Tribological and mechanical properties of AlCrBN hard coating deposited using cathodic arc evaporation

Abstract

Transition metal nitride coatings, such as CrN, AlCrN and AlTiN, have excellent mechanical properties such as high strength, hardness, wear resistance and thermal stability. In this study, AlCrN and AlCrBN thin films were deposited by cathodic arc evaporation (CAE) using binary AlCr and ternary AlCrB alloy targets. The adhesion strength of the films to the substrate was effectively improved using composition-gradient interlayers. To study the thermal stabilities, the AlCrN and AlCrBN coatings were annealed at high temperature up to 900 °C, and their oxidation resistance, mechanical properties and thermal stabilities were studied. AlCrN and AlCrBN coated WC-Co samples were tested using pin-on-disk wear test configuration to evaluate the tribological performance. According to experimental results, the AlCrBN is composed of a face-centered cubic B1 (FCC) nanocrystalline structure, which can effectively inhibit the growth of grains, resulting in formation of a compact structure of grain refinement, and hinder the plastic deformation, thus obtaining high hardness and excellent wear resistance. The addition of 0.6 at.% B into the AlCrN decreased the grain size to 8.7 ± 0.8 nm from 13.7 ± 1.1 nm of AlCrN. Due to the addition of B element, the grains of AlCrBN coatings were refined to form a compact structure. Oxygen (O) did not penetrate and oxidize easily along the grain boundaries during annealing at high temperature. In addition, the AlCrBN coatings maintained a certain hardness (27.9–30 GPa) after high temperature oxidation, and the AlCrBN coating after annealing at 900 °C had the lowest wear rate (1.25 × 10−7 mm3/Nm). The AlCrBN coating annealed at high temperature still possessed predominant tribological properties, excellent thermal stability and good adhesion. This study demonstrates the feasibility of improving the life and performance of WC-Co tools by the application of cathodic arc deposited AlCrBN coatings using ternary AlCrB alloy targets.