Thermal barrier coatings (TBC) are normally based on yttria partially stabilised zirconia (YPSZ) coatings and are commonly used coatings in the high temperature, combustion region of gas turbines. TBC permit to increase the temperature of combustion, increasing the thermodynamic efficiency of the engine. Therefore, an engine equipped with TBC can produce a larger amount of energy over its lifetime. This increase in produced energy can be compared with the energy needed for the manufacturing and installation of TBC. The comparison can be performed in terms of the “energy return” (or “energy returned for energy invested”, EROI or EROEI). The qualitative analysis performed in the present study indicates that this return is large in comparison to that of other energy producing systems.

This research aims to investigate the effects of employing cryo-milled and milled MCrAlY feedstock powders on the oxidation behaviour of low-pressure plasma sprayed (LPPS) and HVOF-sprayed coatings deposited onto a Ni-based superalloy substrate. Commercially-available powders with three different chemical compositions were selected and sprayed both in standard condition and after milling and cryo-milling processes. The LPPS and HVOF coatings, deposited onto an Inconel substrate, were diffusion-treated at 1080 °C (according to the industrial standard) and subjected to isothermal and cyclic oxidation tests. The outcomes of these tests show that transient oxidation is suppressed in the coatings obtained from milled MCrAlY systems, whose overall resistance to cyclic oxidation (number of cycles to failure) is approximately two times greater than that of standard coatings. This difference is not related to the nanostructural features induced on the powder particles by the milling process, because, after the diffusion treatment, all coatings exhibit identical γ-β two-phase microstructure, with no trace of the original nanostructure. The improvement is ascribed to the fine dispersion of nanometric Al 2 O 3 grains within the milled powder particles: in the sprayed coatings, these nanometric oxides act as nuclei and favour the direct formation of an Al 2 O 3 oxide scale.

The current critical situation of the world economy pushes the companies to make themselves adaptable and to change their usual rigid behaviour in order to survive globalization of the market, to face the competition of the so called low cost countries (LCCs) and to overcame the current financial crisis. For the western companies, the possible way to face the movement of production to the LCCs, is to invest and increase the technological level of their products by means of effective R&D. This is even more valid for the Small and Medium Enterprises (SMEs) and is particular valid for the power generation sector. This paper addresses the policies adopted by the Public Administrations in the different countries in order to support the companies. The Public Administrations have the interest to support the companies not only in order to promote their own growth but, above all, in order to support the development of the territory where the company is located with the growth of the job numbers and the increasing of the subsuppliers activities. A review of the financial instruments available for companies in order to obtain financial help for research and innovation is provided, advantages and disadvantages are discussed. The focus is placed to the energy sector. An industrial case study is shown, related to a thermal spray shop dealing with gas turbine components, where the efficient and effective use of research allows the set up and the development of the company and also contributes to the surrounding market.

The current critical situation of the world economy pushes the companies to make themselves adaptable and to change their usual rigid behaviour in order to survive globalization of the market and the current financial crisis. A large quantity of people entering into the market created a sudden economic earthquake: the needs of goods and their way of production have changed with a subsequent unbalancing of supply and demand. The so called low cost countries (LCC) can offer a significant amount of goods at extremely low prices, with a high capability to “copy” the non-protected technologies. As consequence, it could be noted a movement of production from the rich western countries to the low cost countries, already established in several sectors (textiles, automotive, consumption goods, etc.) and in progress for higher technology sectors. The possible way to face this problem for European and US companies is to invest and increase the technological level of their products by means of effective Research and Development. This is even more valid for the SMEs. The help of the public bodies in funding R&D is crucial in order to make R&D costs acceptable for companies. This paper addresses the study of the financial instruments available for companies in order to obtain financial help for research and innovation: advantages and disadvantages are discussed. An industrial case study is shown, related to a thermal spray shop dealing with gas turbine components, where the efficient and effective use of research allows the set up and the development of the company and also contributes to the surrounding market.

