Search

The microstructural evolution of partially amorphous, atmospheric plasma-sprayed Yb-silicate coatings was investigated after heat treatment (HT, 1300 °C). Open porosity as well as crack area and widths in the coatings were characterized. A correlation was found between the increasing amorphous content of the as-sprayed coatings and the reduction in crack area due to crack healing after HT. Characterization results also suggested larger crack widths in the coatings after HT. The first crack-healing mechanism proposed was the capillarity-driven viscous flow of the amorphous phase in the coatings. It was experimentally shown that viscous flow-driven crack spheroidization (crack width enlargement), and crack healing started in the coatings at 1050 °C. Secondly, metastable to stable phase transformation (> 1100 °C) induced expansion in the constrained coatings was discussed as a crack healing mechanism. Finally, a two-step heat treatment was designed to prevent crack width enlargement during HT resulting in reduced porosity.

The water vapor corrosion of Yb-silicates is of interest to their application as environmental barrier coatings in gas turbine technology. In this study, densified samples from the Yb-silicate powder, as well as plasma-sprayed free-standing Yb-silicate coating were tested at a high-velocity steam rig (T = 1400 °C, v = 90 m/s, PH2O = 0.19 atm) for microstructural comparison. After the test, the measured weight losses of the coatings were larger than that of the densified sample. At the same time, the thicknesses of the corroded scales at the coating surfaces were found to be thicker than that of the sintered sample by a factor of two.

Yb-silicate is used as volatilization barrier material in environmental barrier coating applications. In this study, metastable to stable phase transformation in highly amorphous atmospheric plasma sprayed Yb-silicate coating was investigated during post-heat treatment. High-temperature X-ray diffraction (HT-XRD) was used to analyze the phase composition of the coating at elevated temperatures. Three metastable phases (Yb2Si2O7 (P-1), Yb2SiO5 (P21/c), Yb4.67Si3O13 (P63/m)) and two stable phases (Yb2Si2O7 (C2/m), Yb2SiO5 (I2/a)) preferentially crystallized from the amorphous coating starting at 1000 °C. Metastable phases transformed into stable Yb2Si2O7 and Yb2SiO5 at higher temperatures. HT-XRD data were used to estimate the volume expansion in the coating due to the phase transformation and the results were compared to the dilatometry measurements. The estimated expansion from HT-XRD data was larger than the measured expansion in dilatometry. Microstructural investigation revealed crack healing in the coating during the measurements which was associated with the lower expansion measured in dilatometry

In this study, 8 novel pyrazole disperse dyes which were synthesized in our previous work [1] were applied to polyethylene terephthalate (PET), poly (lactic acid) (PLA) and polyamide 6.6 (PA 6.6) fiber fabrics and their colorimetric and fastness properties were evaluated. The measured a*, b* and hue angle (ho) values of all dyed fabrics exhibited yellow, orange and red colour shades. Quite high colour strength values (K/S) were measured particularly for dyes containing substitute groups; p-OCH3 and o-OCH3. Shade changes of all fabrics after standard washing and sublimation tests were in the commercially adequate range. All dyed PET, PLA and PA 6.6 fabrics exhibited commercially acceptable fastness staining performances with very good to excellent levels. Synthesized novel disperse dyestuffs led to moderate to high light fastness levels particularly in the case of PLA and PET fabrics.

Unlike other thermal spraying methods, it is difficult to determine the temperature of the particles during cold gas spraying due to the relatively low radiation. In the present study, the velocities and in-flight temperatures of metal particles were measured during cold gas spraying. A state-of-the-art high-speed infrared camera was used to study the behavior of two different base materials, In718 and TiAlCrNb, both used as structural materials in gas turbine engines. The experiments aimed to improve the fundamental understanding of the process, in particular the heating of the particles, and to compare the experimental results with theoretical calculations of the particle temperatures.

