Ultra hard materials are the result of modern research and development. The last century witnessed extra ordinary growth in many fields of science and technology including material science. The latest developments in science and technology resulted in the use of very hard materials in mechanical, automobile and aviation fields. This in turn resulted in the development of new ultra hard cutting materials to machine these parts. Beside carbide cutting tools several other ultra hard materials like ceramic, polycrystalline diamond (PCD), monocrystalline diamond (MCD-natural diamond), diamond coatings on cutting tools, synthetic monocrystalline diamonds as well as polycrystalline cubic boron nitrite are developed.
Polycrystalline Diamond (PCD)
Polycrystalline diamond plates are manufactured by high temperature and high pressure process where the diamond coating is directly combined with a carbide support. Polycrystalline diamond is made by sintering of high quality diamond powder with metallic binder. Depending upon the application polycrystalline diamond materials are available in various grain sizes. For example the diamond with rough grain sizes are used for making cutting tools with excellent wear resistance due to its ability to retain cutting edge for a longer period. Incase you need very high surface finish on machines parts, then ultra micro grain sizes are highly preferred. Medium grain sizes are used for general all purpose cutting tools since it is a balance between high wear resistance of rough grain size and superior finish of ultra micro grains. This makes the medium grain sized polycrystalline diamond as an excellent ultra hard material for manufacturing high quality metal cutting tools.
Mono crystalline diamond (MKD) is natural diamond out of pure carbon. These natural diamonds enable the production of geometric defined flutes with absolutely notch free flutes. Natural diamond (MKD) is on of the ultra hard materials which is suitable for achieving very high surface finishes for mirror bright surfaces, machining of non-ferrous materials, micro machining and machining of titanium without burr.
Synthetic Monocrystalline Diamond
Further research and development resulted in synthetic mono crystalline diamonds which are available in triangles and rectangles with an edge length of approximately 8mm. The natural diamonds often contains nitrogen and the it could have varying hardness and thermal conductivity. Whereas the synthetic monocrystalline diamonds have uniform structure with constant thermal conductivity and less internal stress. Today synthetic monocrystalline diamonds are being produced in various shapes and sizes which offers great application possibilities of this ultra hard material in future. Researches have found considerable improvements in synthetic monocrystalline tool life, improved surface finish and constant wear behavior compared to other ultra hard materials like PCD and natural diamond.
Diamond Film Coating (CVD Process)
Diamond film coatings are done to improve the surface hardness of cutting tools. Generally diamond film coatings can be classified into two. The thin diamond film coating with a layer thickness of approximately 5-20 microns and thick diamond film coating with a layer thickness of approximately 0.5mm. Higher thermal and chemical stability and ultra surface hardness are the advantages of diamond film coating. Low fracture toughness is the disadvantage of of diamond film coatings. And compared to polycrystalline diamonds no binder is used while producing diamond film coatings which causes higher splintery fracture.
Diamond film coated ultra hard materials are best suitable for machining of aluminium alloys with high silicium contents as well as graphite and carbon. Tests show very good use of diamond coated tools in machining plastics, gold alloys and wood machining.
Polycrystalline Cubic Born Nitrite (CBN)
Polycrystalline Cubic Born Nitrite is the hardest cutting material after ultra hard materials like ceramics and diamond. CNB is manufactured by a sinter process of high temperature and pressure using selected particles of Cubic Born Nitrite. Depending on various cutting applications polycrystalline cubic born nitrite are available with with different binder phases as well as in fine, medium and rough grain structure. CNB is an ultra hard material with excellent thermal stability up to 1200°. Polycrystalline Cubic Born Nitrite with low cbn contents is mainly used in precision machining of hardened steel and other hard ferrous materials. diamond paste