High pressure and high temperature behaviour of TiAlN coatings deposited on c-BN based substrates

Abstract

High pressure and high temperature experiments with a Hall belt apparatus of cathodic arc deposited Ti0.63Al0.37N and Ti0.37Al0.63N on polycrystalline cubic BN substrate reveal a strong influence of pressure on the decomposition rate of TiAlN. The pressure induces enhanced phase stability while keeping the interfaces between coatings and the substrates intact. Hardness measurements of the as-deposited coatings and after high-pressure high-temperature treatment show that the hardness after treatment of Ti0.63Al0.37N at 5.35 GPa, 1300 °C and after 66 min drops from 29.6 to 27.8 GPa, because after this treatment this sample contains cubic TiN and hexagonal AlN. This drop is much smaller than if the coatings are just heat treated at 1300 °C and suggests that an enhancement of TiAlN-coatings on cubic BN cuttings tools can be achieved by increasing the pressure/stress during cutting. For Ti0.37Al0.63N treated at 5.35 GPa, 1300 °C and after 66 min the hardness drops from 36.1 to 28.6 GPa, which means that the coating has first decomposed through spinodal decomposition and one of products of this decomposition has further phase transformed and the final products are cubic TiN and hexagonal AlN.