Determination of the compatibility of various coatings with a branched perfluoropolyalklyether in a high temperature oxidative environment

Six commercially available titanium based coatings were deposited onto M-50 and carburized Pyrowear 675® substrates and were studied in a high temperature oxidative environment while immersed in a branched perfluoropolyalklyether (PFPAE), Krytox AC®. The responses of the coated substrates to this environment were compared to M-50 and carburized Pyrowear 675®. The coatings investigated were physical vapor deposited (PVD) TiN, TiCN, TiAICN, TiCrCN/TiB4C multilayer, E-Ni TiN, and E-Ni TiCN. Experiments were conducted at temperatures ranging from 315 to 360°C for a duration of 24 hours. Post-test analysis of the metal/coated coupons consisted of visual inspection, weight change per area, scanning electron microscope (SEM), energy dispersive x-ray spectroscopy (EDS), and x-ray photoelectron iii spectroscopy (XPS). Post-test analysis of the fluid consisted of visual inspection, viscosity change, acid number change, and fluid weight loss. Coated Pyrowear 675® coupons demonstrated superior corrosion resistance compared to coated M-50. The coatings most resistant to chemical attack in the PFPAE fluid in order of increasing resistance were TiCN, E-Ni TiN, and E-Ni TiCN. “Blisters” were observed with all coatings except for those with an E-Ni layer