Micromechanical characterization of coated PCBN inserts

Polycrystalline cubic boron nitride (Pc-BN) is a super-hard material with a multiphase composite character. Indeed, it is a composite material composed of c-BN particles (as reinforcement) embedded in a binder (ceramic or metallic), mainly used as a cutting tool material. Within this context, information on the small-scale mechanical response of Pc-BN is rather scarce. Thus, the main objective of this project is to determine the intrinsic hardness of the constitutive phases of three different commercial PcBN-base inserts, including the coatings deposited on them. First of all, after sample preparation, substrates of inserts will be microstructurally characterized by means of optical and electron microscopy inspection. Then, aiming to conduct mechanical tests at small length scales, the surface roughness of the coated inserts will be decreased to get a suitable surface finish for reliable testing. Hardness of the different effective substrates within the inserts: Pc-BN, hardmetal tip and hardmetal base, will be determined by analyzing nanoindentation data. Nanoindentation tests were carried out with a Berkovich diamond tip using a continuous stiffness measurement module, with a maximum penetration depth of 2000 nm. The results indicated that the measurements taken at 2000nm are not affected by possible indentation size effect or length scale. It is found that hardness of the coatings for the three different inserts studied are quite different, ranging between 22 and 40 GPa. Such differences are linked to the chemical nature of the films. With respect to substrates, as expected, Pc-BN part is harder (around 35 GPa) than the hardmetals used as base (around 20 GPa) or tip (around 15 GPa). The relative differences discerned for both hardmetals are rationalized by the higher fraction volume of tungsten carbides particles in the base one, as compared to the hardmetal tip.Incomin