Tuning the H/E* ratio and E* of AlN coatings by copper addition

Hard coatings with H/E* > 0.1 and low E*, where H is the hardness and E* is the indentation modulus, are highly desirable for wear-resistant applications. Copper has been added into the AlN coatings to tune such mechanical properties. Specifically, Al–Cu–N coatings with 0–25.4 at.% copper have been deposited by reactive magnetron co-sputtering from independent aluminum and copper targets. The increased copper addition caused the growth structure to evolve from columnar and porous, through column-free and dense, to column-free yet porous. While the crystalline AlN phase (hexagonal, P63mc) was seen in all coatings, the crystalline copper appeared only in coatings with a high Cu content (11.5 at.% or higher). A nanocomposite structure, in which the < 10 nm isolated Cu grains were embedded in the AlN phase, was identified. In the nanocomposite coating, a significant amount of CuAl bonding was also revealed by X-ray photoelectron spectroscopy (XPS) studies. The copper addition resulted in a threefold increase in hardness (up to 40 GPa). Particularly noteworthy is that we were able to tune the H/E* ratio in the ranges of 0.053–0.124. In addition, dense coatings with H/E* > 0.1 were obtained over the copper content range of 7.3–17.7 at.%. These coatings exhibited sliding wear rates on the order of 10− 16 m3/nm.