Nickel-based Alloy Substrate Research Articles

Fabrication of YSZ coatings on nickel-based alloys by anodic electrophoretic deposition

Abstract In the paper, YSZ coatings were prepared on nickel-based alloy substrates by anodic electrophoretic deposition. The YSZ suspension solution was obtained under stirring and ultrasonic treatment, in which the anhydrous ethanol and acetylacetone were used as the dispersion medium and ammonium polyacrylate was used as the dispersant of the suspension. The effects of different deposition voltage and deposition time on YSZ coating were investigated. Meantime, the microstructure of the coating surface was observed by metallographic microscope. It was found that the high-quality YSZ coating could be obtained by deposition at 60 V for 2–3 min. Finally, the effect of sintering temperature on coating quality was investigated by X-ray diffractometer and scanning electron microscopy. The results showed that the YSZ coating bonded closely with the substrate after sintering at 1200 oC, and the porosity of the YSZ coating increased after sintering

Development and Evaluation of Temperature Sensing Smart Skin for High-Temperature Measurements in Pipes

We designed a temperature sensing smart skin with a composite insulation layer for high-temperature monitoring of pipelines and engine combustion chamber walls, and proposed a thin/thick film hybrid integrated manufacturing process to improve the high temperature stability of the sensor. A PtRh/Pt thick-film thermocouple was installed on an ultra-thin nickel-based alloy substrate by screen printing and then fixed on a pipe inner wall by spot welding. The morphology of the prepared composite insulation layer was studied by scanning electron microscopy, and its insulation resistance was tested at high temperatures, verifying its high insulation performance. In addition, the output voltage has high linearity in the temperature range of 25–1000 °C, and the prepared thermocouple shows consistency and reusability with an average Seebeck coefficient of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.016 ~ \mu \text{V}$ </tex-math></inline-formula> /°C. Upon testing the thermocouple at 1100 °C for 10 hours, the peak voltage output was 10.094 mV and the average output voltage was 10.051 mV. Experiments show that the thick-film thermocouple operates stably at high temperatures and can work at 1400 °C in a short time.

Additive-Manufactured Platinum Thin-Film Strain Gauges for Structural Microstrain Testing at Elevated Temperatures

This paper investigates the feasibility and performance of the fabrication of platinum high-temperature thin-film strain sensors on nickel-based alloy substrates by additive manufacturing. The insulating layer was made of a dielectric paste by screen printing process. A 1.8-micron-thick platinum film was deposited directly on the insulating layer. The four-wire resistance measurement method was used to eliminate the contact resistance of the solder joints. Comprehensive morphological and electrical characterization of the platinum thin-film strain gauge was carried out, and good static and dynamic strain responses were obtained, which confirmed that the strain gauge was suitable for in situ strain monitoring of high-temperature complex components.

Hydrothermal growth of c-axis oriented ferroelectric (Bi1/2K1/2)TiO3 films on metal substrates

Ferroelectric films fabricated on metal substrates are desirable for use in piezoelectric vibration energy harvesters. In this report, we demonstrate that dense films of lead-free ferroelectric (Bi1/2K1/2)TiO3 (BKT) with preferred c-axis orientation can be grown on nickel-based alloy substrates by utilizing the hydrothermal synthesis method. A buffer layer of LaNiO3 (LN) was formed on the substrates by the sol-gel spin coating method, and then BKT was grown by a hydrothermal reaction at a low temperature of 150 °C. The surface structure and thickness of the final BKT films were found to strongly depend on the numbers of the deposition cycles for LN and BKT, respectively. As a result, highly c-axis oriented BKT films with a smooth surface and a thickness up to 830 nm were obtained. Although the as-deposited BKT films were suggested to contain hydroxyl groups in their crystal lattice, a post-annealing process at 650 °C in air was found to be effective to remove them. The polarization response of the annealed BKT film proved the ferroelectric polarization switching in the film.

Preparation and evaluation of PdCr thin film resistive strain gauges

Thin film resistive strain gauges using PdCr alloy as sensing material were fabricated on nickel-based alloy substrate, and evaluated for strain response, apparent strain and drift strain over a temperature range to 800 °C. The results indicated that the PdCr thin film strain gauge showed an excellent linear response to applied strain and stable gauge factor at different temperatures. The apparent strain can be estimated and compensated due to its repeatability and low value. The drift strain can be neglected until 600 °C. Even at 800 °C the drift strain can also be corrected since it drifted slightly and linearly. The repeatability of PdCr thin film strain gauge was also evaluated. It showed that the repeatable measurement error was 6.4%.

