The Effects of pH and Temperature on Electrodeposition of Re-Ir-Ni Coatings from Aqueous Solutions

Abstract

The Re-Ir system is of great interest for high-temperature applications and extreme environments. Here, Re-Ir-Ni alloy coatings were electroplated from aqueous solutions. The effects of pH and temperature on the faradaic efficiency (FE), chemical composition, surface morphology and crystallographic structure of the coatings were studied. The results show that the pH and temperature of electrolytes have a significant effect on the electrodeposition of Re-Ir-Ni. As the pH was increased from 2.0 to 8.0, the FE, partial current densities for deposition of the three metals, and deposition rate increased. The highest Re-content (82 at%) was obtained at pH = 2.5. At pH = 2.0, the coating consisted of an amorphous phase, and no cracking was observed. When raising the pH to 4.0 and above, crystalline phases (including hydrides) formed, and both columnar crystals and micro-cracks were observed. The bath temperature affected the surface crack density and the size of the grains that form the mesoscopic colonies. At the two lowest temperatures studied herein (50 and 60 • C), no codeposition of Ir was observed. The phase composition of the coating changed from amorphous Re-Ni at 50 • C; to amorphous Re-Ni, hcp-Ni and hexagonal Pure rhenium (Re) has high melting point (3,186• C), excellent wear resistance, and superior strength and ductility at elevated temperatures. In addition, it does not suffer from ductile-to-brittle transition, and it does not form carbides while having good mutual wettability with carbon. 1,2At present, the main manufacturing processes of Re and its alloys are powder metallurgy and chemical vapor deposition (CVD). 1-3In recent years, we have studied electroplating 4-12 and electroless plating 13,14 as alternative processes. Electrodeposition of pure Re was found to have a low faradaic efficiency (FE) and poor quality.4 Addition of iron-group metal salts to the plating bath results in the formation of Re-Me alloys (Me = Ni, Co or Fe) with high Re-content and at high FE, thus showing a catalytic effect of the iron-group metals on the electrodeposition of Re. 5,7 Rhenium and its alloys with iron-group metals tend to oxidize readily in moist air at temperatures above 600• C. 1,2 In order to protect them from high-temperature oxidation, a top coating such as rhodium (Rh) or iridium (Ir) is often applied. Iridium has high melting point (2,446• C) and excellent corrosion resistance. 15,16 Re and Ir show extensive mutual solubility and no intermetallic compounds in their binary phase diagram. Iridium can also act as an effective diffusion barrier for inward-diffusing oxygen and outward-diffusing carbon. It is thus one of the most promising candidates for protective coating of either structural carbons or Re-based components for extreme environments.2,17,18 Iridium-coated Re nozzles are used in aerospace applications for small chemical rockets and resistojet thrusters.19 A combustion chamber composed of Re substrate and Ir coating has been demonstrated to be stable for extended lifetimes at temperatures as high ...

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

“…[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. [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.…”

“…[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. 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).…”

Effect of plating temperature on electroless amorphous Ni–P film on Si wafers in an alkaline bath solution

“…These features indicate the film growth is a Volmer-Weber growth mode. The formation of mesoscale nodules resulted from nucleation extending laterally from an existing structural defects (Wu et al 2015). As shown in Fig.…”

Electrodeposition and Thermal Stability of Re₆₀Ni₄₀ Amorphous Alloy

“…These cracks may result from volumetric changes due to hydrogen absorption during electroplating, from hydride decomposition shortly after electroplating, or from residual stresses. 1,29 The thickness of the alloy was uniform, about 16.5 µm, indicating the deposition rate was 16.5 µm h ¹1 . The fibrous type of grain is the result of orientated growth of grains.…”