Exploring the oxidation characteristics of binary and ternary transition metal carbide coatings

Abstract

This study explores the oxidation properties of binary and ternary Al/Si alloyed transition metal carbide (TMC) thin films, focusing on group IV to VI metals, specifically Ti, Zr, Hf, Ta, and W. TMCs are classified as ultra-high temperature ceramics (UHTCs) and are recognized for their high melting temperatures, exceeding 3000 °C, along with their exceptional thermal stability. However, they typically suffer from poor oxidation resistance. Binary TMC thin films start to oxidize at temperatures below 600 °C. To expand the application possibilities of TMCs, particularly in high-temperature fields such as aerospace, automotive, and tooling industries, alloying concepts with Al and Si are being explored to enhance their oxidation resistance. In detail, ten different sputter deposited ternary TM-X-C coating families were isothermally oxidized at 750 °C for 1 h and their oxidation kinetics have been benchmarked. For Al alloyed thin films, the best performing systems are Ti-Al-C and Ta-Al-C, forming scales below 750 nm at alloy contents above 25 at.% Al. In contrast, Ti-Si-C only requires around 20 at.% Si to form a dense and adherent scale (below 300 nm). Both Ti0.26Al0.32C0.42 and Ti0.29Si0.26C0.45 exhibit a two-layered oxide scale, consisting of a metal oxycarbide zone at the interface to the unaffected, nonporous Ti-Al/Si-C coating, followed by a mixed Ti-(Al/Si)-oxide scale on top. Based on detailed TEM analysis Al alloyed TiC obtains a better ability to act as an oxygen diffusion barrier.