Evaluation of the distribution of the strength properties in AlCrSiN gradient coating by a micro slurry-jet erosion (MSE) method

Several experimental techniques are ordinarily used to evaluate the strength properties of metal nitride coatings used for cutting tools and molds. However, for gradient coatings, in which the chemical composition changes gradually in the normal direction of depth relative to the surface, the properties at different depth positions of the gradient layer are difficult to evaluate. In this study, our previously developed micro slurry-jet erosion (MSE) test was applied to swiftly evaluate the strength properties of AlCrSiN gradient coating. The specimens of AlCrSiN gradient coating and also with AlCrSiN single layer coatings of different (Al + Si) concentration were deposited on high speed steel by a cathodic arc method. The AlCrSiN gradient coating had (Al + Si) concentration continuously increasing towards the surface. The MSE tests were conducted by impacting the slurry-jet containing 1.2 μm sized alumina particles perpendicular to the coated surface, and the depth profiles of the eroded surfaces were measured and the erosion rate was obtained. For the AlCrSiN single layer coatings, the erosion depth curves changed linearly, and their erosion rates became remarkably larger with increasing (Al + Si) concentration although the hardness decreased gradually. Moreover, for the AlCrSiN gradient coating, the erosion depth curve was approximated by a cubic B-spline curve because the erosion rate changed gradually in the depth direction. From the characterization by transmission electron microscopy and selected area diffraction, the change of the erosion rate was caused by forming nano-composites and also by segregation of a hexagonal closed-packed phase (hcp). It was found that the MSE method is an easy to apply and useful technique to evaluate the distribution of the properties of hard gradient coatings.