Super-hard materials are crucial tools in modern industrial processing, and diamond abrasive powder and CBN abrasive wheels have become key tools for grinding and polishing due to their unique physical properties. Although both possess extremely high hardness and wear resistance, their specific applications differ. This article will delve into and compare the application fields of diamond abrasive powder and CBN abrasive in three aspects.
Diamond abrasive powder and CBN abrasives are currently the most commonly used super-hard abrasives. Diamond abrasive powder features an atomic crystal structure formed by carbon elements in sp3 hybrid orbitals, with a Mohs hardness of 10, making it the hardest substance in nature. Therefore, diamond abrasive powder is highly effective for grinding hard and brittle materials such as hard alloys, ceramics, and glass, and is especially suitable for high-hardness materials exceeding HRC65.
In contrast, CBN abrasives have slightly lower hardness but are still close to the top of the Mohs scale (around 9.7). CBN abrasives are made up of cubic boron nitride, with a structure similar to diamond but with slightly longer bond lengths and slightly lower hardness. However, CBN abrasives excel in grinding hard steels and hardened steels, overcoming the high-temperature reaction issues between diamond and ferrous metals, making them suitable for precision machining of iron-based materials.
Therefore, for hard alloys such as tungsten steel, the hardness advantage of diamond abrasive powder is more pronounced, while CBN abrasives are more suitable for processing ferrous metals.
The heat resistance of abrasives determines their performance in high-speed and ultra-high-speed grinding. Diamond abrasive powder, as a typical heat-decay abrasive, has relatively poor heat resistance. At high temperatures (exceeding 720°C), the surface carbon atoms of diamond easily combine with oxygen to form carbon oxides, causing the crystal to peel off gradually and reducing cutting force.
Therefore, diamond abrasive powder is suitable for use under medium-speed conditions but may not perform as well as CBN abrasives in extreme high-speed grinding or high-temperature environments.
CBN abrasives have better thermal stability than diamond abrasive powder. In its crystal structure, the covalent bond between boron and nitrogen atoms is very stable, allowing it to remain sharp at temperatures above 1200°C. This makes CBN abrasives very suitable for high-speed and ultra-high-speed grinding processes, especially in the machining of precision devices or long-term high-temperature grinding. The CBN abrasive wheel possesses self-sharpening properties, allowing it to maintain stable grinding force.
Therefore, diamond abrasive powder is suitable for medium-to-low-temperature precision machining, while CBN abrasives perform better in high-temperature and high-speed grinding.
In terms of chemical stability, diamond abrasive powder and CBN abrasives show significant differences. Diamond abrasive powder, despite its extreme hardness, easily reacts with ferrous materials at high temperatures. Diamond has a strong affinity with metals such as iron, cobalt, and nickel, and tends to transition to a graphite structure at high temperatures, leading to increased abrasive wear and decreased cutting force. Therefore, diamond abrasive powder is not suitable for processing ferrous materials.
Conversely, CBN abrasives do not react with ferrous metals at high temperatures, maintaining good chemical stability below 1150°C and forming a boron oxide thin layer in an oxidizing environment, which further enhances its durability. Therefore, CBN abrasives excel in grinding hardened steels, cold steels, and other ferrous materials. However, it should be noted that CBN abrasives will react in alkaline aqueous solutions, so it is necessary to avoid using water-based coolants when using them, and instead use oil-based coolants.
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