Annealing of chromium oxycarbide coatings deposited by plasma immersion ion processing (PIIP) for aluminum die casting

Chromium oxycarbide coatings have been investigated for use as non-wetting coatings for aluminum die casting. This paper examines Cr-C-O coating stabi lity and non-wetability at elevated temperatures for extended periods. Coat ings were deposited onto 304 stainless steel from chromium carbonyl [Cr(CO) (6)] by plasma immersion ion processing. The coatings were annealed in air at an aluminum die casting temperature of 700 degreesC up to 8 h. Coatings were analyzed using resonant ion backscattering spectroscopy, nanoindentati on and pin-on-disk tribometry. Molten aluminum was used to determine coatin g wetting and contact angle. Results indicate that the surface oxide layer reaches a maximum thickness of 900 nm. Oxygen concentrations in the coating s increased from 24% to 34%, while the surface concentration rose to almost 45%. Hardness values ranged from 22.1 to 6.7 GPa, wear coefficients ranged from 21 to 8 x 10(-6) mm(3)/Nm and contact angles ranged from 156 degrees to 127 degrees. (C) 2001 Elsevier Science B.V. All rights reserved.