Thermal stability and oxidation resistance of ZrSiN nanocomposite and ZrN/SiNx multilayered coatings: A comparative study

Abstract

In the present work we comparatively study the thermal stability and oxidation resistance of ~300nm thick Zr-Si-N coatings with either 2D or 3D interface geometry: 1) Zr-Si-N nanocomposites and 2) ZrN/SiNx nanoscale multilayers. Both types of films were prepared by reactive magnetron sputter-deposition on Si wafers under Ar+N2 plasma discharges. Zr-Si-N films were deposited by co-sputtering from Zr and Si targets at substrate temperature Tdep of 600°C, with Si content ranging from 0 to 22.1at.%, while ZrN/SiNx multilayers with ZrN (resp. SiNx) layer thickness varying from 2 to 40nm (resp. 0.4 to 20nm) were synthesized by sequential sputtering from elemental Zr and Si3N4 targets at Tdep=300°C. According to transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis the microstructure of Zr-Si-N films changes from dual-phase nanocomposite structure, consisting of ZrN nanograins (4–7nm) surrounded by an amorphous tissue, towards X-ray amorphous with increasing Si content. The multilayered films consist of nanocrystalline (002)-oriented ZrN and amorphous SiNx layers. The structural evolution has been investigated by XRD after vacuum annealing at 1000°C, while the oxidation resistance under air was studied using in situ XRD in the temperature range from 400 to 950°C, as well as by scanning electron microscopy (SEM) and wavelength dispersive X-ray spectrometry (WDS) after air annealing procedure. While the reference ZrN film starts to oxidize at Tox.=550°C, a much higher oxidation resistance is found for multilayered films, till Tox.=860–950°C for ZrN/SiNx coatings with the elementary layer thickness ratio of 5nm/10nm, 3nm/5nm and 2nm/5nm. ZrSiN nanocomposites exhibit an improved oxidation resistance with increasing Si content compared to binary ZrN compound, but their stability is worst comparatively to the multilayers case.