The present article describes aspects of the cold gas spray processability of the intermetallic Ti-48Al-2Cr-2Nb (at. %) alloy, which is employed as a structural material in gas turbine engines. The effects of processing parameters, namely, gas pressure, gas temperature, spray distance, as well as the gas atomized feedstock particle size (d50 = 30 and 42 μm, respectively) and phase composition on deposition, were investigated. The results showed that when the highest available gas pressure (40 bar) and temperature (950 °C) were combined with a short spray distance (20 mm), well-adhering coatings could be deposited regardless of the investigated particle size. However, the maximum coating thickness could be achieved was about 30 μm with a deposition efficiency of 1%. Phase composition of the gas atomized feedstock was investigated with HT-XRD and according to the findings, heat treatment of the feedstock under vacuum was carried out. With this treatment, non-equilibrium, disordered α phase of the atomized powder was transformed into an α, α2 and γ phase mixture. At the same time, an increase in the hardness and oxygen content of the powder was detected. Swipe test performed with the heat treated powder revealed no improvement in terms of deposition, in fact, the number of adhering particles on the substrate was decreased in comparison with that of the untreated powder.

Human life depends entirely on natural resources. As we know, these sources, as well as everything else, have an end. In this case, we need to ensure its sustainability by providing a balance between nature and human in all our possibilities. When it comes to sustainability, it comes to mind that knowing the value of existing possibilities and transferring them to future generations without harming the environment should be the main objective. In order to sustain something, it is necessary to protect and value it. If we are talking about the sustainability of a phenomenon/situation, we also need to ensure that it continues in a certain life cycle. This means years of continuity as well as using the right paths and resources to achieve goals and objectives. In this process, the whole life cycle should be considered as a whole, and the essence should be protected. This situation is necessary as a treasure for the continuation of cultures. In fact, considering that we inherit many things in nature from our ancestors as well as borrow from our children, we can succeed in transferring many of our spiritual values to future generations. The concept of sustainability in the global sense was announced in 1987 with the report named “our common future” published by the World Environment and Development Commission. Decisions were made to make the development sustainable without endangering the needs of future generations at times when it was alarmed that humanity was beginning to consume many things in nature and end its generation. In this direction, in Turkey, as in other countries, priority has been given to local and regional sustainable projects realized in line with the decision of the United Nations and the Sustainable Development Goals. The most important fact that forms the basis of cultures is the crafts in those regions. Unfortunately, over the years, existing crafts have disappeared due to the increase in mechanization, the effect of technology and the fact that fast consumption phenomenon has entered our lives. Some of the most important art forms in the culture of Turkey are as follows; pots and pans, milling, stone chipping, bone chipping, carpentry, weapon manufacturing, metalworking, jewelry and accessories craftsmanship, shoemaking, spinning, weaving, animal husbandry, felt making, carpet making, leather making, and tailoring. Unfortunately, many of these crafts began to disappear over time or fell into a decline in the amount of production. Carpet hand weaving and rug hand weaving have an important place in these crafts for Turkey case. Hand weaving carpets and rugs hand weaving is still being kept alive especially in Turkey's province of Usak. Over the years, textiles that provide protection and shelter for people from heat and cold have been influenced by many factors such as people’s joys, sorrows, cultures, and places they live, and this is reflected in their motifs. “Rug hand weaving” is a type of hand weaving that started and developed long before carpet hand weaving. Rugs were mostly used in tents in nomadic civilizations because of its light weight and easy folding and transportation, and over time it became an indispensable item of our settled houses. The city of Usak has reflected the culture of civilizations living on its land from the past to the present on its loop-by-loop hand-woven carpets and rugs. The fact that the wool of the sheep raised in this region is white, shiny, flexible, and durable, and the plants that give natural dye are abundant in the environment make this region the land where the foundations of the art of weaving were laid. It is very important that the fibers (such as wool), the coloration method (such as natural dyeing), and the fabric surface forming process (hand-woven) that enable the creation of Usak carpets and rugs are sustainable. For this reason, Usak hand-woven carpets and rugs produced in this way make significant contributions to the sustainability of the environment and the world. Carpets woven with 89,600 loops per square meter in Usak are still considered as very valuable carpets in auctions in Europe and America today. Usak is one of the most important centers of hand weaving carpets and rugs in Turkey. Usak Governorship and Usak Municipality have carried out many projects on the production of sustainable carpets and rugs produced by hand weaving. Thanks to many different projects such as these, carpet and rug hand weaving has an important place in Usak. Each year, many different hand-woven carpets and rugs are produced in Usak and sold domestically and abroad. Hand-woven carpets and rugs produced in Usak are exhibited all over the world and have been decorating palaces, European castles, mosques, churches, and museums (Paris Louvre Museum, Florence Bardini Museum, New York Metropolitan Museum of Art, Philadelphia Museum, Victoria and Albert Museum in London, National Gallery of Art, Budapest National Museum, Istanbul Turkish and Islamic Arts Museum, Berlin Museum of Islamic Art, Metropolitan National Museum of Kuwait, Istanbul Foundations Carpet Museum, Konya Mevlana Museum, etc.) for centuries. In this chapter, the detailed information regarding carpet and rug hand weaving which are still underway and alive in Turkey and especially in the Usak province of Turkey was given. In here, the history of hand weaving, carpet and rug hand weaving, traditional rug and carpet hand weavings in Usak and in Turkey and the patterns of carpets and rugs varieties in Usak province and the different regions of Turkey were examined and reviewed.

