Impedance Measurement and Demonstrator Tests of Developed Thermally Sprayed and Sealed Coating Systems for Bearing Applications

The Committee on Metallizing of the American Welding Society sponsored a test program to study the corrosion protection afforded by thermal sprayed aluminum and zinc coatings applied to structural at eel. The first panels were exposed in January, 1953. Inspections were made at 1, 3, 6, and 12 year intervals. Reported results examined the performance of the subject metallized coatings in marine atmospheric and seawater environments. Seawater tests included full and half tide immersion in quiet seawater and full immersion in flowing seawater (approximately 3 knots). The subject conditions are highly representative of those found on off-shore structures. The results indicate that low carbon steel can be protected from the corrosive effects of these environments for 18 years or more by the application of flame sprayed zinc or aluminum coatings. INTRODUCTION This paper reports the results of an l8-year study of the corrosion protection afforded by metallized aluminum and zinc coatings applied to low carbon steel. Test sites were selected throughout the United States to provide a wide variety of environmental conditions. These included urban, industrial, salt air, and severe marine atmospheric exposure. Also below mean tide, mean tide, and total seawater immersion conditions were tested. This paper will only be concerned with the marine atmospheric and seawater environments. There were three major program objectives:To determine the life of any given thickness of coating in a specific environment (and the protection afforded the base metal).To determine the effect of various methods of steel preparation on the corrosion protection properties of the flame sprayed coating.To determine the increase in life of the aluminum and zinc flame sprayed coatings with the addition of seal coats. Steel panels, numbering 4,248, were employed in the study; half were coated with commercially pure zinc and the balance coated with commercially pure aluminum. Steel panels for atmospheric exposure were 4 × 6 × 1/8 inch and 4 × 12 × 1/8 inch for seawater exposure. Aluminum and zinc coatings for atmospheric exposure tests were 0.003, 0.006, 0.009 inch. In addition, a coating thickness of 0.018 inch was included in seawater exposure tests. Originally, exposure periods of 1, 3, 6, and 12 years were scheduled. At the end of each of the above periods, a complete set of panels, consisting of three identical panels of each type, was to be removed from the exposure racks for laboratory examination. At the same time, the panels of each type remaining on site were to be inspected and their condition recorded. However early inspections indicated that nearly all coatings would last for more than 12 years, at all exposure sites. Accordingly, the panels intended for removal at 6 years were left on exposure for 12 years, and the 12year set was left exposed for 18 years. Results of the 6- and l2-year inspections are reported in American Welding Society publications C2.8-62 and C2.ll-67, respectively.

A Vickers indentation method has been applied to determine the interfacial fracture toughness of modern multilayer thermal barrier coatings. The delamination behavior of four types of coating systems will be discussed and compared with results based on modified four-point bending (4PB) tests. The investigated multi-layer coating system consists of a CoNiCrAlY-bond coat applied via low-pressure plasma spray (LPPS) on a nickel-based superalloy and an atmospheric-plasma sprayed (APS) top layer of type gadolinium zirconate (GZO) and yttria-stabilized zirconia (YSZ). A conventional YSZ mono-layer system is used for reference. The effects of GZO and YSZ microstructure were investigated using top coats with low and high porosities for both (multi- and single-layer) coating systems. Isothermal oxidation tests at 1100 °C up to 500 hours were performed to study the interaction between thermal aging and fracture behavior. Investigations of microstructure and sintering behavior show a significant influence of the annealing conditions on fracture toughness. It has been observed, that with increasing annealing time, the stiffness and thus the crack driving force of the GZO layer is increased due to sintering effects and healing of submicron defects. The lower stiffness and higher defect density of GZO seem to be the main reason for the reduced fracture toughness of the YSZ / GZO interface compared to the YSZ / CoNiCrAlY interface. As a result, the delamination of the top coat is observed to shift from the top coat / bond coat interface into the top coat double-layer.

Thermal spraying is a widely used technology for industrial applications to provide coatings that improve the surface characteristics. According to the specificities of processes (APS, VPS, flame, electric arc), any kind of material can be sprayed. Among materials, ceramic coatings present several interesting aspects such as wear resistance, corrosion protection as well as thermal or electrical insulation; particularly alumina coatings which appear as the most commonly used. From all spraying processes, atmospheric plasma spraying (APS) is a rather well-established process but some others can also be used with a lower economical impact such as the flame technology. The aim of this study was to analyze the alumina coating properties according to the technology employed such as APS or wire flame spraying using the Rokide™ and the Master Jet® guns. After micrographic analyses by SEM, physical and mechanical properties were measured considering the thermal conductivity and the hardness.

