Titanium porous transport layers (PTL) are important components in proton exchange membrane water electrolysis (PEMWE) cells. The performance enhancement and the reduction of manufacturing cost of PTLs are of importance for market expansion of PEMWE. Vacuum plasma spraying (VPS) was used to prepare PTL or modify PTL of sintered titanium powders and the PTLs by VPS showed a high performance. Regarding the cost efficiency, it is of great interest to produce PTLs using more economical spray processes than VPS. In this study, high velocity oxy-fuel spraying (HVOF) was used to produce highly porous titanium coatings for this purpose. The spray process was developed to achieve a high porosity of up to Φ = 30 % using three titanium powders with size distributions of fA = -90 +45 μm, fB = -63 +20 μm and fc = -45 +11 μm. The coating structures were examined on the cross sections of the titanium coatings with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The porosity was determined using the image analysis system ImageJ. The deposition efficiency of the titanium powder fC = -45 +11 μm was determined. The results show that the coating structure significantly depends on the titanium powders. Highly porous titanium coatings of Φ = 24 - 40 % can be produced with the titanium powders of fB = -63 +20 μm and fc = -45 +11 μm. Titanium oxides are hardly visible on the cross-sections of the titanium coatings. A high deposition efficiency of approximately DP ≈ 70 % was measured for the titanium powder of fc = -45 +11 μm.

MCrAlX powder compositions (M=Ni, Co and X=Y, Hf, Si or combination) are often thermally sprayed (TS) via vacuum plasma spray (VPS), low pressure plasma spray (LPPS) or high velocity oxy-fuel (HVOF) to produce high temperature oxidation and hot corrosion resistant bond coats (BC) for thermal barrier coatings (TBCs). Cold spray (CS) technology is currently considered as a promising alternative to the traditional TS solutions having the advantage of delivering oxide-free and very dense metallic coatings at relatively lower costs compared to VPS and LPPS. Here, we first present high-pressure CS deposition of NiCoCrAlY and NiCoCrAlYHfSi and discuss the influence of feedstock properties on the deposited BCs. CFD numerical simulation is employed to tailor the spray conditions based on the feedstock characteristics. Secondly, we present the laser assisted cold spray (LACS) deposition of NiCoCrAlYHfSi BCs using a low-pressure CS system. We show that LACS can be successfully used to deposit this particular powder while eliminating nozzle erosion and low deposition efficiency disadvantages observed during conventional CS. Lastly, high temperature isothermal oxidation of a TBC architecture having LACS BC is presented.

Dual layer electrode coating for alkaline water electrolysis was prepared by plasma spraying. For improving performance this work aims at reducing the oxide in electrode coating. Regarding the necessity of obtaining high specific area, atmospheric plasma spray was employed under protection of argon which was used as shrouding gas. Composite cathode was established on Ni-coated perforated steel sheet with crushed and gas atomized Nickel-based alloy powders. The dual-layer structure was a composite of 5 layers of NiAl at the bottom and 10 layers of NiAlMo as the top layer. Microstructure and morphology were studied by scanning electron microscope (SEM). Element content was estimated by energy dispersive spectrometer (EDS). Enthalpy probe was introduced for measuring plasma temperature and velocity as well as gas composition. Numerical calculation was carried out with same condition for better understanding the shrouding effect. The results showed moderate protection by using of arranged gas shrouding. Overall, in the dual layer region, oxygen content was decreased by 0.3%, from 3.46% to 3.15%. With gas shrouding coating exhibited similar element contents as coating sprayed by VPS. However, no obvious difference was observed in microstructure and morphology with or without gas shrouding.

In this work, ZrB 2 -MoSi 2 (ZM) composite coatings are fabricated using two plasma spraying techniques: VPS and APS. Phase composition and coating microstructure were assessed and microstructural changes at 1500 °C were investigated along with corresponding oxidation behaviors. The results show that the VPS composite coatings have lower oxide content, surface roughness, and porosity and much higher oxidation resistance than coatings produced by atmospheric plasma spraying. Possible reasons for the differences observed are presented.