Thermally sprayed ceramic coatings are often tested as free-standing layers to investigate different properties such as thermal expansion coefficient, thermal conductivity, sintering, mechanical behavior, corrosion resistance, gas tightness, or electrical properties. In this paper, four different substrate removal methods were used to obtain free-standing YSZ coatings. At first, spraying on a steel substrate and subsequent dissolution of the substrate-coating interface by hydrochloric acid (HCl) was used. Second, the steel substrate was removed by applying an electrical field via electrochemical corrosion of the surface of the substrate. In a third method, the coating was sprayed on a salt (NaCI) interlayer, which was removed later by dissolution in water. At last, the coating was sprayed on a graphite substrate and the substrate was removed by heat treatment. After the preparation of free-standing coatings, these were characterized using scanning electron microscopy, mercury porosimetry, indentation tests, and room temperature three-point bending tests, which allowed the determination of Young’s modulus and viscosity. The results revealed measurable differences in coating properties as a result of the substrate removal methods, i.e., HCl method led to higher porosity and lower modulus in the YSZ coating.

In this work, silicon–hafnia (Si-HfO2, 80/20 mol. %) feedstock was plasma sprayed for Environmental Barrier Coating bond coat application. In the as-sprayed coating, hafnium disilicide (HfSi2), HfO2 tetragonal (t), and cubic (c) phases with a total volume of ~20 % were detected together with Si and HfO2 monoclinic (m). The temperature-dependent evolution of these phases was analyzed and paired with microstructural observations. It was found that above 700 °C, HfSi2 oxidizes and HfO2 (t) and (c) transforms into (m) polymorph. Up to this temperature, as-sprayed coating showed a non-linear expansion behavior. Estimated volume expansion at ~750 °C was 3.6 % based on dilatometry measurement. The primary and secondary mechanisms leading to the expansion in the coating were identified as oxidation of HfSi2 and polymorphic phase transitions in HfO2, respectively. As a consequence of the volume expansion, the coating was extensively cracked during cyclic oxidation and hence not protective anymore. After 100 h at 1300 °C, the volume fraction of oxidation product SiO2 was significant in the coating (0.34), while HfO2 was largely consumed (0.1) in the formation of HfSiO4 (0.56). This result suggested that reversible α↔β phase transitions in SiO2-cristobalite could be another factor contributing to the cracking in the coating during cyclic oxidation.