Thermal barrier coatings have got considerable importance for the improvement of gas turbine efficiency. These materials are applied on the surface of gas turbine blades and vanes and are based on a layer of low-oxidation material (mainly MCrAlY alloys, where M stay of Co, Ni or a combination of both) and a ceramic top layer that acts as proper thermal barrier (normally Yttria Partially Stabilized Zirconia). Coating removal is an important aspect in the production of these blades and vanes. “Decoating” or “stripping” is needed during the production of new components as well as for the reconditioning of existing ones. The present paper is dedicated to a new removal method of the ceramic Zirconia layer, based on dry ice blasting. This method will not impact on the roughness and morphology of the bond coat surface, making it suitable for re-coating with TBC, without any further operation before TBC recoating. This possibility has an important impact on the stripping costs and time, avoiding all the operations related to the bond coat. The paper presents the process tests to get the process set up and the characterization of the surfaces comparing the stripped ones with the “original ones” coated by LPPS on new components, ready to be TBC coated. Optical and SEM microscopy, 3D profilometry have been used for characterization. Finally a Thermal Cycling Fatigue test has been carried out in order to validate the procedure of stripping and re-coating.

Thermal barrier coatings (TBCs) are widely used in gas turbines to reduce thermal exposure of structural components and increase turbine efficiency. They typically consist of a MCrAlY bond coat and a YSZ topcoat. At high temperatures, a thermally grown oxide (TGO) layer forms between the bond coat and topcoat. If this layer is a continuous scale of alumina, it will act as a diffusion barrier to suppress the formation of other detrimental oxides, thus helping to protect the substrate from further oxidation. It has been reported, however, that other oxides, such as chromia, spinel, and NiO, may form along with the TGO layer, ultimately leading to TBC failure. To investigate such claims, coatings of comparable thickness were deposited by various spraying methods onto a superalloy substrate using a powder of the same composition. Samples were isothermally oxidized at 1273 K for different periods up to 3000 hours. The samples were examined before and after furnace tests and the results are presented and discussed.

The most commonly used structural materials for blades and other high temperature components of gas turbines are nickel base superalloys. A TBC protection coating system consists of a top coat of yttria partially stabilized zirconia and an underlying bond coat, usually MCrAlY (where M stands for Ni, Co or a combination of both). MCrAlY is normally deposited by the thermal spray processes: air plasma spray (APS), vacuum plasma spray (VPS/LPPS) or high velocity oxygen fuel (HVOF). The adhesion between the bond coat and the substrate, and therefore of the whole thermal barrier system, strongly depends upon the surface roughness. A high level of roughness generally denotes better adhesion, especially with the HVOF thermal spray process, where it is a necessity. Generally the roughness is reached by means of grit blasting with an abrasive media; this results in a certain level of surface contamination due to the entrapment of abrasive particles. The aim of this work was to set up a new surface preparation process in order to obtain a completely clean surface with a suitable roughness, which can be coated afterwards with HVOF or VPS/LPPS thermal spray technology. The tests carried out by this process on turbine blades, coated with a HVOF system, led to obtaining a coating/base material interface without any contamination caused by the surface preparation.

High temperature thermal fatigue causes the failure of Thermal Barrier Coating (TBC) systems. Due to the difference in thickness and microstructure between thick TBCs and traditional thin TBCs, they cannot be assumed a-priori to possess the same failure mechanisms. Thick TBCs, consisting of a CoNiCrAlY bond coat and Yttria Partially Stabilised Zirconia top coat with different values of porosity, were produced by Air Plasma Spray. Thermal fatigue resistance limit of TBCs was tested by Furnace Cycling Tests (FCT) according to the specifications of an Original Equipment Manufacturer (OEM). TBC systems were analyzed before and after FCT. The morphological and chemical evolution of CoNiCrAlY/TGO microstructure was studied. Sintering effect, residual stress, phase transformation and fracture toughness were evaluated in the ceramic Top Coat. All the tested samples passed FCT according to the specification of an important OEM. Thermal fatigue resistance increases with the amount of porosity in the top coat. The compressive in-plane stresses increase in the TBC systems after thermal cycling, nevertheless the increasing rate has a trend contrary to the porosity level of top coat. The data suggest that the spallation happens at the TGO/Top Coat interface. The failure mechanism of thick TBCs subjected to thermal fatigue was eventually found to be similar to the failure mechanism of thin TBC systems made by APS.