Currentless Deposition of Niobium-Based Protective Coatings for Application in Molten Salts

A novel method of forming niobium-based coatings by currentless deposition in molten salts was developed. The protective coatings were produced on nickel and various nickel-based alloy substrates. The corrosion resistance of the obtained coatings was tested and characterized in fused niobium- and uranium-containing chloride electrolytes at different temperatures. The method of protecting nickel-based alloys by currentless niobium deposition can be used in industrial technologies of rare earth and refractory metal electrowinning from molten salt baths.

Synthesis and characterization of binder-free Cr3C2 coatings on nickel-based alloys for molten fluoride salt corrosion resistance

Under various conditions, chromium carbides appear to be relatively stable in the presence of molten fluoride salts and this suggests that their use in corrosion resistant coatings for fluoride salt environments could be beneficial. One method for producing these coatings is the carburization of sprayed Cr coatings using methane-containing gaseous precursors. This process has been investigated for the synthesis of binder-free chromium carbide coatings on nickel-based alloy substrates for molten fluoride salt corrosion resistance. The effects of the carburization process on coating microstructure have been characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) in conjunction with energy dispersive spectroscopy (EDS). Both plasma-sprayed and cold-sprayed Cr coatings have been successfully converted to Cr3C2, with the mechanism of conversion being strongly influenced by the initial porosity in the as-deposited coatings.

THERMAL SHOCK BEHAVIOR OF AIR PLASMA SPRAYEDCoNiCrAlY/YSZTHERMAL BARRIER COATINGS

The structural changes and failure mechanism of thermal barrier coatings (TBCs) during thermal shock cycling were investigated. TBCs consisting of CoNiCrAlY bond coat and partially yttria-stabilized zirconia (YSZ) top coat were deposited by atmospheric plasma spraying (APS) on a nickel-based alloy substrate and its thermal shock resistance performance was evaluated. TBCs were heated at 1100°C for 15 min followed by cold water quenching to ambient temperature. Microstructural evaluation and elemental analysis of TBCs were performed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The crack features of YSZ coatings in TBCs during thermal shock cycling, including those of horizontal (parallel to the substrate) and vertical cracks (perpendicular to the substrate), were particularly investigated by means of SEM and image analysis. Results show that horizontal and vertical cracks have different influences on the thermal shock resistance of the coatings. Horizontal cracks that occur at the interface of YSZ and thermally growth oxidation (TGO) cause partial or large-area spalling of coatings. When vertical and horizontal cracks encounter, network segments are formed which lead to partial spalling of the coatings.

Highly enhanced infrared spectral emissivity of porous CeO2 coating

A porous CeO2 coating was prepared by electron beam physical vapor deposition technique. The microstructure and infrared spectral emissivity in wavelength range 2.5∼25μm were investigated. The surface morphology could be tuned by deposition power density. The as-deposited coating shows (311)-preferred orientation. The great enhancement of infrared spectral emissivity in the whole wavelength range was observed in the porous CeO2 coating, compared to a dense CeO2 coating. The porous surface structure provides multiple reflection and absorption, thus improves the spectral emissivity. Moreover, the CeO2 coating also shows excellent adhesion property to nickel-based alloy substrate. These results show a potential application at high temperature.

Erosion Behavior of TiC-xNi Composite Coatings &lt;i&gt;In Situ&lt;i&gt; Synthesized by Electro-Thermal Explosion Ultra-High Speed Spraying

With aim to investigate the effect of the content of Ni on erosion behavior of the TiC-xNi coating at elevated temperatures, The TiC-xNi (x=0, 5, 10, 15 , 20wt.%) composite coatings were in-situ synthesized on nickel-based alloy substrate by the self-developed electro-thermal explosion ultra-high speed spraying (EEUSS) device with the cored wire. Erosion properties of the coatings were assessed by the erosion tester under 90° incidence angle and 650°C. X-ray diffraction (XRD) and microhardness tester were used to investigate the coating phases and microhardness. The coatings consisted of TiC phase and Ni binder phase, as well as the residual C. The microhardness of TiC-xNi coating with the Ni content from 5 wt.% to 20wt.% decreased with the increase of the content of Ni. Elevated temperature erosion test indicate that the spiculate quartz particles impact the surface of the coating which lead to the loss of material. The erosion resistance of the TiC-xNi coatings increased first and decreased afterwards with the increase of the content of Ni. The relative erosion resistance of coating with 10 wt.% Ni addition is excellent which is about 2 times than that of TiC-20Ni coating under 650°C and 90° incidence angle.

