Boron nitride is a heat and chemically resistant refractory compound of boron and nitrogen with the chemical formula BN. It exists in various crystalline forms that are isoelectronic to a similarly structured carbon lattice. The hexagonal form corresponding to graphite is the most stable and soft among BN polymorphs, and is therefore used as a lubricant and an additive to cosmetic products. The cubic structure variety analogous to diamond is called c-BN; it is softer than diamond, but its thermal and chemical stability is superior.
Because of excellent thermal and chemical stability, boron nitride ceramics are traditionally used as parts of high-temperature equipment.
Now let's look at the properties of the films that are obtained by boron nitride sputtering targets.
Cubic boron nitride (c-BN) has been utilized as a significant coating material for cutting tool applications in recent years due to its excellent mechanical and chemical properties. The most important outstanding properties of boron nitride can be counted as high hardness, low friction coefficient, good thermal conductivity, high electrical resistivity, high wear resistance and chemical inertness at high temperatures. Boron nitride is the hardest material after diamond. Furthermore, boron nitride is also superior to diamond due to its chemical stability against oxygen and ferrous materials at high temperatures.
Boron nitride mostly found in two polymorphs in the coatings; hexagonal boron nitride (h-BN) and cubic boron nitride (c-BN). Hexagonal boron nitride is well-known as a soft, low friction coefficient, lubricating at both low and high temperatures, electrically insulating and thermally conductive material. It has wide applications as a solid lubricant in metal forming dies and metal forming processes at high temperatures in any environment. In contrast to hexagonal phase, cubic phase exhibits high hardness and other extreme properties stated above which puts forward c-BN as a suitable coating material for cutting tools. Owing to these properties, use of cubic boron nitride in cutting tool applications such as dry cutting, high speed machining and cutting of hard materials, is increased within the last years. Sintered cubic boron nitride cutting tools have already been used extensively in the market today. Major drawbacks of sintered c-BN cutting tools are their high cost, poor ductility and difficulty of forming them into various cutting tool shapes. Therefore, demand to thin or thick film deposition of BN not only for cutting purposes but also as a protective coating, optical coatings and electrical insulating layers has grown up rapidly and many researchers attempt to synthesize boron nitride coatings in cubic phase. Among the coating methods, sputtering technique − a physical vapor deposition (PVD) process − comes into prominence because of lower coating temperature, possibility to deposit thinner coatings and possibility to deposit sharp edges and complex forms. For detailed informatin you may read the paper which you can reach by clicking the link below:
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