In order to improve gas turbine performance it is possible to decrease back flow gases in the high temperature combustion region of the turbo machine reducing shroud/rotor gap. Thick and porous TBC systems and composite CoNiCrAlY/Al 2 O 3 coatings made by Air Plasma Spray (APS) and composite NiCrAlY/graphite coatings made by Laser Cladding were studied as possible high temperature abradable seal on shroud. Oxidation and thermal fatigue resistance of the coatings were assessed by means of isothermal and cyclic oxidation tests. Tested CoNiCrAlY/Al 2 O 3 and NiCrAlY/graphite coatings after 1000 hours at 1100°C do not show noticeable microstructural modification. The oxidation resistance of new composite coatings satisfied Original Equipment Manufacturer (OEM) specification. Thick and porous TBC systems passed the thermal fatigue test according to the considered OEM procedures. According to the OEM specification for abradable coatings the hardness evaluation suggests that these kinds of coatings must be used with abrasive tipped blades. Thick and porous TBC coating has shown good abradability using tipped blades.

Invar alloy (Fe – 36%Ni) is used in industrial applications which require high dimensional stability because of its exceptionally low thermal expansion coefficient. Purpose of this work is to enhance the performance of molds for the production of carbon fiber reinforced plastic (CFRP) components. Four different kinds of commercial powders were coated on an Invar substrate: Al 2 O 3 - 12TiO 2 , Cr 2 O 3 and ZrO 2 - 8Y 2 O 3 by Air Plasma Spray (APS) and WC - CoCr by High Velocity Oxygen Fuel (HVOF). Metallographic microscopy observation and SEM analysis were carried out and microhardness and fracture toughness were evaluated by means of the micro - indentation method. Friction behaviour and wear resistance were evaluated in dry sliding conditions with Pin On Disk apparatus for not coated Invar substrate and for the different coated substrates. Chromium oxide and tungsten carbide coatings exhibited higher mechanical characteristics respect to the other coatings: chromium oxide had the higher hardness value and tungsten carbide the higher fracture toughness. Tungsten carbide coating had the lower average coefficient of friction and together the chromium oxide the lower wear mass loss and wear rate. Among APS ceramic coatings, Cr 2 O 3 exhibited the best mechanical and tribological behavior while the HVOF cermet coating exhibited the best behavior among all the coatings.

High temperature thermal fatigue causes the failure of Thermal Barrier Coating (TBC) systems. This paper addresses the development of thick TBCs, focusing attention on the microstructure and the porosity of the Yttria Partially Stabilized Zirconia (YPSZ) coating, in relation to its resistance to thermal cycling fatigue. Thick TBCs, with different grade of porosity, were produced by means of a CoNiCrAlY bond coat and Yttria Partially Stabilised Zirconia top coat, both sprayed by Air Plasma Spray. The thermal fatigue resistance of new TBC systems and the evolution of the coatings before and after thermal cycling were evaluated. The limit of thermal fatigue resistance increases with amount of porosity in the top coat. Raman analysis shows that the compressive in-plane stress increases in the TBC systems after thermal cycling, nevertheless the increasing rate has a trend contrary to the porosity level of top coat.

The most commonly used structural materials for blades and other high temperature components of gas turbines are nickel superalloys such as Inconel 738, MAR M247M or Hastelloy. Thermal barrier coatings (TBCs) are widely used on these substrates as protection against high temperatures and oxidation. A TBC system consists of a top coat of yttria partially stabilized zirconia deposited by air plasma spray and an underlying bond coat (usually MCrAlY, where M is Ni, Co or a combination of both). MCrAlYs are normally deposited by thermal spray processes such as air plasma spray, vacuum plasma spray (VPS/LPPS) or high velocity oxygen fuel (HVOF). In general, the adhesion of the whole thermal barrier system is strongly dependent on the surface preparation of the substrate and it is generally believed that a certain degree of roughness promotes better adhesion. OEM’s (Original equipment manufacturer) procedure for preparation of substrates and analysis have been reviewed and considered as basis of this work. The scope of this work is to set up a new cleaning methodology in order to obtain a completely pollution free surface to be coated afterwards with HVOF or VPS/LPPS. The properties of this new methodology have been compared with standard surface preparation techniques such as blasting with corundum and silicon carbides. The obtained samples have been analysed by means of metallography and chemical composition of the interface in order to measure the interfacial pollution between substrate and coating. Finally adhesion of MCAlY coating have been tested and compared with specification of the main OEMs.