The ceramic top coat has a major influence on the performance of the thermal barrier coating systems (TBCs). Yttria-partially-stabilized zirconia (YSZ) is the top coat material frequently used, and the major deposition processes of the YSZ top coat are atmospheric plasma spraying and electron beam physical vapor deposition. Recently, also new thermal spray processes such as suspension plasma spraying or plasma spray-physical vapor deposition have been intensively investigated for TBC top coat deposition. These new processes and particularly the different coating microstructures that can be deposited with them will be reviewed in this article. Furthermore, the properties and the intrinsic–extrinsic degradation mechanisms of the YSZ will be discussed. Following the TBC deposition processes and standard YSZ material, alternative ceramic materials such as perovskites and hexaaluminates will be summarized, while properties of pyrochlores with regard to their crystal structure will be discussed more in detail. The merits of the pyrochlores such as good CMAS resistance as well as their weaknesses, e.g., low fracture toughness, processability issues, will be outlined.

Dense, crack-free, uniform, and well-adhered environmental barrier coatings (EBCs) are required to enhance the environmental durability of silicon (Si)-based ceramic matrix composites in high pressure, high gas velocity combustion atmospheres. This paper represents an assessment of different thermal spray techniques for the deposition of Yb2Si2O7 EBCs. The Yb2Si2O7 coatings were deposited by means of atmospheric plasma spraying (APS), high-velocity oxygen fuel spraying (HVOF), suspension plasma spraying (SPS), and very low-pressure plasma spraying (VLPPS) techniques. The initial feedstock, as well as the deposited coatings, were characterized and compared in terms of their phase composition. The as-sprayed amorphous content, microstructure, and porosity of the coatings were further analyzed. Based on this preliminary investigation, the HVOF process stood out from the other techniques as it enabled the production of vertical crack-free coatings with higher crystallinity in comparison with the APS and SPS techniques in atmospheric conditions. Nevertheless, VLPPS was found to be the preferred process for the deposition of Yb2Si2O7 coatings with desired characteristics in a controlled-atmosphere chamber.

Double layer thermal barrier coatings (TBCs) consisting of a Gd2Zr2O7 (GZO) top and an ytrria stabilized zirconia (YSZ) interlayer have been tested in a burner rig facility and the results compared to the ones of conventional YSZ single layers. In order to gain insight in the high temperature capability of the alternative TBC material, high surface temperatures of up to 1550 °C have been chosen while keeping the bond coat temperature similar. It turned out that the performance of all systems is largely depending on the microstructure of the coatings especially reduced porosity levels of GZO being detrimental. In addition, it was more difficult in GZO than in YSZ coatings to obtain highly porous and still properly bonded microstructures. Another finding was the reduced lifetime with increasing surface temperatures, the amount of reduction is depending on the investigated system. The reasons for this behavior are analyzed and discussed in detail.

Gadolinium zirconate (Gd2Zr2O7, GZO) as an advanced thermal barrier coating (TBC) material, has lower thermal conductivity, better phase stability, sintering resistance, and calcium‐magnesium‐alumino‐silicates (CMAS) attack resistance than yttria‐stabilized zirconia (YSZ, 6‐8 wt%) at temperatures above 1200°C. However, the drawbacks of GZO, such as the low fracture toughness and the formation of deleterious interphases with thermally grown alumina have to be considered for the application as TBC. Using atmospheric plasma spraying (APS) and suspension plasma spraying (SPS), double‐layered YSZ/GZO TBCs, and triple‐layered YSZ/GZO TBCs were manufactured. In thermal cycling tests, both multilayered TBCs showed a significant longer lifetime than conventional single‐layered APS YSZ TBCs. The failure mechanism of TBCs in thermal cycling test was investigated. In addition, the CMAS attack resistance of both TBCs was also investigated in a modified burner rig facility. The triple‐layered TBCs had an extremely long lifetime under CMAS attack. The failure mechanism of TBCs under CMAS attack and the CMAS infiltration mechanism were investigated and discussed.

The chapter describes the different aspects of ceramic materials in gas turbines. The operation conditions such as high-pressure ratio and high temperatures result in improved efficiencies and make necessary the use of materials with high-temperature capability. In addition to the often used single-crystal alloys ceramic materials are discussed. Different bulk ceramics, for example, based on silicon nitride are described. A special focus is laid on ceramic matric composites, both oxide and nonoxide-based materials, which are of increasing interest for gas-turbine applications. In addition to the structural applications ceramics are also often used as coating material. Standard coating processes for protective coatings in gas turbines are described. Furthermore, thermal barrier coatings, a widely used coating system in gas turbines, and environmental barrier coatings as protective coatings for ceramic matrix composites are discussed in detail. Finally, also degradation and failure modes for the different high-temperature coating systems are the topics of this chapter.

