Comparative Study of Sliding, Scratching, and Impact-Loading Behavior of Hard CrB2 and Cr–B–N Films

Abstract

CrB2 and Cr–B–N films were deposited by magnetron sputtering of CrB2 target in an argon atmosphere or in a gaseous mixture of argon and nitrogen. The films were characterized in terms of their adhesion strength, sliding, and impact wear resistance. Crack resistance of the films was evaluated by micro-indentations. The adhesion strength was studied by means of scratch testing. The wear tests were performed under different loads against chromium steel and WC–Co counterpart materials. In order to determine the film fatigue toughness, dynamic impact tests were carried out. The indentations, scars, wear tracks, and impact cavities on the film surface were examined using optical profilometry, as well as optical and scanning electron microscopy. Comparison of lifetimes of CrB2 and Cr–B–N-coated cemented carbide mills in dry milling of D2 high-chromium steel was also performed. The obtained results show that the CrB2 film has poor adhesion, low fracture toughness, and rapidly fails during sliding and dynamic impact tests. In contrast, the Cr–B–N films with nitrogen content between 7 and 11 at.% exhibited superior adhesion strength (critical load \(L_{{{\text{c}}_{2} }}\) = 70–90 N), good tribological properties (friction coefficient against WC–Co <0.4 and wear rate <2×10−6 mm3 N−1 m−1), and reduced impact wear. The lifetime of mills coated with Cr–B–N films was 1.3 and 2.0 times longer as compared to the tools coated with TiN and CrB2 films and uncoated WC–Co tools, respectively.