Borazon is the trade name given by General Electric (GE) to cubic boron nitride (cBN), a synthetic material known for its exceptional hardness and thermal stability. It is one of the hardest known materials, surpassed only by diamond.
Properties:
- Hardness: Borazon possesses a Vickers hardness comparable to that of diamond, making it an excellent abrasive. Its hardness makes it ideal for cutting and grinding very hard materials.
- Thermal Stability: A significant advantage of Borazon over diamond is its superior thermal stability. It maintains its hardness and strength at temperatures exceeding 1000 °C (1832 °F) in the presence of oxygen, whereas diamond can begin to oxidize and degrade at lower temperatures.
- Chemical Inertness: Borazon exhibits chemical inertness with ferrous metals (iron and its alloys) at high temperatures. This is a critical advantage over diamond, which tends to react with and dissolve in hot iron, leading to rapid wear of diamond tools when machining such materials.
Synthesis: Borazon was first synthesized by Robert H. Wentorf, Jr. at General Electric in 1957, shortly after GE's successful synthesis of artificial diamonds. Its creation involves subjecting hexagonal boron nitride (hBN), which has a soft, graphite-like structure, to high pressures and high temperatures, similar to the conditions used for synthetic diamonds. This process transforms the hexagonal structure into a compact, cubic lattice, analogous to how graphite transforms into diamond.
Applications: Due to its unique combination of extreme hardness, high thermal stability, and chemical inertness, Borazon is widely used in industrial applications, particularly for:
- Abrasives: It is a primary material for grinding wheels and other abrasive tools used for shaping and finishing hardened steels, cast irons, superalloys, and other ferrous metals and alloys that are difficult to machine.
- Cutting Tools: Borazon inserts are used in machining operations for difficult-to-cut materials at high speeds and temperatures, where diamond tools would quickly degrade due to chemical reaction or thermal breakdown.
- High-Pressure Applications: Its stability under extreme conditions makes it valuable in various high-pressure and high-temperature research and industrial processes.