Microstructural and Nanomechanical Characterization of CrCoAlHf/YSZ Multilayer Coatings Deposited by DC/RF Magnetron Sputtering

Abstract

This study presents the microstructural, chemical, and nanomechanical behavior of multilayer coatings of Cr/CoAlHf/YSZ deposited on Inconel 718 alloy using combined DC/RF magnetron sputtering with a focus on coatings deposited at 300°C for high-temperature aerospace applications. FESEM and EDS analyses indicate the formation of a multilayer structure with high density and minimal porosity, as well as homogeneous elemental distribution of the Cr, CoAlHf, and YSZ layers, implying that no interfacial diffusion is occurring. X-ray diffraction (XRD) patterns confirm the formation of stable phases, including ZrO₂, Y₂O₃, Cr, HfO₂, and a Co–Cr–Al–Hf solid solution. Nanoindentation shows stable deformation behavior and high load-bearing capacity, where hardness exhibited an increasing trend from 7.94 to 11.25 GPa in the range of 500–2500 µN, decreasing to 10.70 GPa at 3500 µN, which is explained as the change of reverse indentation size effect (r-ISE) to conventional indentation size effect (ISE) for the change of applied loads. Nano-scratch testing at gradually increased ramp loads confirms good coating adhesion, characterized by stable frictional behavior and minimal surface damage. XPS survey analysis confirms the chemical integrity of the multilayer system, with both strong Zr3d and Y3p peaks indicating the YSZ top layer, and distinct signals for Co, Cr, Al, and Hf, indicating the underlying bond coat. Overall, the results reveal that deposition at 300°C is beneficial for favorable microstructural evolution, chemical stability, and enhanced nanomechanical performance, making the CoCrAlHf/YSZ multilayer a promising protective coating for Inconel 718 components exposed to extreme aerospace service environments.