Oxidation of carbon on nickel-based metallic substrates: Implications for high-temperature superconductor coated conductors

Adhesion of thin films of epitaxial oxides to nickel-based metallic substrates is important for the successful development of high-temperature superconductor coated conductors. Detachment of epitaxial oxide buffer layers at the oxide/metal interface during either oxide growth or subsequent processing renders the conductor useless. In this study, thermal desorption spectroscopy (TDS) has been used to identify and understand one of the causes of buffer layer detachment, oxidation of carbon at the oxide–metal interface to form carbon monoxide. Results of TDS indicate that on the surface of a bare nickel-based alloy substrate, the rate of carbon oxidation depends on both the supply of carbon from the substrate and the supply of oxygen from the vapor. Sulfur at the surface of the alloy substrate reduces the rate of carbon oxidation. The effectiveness of various treatments of the bare substrate to eliminate CO formation and epitaxial oxide detachment has been demonstrated. TDS provides both a means to evaluate the kinetics of the oxidation reaction and a tool to assess the need and effectiveness of a substrate oxidation treatment.

Characteristics and porcelain bond strength of (Ti,Al)N coating on dental alloys.

The effect of a novel titanium-aluminum nitride film, or (Ti,Al)N film, on the bond strength between a dental porcelain and two nickel-based dental alloy substrates was investigated. A thin layer of (Ti,Al)N film was deposited on flat metal samples using a reactive radio-frequency sputtering method. A uniform thickness of porcelain was applied to the film- coated metal samples. Metal-ceramic specimens were subjected to three-point bending, and failure loads were recorded. Bond strengths between the porcelain and (Ti,Al)N-coated metal alloys ranged from 159.0 +/- 11.7 N to 278.0 +/- 12.3 N. These values were significantly greater (p< 0.05) than bond strengths recorded for control samples that did not incorporate the (Ti,Al)N film. An electron probe microanalyzer with a line profile mode was used to characterize the interface between the (Ti,Al)N film and the porcelain. Results of this investigation suggest that the (Ti,Al)N film (1) increases the flexural bond strength between dental porcelain and nickel-based alloy substrates by permitting elemental diffusion, (2) interferes with the surface oxide formation that characteristically originates from the nickel-based metal alloy substrate, and (3) provides an appropriate oxide layer for porcelain application.

Adhesion and its influence on micro-hardness of DLC and SiC films

Micro-hardness and scratch adhesion testing are the most commonly used techniques for assessing the mechanical properties of thin films. Both of these testing methods utilize single-point contact and induce plastic deformation in the substrate and film. However, the influence of adhesion on the measured hardness has been seldom reported so far. In our experiments, diamond-like carbon (DLC) and silicon carbide (SiC) films deposited on silicon and nickel-based alloy substrates by pulsed laser ablation were indented and scratched by a Vickers micro-hardness tester and a diamond-cutter, respectively. It was found that the composite hardness decreased more rapidly for poor adhesion when increasing the indentation load. The result was explained by the elastic-plastic deformation mode of indentation and helped us to understand the physical meaning of one parameter commonly introduced in the models used to separate film hardness from the composite hardness.

Cryogenic evaluation of epoxy bond strength

The purpose of the work presented here was to determine methods of optimizing the adhesion of a particular epoxy (CTD-101K, Composite Technology Development Inc.) to a particular nickel-based alloy substrate (Incoloy ® 908, Inco Alloys International) for cryogenic applications. Initial efforts were focused on surface preparation of the substrate material via various mechanical and chemical cleaning techniques. Test samples, fabricated to simulate the conduit-to-insulation interface, were put through a mock heat treat and vacuum/pressure impregnation process. Samples were compression/shear load tested to compare the bond strengths at room temperature and liquid nitrogen temperature. The resulting data indicate that acid etching creates a higher bond strength than the other tested techniques and that the bond formed is stronger at cryogenic temperatures than at room temperature. A description of the experiment along with the resulting data is presented here.