In this study, burner rig testing of Si/Yb2Si2O7 environmental barrier coating protected SiC-based ceramic matrix composites was conducted. Tests were performed at standard conditions as well as with liquid water injection to the flame. Furthermore, the influence of the impingement angle of the flame (45° vs. 90°) on water vapor corrosion was explored. Gas flow rates were adapted in each test to adjust 1250 °C at the sample surface. The comparison of test results showed that water injection advances the corrosion of the Yb2Si2O7 topcoat and the impingement angle affects the size and shape of the corroded area on the sample surface.

Gas turbine components are often operated in harsh conditions, which can lead to severe damage. As it is highly desirable from both an economical and an ecological point of view to restore these worn areas instead of manufacturing new components, repair technologies are of huge interest for companies supplying maintenance and overhaul of gas turbines. In this article, two thermal techniques are described that can be used for this application: cold gas spraying (CGS) and vacuum plasma spraying (VPS). The CGS process allows the deposition of metallic coatings with excellent mechanical properties; several examples including γ‐TiAl, Inconel (IN) 718, and IN 738 are given. Essential for the deposition of high‐performance coatings in CGS is to exceed the so‐called critical velocity. This is discussed also with experimental findings. As a final topic, experiments that use VPS for the repair of single‐crystal alloys are described.

Environmental barrier coatings (EBCs) are essential to protect ceramic matrix composites against water vapor recession in typical gas turbine environments. Both oxide and non-oxide-based ceramic matrix composites (CMCs) need such coatings as they show only a limited stability. As the thermal expansion coefficients are quite different between the two CMCs, the suitable EBC materials for both applications are different. In the paper examples of EBCs for both types of CMCs are presented. In case of EBCs for oxide-based CMCs, the limited strength of the CMC leads to damage of the surface if standard grit-blasting techniques are used. Only in the case of oxide-based CMCs different processes as laser ablation have been used to optimize the surface topography. Another result for many EBCs for oxide-based CMC is the possibility to deposit them by standard atmospheric plasma spraying (APS) as crystalline coatings. Hence, in case of these coatings only the APS process will be described. For the EBCs for non-oxide CMCs the state-of-the-art materials are rare earth or yttrium silicates. Here the major challenge is to obtain dense and crystalline coatings. While for the Y2SiO5 a promising microstructure could be obtained by a heat-treatment of an APS coating, this was not the case for Yb2Si2O7. Here also other thermal spray processes as high velocity oxygen fuel (HVOF), suspension plasma spraying (SPS), and very low-pressure plasma spraying (VLPPS) are used and the results described mainly with respect to crystallinity and porosity.

In this study, new heterocyclic disazo disperse dyes, substituted with methyl, nitro and chloro groups at their o-, m-, p- positions were synthesized (4a-4j). These newly synthesized ten disazo disperse dyes were characterized by elemental analysis and spectral techniques. Spectroscopic data for novel synthesized dyes, dissolved in six solvents, were procured. The influences of six different acidic and alkaline solutions were also reported. In addition, the absorption capability of these ten-novel heterocyclic disazo disperse dyes at their o-, m- and p- positions were explored in detail. © 2018 Elsevier B.V. 109M578 This study is sponsored and supported by The Scientific and Technological Research Council of Turkey (TUBITAK) with the TUBITAK project number of 109M578 .

