Detailed investigations of thermally grown oxides (TGO) zone and areas adjoining to it were presented in this article. The thermal barrier coating (TBC) based on gadolinium zirconate (Gd 2 Zr 2 O 7 , GZ) and deposited by air plasma spraying (APS) on AMS 5599 superalloy with NiCrAlY type of bond-coat was the analysed material. Analyses were made on TBC system after spraying process and after time to 500 hours of oxidation at temperature 1100°C in atmosphere of laboratory air. Ultrahigh resolution scanning-transmission (S/TEM) electron microscope TITAN 80-300 was used to conduct the tests. Quanta 200i Dual Beam apparatus by FEI for precise and localized focused Ga+ ion beam (FIB) sample preparation was used as well.The basic aim of presented investigations was related with detailed characterization of interface zone between ceramic top-coat (TC) of Gd 2 Zr 2 O 7 type and NiCrAlY bond-coat after spraying process and after 500 hours of deposition in oxidized atmosphere where the TGO zone was formed with the thickness ca. 5-10 µm. The special emphasis was placed on research of this zone and its morphology due to very strong influence of formed thermally grown oxides on overall life-time and destruction processes which took place on the interface between TGO and ceramic top-coat. Obtained data revealed that the most important factors influenced on destruction processes are related with the thickness of TGO zone (consisted mainly Al 2 O 3 , NiAl 2 O 4 and eventually NiO) rather than formation of undesirable phases such as GdAlO 3 complex oxide.

SiC coatings were prepared with pack powder in different particle sizes in a vacuum atmosphere by pack cementation technique to protect the C/SiC composites substrate from oxidation. The phase and microstructure of the coatings were investigated by XRD, SEM analyses. The relationship between powder granularity in the pack and microstructure of SiC coatings was studied. Cyclic oxidation test at 1573K in air atmosphere was performed and the effect of powder particle size in the pack on high-temperature oxidation resistance of SiC coatings was discussed in detail. It is observed that with powder granularity in the pack increasing thickness and density of SiC coatings increases, corresponding oxidation resistance of the coating is improved. Possible mechanisms related to oxidation were preliminarily discussed.

The paper is devoted to thermal and thermo-mechanical analysis of the plasma sprayed thermal barrier coatings (TBC). The temperature and stress distribution using the finite element method in the microscopic scale is presented. The finite element model is based on the microscopy scan (dimension 5mmx3.5mm) and represent three levels of barrier structure: basement AMS 5599,undercoat NiCrAlY and ceramic layers of ZrO 2 ×8Y 2 O 3 , Gd 2 Zr 2 O 7 and DCL (double ceramic layer) Gd 2 Zr 2 O 7 /ZrO 2 ×8Y 2 O 3 type. The layers material properties are fully temperature dependent and coupled thermo-mechanical analysis is performed. The numerical results will be compared with the experimental one.

In the present work, a metal-polymer composite coating containing Al and ethylene-vinyl acetate copolymer (EVA) was prepared on the surface of a polymer matrix composite (PMC) using a detonation spraying process. The microstructure and bond strength of the as-prepared coatings were analyzed. The bonding mechanism of the coatings, especially the deposition behavior of the Al and EVA particles on the PMC surface is discussed. Results had shown that detonation spraying technique enables the deposition of metal-polymer coatings directly onto the PMC surface under precise process control. The preparation of metal-polymer composite coating on PMC via detonation spraying process presents promising application as an interlayer for the surface metallization of PMC.

300M steel is one of most important aerial materials, which can be used for landing gear and flap & slat track. Some surface engineering technologies are needed to be adopted on its surface, because of its bad corrosion performance. WC10Co4Cr Coatings by high velocity oxygen-fuel spray processing (HVOF) is an environmental friendly method for this protection. In this paper, WC10Co4Cr coatings were prepared on 300M by optimized HVOF processing. And their corrosion performance has been estimated by neutral salt fog test, according with ASTM B117. The results indicate that the porosity gets larger and the hardness gets higher for the dissolution of bonding phases after the test. And for the optimized coatings, there are no corrosion products in the surface and interface between the coating and 300M steel, after 2000 hours ASTM B117 test. So the coatings have a good corrosion performance.

