In this study, Al 2 O 3 -based coatings with varying TiO 2 contents (0, 3, 13, and 40%) were fabricated using atmospheric plasma spraying technique. To compare the superiority of the samples, their thermal properties (thermal conductivity and thermal shock resistance) were characterized. As observed, Al 2 O 3 - 40%TiO 2 (A-40T) coating exhibited relatively superior thermal insulation and thermal shock resistance at 600°C. According to the microstructure and phase analysis, this finding can be attributed to the special phase, Al 2 TiO 5 , and the pre-existing microcracks inside the coating. Thus, A-40T manifested excellent characteristics for thermal insulation application compared with pure Al 2 O 3 and low-TiO 2 content coatings.

Hybrid plasma spraying combines plasma spraying of dry powders and liquids (suspensions and solutions). Combination of these two approaches allows deposition of microstructures consisting of both conventional coarse and ultrafine splats. Moreover, splats with dissimilar size may have also different chemistry. Such combination is potentially interesting for many fields of thermal spraying, including thermal barrier coatings (TBCs), as novel microstructures may be economically and relatively easily obtained. The technology has recently reached a level, where coatings with interesting hybrid microstructures may be reliably deposited, so that their potential for practical applications may be evaluated. In this study, first experimental TBCs with YSZ-based hybrid topcoat were deposited by hybrid water/argon stabilized plasma (WSP-H) technology. Al 2 O 3 and YAG were selected as secondary phase deposited from suspension as both provide strong materials contrast in scanning electron microscope (SEM) so they can be used as “markers” in the coating microstructure. Samples were exposed to thermal cycling simulating in-service TBC conditions in order to test their thermal shock resistance. Changes of the coating microstructure were studied by SEM analysis and X-ray diffraction.

Abradable seal coatings are widely employed in the gas turbine of aero-engine, which not only strength enough to resist the impact of external particles and airflow, but also excellent wear resistance. In the current study, we concentrate on APS sprayed Aluminum Bronze Polyester abradable coating that can be used in turbo engines both for seals and clearance control. A composite thermal spray powder, substantially in the form of clad particles each of which has coarse polyester powders and sub-particles of Cu-Al alloy powders, was prepared using mechanically clad process. Abradable seal coating was prepared by atmospheric plasma spraying. The microstructure, hardness, bonding strength, thermal shock resistance and corrosion resistance of coatings were researched. Properties of the coating were able to meet the application requirements. The coating microstructures and phase compositions were evaluated via SEM. The corrosion mechanisms of the coating were compared by analyzing the cross-sectional and top surface microstructures of the as-sprayed and eroded coatings.

The abradable coatings had significantly enhanced turbomachinery performance by acting as a sacrificial seal between rotating blades and stationary casing. Further improvement in seal design to meet the higher energy demand and increase the service time has been the key challenges to solve in the gas turbine industry. Honeycomb seals have become the industry standard clearance seal technique due to their unique design and high structural strength with minimum weight. The present study proposes a concept to form a thermal shock resistance structure to achieve higher temperature capability and improve the reliability of abradable seal structures. A cavity layer of honeycomb seal structure made of SS 321 alloy was coated with advanced high-temperature ZrO 2 +7.5%Y 2 O 3 +4% polyester seal material using TriplexPro-210 plasma spray system. The integrity of a seal structure was assessed by a cross-sectional analysis and evaluation of the coating microstructure. Additionally, the microhardness test was performed to estimate coating fracture toughness, and Object-Oriented Finite Element analysis was used to assess its thermo-mechanical performance. The concept proposed in this study should be further validated to develop the most capable innovative technology for advanced gas turbine abradable seal structures.

When testing the thermal cycling resistance of thermal barrier coatings, the surface temperature of the materials must be controlled so that test results can be used for coating life prediction. In this study, the temperature at the surface of plasma-sprayed TBCs was controlled during thermal shock testing using feedback from a double-color IR thermometer and high-rate cooling. The results are presented and discussed, highlighting the capability of the recently designed thermal shock test.