The purpose of this research was to investigate the corrosion behavior of the low/high Yb2SiO5 containing Yb2Si2O7 coatings under high-velocity water vapor flow. To that end, Yb2Si2O7 and Si coatings were deposited by atmospheric plasma spraying on SiC substrates. The corrosion tests were performed in the burned natural gas under atmospheric pressure, with a gas flow velocity of 100 m/s at 1200 °C for 200 h. After the test, a 25 mm thick, porous corrosion layer at the surface of the Yb2Si2O7 rich coatings was found accompanied with a mass reduction, whereas samples with Yb2SiO5 rich coatings showed mass gain indicating the greater resistance of Yb2SiO5 against water vapor. A comparison of the Yb2Si2O7 rich coatings tested in this work and Yb2Si2O7 bulk samples tested in an earlier work at the same facility revealed significantly different recession rates. Possible mechanisms responsible for this distinct behavior are discussed in the manuscript.

In this work, the delamination toughness and the sintering behavior of modern double-layer thermal barrier coatings of type gadolinium zirconate (GZO)/yttrium-stabilized zirconia (YSZ) are investigated in detail. These properties mainly determine the strain tolerance and thus the performance of thermal barrier coatings (TBCs). The delamination toughness was determined using a modified four-point bending setup. It is shown that the delamination behavior differs significantly from conventional monolayer coatings and is highly dependent on the specific microstructure of the GZO layer. The stiffness and sintering behavior of freestanding GZO layers were determined using impulse excitation, a test method sensitive to the global stiffness of the ceramic coating. The increase in stiffness is thereby correlated to microstructural changes, explicitly the healing of micro-cracks and the sintering of inter-lamellar cracks and unmolten particles. The results reveal that the specific spray structure of GZO has a great influence on the sinter stability which results in a characteristic temperature dependency. In this case the GZO coatings have an advantage in comparison to conventional YSZ coatings at temperatures above 1300 °C.

During the past decade, gadolinium zirconate (Gd2Zr2O7, GZO) has attracted interest as an alternative material to partially yttria-stabilized zirconia (YSZ) for thermal barrier coatings (TBCs). Despite the well-known benefits of GZO, such as lower thermal conductivity and superior temperature capability compared to YSZ, processing of GZO via atmospheric plasma spraying (APS) still remains a challenge. Here, we report on APS experiments which were performed to investigate the influence of processing on GZO microstructure and lifetime of GZO/YSZ double-layer TBCs. Different microstructures of GZO were produced and characterized in terms of porosity, stoichiometry, Young′s modulus, and their effects on the lifetime of YSZ/GZO double-layer TBCs were discussed. Particle diagnostics were utilized for the optimization of the process parameters with respect to different microstructures of GZO and stoichiometry. It was found that both cumulative porosity of GZO and pore size distribution, which alter the Young′s modulus significantly, govern the lifetime of double layers. In addition, it was shown that the deviation in GZO stoichiometry due to gadolinia evaporation in the investigated range does not display any critical effect on lifetime.

A series of disazo pyrazole disperse dyes were synthesized and reported at our previous work. These 8 synthesized disazo pyrazole disperse dyes (3a-3h) were applied to poly(lactic acid) (PLA), poly(ethylene terephthalate) (PET), and polyamide 6.6 fibers. Their colorimetric and color fastness properties were investigated. All studied fibers dyed with these synthesized dyes exhibited yellow-red shades. 3c (p-Cl), 3e (m-Cl), and 3h (o-Cl) disazo disperse dyes, having auxochrome -Cl, led to the lowest color yield values for all three studied fibers. The same dyes resulted in higher color strength with darker shades on the PET and PLA fabrics in comparison PA 6.6 fabrics. 3a (p-NO2), 3b (p-OCH3), 3d (m-NO2), 3f (o-NO2), and 3g (o-OCH3) disazo disperse dyes can be recommended for PLA and PET dyeing from the color point of view leading to medium to heavy depth of shades. The wash, alkaline and acidic perspiration, dry and wet rub, water and sea water fastness levels of PLA, PET, and PA 6.6 samples dyed with 3a-3h dyes were generally quite high and in the commercially acceptable range with few exceptions. Dyed PLA fabrics displayed better sublimation fastness levels than dyed PET and PA 6.6 fabrics. Synthesized disperse dyes resulted in high light fastness performance on especially PET and PLA fibers. Light fastness level was better for dyed PET samples by comparison with dyed PLA and PA 6.6 fabrics. © 2018, The Korean Fiber Society and Springer Science+Business Media B.V., part of Springer Nature. Firat University Scientific Research Projects Management Unit: 2012FBE035 This study is sponsored and supported by Pamukkale University Scientific Research Project Coordination Unit PAUBAP by the project number of 2012FBE035.

