This paper is a first report of thermally sprayed Ti 60 Cr 32 Si 8 (at-%) alloy coating. It has been reported previously that such an alloy assumes quasicrystallinity in presence of oxygen, when made to undergo rapid quenching. In these cases, either TiO or SiO 2 is used as an ingredient in the alloy so that it can act as a source of oxygen. This paper describes an attempt to produce a quasicrystal by thermally spraying the alloy in air, i.e. in presence of oxygen, either by flame or atmospheric plasma spraying. The spray parameters for both the processes have been varied in the experiment in a wide range. A vacuum plasma sprayed coating served as the reference. This investigation includes a detailed study of the microstructure and phases by optical microscopy, Scanning Electron Microscopy (SEM), X–Ray diffractometry (XRD), microhardness and porosity. An estimate of the composition of the coating has been done using Glow Discharge Optical Emission Spectroscopy (GDOES). The parametric variations have been correlated with the coating microstructure. It has been found in the study that there is a likelihood of obtaining quasicrystalline phase by atmospheric plasma spraying of this alloy under favourable parametric conditions. The tribological properties of these coatings were studied using a ball on disc reciprocating tribometer.

This investigation deals with a study of the friction, wear and corrosion behavior of vacuum plasma sprayed quasicrystalline (QC) Ti 41.5 Zr 41.5 Ni 17 coatings. During pin on disc experiments, a change in the mode of wear has been found to occur with corresponding changes in normal load and sliding velocity. The low thermal conductivity of quasicrystals and its brittleness play a vital role in determining the friction and wear behavior of such materials. When these coatings are subjected to rubbing for a longer period of time, wear occurs by subsurface crack propagation and subsequent delamination within the coated layer. By comparing the QC to its polycrystalline counterpart during potentiodynamic measurements according to ASTM G 31, higher currents were found over the whole range of potentials for QC when immersed in 1MHCl solution.

Nanoparticles show novel properties compared to the bulk material of same chemistry. The small size is responsible for many changes in the thermo-physical properties. Thus, there was an increasing interest in nanomaterials since the past five years. Among other methods, inductively coupled plasma (ICP) torches can be used for the synthesis of nanoparticles. In this process, the precursor material is vaporized in a first step in the plasma core. In a second step, nucleation and condensation occur in the synthesis chamber where the plasma gets colder and form high-purity nanoparticles, the growth of which is stopped by gas quenching. From their low velocity and high temperature, induction plasmas are particularly adapted for this application. Numerical modeling is a good way to achieve a better knowledge and understanding of the process. In the present paper, a two-dimensional model of an inductively coupled plasma torch was developed and validated on the basis of comparisons with data obtained by some other authors. Finally, the current frequency (13.56 MHz), pressure level (400 mbar) and gas flow rates were adjusted for the specific conditions of nanoparticles synthesis.

Three adhesion measurement methods for thermal spray coatings, namely tensile adhesive strength (according to EN 582), interfacial indentation and in-plane tensile tests were investigated in terms of accuracy of the results and application potential for different coating / substrate conditions. Whereas the tensile adhesive strength test is widely used in industry, the other two methods are still under development in research laboratories and therefore only few experimental data on the accuracy of the methods and on the potential in an industrial context are available. For that reason, dissimilar coating-substrate combinations covering a wide range of types of thermal spray coating-substrate systems were tested using all these methods. Ceramic (Al 2 O 3 ) and metallic (NiCr 80-20) coatings were thermally sprayed by flame spraying with two different thickness on titanium alloy and steel substrates exhibiting each two distinct roughness levels. The distinguished coating properties include the coating toughness, shear strength, interfacial toughness, and adhesive strength. Thermally sprayed coatings do not only show an interfacial complexity, but also the integrity of the interface of substrate and coating has to be considered, as well as porosity, cracks and residual stresses. In this paper, each measurement method was found to be related to certain type of loading conditions and fracture mode. The results of the different methods are compared and the limits of applicability of the different methods are discussed.

In many empirical studies on the structure and properties of thermally sprayed coatings, a set of two predefined parameters (e.g. porosity and elastic modulus) is correlated over a narrow range of structural variation assuming a continuous correlation function. Such a data evaluation assumes the existence of physical correlation’s between material behavior and microstructure. The experimental approach, undertaken in this study, comprises a maximum range of morphologies for starting materials with nearly identical chemical compositions to reveal the influence of microstructural changes of diverse defect species on different coating properties. The large matrix of structural and physical data is statistically correlated without any preconceived assumptions concerning the mathematical functions or the physicochemical nature of the property-microstructure-correlation’s. The divergent morphologies are realized by using different coating processes such as vacuum (VPS) and atmospheric (APS) plasma spraying, water stabilized plasma spraying (WSP), wire arc (WAS)- and flame spraying (FS), including variation of process specific parameters. The microstructure is systematically analyzed along length scales starting from defects in the micrometer down to the nanometer range. The microstructure and its anisotropy is quantified by small angle neutron scattering (SANS). The phenomenological coating behavior is successively investigated starting from basic properties such as electrical and thermal conductivity, elastic constants, residual stresses up to application oriented properties such as wear resistance. Property combinations presuming high sensitivity to microstructural changes are preferentially characterized and statistically correlated.