A novel strategy is proposed to design an exclusive nanostructured mullite spherical feedstock for environmental barrier coatings (EBCs) via atmosphere plasma spraying (APS). The nanostructured mullite spherical feedstocks are successfully obtained by the procedure of spray drying, solid-phase sintering and flame spheroidization. The crystal grain size of nano-mullite increases with annealing temperature. When the temperature is as high as 1500 °C, the reaction of Al2O3 and SiO2 can be fully completed. The average size is 52 nm for the grain of mullite in feedstocks sintered at 1500 °C, which can be reduced from 52 nm to 48 nm by flame spheroidization treatment as well. Meanwhile, the nanostructured spherical feedstocks show high density and good flowability, which is suitable for APS. The mullite coatings is successfully prepared on a SiC substrate by APS, in which both the nanoscale crystals and nanostructures are perfectly kept as designed. Furthermore, there is no crack appeared in the nanostructured mullite coatings. Thus, the nanostructured mullite feedstock is one of promising candidates for the high performance EBCs.

Influence of silane on corrosion resistance of magnesium alloy AZ31 with thermally sprayed aluminum coatings

In the current scenario, climate change is occurring all over the world, which directly or indirectly affecting the agricultural production as well as the production of livestock. The arid and semiarid region of the world, where more than 75 % population of livestock exists, will be going to have pronounced effect of climatic change. Amongst the other stresses, heat stress is the most vital climatic stress which drastically affects the productive potential of livestock, and sometimes it is lethal to animal survival in harsh conditions. High ambient temperature, air movement, solar radiation, wind speed and relative humidity are important attributes of the climatic variables. Amongst the above-mentioned variables, high temperature, radiation and humidity are the most important factors, which drastically affect the overall performance of livestock with substantial reduction in meat, milk and egg production. In this context, the chapter highlights the significance of studying the impact of multiple stresses impacting livestock production simultaneously. The different adaptive means by which livestock respond to fluctuation of climatic changes are physiological, blood-biochemical, neuroendocrine, cellular and molecular mechanisms, respectively. In present climate change scenario, several mitigation strategies are to be implemented by which the production of livestock may be sustained to an extent even in harsh climatic conditions.

The content of this work is the development and investigation of a high temperature coating system for gas turbine blades. On a single crystal CMSX4 substrate a thin CVD layer of α-alumina is deposited as diffusion barrier coating. As a protection against high-temperature corrosion it is covered with a PVD NiCoCrAlY layer, which also performs as a bond-coating for the following thermal barrier coating deposited by Atmospheric Plasma Spraying. The surface preparation techniques and coating parameters for the multilayer coating were optimized with respect to the bonding mechanisms of the different deposition techniques. The samples were annealed at 1100°C for 100 h under neutral atmosphere. Furthermore thermocycle experiments were carried out to investigate thermocycle behaviour. The coating system proved its efficiency: No cracks were observed except vertical segmentation cracks in the TBC, all layers showed good adhesion and the diffusion barrier remained intact suppressing any noticeable diffusion of Al, Cr, Ta, Re, W and Ti. Untersuchungen zur Herstellung und Wirksamkeit eines Hochtemperaturschichtverbundes für Gasturbinenschaufeln Die hier vorgestellte Arbeit umfaßt die Entwicklung und erste Untersuchungen eines Hochtemperaturschichtverbundes für Turbinenschaufeln. Zunächst wurde auf einkristallinen CMSX4-Substraten mittels CVD eine dünne α-Al2O3-Schicht als Diffusionsbarriere abgeschieden. Als Schutz gegen Heißgaskorrosion wurde eine PVD NiCoCrAlY-Schicht verwendet, die gleichzeitig als Haftschicht für die nachfolgende plasmagespritzte Wärmedämmschicht dient. Die Oberflächenpräparation und Beschichtungsparameter der Mehrlagenschicht wurden im Hinblick auf die unterschiedlichen Bindungsmechanismen der verschiedenen Beschichtungsverfahren optimiert. Die Proben wurden für einen Zeitraum von bis zu 100 h bei einer Temperatur von 1100°C unter einer inerten Atmosphäre geglüht. Thermozyklusversuche wurden ebenfalls durchgeführt. Die Tauglichkeit des Mehrlagensystems für hohe Temperaturen konnte gezeigt werden. Es traten, abgesehen von Segmentationsrissen in der Wärmedämmschicht, keine Risse im Schichtverbund auf, da alle drei Schichten eine gute Haftung aufwiesen. Insbesondere die Diffusionsbarriere wies keine Schäden auf und konnte die Interdiffusion von Al, Cr, Ta, W und Ti wirkungsvoll unterbinden.

The corrosion behavior of thermal spray aluminum coatings deposited on AZ31 (UNS M11311), AZ80 (UNS M11800), and AZ91D (UNS M11916) Mg-Al alloys was evaluated in salt water (3.5 wt% sodium chloride [NaCl]), neutral salt fog (ASTM B117), and high relative humidity (98% RH, 50°C) environments. The changes in the morphology and corrosion behavior of the aluminum coatings induced by cold-pressing posttreatment were also examined. In chloride-containing environments, the presence of interconnected pores in the as-sprayed aluminum coatings facilitated the galvanic acceleration of the corrosion of the magnesium substrates. The cold-pressed aluminum coatings revealed improved corrosion behavior associated with a lower level of porosity. In high-humidity environments, even though the corrosion rates for all the examined materials were lower than in the case of salt fog, similar corrosion features were observed; formation of hydromagnesite on the surface of untreated materials, galvanic corrosion in the Al-TS specimens, and almost negligible corrosion attack of the aluminum coating with formation of bayerite (b-Al2O3·3H2O) in the case of the cold-pressed specimens.

