Combinatorial Sampling and Wear Behavior of Cr-Al-C-N Coatings Deposited by HiPIMS

CrAlN PVD coatings are frequently used to protect cutting tools because of their superior hardness and wear resistance. However, the influence of carbon addition to such coatings remains largely unexplored. Therefore, Cr-Al-C-N coatings were deposited by HiPIMS using a commercial PVD unit equipped with a segmented sputter target. The target consisted of an upper half of Cr and a lower half of Al. Carbon was added under reactive sputtering conditions with the aim of reducing internal stress and introducing a friction-reducing component. A range of different Al-Cr-C compositions could be efficiently explored by varying the acetylene reactive gas flow. Depending on the positioning of the samples, Cr/Al ratios could be varied between about 4/1 and 1/2 while three different levels of carbon concentration (0, 11, and 25 atomic % of total coating composition) were investigated. It was found that an intermediate carbon concentration effectively increased the hardness of Cr-rich coatings, achieving maximum plastic hardness values over 40 GPa. With increasing Al content, hardness drops to below 30 GPa. The cubic CrN phase with mostly 200-oriented grains was detected for most variants. With increasing Al and C contents, a rapid decrease in crystallite size is observed, accompanied by a reduced intensity of the (200) XRD reflection. A turning test on stainless steel showed decreasing flank wear with higher Al contents. However, no improvement associated with carbon addition could be confirmed within the investigated concentration range.