This work investigates the high-temperature oxidation kinetics of CoCrAlSiY coatings with different Si concentrations. Hot-corrosion resistance is determined at 800 and 900 °C via hot salt coating, thermal shock resistance is measured at 1050 °C, and the oxidation and corrosion products are analyzed through mineralogical and micro analysis. The results show that Si promotes the formation of an Al 2 O 3 film that improves oxidation and corrosion resistance, but excessive amounts reduce thermal shock resistance.

Yttria stabilized zirconia with a composition of ZrO 2 -8wt%Y 2 O 2 typically serves as the topcoat in thermal barrier coating systems. It has been reported, however, that YSZ with lower yttria content is more resistant to thermal shock and the effects of high-temperature sintering. To investigate these reports, nano-agglomerated 5YSZ and 8YSZ powders were deposited on FeCrAl substrates by atmospheric plasma spraying and the coatings were heat treated at 1400 °C for 1, 5, and 20 h. The nanostructure content in the 5YSZ samples was found to be about 20% higher, the microhardness 11% lower, and the size of unmelted particles about 27% smaller, which shows that bimodal structured 5YSZ has higher sintering resistance than traditionally used 8YSZ.

Lowering the impurity content in the thermal barrier coating has the effect of improving the high temperature stability and service life. SiO 2 , Al 2 O 3 , TiO 2 and Fe 2 O 3 are several common low melting point oxide impurities in the YSZ (Yttria- Stabilized Zirconia) top coatings, and they all have some influence on the performance of the coatings. But there is no quantitative research on the relationship between impurity content and the properties of the coatings. In this paper, YSZ spraying materials with SiO 2 , Al 2 O 3 and Fe 2 O 3 with the content changing from less than 0.01wt% to 1wt% were designed. The bond coatings were all NiCoCrAlY and were prepared by HVOF (High-Velocity Oxygen-Fuel). The top coatings were prepared by APS (Atmospheric Plasma Spraying). The microstructure, phase structure and thermal shock resistance of the above coatings were investigated. The results showed that the increase of oxide impurity content was more prone to thermal shock failure. It shows that the oxide impurity has a significant influence on the properties of YSZ coating.

This study investigates the heat-shock properties of metal-oxide films synthesized from ethylenediamine tetraacetic acid (EDTA) complexes using conventional flame-spray equipment. An EDTA·Y·H powder was placed in the feed unit of the sprayer and transported by a flow of oxygen to the gun. The powder was sprayed using a mixture of H 2 and O 2 as the flame gas, producing a layer of yttrium oxide on a stainless steel substrate. XRD analysis was used to examine the crystal structure of the deposits and SEM imaging revealed the surface and cross-sectional microstructure. A cyclic thermal shock test was conducted and the deposited film was analyzed for the existence of cracks, deformation, and delamination. Although the number of cracks, crack lengths, and cracks per unit area increased due to heat shock, delaminations were not observed. The results show that the Y 2 O 3 films have high thermal-shock resistance and are suitable for use as thermal barrier coatings.

This study evaluates the thermal and mechanical properties of plasma-sprayed lanthanum zirconate thermal barrier coatings and compares them with conventional 8YSZ TBCs. The La 2 Zr 2 O 7 coatings were found to have a lower thermal conductivity than 8YSZ, although this is offset by lower bond cap tensile strength and poor erosion resistance. A double-layered structure with a La 2 Zr 2 O 7 coating on porous YSZ was also tested and is shown to have better thermal shock performance than single-layer La 2 Zr 2 O 7 and double-layer structures formed on dense 8YSZ sublayers.

