Study on Polycrystalline Diamond for Rock Drilling Application Utilizing Shock Consolidation Technique

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This project has been conducted in Fy 1995-79 as a feasibility study for industrialization of polycrystalline diamond for rock drilling application utilizing shock consolidation technique. The rock drilling bit consists of tungsten carbide alloy body and polycrystalline diamond layr, which formed by shock wave consolidation processing. The most serious problem is crack generation in the diamond layr during shock processing. Number of macro and micro cracks generated in the daiamond layr were decreased drastically by addition of silicon to diamond powder. Suitable contents of silicon is 3-7% for rock drilling bit application. Results of this study is summarized as following ;(1) Grain boundary between diamond particles in the compact was observed by high resolution electron microscope. Diamond particles are bonded with high dense from glassy carbon having Sp^3 chemical bond transformed from diamond. Very fine silicon carbide particles dispersed in the carbon layr.(2) The above boundary layr in the diamond compact has a kind of nano composite structure and it is expected a kind of mechanical toughening effect.(3) A few micron size coarse silicon carbide and graphite particles were observed in the diamond layr. these particles with comparatively large size deteriorate its mechanical property.Generation of both micron size particles is caused by lack of uniform mixing of silicon and diamond particles.(4) A plasma silicon coating technique was applied to form homogeneous coating to diamond particles with 2-4 micron. However coarse silicon particles were formed during the coating process. Industrialization of this technology is realized by development of extreme uniform coating method of silicon to diamond particles.