Microstructure and mechanical properties of nanocrystalline Al–Cr–B–N thin films

Al–Cr–N is a well-established hard film system with excellent mechanical and tribological properties. The effect of B addition on structure and mechanical properties of Al–Cr–N films grown by cathodic arc evaporation was systematically investigated. The B content in the targets was varied between 10 and 30 at.% at a constant Al/Cr atomic ratio of 1.8. X-ray diffraction revealed that all coatings exhibit a face-centered cubic structure, with texture and grain size affected by B content and substrate bias voltage. X-ray photoelectron spectroscopy indicates formation of a nanocomposite structure consisting of a crystalline face-centered cubic Al–Cr–(B)–N solid solution and an amorphous BNx phase. Nanoindentation experiments revealed a significant hardness enhancement of Al–Cr–(B)–N with respect to B-free films, accompanied with a reduction of residual compressive stress.

► Synthesis of AlCrBN films by reactive arc evaporation from AlCrB targets ► Nanocomposite structure of fcc Al–Cr–(B)–N grains surrounded by a-BNx ► Reduced grain size as a result of increased BNx phase fraction ► Highest hardness obtained for 10 at.% B in the target