This study evaluates the thermal cycling performance of thick thermal barrier coatings (TTBCs). YSZ topcoats with segmentation cracks were deposited by suspension plasma spraying (SPS) on Ni-base superalloy substrates with the aid of a CoNiCrAlY bond coat applied by HVOF spraying. The as-sprayed SPS coatings were characterized based on surface morphology, cross-sectional microstructure, and phase composition. Thermal cycling tests were then carried out on a burner rig that heated the coating surface to 1523 K, followed by quenching to 423 K using compressed air. The SPS coatings exhibited longer thermal shock life than atmospheric plasma sprayed (APS) YSZ, which is attributable to improved strain tolerance due to the presence of vertically segmented cracks.

This study demonstrates a new surface treatment for thermal barrier coatings that combines ultrasonic vibration and laser remelting and assesses its effect on crack distribution, surface morphology, and grain refinement. YSZ coating samples were vibrated at 20 kHz at different power levels while being irradiated by a Nd:YAG pulsed laser operated at 5.2 J and 6 J. SEM examination revealed a uniform distribution of segmented network cracks in treated samples, which are shown to play an important role in relieving stress and increasing strain tolerance in topcoat layers, thus improving fracture toughness and thermal cycle life. Another important finding is that visible ribbon-like loops induced by variations in surface tension were eliminated as a result of improved surface convection facilitated by ultrasonic vibration. At a vibration power of 520 W, coating surfaces were uniform and flat, but at 1300 W, undulations and trough geometries were observed. The results of XRD analysis indicate that tetragonal to monoclinic phase transformations are prevented when ultrasonic vibration power is greater than 780 W.

In this work, finite element modeling is used to investigate the influence of segmentation cracks on stress distribution and failure in thermal barrier coatings deposited by atmospheric plasma spraying. The results indicate that the presence of segmentation cracks does not improve thermal insulation, but it may be beneficial in regard to thermal shock resistance, depending on crack density, and residual stress around crack tips, depending on crack length. It may also improve strain tolerance, which is affected by crack density as well as length. A model is proposed to explain the mechanism of failure in thick TBCs exposed to thermal shock. Damage caused by thermal shock can be attributed to the propagation of segmentation cracks and the formation of horizontal cracks at the bond coat-topcoat interface.

In this study, (La 0.9 Ca 0.1 )(Cr 0.9 Mg 0.1 )O 3 ceramic powders prepared by solid-state synthesis were deposited on nickel-base superalloy substrates by atmospheric plasma spraying. Powder morphology and coating surfaces were examined by SEM, and composition and phase structure were evaluated by EDS and XRD. Coating porosity and bond strength were measured and emissivity and thermal shock tests were carried out. The results show that the powders maintained their perovskite structure during spraying and that no impurities were introduced in flight. The emissivity of the coatings was found to be 0.88 at 600 °C and 0.89 at 800 °C, which is attributed to lattice distortion stemming from differences between doping and original ions and the valence states of Mg 2+ and Cr 3+ . Coating crystal structure was stable over the thermal shock range from room temperature to 1100 °C and no spalling or fracture occurred after ten shock cycles.

In this study, TiB 2 -40Ni and TiB 2 -50Ni powders are deposited on mild steel substrates by HVOF spraying in order to investigate the influence of Ni on coating hardness and corrosion, wear, and thermal shock resistance. The surface morphology and cross-sectional microstructure of the ball-milled powders and composite coatings are examined, and various tests are conducted to measure properties of interest. The findings are presented and discussed in the paper.

This investigation evaluates the microstructure and properties of thermal barrier coatings produced by suspension plasma spraying. A YSZ suspension was injected axially into a plasma jet and deposited on a superalloy substrate with a CoNiCrAlY bond coat. SEM examination revealed a columnar microstructure with a network of vertical segmentation cracks and horizontal branching cracks. In furnace cycle testing, the TBCs withstood 166 thermal shock cycles with failure attributed to partial spallation of the columnar segments initiating at the edge and center of the coatings. The TBCs were also subjected to burner rig tests to assess thermal insulation properties and to heat treatments up to 1600 °C to evaluate thermal stability based on phase composition, grain size, and microhardness.

