Enhancing thermal stability and corrosion resistance of carbon-carbon composites with iridium coatings deposited by electron beam physical vapor deposition

Abstract

Abstract Carbon–carbon (C−C) composites are extensively used in high-temperature environments such as Combustor Liners and Turbine Blades in jet engines and Throat Inserts, Nozzle Extensions and Exit Cones in rocket engines due to their excellent thermal stability and mechanical properties. However, at temperatures exceeding 800 °C, these composites require additional protection to prevent degradation. This study aims to investigate the behavior of C−C composites when coated with high-purity metallic iridium using Electron Beam Physical Vapor Deposition (EBPVD). The research problem focuses on enhancing the high-temperature performance and corrosion resistance of C−C composites for aerospace applications. The methodology involves depositing a uniform 5.6 microns thick iridium coating on C−C substrates and characterizing the coating’s microstructure, hardness, and corrosion resistance. FESEM micrographs reveal that the iridium coating adheres uniformly to the substrate without any seepage, and XRD analysis confirms an FCC crystal structure with a densely packed grainy surface. Corrosion tests were conducted using a BIOLOGIC electrochemical workstation in a sodium chloride environment indicate a corrosion rate of 0.00307 mm year−1. The Nyquist, Bodo plots, and Taffel plots were constructed for the better understanding of the corrosion mechanism. While the OCP was constructed to understand the stability and the corrosion resistance of the C−C samples. Microhardness of the coating, measured under a normal applied load of 0.20 N, is 702 HV. The coated samples also could withstand thermal shocks between −40 °C and 1500 °C for 40 h without observable damage or color change. These findings demonstrate the potential of iridium-coated C−C composites to maintain structural integrity and performance in extreme aerospace environments, significantly impacting the field by providing a reliable protective solution for high-temperature applications.