From the literature, it is known that due to their glass formation tendency, it is not possible to deposit fully-crystalline silicate coatings when the conventional atmospheric plasma spraying (APS) process is employed. In APS, rapid quenching of the sprayed material on the substrate facilitates the amorphous deposit formation, which shrinks when exposed to heat and forms pores and/or cracks. This paper explores the feasibility of using a high-velocity oxygen-fuel (HVOF) process for the cost-effective fabrication of dense, stoichiometric, and crystalline Yb2Si2O7 environmental barrier coatings. We report our findings on the HVOF process optimization and its resultant influence on the microstructure development and crystallinity of the Yb2Si2O7 coatings. The results reveal that partially crystalline, dense, and vertical crack-free EBCs can be produced by the HVOF technique. However, the furnace thermal cycling results revealed that the bonding of the Yb2Si2O7 layer to the Silicon bond coat needs to be improved.

Processing of Gd2Zr2O7 by atmospheric plasma spraying (APS) is challenging due to the difference in vapor pressure between gadolinia and zirconia. Gadolinia is volatilized to a greater extent than zirconia and the coating composition unfavorably deviates from the initial stoichiometry. Aiming at stoichiometric coatings, APS experiments were performed with a TriplexPro™ plasma torch at different current levels. Particle diagnostics proved to be an effective tool for the detection of potential degrees of evaporation via particle temperature measurements at these varied current levels. Optimized spray parameters for Gd2Zr2O7 in terms of porosity and stoichiometry were used to produce double-layer TBCs with an underlying yttria-stabilized zirconia (7YSZ) layer. For comparison, double layers were also deposited with relatively high torch currents during Gd2Zr2O7 deposition, which led to a considerable amount of evaporation and relatively low porosities. These coatings were tested in thermal cycling rigs at 1400°C surface temperature. Double layers manufactured with optimized Gd2Zr2O7 spray parameters revealed very good thermal cycling performance in comparison to standard 7YSZ coatings, whereas the others showed early failures. Furthermore, different failure modes were observed; coatings with long lifetime failed due to TGO growth, while the coatings displaying early failures spalled through crack propagation in the upper part of the 7YSZ layer.

From the literature, it is known that due to their glass formation tendency, it is not possible to deposit fully-crystalline silicate coatings when the conventional atmospheric plasma spraying (APS) process is employed. In APS, rapid quenching of the sprayed material on the substrate facilitates the amorphous deposit formation, which shrinks when exposed to heat and forms pores and/or cracks. This paper explores the feasibility of using a high-velocity oxygen-fuel (HVOF) process for the cost-effective fabrication of dense, stoichiometric, and crystalline Yb2Si2O7 environmental barrier coatings. We report our findings on the HVOF process optimization and its resultant influence on the microstructure development and crystallinity of the Yb2Si2O7 coatings. The results reveal that partially crystalline, dense, and vertical crack-free EBCs can be produced by the HVOF technique. However, the furnace thermal cycling results revealed that the bonding of the Yb2Si2O7 layer to the Silicon bond coat needs to be improved.

5-amino-4-arylazo-3-methyl-1-phenylpyrazoles (2a-k)were diazotised and coupledwith 5-hydroxy-3-methyl-1H-pyrazole and 5-hydroxy-3-methyl-1-phenylpyrazole to generate two series disazo pyrazole disperse dyes (3a-k and 4a-k). These novel synthesized disazo pyrazole disperse dyes were characterized by elemental analysis and spectral methods. Absorption ability and tautomeric structure of synthesized disazo pyrazole disperse dyes substituted with electron-withdrawing and electron-donating groups at their o, m- and p-positions were also examined in detail. © 2015 Published by Elsevier B.V.