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.

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.

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.

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.

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.

“Testing Method for Thermal Cycle and Thermal Shock Resistance of Thermal Barrier Coating (TBC)” is a Japanese Industrial Standard (JIS) newly established by the Minister of Economy, Trade, and Industry in 2008, after deliberations by Japanese Industrial Standards Committee, in accordance with the Industrial Standardization Law. The standard specifies a testing method that evaluates the spalling resistance of TBCs based on operating conditions in gas turbines. This paper provides an overview of the standard along with examples of its use.

Suspension plasma spraying facilitates the production of thick coatings structured at the submicron or even nanometer scale. Due to the large volume fraction of internal interfaces, nanostructured coatings tend to be superior to their microstructured counterparts. Suspension plasma sprayed oxide ceramics, for example, have higher coefficients of thermal expansion, lower thermal diffusivity and hysteresis, higher hardness and toughness, and better wear resistance. In this work, Y-PSZ thermal barrier coatings are manufactured by means of SPS using two commercial submicron powders with different particle size distributions. By varying spray parameters, several coating architectures and thicknesses were achieved. The coatings were subjected to a series of thermal and isothermal shocks in order to assess the effect of particle size distribution, layer thickness, and substrate roughness on thermomechanical behavior.

Carbon-fiber-reinforced plastic (CFRP) rolls are increasingly employed in manufacturing equipment due to their light weight, high stiffness, and low inertia and flexure. These rolls, however, are rarely used without a surface coating due to their lack of wear resistance and gripping properties. This paper examines the effects of thermal shock on an experimental carbide-type cermet coating deposited by atmospheric plasma spraying on a CFRP test roll. After thermal shock testing, coating cracks and peeling were observed. The underlying cause was determined and an improved coating, a nickel-base composite with high thermal shock resistance, has been developed, tested, and put to use in a papermaking line, where the rolls have been maintenance-free for more than four years.

Multilayer ceramic chip capacitors (MLCCs) are produced in large numbers for use in automobiles, cell phones, flat panel displays, and other products. Like many circuit components, they are being required in more compact sizes, larger capacities, and reduced costs year by year. MLCCs are kiln-fired on stacked carriers made from Al 2 O 3 -SiO 2 covered with a Y 2 O 3 -stabilized ZrO 2 topcoat and an Al 2 O 3 basecoat. This paper presents the rationale behind the selection of the coating materials and evaluates processes by which they can be applied. It compares the microstructure and properties of sintered, atmospheric plasma sprayed (APS), and water stabilized plasma sprayed (WSP) yttria-stabilized zirconia and discusses the advantages and disadvantages of each process.

Zircon (ZrSiO 4 ) is a technologically important oxide ceramic material known for its high refractoriness and chemical stability. It shows excellent thermal shock resistance as a result of its very low thermal expansion coefficient and a low heat conductivity coefficient. Plasma spraying is a convenient method to produce large area coatings with high growth rates, necessary for many applications. ZrSiO 4 is among the least expensive spraying materials for refractory applications. In this study, a single-step process was used to prepare mullite/zirconia ceramic composites by plasma spraying zircon/alumina mixtures. Mixtures of ZrSiO 4 and Al 2 O 3 powders with Al 2 O 3 to SiO 2 molar ratios of 3:2 were milled for 2 h in a zirconia medium using a ball mill. The as–milled powders were dried in the furnace and sintered at 1300 and 1350 °C for 2h then crushed to a size less than 100 μm. The powders were sprayed by an atmospheric plasma spray gun (Metco 3MB) using C/C+SiC ceramic matrix composite substrates. Scanning electron microscopy (SEM) was used to analyze the microstructures of the powders and plasma coatings. The phase composition analysis of the powder showed the presence of alumina and zircon. After plasma coating, alumina, zircon, and zirconia phases were determined.

Carbon fibre reinforced carbon (CFC) composites have been more and more used in different industrial areas as high temperature materials. Some application examples are CFC components in modern furnaces for heat-treatment and brazing. Because CFC components can react with metallic materials when they contact each other, diffusion barrier coatings are essentially important for such CFC components. The aim of the project IGF 14.880 N “Thermally sprayed diffusion barrier coatings for CFC components in high temperature applications” is to develop diffusion barrier coatings by thermal spraying technology. In the project, different coating systems have been developed and investigated regarding the coating build-up, coating microstructure, bonding, thermal shock resistance and diffusion barrier function. The research results reveal that some developed coating systems are suitable for applications in furnaces. In the present paper, some research results of this project are reported.

