Study on Dynamic Compaction of Diamond Powders

可以理解，金刚石粉末的冲击压缩可以在金刚石颗粒之间产生冶金结合。目前的研究人员已经发现，用2-4 μ m颗粒的金刚石粉末获得具有最高密度的强压坯，但是用小于1 mm颗粒的粉末不能获得良好的压坯。获得大金刚石复合片的最困难的问题之一是裂纹的产生。这种产生是由从冲击压缩状态的非常快速的压力释放以及由金属囊中的压力和温度的陡峭分布引起的。压坯中产生的应力松弛过程可以避免裂纹的产生。作为一种有效的技术，我们开发了一种新的方法，通过放热化学反应的残余温度控制。添加化学反应性添加剂后，观察到两种显著的效果。一个是随着添加剂的加入压坯的显微硬度的增加。另一个效果是减少宏观和微观裂纹的恢复压坯。后一种效果被认为是占主导地位的压实2-4微米级金刚石粉末与硅添加剂。在含有或不含有添加剂的压坯的后表面中发现的裂纹数量比前表面中发现的裂纹数量大，这显然是由于在冲击压实过程中粉末压坯内的压力和温度的陡峭梯度造成的。金刚石粉末在金属包壳中伴随放热化学反应的致密化过程尚不清楚。数值模拟是了解粉末冲击压缩过程的有效工具。通过与北卡罗来纳州州立大学的Y.Horie教授的合作研究，模拟的可靠性得到了提高。

It is understood that shock compression of diamond powders can originate metallurgical bonding among diamond particles. The present investigators have found that strong compacts with the highest density were obtained with diamond powders of 2-4 mum grains, but good compacts were not gained with powders less than 1 mm grains. One of the most difficult problems in obtaining a large diamond compact is the generation of cracks. This generation is caused by a very rapid pressure release from the shock compression state and by steep distribution of pressure and temperature in the metal capsule. The crack generation can be avoided by relaxation process of stress produced in the compact. As a useful technique for the process, we have developed a new method of residual temperature control by means of exothermic chemical reaction. Two kinds of notable effects were observed, concerning the supplement of the exothermically reactive additives. The one was the increase in the microhardness of the compacts with the addition of the additives. The other effect was the decrease of macro- and micro-cracks in the recovered compacts. The latter effect was seen predominant in the compacted 2-4 mum grade diamond powders with silicon additives. The larger number of cracks found in the rear surfaces of the compacts with or without additives than in the front surfaces was apparently caused by the steep gradient of pressure and temperature within the powder compacts during the shock compaction process. Densification process of the diamond powder accompanying exothermic chemical reaction in the metal capsule is not clear. Numerical simulation is a useful tool to understand the process during shock compression of powders. Reliability of the simulation has been increased with cooperative research with Prof.Y.Horie of North Carolina State University.