Yttria-stabilized zirconia (YSZ) coatings have been frequently used as a thermal protective layer on the metal or alloy component surfaces. In the present study, ZrO 2 -7%Y 2 O 3 thermal barrier coatings (TBCs) were successfully deposited by DC (direct current) plasma spray process under very low pressure condition (less than 1 mbar) using low-energy plasma guns F4-VB and F100. The experiments were performed to evaluate the thermal shock resistance of the different TBC specimens which were heated to 1373 K at a high-temperature cycling furnace and held for 0.5 h, followed by air cooling under room temperature during 0.2 h. For comparison, the corresponding APS counterparts were also elaborated to carry out the similar experiments. The results indicated that the VLPPS coatings displayed better thermal shock resistance. Moreover, the failure mechanism of the coatings was also elucidated.

Agglomerate sintered and blended NiCrAlY-Y 2 O 3 cermets were prepared from NiCrAlY and Y 2 O 3 powders by two process routes. The particle morphologies and powder characteristics of both cermets feedstock using for thermal spraying were investigated. Both types of NiCrAlY-Y 2 O 3 cermets and one commercial CoCrAlY-Y 2 O 3 cermets were HVOF thermal sprayed onto the stainless steel substrate to obtain coatings having a thickness about 100 microns. Porosity and thermal shock resistance of coatings were examined. Four thermal sprayed coatings were comparatively evaluated build-up resistance by contacting reaction with MnO, Fe 3 O 4 powders and manganese bearing carbon steel statically at high temperatures. The agglomerate sintered NiCrAlY-Y 2 O 3 coatings have good resistance to manganese oxide build-up but bad resistance to iron oxide build-up. The agglomerate sintered cermets coating has better build-up resistance than blended cermets coating.

Gadolinium zirconate (Gd 2 Zr 2 O 7 , GZ) as one of the promising thermal barrier coating materials for high-temperature application in gas turbine was toughened by nanostructured 3mol% yttria partially-stabilized zirconia (3YSZ) incorporation. The fracture toughness of the composite of 90mol%GZ-10mol% 3YSZ (GZ-YSZ) was increased by about 60% relative to the monolithic GZ. Both the GZ and GZ-YSZ composite coatings were deposited by atmospheric plasma spraying on Ni-base superalloys and then thermal-shock tested under the same conditions. The thermal-shock resistance of GZ-YSZ composite coating was improved significantly, which is believed to be mainly attributed to the enhancement of fracture toughness by the addition of nanostructured 3YSZ. In addition, the failure mechanisms of the thermal-shock tested GZ and GZ-YSZ composite coatings were also discussed.

The thermal shock resistance of plasma-sprayed thermal barrier coatings (TBCs) with different top coats was investigated according to the Japanese Industrial Standard "Testing methods for thermal cycle and thermal shock resistance of thermal barrier coatings" (JIS H 8451:2008). Three types of ceramics powders, namely, Al 2 O 3 , 8 mass % Y 2 O 3 -stabilized ZrO 2 (YSZ) and La 2 Zr 2 O 7 (LZ) were used in the top-coat spray. After the specimens were subjected to a thermal shock, the tensile adhesive strength of the TBCs was measured and the thermal shock resistance as defined in JIS H8451 was determined. The thermal shock properties of the TBCs were found to depend strongly on the chemical composition of the top-coat material. For TBCs with Al 2 O 3 and LZ, the adhesive strength decreased with increasing thermal shock temperature difference (ΔT). On the other hand, little change in the adhesive strength was observed with increasing ΔT for YSZ TBC. From these results, the thermal shock resistance, ΔTc, was determined to be 480 °C for Al 2 O 3 , 680 °C for LZ and more than 880 °C for YSZ TBC. Furthermore, the influence of thermal shock on the adhesive strength of TBCs was investigated in detail through observations of cross-sectional microstructures and fracture surfaces after adhesive testing.