Plasma Facing Materials (PFMs) suffer from very high heat load including quasi-stationary high heat load during normal operation and transient events with extremely high heat load during normal plasma operation and off-normal events. In this paper, W/Cu functional gradient coating was applied on CuCrZr substrate (250mm × 120mm × 30mm) with compositionally gradient W/Cu as bond coat (0.4-0.6 mm) and 1.5 mm thickness W coating as top coat via VPS for continuous deposition duration of 5 h. VPS-W/CuCrZr mockup with built-in cooling channel was prepared for evaluating the transient vertical displacement and plasma disruption events applied by high energy electron beam. The formation of cracks and surface melting of VPS W/Cu mockup were investigated under the two transient high heat loads (HHL). The coatings were able to absorb about 2 MJ/m2 in HHL without significant damage.

HVOF spraying has established itself in the last decade as a very cost competitive method, increasingly replacing VPS/LPPS for the application of typical high temperature protective metallic coatings on IGT hot gas path components. In order to further improve this technology, ALSTOM recently developed a new design of a 4-injector-block for the K2-gun. This advanced design does not only significantly optimize the energy consumption and spraying time, but also enables the future application of new complex metallic coatings. A CFD simulation of the K2-gun was performed in order to identify the optimization potential. Based on the results, an improved prototype was manufactured, validated and successfully introduced into manufacturing. The aim of the study was also to investigate in detail the impact of the hardware modification on parameters such as spray spot geometry, deposition efficiency, fuel consumption and the corresponding coating quality (porosity, bonding etc.), which shall be discussed within this paper.

The current paper reports self-healing plasma sprayed Mgspinel (MgAl 2 O 4 ) coatings. The coatings were used for electrical insulation in high temperature fuel cells. A range of potential self-healing additives consisting of SiC+X (where X was BaO, CaO, ZnO, Y 2 O 3 , GeO 2 , Ta 2 O 5 , V 2 O 5 ) were characterized and SiC+Y 2 O 3 was initially selected for coating development. Coatings of spinel with 20wt% additive were developed using vacuum plasma spraying (VPS) or atmospheric plasma spraying (APS). In the developed coatings, self-healing was demonstrated after heat treatment at 1050°C in air for 10 hour. Thermophysical and thermomechanical properties of self-healing coatings were determined and compared to spinel coatings. Lastly, a modelling technique is presented to simulate the effective elastic moduli of the coatings. Numerical results based on microstructural simulations showed good agreement with experimental data.

This study assesses the strength and adherence of VPS titanium coatings on ultrahigh molecular weight polyethylene (UHMWPE) substrates. Four-point bend tests show the existence of a critical tensile strain of 1% corresponding to the onset of cracking. For strains up to 6%, crack density increases with no observed debonding. Fatigue tests over 106 cycles reveal that the coating remains uncracked at a strain of 1% and stays in a stable cracked state without debonding as strain is increased to approximately 6%. A laser shock test developed specifically for titanium-polymer interfaces revealed the existence of a debonding threshold corresponding to the adhesion strength. The results serve as a guide for the design of orthopedic implants on which VPS titanium coatings are used and, more generally, open the way for systematic measurement of adhesion between metallic coatings and polymer substrates.

This study compares the deposition and oxidation behavior of two oxide-dispersed CoNiCrAlY powders, one commercially obtained, the other prepared in a high-energy attrition ball mill using CoNiCrAlY and nanosize α-alumina powders. The custom powder was deposited by HVOF spraying using two sets of parameters, one optimized for CoNiCrAlY powder, the other for fine alumina. Coatings produced under the latter conditions were found to be porous, which can be attributed to a low degree of melting in the dispersed alumina. Isothermal oxidation testing at 1373 K for up to 1000 h in air caused oxidation not only at the surface, but also inside the coatings due to the movement of oxygen through the pores. The coatings deposited under the other set of parameters, i.e., at higher power levels, were free of pores. Isothermal oxidation tests were also carried out on coatings produced from the commercial powder, in this case, by HVOF and as well as vacuum plasma spraying. The coatings obtained by HVOF spraying were found to have a thinner thermally grown oxide layer than not only the VPS coatings, but also conventional metallic bond coats. Internal oxidation in the HVOF coatings is due to insufficient cohesion of the spray particles. Furnace cycling tests were conducted on specimens with an additional ceramic thermal barrier coating. Specimens with VPS bond coats produced from commercial oxide-dispersed powder achieved almost same number of cycles to delamination as specimens with conventional metal bond coats.

