Modifying Cr/CrN composite structure by Fe addition: Toward manufacturing cost-effective and tough hard coatings

Abstract High-performance cutting tools require hard yet tough coatings. Physical vapor deposited CrN ceramic coatings exhibit great hardness but also high brittleness. Introducing metal phase to form Cr/CrN composite structure is effective to enhance their toughness. However, high cost hot-pressed Cr targets and narrow processing window of coating deposition limit the application of Cr/CrN composite coatings. In this work, up to 20 at.% Fe was selected to alloy with Cr in the target, aiming at simultaneously facilitating the HP process and modifying the Cr/CrN composite structure. With the help of Fe, dense targets with relative densities beyond 98% can be fabricated at the low sintering temperature of 1100 °C, 100 °C lower than that for pure Cr target. With the Cr-Fe targets, Cr(Fe)/(Cr,Fe)N composite coatings were deposited by magnetron sputtering under a N2/Ar mixed atmosphere. The hardness of coating increases from 7.26 to 11.27 GPa when Fe content in target increases from 0 to 5 at.%, due to the solution strengthening. The toughness of coating is also enhanced because of the increased amount of Cr(Fe) phase. Cr(Fe) and (Cr,Fe)N in the coating display a “pearlite-like” distribution, and in this structure, the Cr(Fe) phase is helpful to crack bridging and strain relaxation.