Structural, mechanical and tribological properties of CrAlN coatings deposited by reactive unbalanced magnetron sputtering

In this work, a series of CrAlN coatings with Al/Cr atomic ratio between 0 and 0.6 were deposited on high speed steel substrates by reactive unbalanced magnetron sputtering. The structural, mechanical and tribological properties of the as-deposited CrAlN coatings were characterized by energy dispersive X-ray spectroscopy, X-ray diffraction, nanoindentation, and pin-on-disc tribometer experiments. It was found that pure CrN coating exhibited an amorphous structure. With the addition of aluminum, the CrAlN coatings gradually crystallized in the cubic structure, showing a (111) preferential orientation. With increasing aluminum content, coating hardness increased gradually from about 18 GPa up to a maximum value of 30 GPa, and then dropped slightly with further increase in aluminum content. The wear resistance of all the CrAlN coatings is about six times better than that of the pure CrN coating deposited under similar conditions.