation of Low defect and Super High Strength Ceramics by High-Speed Centrifugal Compaction Process

本研究的内容分为三个部分。首先，研究了高速离心压实过程的压实机理。然后，在不同的压制条件下制备了HCP氧化铝，阐明了压制条件对烧结氧化铝性能的影响。结果表明：(1)由于HCP的致密机理与压力铸造完全不同，因此，HCP具有比压力铸造更高的致密速度。压实速度与转速的平方成正比，但不受初始滑移浓度的影响。因此，使用易于制备的稀浆和更高的转速可以提高生产效率。利用Kynch理论可以定量地估算出压实速度。(2)压坯堆积密度随轧制速度的增加而增加。此外，在较高的转速下，滑块内的缺陷被更有效地去除。因此，可以在较高的转速下获得致密、低缺陷的坯体。(3)HCP氧化铝的高强度源于其细小、低缺陷的烧结组织。HCP氧化铝具有有史以来制造或商用氧化铝中缺陷最少的微结构之一。(4)上述特性对WC微粉的压制同样有效。将WC粉末分散于正庚烷中，可在短时间内获得致密的生坯。这种生坯压坯可以在不添加钴的情况下烧结到几乎100%的相对密度，并显示出Hv2300的高硬度。

The contents of the present research is divided into three sections. Firstly, the compacting mechanism of High-Speed Centrifugal Compaction Process (HCP) is investigated. Then, the HCP alumina are made under a variety of compacting condition, and the effect of the condition on the properties of sintered alumina is clarified. And finally, the WC sintered material is made by HCP.The results are as follows :(1) Since the compacting mechanism of HCP is entirely different from that of pressure casting, HCP possesses much higher compacting velocity than pressure casting. The compacting velocity of HCP increases in proportion to the square of rotational speed, but it does not affected by the initial concentration of slip. Therefore, the efficiency of the production can be improved using a easy-to-prepare dilute slip and higher rotational speed. The compacting velocity of HCP can be estimated quantitatively applying Kynch's theory.(2) The packing density of HCP green compact increases as rolational speed increases. In addition, the defects within the slip are removed more effectively at higher rotational speed. Thus, a dense and low defect green compact can be obtained with higher rotational speed.(3) The high strength of HCP alumina is due to the fine and low-defect sintered microstructure. The HCP alumina possesses one of the most low-defect microstructure among ever fabricated or commercially available aluminas.(4) The above mentioned characteristics are also effective for the compaction of WC fine powder. By dispersing the WC powder in heptane, a dense green compact is obtained within a short time. This green compact can be sintered to almost 100% in relative density without adding cobalt, and it shows high hardness of Hv 2300.