Characterization of (Cr,Ta)N hard coatings reactively sputtered at low temperature

Two (Cr,Ta)N coatings with different composition were deposited in a Sputro n plasma beam sputtering apparatus at a temperature below 200 degrees C on polished tool steel disks, polished alumina substrates and silicon wafers. Microhardness, adhesion and internal stress were measured by Vickers microi ndentation, the scratch test and sample deflection, respectively. The mecha nical and electrical properties were compared to the values of CrN and TaN binary nitride coatings prepared in the same device under similar condition s. Like CrN and TaN, (Cr,Ta)N crystallizes in a cubic (NaCl) structure. Oxi dation resistance was tested in the temperature range 550-850 degrees C. We observed that a chromium-rich protective oxide layer developed on the Cr0. 58Ta0.42N coating, while on the Cr0.17Ta0.83N coating the oxidation was mor e rapid, with cracks appearing at temperatures as low as 600 degrees C. (C) 1999 Elsevier Science Ltd. All rights reserved.