Chemical and microstructural characterization of (Y or Zr)-doped CrAlN coatings

Abstract

Magnetron sputtered chromium aluminium nitride films are excellent candidates for advanced machining and protection for high temperature applications. In this work CrAlNbased coatings including Y or Zr as dopants (2 at. %) are deposited by d.c. reactive magnetron sputtering on silicon substrates using metallic targets and Ar/N 2 mixtures. The hardness properties are found in the range of 22-33 GPa with H/E ratios close to 0.1. The influence of the dopant element in terms of oxidation resistance after heating in air at 1000ºC is studied by means of X-ray diffraction (XRD), cross-sectional scanning electron microscopy (X-SEM) and energy dispersive X-ray analysis (EDAX). The microstructure and chemical bonding are investigated using a transmission electron microscope (TEM) and electron energy-loss spectroscopy (EELS) respectively. The improvement in oxidation resistance as compared to pure CrN coating is manifested in the formation of a Al-rich outer layer that protects the underneath coating from oxygen diffusion. The best performance obtained with the CrAlYN film is investigated by in situ annealing of this sample inside the TEM in order to gain knowledge about the structural and chemical transformations induced during heating. *Manuscript with changes highlighted Click here to view linked References

Role of Y in the oxidation resistance of CrAlYN coatings

“…1. The CrAlYN-A and CrAlYN-B coatings present a typical columnar structure similar to that observed by the pure CrAlN in our previous publication [13]. A multilayer structure can be clearly seen in the inset images at higher magnification.…”

“…In a previous work, we demonstrated that yttrium (1.7 at.%) was better than zirconium to increase the oxidation resistance of CrAlN coatings deposited on silicon at 1000 • C in air with Al contents below 10 at.% [13], although zirconium was better to reduce friction [4]. Moreover, the protectiveness of nanostructured CrAlYN coatings [∼4-12 at.% of Al; ∼2-5 at.% of Y] deposited on P92 steel against steam oxidation at 650 • C was found to be comparable to conventional microstructured aluminides at much lower thickness than used for steam turbine components [21,22] the location of the metallic elements inside ternary or quaternary nitrides and their chemical state may have a significant influence on the oxidation behavior and protective mechanism.…”

“…When exposed to air at elevated temperatures, Cr 1-x Al x N films form dense and adherent mixed aluminum and chromium oxide scales [1,8,9], which eventually suppress the oxygen diffusion into the bulk, providing excellent oxidation resistance up to temperatures as high as 900 • C [10][11][12], even at low Al content [13]. Current investigations seek to improve the thermal and oxidation resistance above this limit temperature by incorporation of large (substitutional) atoms, as they effectively retard diffusion related processes (recovery, decomposition and recrystallization).…”

Tribological behaviour at high temperature of hard CrAlN coatings doped with Y or Zr

“…Moreover, the addition of a reactive element was suggested to reduce the accumulation of voids at the substrate/scale interface [21]; to improve the mechanical properties of the scale by modifying its structure [22] or to prevent the grain coarsening at elevated temperatures [23]. In a previous work we also confirmed the improved oxidation resistance of a CrAlYN coating in comparison to CrAlZrN [24]. The tribological properties of CrAlN coatings have been investigated previously [6,7,[25][26][27] but only limited information is available about their tribological behavior at high temperature [28][29][30].…”

Substrate Finishing and Niobium Content Effects on the High-Temperature Corrosion Resistance in Steam Atmosphere of CrN/NbN Superlattice Coatings Deposited by PVD-HIPIMS

“…In order to improve their behaviour, additional elements have been included in their composition such as Al, Ti, Nb and rare earths as Y or Zr [10][11][12]. Following other approach different arrangements of the coating multilayers have been also tested exploring the effect of alternating layers with thickness and composition variations [13][14][15].…”