In this study, dense multicomponent NiCoCrAlTaY bond coats and feather-structured YSZ topcoats are deposited on DZ40M alloy vane surfaces by the PS-PVD method. Based on thickness measurements and microstructure examination, it is shown that the double vane surface was completely covered by both layers. The thickest portion of the coating was found close to the leading and trailing edges of the vane. The results show that it is possible to manufacture TBCs, including the bond coat and topcoat, on first-stage turbine blades by a single PS-PVD process.

A series of abradability tests were conducted on AlSi-hBN coatings, which are commonly used in the compressor section of aeroengines for clearance control. The coatings were sprayed on test plates to a thickness of 1.9-2.0 mm and ground to a finish of 10 μm with 400 grit paper. The tests were carried out in an automated test rig with adjustable temperature, blade tip velocity, and incursion rate. The rig is configured such that the coatings are exposed to rotating blades, making contact with the tips as they pass. In this study, investigators monitored the number of contacts, removing and examining abraded coating samples at a given count total ranging from 200 to 4000. It was found that wear characteristics change with each contact between the coating and blade tip, indicating that pass number is a factor that must be considered when testing abradable coatings.

The attachment hooks of training missile wings are worn out. A technology must be found to repair the hooks. The hooks cannot be replaced. They are made of annealed steel of approx. 50 HRC hardness. A similar hardness should be achieved by the repair procedure without changing the basic material in its hardness and strength characteristics through heating. Additional annealing of the assembly is not possible due to its size. To find a solution to this problem, the cold gas spraying procedure was tested first. Cold gas spraying is a highly kinetic coating procedure in which powdery metal particles are strongly accelerated using inert gases at pressures of up to 40 bars and gas velocities far beyond 1000m/sec. When the particles hit the component surface, they form compact, strongly adherent layers of very low oxide content without preceding melting. As a second procedure, manual laser welding was tested using an Nd:YAG laser under a microscope with filling material. In this procedure, a weld pool can be generated within a few milliseconds. Due to the high velocity with which the energy is applied to the material and absorbed by it, a physical reaction is almost ruled out due to its thermal conductivity. Both procedures have the following advantages: function-related composition of the material applied is possible; the characteristics of the base material are not changed due to the low heating levels; and repeated treatment is possible. This paper compares the results of the procedures and discusses the limits of the technology for this specific application.

Presently, highly stressed components in gas turbines are mainly made of single crystal nickel based alloys and the maximum application temperature (without coatings) is typically limited to 1100°C. Superalloys are now reaching limits posed by their melting temperatures. Increasing the substrate temperature beyond 1200°C will increase the efficiency of the turbine significantly. A new generation high temperature Co-Re alloys are aimed for use at +100°C above present single crystal nickel-superalloys. The substrates will be protected against the higher gas temperatures by thermal barrier coatings. For Co-Re alloy substrates CoReCrSi is a promising bond-coat material. CoReCrSi is thermo-chemically compatible to Co-Re due to the very similar mechanical and chemical properties. The oxide formation and the adhesion of the top coat are being investigated by studying a simplified coating system. The coating system consists of a CoReCrSi bond coat bulk material, and an yttria-stabilised zirconia top coat. The system was tested under cyclic conditions at 1200°C. This study provides a first insight into the TGO growth, the basic failure mechanism of the top coat, and the diffusion processes at the top coat/bond coat interface. It is shown that CoReCrSi with 2 at.% silicon promotes a good adhesion of the top coat by forming a dense chromium oxide layer. The critical TGO thickness beyond which the TGO fails by spallation was determined to be 25 microns and is roughly 2.5 times the critical thickness in MCrAlY based system in nickel-alloys.

