Effects of thickness ratio on phase structures, mechanical properties, and wear behaviors of CrN/ZrB 2 bilayer films

Abstract

CrN/ZrB 2 bilayer films leveraging the wear resistance of CrN and the mechanical properties of ZrB 2 were successfully produced and characterized. DC magnetron sputtering was used to deposit CrN/ZrB 2 bilayer films with a thickness of approximately 1 mu m and various ZrB 2 /CrN sublayer thickness ratios ( T ZrB2 / T CrN = 10.85, 5.78, 4.50, 2.29, and 1.04). The thickness ratio was controlled by adjusting the deposition times of the individual sublayers. The effects of thickness ratio on the films' phase structures, mechanical properties, and wear resistance were investigated. The ZrB 2 sublayer initially formed with a nanocrystalline structure; as its thickness increased, its texture became (001). As the thickness of the CrN sublayer increased, the CrN (111) reflection became more dominant, and the hardness of the CrN/ZrB 2 bilayer films decreased from 19.8 to 11.6 GPa. In the CrN/ZrB 2 bilayer films, the CrN sublayer was softer than the harder ZrB 2 sublayer; specifically, the wear rate of the monolithic ZrB 2 film was 6.45 x 10 -5 mm 3 /N center dot m. This hardness enabled the bilayer films to exhibit excellent wear resistance with wear rates of 1.04 -1.68 x 10 -6 mm 3 /N center dot m. The wear behaviors of the CrN/ZrB 2 bilayer films were classified into two tribological mechanisms in accordance with wear track observations. For the samples with high T ZrB2 /T CrN ratios, the shear mechanism dominated the wear behavior and resulted in the formation of a transfer layer on the worn surface. By contrast, the samples with low T ZrB2 /T CrN ratios had a ploughing mechanism in which a deformed track was generated on the surface.