Influence of substrate temperature on morphology and behavior under cyclic thermal load of gas flow sputtered zirconia coatings

• Published in: Surface & coatings technology 2017-09, Vol.324, p.7-17
• Main Authors: Rösemann, N., Ortner, K., Petersen, J., Stöwer, M., Bäker, M., Bräuer, G., Rösler, J.
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Coatings; Crystallography; Cyclic loads; Diffraction patterns; Failure mechanism; Gas flow; Gas flow sputtering; Grain orientation; Microstructure; Morphology; Partially stabilized zirconia; Porosity; Reactive sputtering; Ridges; Scale (corrosion); Spallation; Substrate temperature; Substrates; Temperature; Thermal analysis; Thermal barrier coatings; Thermal cycling; X-ray diffraction; Yttria stabilized zirconia; Yttrium oxide; Zirconium; Zirconium dioxide
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2017.05.041

The aim of this work is to gain an understanding of the influence of substrate temperature during deposition on the resulting microstructure and crystallographic properties of gas flow sputtered (GFS) partially yttria stabilized zirconia coatings (PSZ). PSZ coatings were deposited on a FeCrAl-Alloy substrate, varying the substrate temperature between 500°C and 800°C. Regardless of the substrate temperature, all coatings were columnar, but varied in their morphology. Four different groups of sub-microstructures, each defined by a substrate temperature range, were identified based on morphology and X-ray diffraction (XRD) pattern. The two low-temperature groups exhibit a novel microstructure characterized by three dense ridges at intervals of 120° converging at the column center. Supported by these ridges small stacked plates lead to a featherlike porosity. The XRD pattern revealed a monoclinic fraction, besides the tetragonal and/or cubic one, and a 〈111〉 growth direction. Higher temperatures diminish the monoclinic fraction until it vanishes at 800°C accompanied by a change in growth direction to 〈100〉. Thermal cycling experiments were conducted between 1050°C and 100°C. Macroscopic spallation occurred for one group while the other samples were intact after the end of the experiment at 1300cycles. Microscopic delaminations were found between a pure alumina scale and a mixed oxide zone, consisting of zirconia particles embedded into an alumina matrix. A hypothesis was proposed explaining the observed failure mode. [Display omitted] •Depending on the substrate temperature 4 groups of microstructures are identified.•Higher substrate temperatures decrease the deposition rate and the porosity.•The growth direction of the columns changes from ⟨111⟩ to ⟨100⟩ at 800°C.•Highly porous coatings fail due to the formation of a mixed oxide and buckling.•Denser coatings fail due the coalescence of segmentation and delamination cracks.