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

本文的研究内容分为三个部分。首先，对高速离心压实工艺的压实机理进行了研究。然后，在不同的压实条件下制备了HCP氧化铝，并阐明了压实条件对烧结氧化铝性能的影响。最后，采用HCP法制备WC烧结材料。结果表明：(1)由于HCP的压实机理与压力铸造完全不同，因此HCP的压实速度远高于压力铸造。HCP的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，使用易于制备的稀滑块和较高的转速可以提高生产效率。应用Kynch理论可以定量估计HCP的压实速度。(2) HCP绿坯的堆积密度随着转速的增加而增加。此外，在较高的转速下，滑移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和低缺陷的绿色压块。(3) HCP氧化铝的高强度是由于烧结组织精细、缺陷少。HCP氧化铝具有有史以来制造或市售氧化铝中最低缺陷的微观结构之一。(4)上述特性对WC细粉的压实也是有效的。将WC粉末分散在庚烷中，可在短时间内得到致密的绿色压坯。该绿色坯体在不添加钴的情况下可以烧结到接近100%的相对密度，硬度高达hv2300。

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.