The use of a superhard boron nitride composite c-BN+h-BN with increased resistance to brittle cracking for anti-wear coatings

Abstract

In order to reduce the brittleness of boron nitride (BN) coatings while maintaining a sufficiently high abrasion resistance, a composite material consisting of a cubical (c-BN) and additionally hexagonal (h-BN) variety was produced, slightly lowering the hardness, but significantly increasing the fracture toughness of the coating. For this purpose, the pulse plasma method was used, which made it possible to produce such material. In the presented tests, BN was produced with this method at various voltage parameters of the process, examining the influence of this parameter on the susceptibility of coatings to brittle cracking, the value of the critical load and the work of fracture for an average total crack length of 300 µm. The Palmqvist’s method was used to assess the brittleness of the coatings. Through the use of different discharge voltage values, it was possible to obtain BN coatings with different structures and the share of chemical bonds. These studies contribute to the process of conscious design of coating materials with the most advantageous technological and operational properties. The final verification and selection of the variant of the anti-wear coating manufacturing process from the c-BN+h-BN composite material was made based on cutting ability tests. Based on cutting ability tests, diagrams of wear and durability of replaceable carbide inserts with composite coatings were determined for the assumed value of the blunting index VBmax = 0.7 mm.