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CrAlN coatings have earned significant attention for use in cutting tool coating applications due to their excellent properties such as high hardness and superb oxidation resistance. It is well known that the interlayer between the coating and the substrate can influence the mechanical properties of the coatings. In this work, three interlayers—CrN, CrZrN, and CrN/CrZrSiN—were synthesized between a CrAlN coating and a tungsten carbide substrate to improve the mechanical properties and thermal stability of the CrAlN coating. All the CrAlN coatings with their respective interlayers showed high hardness values in the range of 34.5 to 35.1 GPa, and they were not significantly affected by the interlayer type. However, wear and scratch tests showed that the CrAlN coatings with CrN and CrN/CrZrSiN interlayers exhibited an improved friction coefficient of 0.33 and adhesion strength (Lc2) of 69 N compared to the CrAlN coating with the CrZrN interlayer. These improved wear properties were attributed to the H/E ratio of the interlayer between the coating and the substrate, in that the CrN and CrZrSiN interlayers effectively induced a smooth transition of the coating stress under a loading condition. During the thermal stability tests, the hardness of the CrAlN coating with the CrN/CrZrSiN interlayer was maintained up to 1000 °C due to the excellent oxidation resistance of the CrZrSiN layer, which contained an amorphous SixNy phase.

The CrZrN/CrZrSiN multilayer coatings at a bilayer period range decreasing from 1.35 μm to 0.45 μm were synthesized on a Si (100) wafer and WC-6 wt.% Co substrate using a closed-field unbalanced magnetron sputter, and the thickness effects on the mechanical properties and thermal stability were investigated. The CrZrN/CrZrSiN multilayer coatings showed high hardness and elastic modulus in the ranges of 28 to 33 GPa and 255 to 265 GPa, respectively, and the friction coefficient showed the lowest value of 0.24 on the multilayer coating with a bilayer period of 0.54 μm. The bilayer periods affected the adhesion strength of the multilayer coatings. From the scratch test, the critical load (Lc2) steadily increased with the decreasing of the bilayer period, and the CrZrN/CrZrSiN multilayer coating with a bilayer period of 0.45 μm showed the highest critical load (Lc2) of 79 N. In the case of the annealing test, the bilayer periods affected the thermal stability of the multilayer coatings, and the CrZrN/CrZrSiN multilayer coatings with 0.54 μm showed a maximum hardness value of approximately 30 GPa up to 800 °C.

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To confirm the influence of the interlayer thickness and substrate material on adhesion properties, CrZrN coatings with various Cr interlayer thickness were deposited on AISI H13, high speed steel, and tungsten carbide using unbalanced magnetron sputtering. The adhesion strength showed maximum value at 300 nm of the interlayer, but as the interlayer increased further to 450 nm, the adhesion strength decreased. The adhesion properties of the coatings were dependent upon not only interlayer thickness but also the substrate materials. The adhesion strength of the coating were measured 12, 32, 53 N on the tungsten carbide, AISI H13 steel, high speed steel, respectively and three different failure modes such as buckling spallation, wedging spallation, and chipping were observed on each substrate. The difference in adhesion properties could be attributed to the difference in value of elastic strain to failure (H/E) among the CrZrN coating, the interlayer, and the substrates material.