Abstract
Abstract Crack resistance of CrBN coatings in relation to B concentration was investigated via nano-indentation and scratch tests. A nano-composite structure consisting of CrN nano-grains embedded in amorphous BN (a-BN) matrix was observed by transmission electron microscope (TEM). XRD and XPS analyses revealed a decrease of crystallinity in coatings as B content increased from 16.4 to 27.2 at.%, which led to a hardness decrease from 28.9 GPa to 23.6 GPa. All CrBN coatings, regardless of composition, prevented radial cracks due to superior mechanical properties (H/E ≥ 0.077). However, owing to high compressive stress (3.27–4.74 GPa), circumferential cracks were found along indent edge, and the number of circumferential cracks was proportional to B concentration. Meanwhile, the critical load of initiating crack dropped from 17.9 to 13.4 N when B concentration raised from 12.8 to 22.2 at.%. The results of nano-indentation and scratch tests indicated that the crack resistance of CrBN coatings became poor when the B doping content increased. In here, the CrBN coating with 12.8 at.% B exhibited the best crack resistance.
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