With the rapid advancement in technology and modern research and development, new discoveries have also been made in the field of material science. Scientists have over the past few years succeeded in formulating materials that are harder than diamond, which is the hardest known naturally occurring material.
Most of the extra hard substances are variations of diamonds and are often referred to as synthetic diamonds. They can be produced through various chemical processes, which include Chemical Vapor Deposition (CVD) and High Pressure High Temperature methods.
Chemical Vapor Deposition
CVD is a method in which a diamond is ‘grown’ using a hydrocarbon gas mixture. To put it simply, the process involves
• Preparing a substrate of an appropriate material
• Cleaning it, usually with diamond powder
• Placing it in a chamber and feeding various hydrocarbon gases at high pressure, while the temperature of the chamber is maintained at around 800 degrees Celsius
Elements from the hydrocarbon gases react and decompose on the substrate surface to produce the required amount of deposition. Properties of the synthetic material, like hardness and crystallinity, are derived from the levels of the deposits.
High Pressure, High Temperature
Another process for producing is the High Pressure, High Temperature (HPHT) method. In this method, a diamond substrate is directly coated with carbon using very high pressure and temperature ranging up to 1400 degrees Celsius.
The process involves melting a metal and making it come in contact with a high purity carbon source. The metal dissolves the carbon and is then transported to the diamond, where it precipitates, resulting in the formation of synthetic diamonds.
Polycrystalline Diamond (PCD)
PCD is manufactured using the HPHT method. It can be used for various applications depending on grain size. Larger grain sized (microcrystalline) diamonds are used for coating and cutting tool tips as they have excellent durability and wear resistance and can retain their cutting properties for longer durations. Smaller grain size (nano-crystalline) diamonds are used for providing excellent surface finishes.
Polycrystalline diamonds are one of the most popular ultra-hard materials used for manufacturing cutting and finishing tools.
Polycrystalline Cubic Boron Nitrite
PCBN is one of the hardest cutting materials, also manufactured using the HPHT method. One of its most important properties is its ability to stand temperatures up to 1200 degrees Celsius. The low carbon contents make it an excellent material for accurate machining of hard steel and other hard materials.
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