In rocket engine combustion chambers the cooling channels are subjected to extremely high temperatures and environmental attack. Because of the good heat conduction the inner combustion liner is made of copper. Thermal and environmental protection can be provided by Thermal Barrier Coating Systems. The performance of an APS-sprayed standard coating system for nickel based substrates (NiCrAlY and YPSZ) on copper substrates is investigated. Because mechanical and thermal properties (e.g. the coefficients of thermal expansion) of the two substrates are different, known failure mechanisms for nickel based substrates can not be directly transferred to the new application. Thermal cycling and laser shock testing is performed to identify possible failure mechanisms. The laser shock setup consists of a high-power diode laser (3kW) and realizes surface temperatures of up to 1500°C. Furthermore, it is possible to realize high thermal gradients inside the specimen, similar to those in real service. Delamination of the thermal barrier coating at the interface between bond coat and substrate is observed. Usually, this interface is not failing in standard applications, which gives an important hint for further research. Furthermore, FEM analysis confirms that stresses are maximal at this interface.

The most recent increase in turbine entry temperature (TET) can be obtained by the use of Thermal Barrier Coatings (TBCs) on cooled hot section components. The TBC systems are comprised of Ni-based super-alloy substrate which provides certain mechanical properties and blade geometry consisting of a ceramic top coat with low thermal conductivity applied to a metallic bond coat resulting in a significant temperature drop across the coating. The bond coat provides oxidation resistance and adherence of the top coat to the substrate. In this study different bond coat layers were applied on carbon steel substrates which were covered by yttria stabilized zirconia (YSZ) as a top coat layer using atmospheric plasma spray technique (APS). Al-12%Si and Al 99% were deposited by cold gas dynamic spray technique (CGDS) while Ni-5%Al layer was deposited by high velocity oxy fuel technique (HVOF). Heat treatment was performed on the samples under controlled atmosphere for 15 hrs. The microstructure and micro hardness of as sprayed and after heat treatment samples were investigated. Adhesion strength for top coat / bond coat interface and bond coat / substrate interface were investigated. The residual stresses for as sprayed and after heat treatment was estimated by XRD measurement on the top coat layer with different bond coat material. The results indicate that the adhesion strength either for as sprayed or after heat treatment was enhanced using this new bond coat materials compared to the traditionally as deposited Ni Co Cr Al Y bond coat material.

Mullite (Al 6 Si 2 O 13 ) is the basis of efficient environmental barrier coatings (EBCs) for protecting Si-based ceramic matrix composites (CMCs) selected to replace specific hot-section metallic components in advanced gas turbines. Furthermore, YSZ-mullite multilayer architectures with compositional grading between the bond coat and YSZ top coat were envisioned as solutions to ease their coefficient of thermal expansion (CTE) mismatch induced stress. Consequently, a proper understanding of the mechanical properties such as the elastic modulus, hardness or plastic/elastic recovery work serve for an efficient design of such refractory oxide multilayers. In this work, three different mullite powder morphologies (fused and crushed, spray-dried and freeze-granulated) were employed. Using depth-sensing indentation with loads in the range 100 – 500 mN, the role of the microstructure and morphology of the powder feedstock on the mechanical behaviour of air plasma sprayed mullite bond coats deposited on SiC Hexoloy substrates was investigated. Fully crystalline as-sprayed mullite coatings were engineered under controlled deposition conditions. Mechanical properties were measured for the as-sprayed coatings as well as for coatings heat-treated at 1300°C, in water vapour environment, for periods up to 500 h. Both E and H values of the coatings are found to be highly dependent on the morphology of the starting powders.

In this paper, the nanostructured zirconia thermal barrier coatings were prepared on GH3030 high temperature alloy surface by plasma spraying process. The nanostructured agglomerated ZrO 2 feedstock was used as initial powders, and the NiCoCrAlY alloy as bond coating material. The relationship between bonding strength and spray current, secondary gas flow and spray distance were analyzed. The optimum parameters were acquired by orthogonal experimental design methods. The microstructures and phase structures of nanostructured zirconia thermal barrier coating were investigated thoroughly by SEM, TEM and X-Ray.