Atomic‐Scale Structural and Chemical Study of Columnar and Multilayer Re–Ni Electrodeposited Thermal Barrier Coating

Abstract

Rhenium alloys exhibit a unique combination of chemical, physical, and mechanical properties that makes them attractive for a variety of applications. Herein, we present atomic-scale structural and atomic part-per-million level three-dimensional (3D) chemical characterization of a Re-Ni coating, combining aberration-corrected scanning transmission electron microscopy (STEM) and atom-probe tomography (APT). A unique combination of a columnar and multilayer structure is formed by singlebath dc-electroplating and is reported here for the first time. Alternating thicker Re-rich and thinner Ni-rich layers support a mechanism in which Ni acts as a reducing agent. The multilayers exhibit hetero-epitaxial growth resulting in high residual shear stresses that lead to formation of corrugated interfaces and an outer layer with mud-cracks. IntroductionRhenium (Re) is a refractory metal with a unique combination of chemical, physical, and mechanical properties that makes it attractive for high-temperature, catalytic, energy, electrical, biomedical, and other applications, in spite of its high cost. [1,2] Interest in electroless deposition [3,4] and electrodeposition [5][6][7][8][9][10][11][12][13][14][15][16] of Re and its alloys has recently emerged. Electroplating of pure Re yields poor deposition results. The addition of salts of the iron-group metals (Ni, Fe, and Co) to the plating bath improves, however, the coating dramatically, allowing deposition of thick layers of the

Characterization of Re-Ni Films after the Initial Stages of Electrodeposition

“…The bands of the Re-rich phase are thicker than the bands of the Ni-Rich phase because the depletion of nickel ions in the diffusion layer is less significant than the depletion in perrhenate ions. 15 The periodic compositional modulations observed in the SIMS profiles are in agreement with our previous STEM and APT data.…”

“…We have supported this hypothesized mechanism by different experiments. 7,[13][14][15] The initial stages of Re-Ni deposition, which are critical for understanding the catalytic mechanism, were studied in our recent work. …”

“…A unique combination of a multilayer and columnar Re-Ni structure was observed, consisting of thicker Re-rich and thinner Ni-rich alternating layers. 15 In the current work, we used Time-of-Flight Secondary-Ion Mass Spectrometry (TOF-SIMS) and High-Resolution X-Ray Photoelectron Spectroscopy (HR-XPS) for studying the Re-Ni deposits produced in the initial stages of deposition. The results obtained confirm the concept of chemical reaction fading with increasing deposition time, and are in agreement with the compositional changes of the catalytic electrode surface during the Re-Ni deposition process.…”

“…The formation of a multilayer Re-Ni structure has been related to the Re-Ni binary phase diagram-a peritectic phase diagram with an extensive region of mutual solubility and no intermetallic compounds-and to alternate depletion and enrichment of nickel ions in the diffusion layer. 15 When a Re-rich layer forms, more hydrogen is being formed due to the catalytic effect of Re on the hydrogen evolution reactions. Consequently, the pH is increased locally, thus favoring the formation of a nickel hydroxide intermediate at the surface of the cathode.…”

Cross-sectioning spatio-temporal Co-In electrodeposits: Disclosing a magnetically-patterned nanolaminated structure

“…Interestingly, it was recently found that the Co-In system not only exhibits the spatio-temporal selfpattern on the surface, but also a fancy layer-by-layer growth type [28]. Although the spontaneous formation of layered deposits with a repeat length of tens or hundreds of nanometers has been observed in a quite few instances [29][30][31], this growth mode in immiscible systems exhibiting spatio-temporal patterns has not been studied in detail.…”