Plasma-sprayed ceramic coatings are often used as thermal barrier or abradable coatings in high-pressure stages of gas turbines. They are exposed to high thermo-mechanical loadings, due to the harsh operating conditions. Today, a material typically used in engines as thermal barrier coating material is yttria-stabilised zirconia (YSZ). This material has a low conductivity and a high thermal expansion coefficient, but a limited temperature capability of about 1200°C in long-term applications. For the use as abradable coatings, thicker coatings with a thickness above one millimetre are necessary. However with increasing coating thickness and limited cooling efficiency there is a risk of premature failure. As a result new ceramic materials have been developed. For the lifetime analysis they were tested by thermal gradient cycling tests. In the present work an APS ceramic double-layer topcoat composed of 7YSZ and a top layer of non-stoichiometric magnesia alumina spinel (Mg-Al-Spinel) was used. The layer was sprayed on disc-shaped IN738 superalloy substrates which were coated with a VPS bondcoat. Under specific thermal cycling conditions with temperatures above 1400°C, these samples showed a typical failure mechanism with exfoliation of thin coating lamellae, starting from the coating surface. This failure mechanism was analysed in detail, e.g. by scanning electron microscopy (SEM), X-ray diffraction, and chemical analysis. From these findings, a description of the failure mechanism was developed.

Plasma spray – physical vapor deposition (PS-PVD) is a low pressure plasma spray technology to deposit coatings out of the vapor phase. PS-PVD is part of the family of new hybrid processes recently developed by Sulzer Metco AG (Switzerland) on the basis of the well established low pressure plasma spraying (LPPS) technology. Included in this new process family are plasma spray - chemical vapor deposition (PS-CVD) and plasma spray - thin film (PS-TF) processes. In comparison to conventional vacuum plasma spraying (VPS) and low pressure plasma spraying (LPPS), these new processes use a high energy plasma gun operated at a work pressure below 2 mbar. This leads to unconventional plasma jet characteristics which can be used to obtain specific and unique coatings. An important new feature of PS-PVD is the possibility to deposit a coating not only by melting the feed stock material which builds up a layer from liquid splats but also by vaporizing the injected material. Therefore, the PS-PVD process fills the gap between the conventional physical vapor deposition (PVD) technologies and standard thermal spray processes. The possibility to vaporize feedstock material and to produce layers out of the vapor phase results in new and unique coating microstructures. The properties of such coatings are superior to those of thermal spray and EB-PVD coatings. In contrast to EB-PVD, PS-PVD incorporates the vaporized coating material into a supersonic plasma plume. Due to the forced gas stream of the plasma jet, complex shaped parts like multi-airfoil turbine vanes can be coated homogeneously with columnar thermal barrier coatings using PS-PVD. This paper reports on the progress made by Sulzer Metco to develop a thermal spray process to produce coatings out of the vapor phase.

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.

Although the history of using the thermal inductively coupled RF-plasma (ICP) for spraying processes has been started in the early sixties, up to now all but no industrial applications are known. ICP-spraying of coatings has been investigated in various labs for interesting applications like coatings for medical implants and electrodes for SOFC´s. All the processes are VPS-applications. This on one hand of course is caused by the oxygen affinity of the used materials, on the other hand the current view in thermal spraying is, that very dense and excellent adherent coatings can be sprayed only by increasing the particles velocity. In contrast to this mind this contribution will try to show, that also under atmospheric and low vacuum conditions, i.e. using a laminar flowing plasma with nearly no acceleration of the axially injected particles, it becomes possible to spray coatings with comparable values of porosity and bond strength but special features that can not be produced with common technologies. This can be explained by the changed condition of heating, deformation and cooling down of the considerably larger particles. Actual examples are given for various spraying materials like ceramics and hard magnetic materials.

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.

