Characterization of Cr 2O 3/CrN duplex coatings for injection molding applications

Abstract

In this study, we deposited Cr 2O 3/CrN duplex coatings, consisting of a thin Cr 2O 3 oxide film on top of a CrN layer, with an unbalanced magnetron (UBM) sputtering technique. Microstructure characterization was conducted with X-ray diffraction (XRD) and scanning electron microscopy (SEM). Tribological evaluations were also performed with a scratch tester and ball-on-disc tribometer. Experimental results showed a well-adherent Cr 2O 3/CrN duplex coating morphology. The Cr 2O 3 top-layer possesses an amorphous lattice structure. Gas flow rates and bias voltages had an impact upon mechanical and chemical properties of the Cr 2O 3/CrN coatings. To compensate the fluctuation of pumping efficiency, target poisoning and sputtering parameters, the flow rate of the reactive gas was rapidly and accurately regulated via a set of piezo valves and an optical emission monitor (OEM). OEM readings revealed the exact proportions of reactive gas consumed by metal plasma (US Patent 4 525 (1985) 417; Appl. Phys. Lett. 50 (1987) 1056; Surf. Coat. Technol. 49 (1991) 543). Gas flow rates were thus controlled, dynamically, with variations of processing conditions. At an OEM setting of 30–50% and a pulsed bias voltage of −55 V, the Cr 2O 3/CrN duplex coating demonstrated excellent micro-hardness (2533 Hv 25g) and adhesion strength ( L c=75 N). The highest contact angle between water and Cr 2O 3 was measured at 103° at an OEM setting of 30%. An improved mold releasing capability is anticipated, especially compared with the traditional hard chrome plating. Finally, an outstanding wear life of 4250 m was achieved on the Cr 2O 3/CrN duplex coating deposited at 50% of OEM setting. In summary, the enhanced properties of micro-hardness, film adhesion, mold releasing and wear life of the Cr 2O 3/CrN duplex coating demonstrated its potential for injection molding applications.