SEM investigations of TiB2 and TiBN coatings produced by DC magnetron sputtering

Binary nitrides (TiN and CrN) and ternary nitrides (TiAlN and CrAlN) have become excellent coatings for engineering applications, where protective coatings are required to increase the lifetime and performance of cutting tools [1-3]. Research conducted on the development of nanostructured ternary nitride coatings found that with a nanograin structure, the coatings were of much higher hardness than those of the coarser grain size and this was influenced by the nitrogen pressure during deposition [4-5]. More recent research has shown that TiN and TiAlN are excellent coatings for machining ferrous products, whereas CrN and CrAlN have been found to exhibit unique properties for machining non-ferrous alloys. For this reason, alternative surface coatings need to be investigated. Other materials that have been studied for coating purposes are TiB2 and TiBN. The combination of high hardness and chemical resistance make these coatings good for applications such as die casting and aluminium machining [6-8]. Although TiB2 has numerous outstanding properties, there are still a few problems yet to be overcome. Being very hard, the coating is extremely brittle. This in turn can lead to the chipping of the coating, which is no use for corrosion and wear resistant coatings. TiB2 also exhibits very poor adhesion properties when coated on most substrates and has been reported to be soluble in iron and consequently would not be ideal for engineering applications where iron and steel (ferrous materials) are the products to be machined.