Increasing requirements on technical components for high-temperature-applications (e.g., turbine blades) demand for new developments in surface engineering. The selective combination of materials with positive and negative thermal expansion coefficients (NTE) will lead to a reversible activation of the surface depending on surface temperature: The generation of a riblet structure (“shark skin”) in operation condition by thermal expansion of the matrix and shrinkage of the NTE-ceramic and self-cleaning of the surface at cool down as a result of the reversal of the process. Due to its hygroscopicity the chosen NTE-ceramic Y 2 W 3 O 12 needs to be embedded into a binder matrix. Therefore a feedstock powder consisting of MCrAlY, WO 3 and Y 2 O 3 is mechanically alloyed in a high-energy ball mill. The powder is deposited on substrates by thermal spraying (VPS and HVOF) and laser cladding as well. After coating process a lateral- and depth-selective ion implantation of tungsten, yttrium and oxygen will force nucleation in predefined areas. A following heat treatment of the specimens supports the in-situ-formation of Y 2 W 3 O 12 .

A Sulzer-Metco 6P Powder Flame Spray Torch spraying an alumina-titania ceramic powder RX60 6-axis robotic was characterized using an Accura G3(Tecnar Automation; Quebec, Canada) and a DPV-2000 (Tecnar Automation; Quebec, Canada). The two sensors were mounted side-by-side and a robot was used position the torch in relation to each sensor. Process gas flows were set using laminar flow element mass flow controllers. Accura and DPV measurements of particle temperature (Tp) and particle velocity (Vp) were made in succession at each operating condition without changing torch operating conditions. Data for a single designed experiment was collected with both sensors allowing for comparison of the two sensors across the operating space of a typical powder flame spray process.

Elastic properties of 20 and 40 µm thick deposits of yttria fully stabilized zirconia (YSZ), fabricated by vacuum plasma spraying (VPS) and air plasma spraying (APS) with modified injection system were investigated at room temperature by nanoindentation, and 4 point flexion test and at 800°C by 4 point bend test. The data was correlated with structural analysis of different YSZ deposits. At room temperature, E values of VPS YSZ deposit decreased from 237 ± 6 to 105 ± 5 GPa on increasing nanoindentation load from 1 mN to 450 mN. The results indicated change from intrinsic to defect-dependent E values with increasing load. Despite lower porosity of VPS deposit (6 ± 1%) compared to that of APS (24 ± 1%), E values, measured by flexion test at room temperature and at 800°C, of former were 35 ± 1 and 16 ± 1 and of latter were 55 ± 1 and 18 ± 1 GPa respectively. The interlamellar sliding, parallel to applied load, was considered as prime reason of lower rigidity of deposits.

Thermal spray processes represent a cost effective and flexible method for the production of functional coatings by using metallurgical, ceramic and cermet materials. Due to the high kinetic energy of the impinging particles, the HVOF (High Velocity Oxygen Fuel) technique is able to produce extremely dense coatings with very low porosity. In this study, several yttria stabilized zirconia (YSZ) powders have been sprayed by HVOF for the fabrication of electrolyte layers for SOFCs (Solid Oxide Fuel Cells) applications. Coatings were characterized regarding their porosity, leak tightness and electrochemical properties. Results were compared to VPS sprayed coatings. The electrochemical behavior of the cells sprayed with the optimized set of parameters was determined applying U(i)-characteristics and impedance spectroscopy. With a destination thickness of about 40 µm, competitive leak tightness of the electrolyte and performance of the cells could be established.

Thermal spraying is a widely used technology in a range of industrial applications to provide coatings improving the surface characteristics. According to the thermal and kinetic specificities of processes (APS, VPS, flame, electric arc), any kind of material can be sprayed. Among materials, ceramic coatings present several interesting aspects for wear resistance, corrosion protection as well as for thermal or electrical insulation; particularly alumina coatings which appear as the most commonly used. Many techniques can be used to spray such kind of materials. From all of them, atmospheric plasma spraying (APS) is a rather well-established process but some other processes can also be used with a lower economical impact as the flame technology. The aim of this study was to analyse the alumina coating properties according to the technology employed such as atmospheric plasma spraying or wire flame spraying using the Rokide and the Master Jet guns. After usual micrographic analyses by SEM, physical and mechanical properties were measured considering the thermal conductivity and the hardness.

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.