In the present investigation Atmospheric Plasma Spraying (APS) method is selected for coating the materials on 304L Stainless Steel as a substrate material, also called as substrate of Thermal Barrier Coating (TBC) system developed in the present work. Commercially available Ni-Cr metal powder is selected for bond coat and TiO2 powder is selected for Top Coat. The thickness of bond coat is taken as 75 µm where as the top coat thickness is varied as 100 µm, 200 µm and 300 µm. In plasma sprayed coating more attention is given to obtain uniform thickness on the given substrate. The various surface texture parameters of each sample is tested, morphology and coating thickness of above TBC system are studied with the help of SEM and X-Ray Diffraction for phase analysis. Micro-hardness of each layer of coating is measured by using Vicker’s diamond indentation and the abrasive wear resistance of each system has been investigated through Pin-on-disc test, at room temperature by using wear and friction tribometer. The coating system possesses good wear resistance and can be used in various applications.

Thermal cycling behavior of La2Ce2O7/8YSZ double-ceramic-layer thermal barrier coatings prepared by atmospheric plasma spraying

Thermal spraying is an established technology in the coating industry offering high deposition rates and a broad range of processable materials. In addressing the scale‐up of proton exchange membrane water electrolyzers, thermal spraying presents a promising solution for cell component production, despite several challenges that need to be overcome: Firstly, the substrate material is typically characterized by a relatively thin thickness and complex geometries. Secondly, the coatings often exhibit process‐related roughness. This study demonstrates that this rough coating can be beneficial in enhancing the connection between the bipolar plate (BPP) and the porous transport layer (PTL). The developed coldgas sprayed BPP–PTL coating system was tested in an electrochemical accelerated stress test (AST) as well as in an intermittent long‐term single‐cell test. The results indicate that the BPP–PTL coating system is electrochemically stable during the AST, and subsequent measurements of electrical resistance confirm that the interface is preserved from severe oxidation. In the long‐term test, it was demonstrated that a single cell could be operated with a cell voltage of U cell = 1.9 V at a current density of i = 2 A/cm 2 over 3 months. For the first time, a fully cold gas sprayed BPP–PTL coating system has been tested in a single‐cell test for proton exchange membrane water electrolysis applications.

Although it is known that ambient temperature can affect the diagnostic performance of the fecal immunochemical test (FIT), the impact of other weather parameters, including humidity, on the sensitivity of FIT remains to be further investigated. We aimed to evaluate the impact of ambient temperature and humidity on the performance of FIT for screening for advanced colorectal neoplasia (ACRN). We included asymptomatic individuals who had undergone both screening colonoscopy and FIT. The diagnostic performance of FIT, including its sensitivity, was analyzed according to the ambient temperature and humidity on the day that FIT was performed. Temperature and humidity were divided into five levels. Among 35,461 participants, 589 (1.7%) had ACRN. The positivity rate of FIT was lower at ≥24 °C (3.1%) than at <0 °C (3.9%), 0–8 °C (4.3%), and 8–16 °C (3.9%). It was also lower at 80–90% humidity (3.1%) than at < 60% humidity (3.9%). Multivariable analysis showed that high ambient temperature (≥24 °C) with high ambient humidity (≥80%) was associated with a low positivity rate of FIT (odds ratio [OR] 0.62, 95% confidence interval [CI] 0.44–0.86). Sensitivity tended to decrease at high ambient temperature (<24 °C vs. ≥24 °C; 20.8% vs. 14.6%, P = 0.110) and was significantly lower at high ambient humidity (<80% vs. ≥80%; 21.0% vs. 12.5%, P = 0.044). The multivariable analysis also showed that high ambient humidity was independently associated with low sensitivity of FIT (OR 0.54, 95% CI 0.28–0.96). In conclusion, high ambient humidity decreased the sensitivity, while high ambient temperature along with high ambient humidity decreased the positivity rate of FIT.

The flame spraying aluminum coating on surface of Q235 steel was investigated by morphology analysis, saline soak test and salt-fog corrosion test. The results shown that comparing to Q235 steel, corrosion resistance of the aluminum flame spraying coating formed was raised.

Sulfide stress cracking (SSC) and hydrogen induced cracking (HIC) can cause severe damage in steel equipment exposed to wet H2S environments. Metallic thermal spray coatings based on aluminum have been used in some cases to protect carbon steel from the corrosive media, when wet H2S environments are a concern. In this program, a series of electrochemical tests were conducted. These tests involved exposure of coated samples to various environments containing H2S, ammonia, chloride and cyanide to study the behavior of the aluminum coating associated with a stainless steel interlayer both applied by thermal spray. Results showed that the aluminum layer was corroded rapidly in solutions with pH higher than 11. In alkaline solutions with pH lower than 9 a protective deposit was formed on the aluminum layer and the corrosion rate was very low.

The effect of roughness and pre-heating of the substrate on the morphology of aluminium coatings deposited by thermal spraying