A high-purity (HP) HOSP (Hollow Oven Spherical Process) PYSZ powder has been evaluated and compared to standard PYSZ powders. The main difference is these two powders is the starting raw material purity. Four TBC systems (2 standard types and 2 high purity versions) were Air Plasma Sprayed (APS) onto CMSX-4 substrates with APS CoNiCrAlY bond coats. Thermal shock testing was performed to 50 % spallation at 1135°C with 1 hour hot cycles with forced air cooling. The as-deposited coatings and those after thermal shock failure were characterized using X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The thermal cycling results show little difference in the thermal shock resistance of the coatings with all failing in an adhesive manner with failures occurring in excess of 180 hot cycles. XRD and Raman data is used to identify the levels of monoclinic and tetragonal phases present in each coating and SEM analysis used to identify differences between PYSZ with a broad particle size distribution and a tighter controlled PYSZ particle size distribution.

Abradable seals have been used in jet engines since the late 1960's. Today abradable seals are seeing applications not only in low pressure and high pressure sections of the compressor but also in the high pressure turbine module of jet engines and are gaining ever more attention in industrial gas turbines. Thermal spraying is a relative simple and cost effective means to apply abradable seals. These work by minimizing gaps between rotating and stationary components by allowing the rotating parts to cut into the stationary ones. The types of coatings employed are zirconia based abradable material systems with polymer and, in some cases, hexagonal boron nitride additions. The coatings are designed to work at service temperatures of up to 1200 °C. The objective of this paper is to review various types of commercial and experimental ceramic abradable systems and to assess their performance profiles. The paper will review yttria stabilized zirconia based systems with modified polymer additions and with variable particle sizes of the ceramic phase. Alternative stabilizers and their influence on key coating properties such as thermal shock resistance and abradability will be studied. The paper will also review the influence of plasma spray parameters on coating properties and study the general influence of coating porosity on coating erosion properties and abradability.

A functionally graded thermal barrier coating (FG-TBC) of CeO 2 -Y 2 O 3 -ZrO 2 /NiCoCrAlY was prepared using a recently developed supersonic plasma spray (S-PS) system. The system had dual powder feed ports through which the metal alloy powders were fed into the lower temperature region of the plasma plume, to prevent over oxidation, and the ceramic powders were fed into the high temperature region, to produce complete melting. Such an approach enabled fine configurations having a continuously graded composition transition to be obtained. The thermal shock testing of the deposited samples with 1mm thick FG-TBC system on Ni-based alloy substrates was performed using an in-house-designed multi-functional rotational thermal shock tester. In this tester, the heating-cooling curves and surface morphology of tested specimens can also be observed by a microscope with a CCD (charge-coupled device) camera and recorded on line by means of accessorial computer system to evaluate the thermal shock resistance of tested samples while they were heated by a high heat flux of oxygen-acetylene flame to 1200° C in a time interval of 15~20s followed by water-quenched to ambient temperature. The temperature fields and relevant thermal stresses distribution through the thickness of disk samples were calculated by means of ANSYS finite element method. The numerical approach shows that the maximal tensile stress occur at the C-YSZ top coating at the center of disc samples at the start of rapid cooling by water-quenched, where small reticulated surface cracks were observed, which then propagated perpendicularly about 350µm deep to near the interface between the pure C-YSZ coating and the FGMs layer transition between the C-YSZ and the NiCoCrAlY coatings. These vertical cracks appeared to be arrested without any delamination after 200 thermal shock cycles.

The technology and thermal shock properties and thermal conductivity of plasma sprayed nanostructured yttria-stabilized zirconia thermal barrier coatings (TBCs) are studied in this paper. The TBCs on the substrate of Ni 3 Al based alloy IC-10 were fabricated by using the nanostructured yttria-stabilized zirconia powder under certain plasma spraying conditions. By manipulating the plasma spray process, nanostructured TBCs were obtained. The specimens were thermally shocked from 1000°C, 1100 °C and 1200°C into 20°C water and the morphology and microstructure of the TBCs were evaluated by light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermal diffusivity was tested by a laser pulse method. The results showed that the nanostructured TBCs had more than 30% reduction in thermal conductivity and the thermal shock lifetimes were much longer than that of the conventional TBCs.