Systematic measurements of heat fluxes into the substrate under the conditions of APS and HVOF have been performed with the use of a specially designed calorimeter. Results of measurements are presented in terms of the heat absorbed by a 150 mm diameter disk related to the electrical input power (EIP) and/or to the plasma/gas enthalpy. Depending on the process conditions heat flux into the substrate could reach as much as 20 per cent of the torch input power. Influences of gas composition, torch power and standoff distance on the heat transfer efficiency as well as the radial distributions of heat fluxes have been studied in detail and compared for three types of guns. Data obtained from the measurements of the radial distribution of heat fluxes in the plasma plume allowed estimating effective plasma jet diameter and the heat flux density, respectively. Rates of jet expansion differ significantly between the F4 and PlazJet plasma torches. Direct measurements of the substrate temperatures with the use of thermal paints have been performed and temperature patterns were compared with the results of 3D heat transfer modeling. Experimental values of heat fluxes were used in the calculations. Comparison showed that the experimental data on heat transfer efficiency could be used for accurate predictions of the substrate thermal conditions during thermal spraying.

The pore microstructure of thermal spray coatings can be described as a combination of interlamellar pores, intralamellar cracks, and volumetric globular pores. This complex pore morphology can strongly influence the properties of the deposited layer. In this paper, the authors use a multiple small-angle neutron scattering (MSANS) technique to characterize the pore system in NiCrAlY layers. It is shown that the inter-lamella system is of utmost importance. Paper includes a German-language abstract.

Thermally sprayed hardmetal coatings are often used to protect valves in steam turbines against wear. Normally the valve spindles are made of CrMo steel and their bearings are made of Stellite, a cobalt-base alloy. In this investigation, a block-on-ring wear test is used with rings and blocks made of the same materials as the spindles and bearings. The rings were coated with Cr3C2-NiCr by HVOF spraying. Wear tests showed increasing weight loss up to 400°C and a sharp decline at 600°C due to a thin surface oxide layer that begins growing at 450°C. The coatings are characterized based on SEM, EDX, and hardness measurements. Paper text in German.

In this investigation, gas atomized powders derived from Ni-Ti wires are vacuum plasma sprayed, producing free-standing coatings with different geometries and wall thicknesses. XRD measurements show that the dominant phases associated with the shape-memory effect and superelasticity remain during powder and coating production, although a problem with brittleness in uncured samples makes tensile test results unusable. Paper includes a German-language abstract.

This paper evaluates an electrochemical mapping method for determining the corrosion resistance and structural integrity of thermally sprayed coatings. In the test setup, a potentiostat is suspended over the test sample, forming an electrochemical cell. The circuit is completed through an electrolyte-containing porous tip. Capillary forces keep the electrolyte on the surface of the tip, preventing transfer to the substrate surface. In the investigation, electrochemical, spatially resolved measurements are carried out on flame and vacuum plasma sprayed nickel-base coatings and compared with the results of salt spray testing. It is observed that the new method offers many advantages being faster, nondestructive, and quantitative in nature. Paper includes a German-language abstract.

This paper assesses the fracture toughness of thermally sprayed NiCr, NiCrAlY, Mo, and NiCrBSi layers using an indentation method called edge chipping based on fracture mechanics. The procedure is done in a scanning electron microscope, enabling precise positioning and in-situ observation of crack growth. The paper reviews the basic principles of edge chipping, describes the experimental setup, and presents and analyzes the results. Preliminary test results show a clear correlation between edge toughness and wear under particle erosion. The influence of anisotropic properties parallel and perpendicular to the substrate surface is observed as well. Paper includes a German-language abstract.

The increasing demand of the industry for high quality coatings with a low cost aspect has led to the development of ultra thin, nearby finishing free carbide coatings. The R&D work performed for this publication was focused on the tailoring of carbide powders together with the development of a new generation of HVOF-Systems working on higher combustion chamber pressures. An as-sprayed surface roughness of less than 1,5µm has to be envisaged for a thin nearly finishing free coating. Therefore, the starting powder has to have fine particles size with a homogenous distribution of carbides and matrix metals. To ensure the corrosion resistance, the matrix metals have to be completely alloyed and the coatings have to be dense. The used HVOF-System must be able to feed and spray these fine powders without any blockage of the powder feeder or nozzle clocking. The coating quality has to fulfil the requirements of hardchrome plating as wear and corrosion resistance is concerned. The low cost level of thin hard-chrome coatings shall be matched. The suitability for using this coating on applications like hydraulic cylinders has been proven. Generally, this technique of thermal spraying can be used as a hard-chrome alternative as well as for new applications where thermal spraying was not put into account due to cost and technical reasons. The aim was to fill the gap between thin film technologies as PVD or CVD techniques and conventional thermal spraying. The new technology enables the industry to coat large components with nearly no restrictions in size and for competitive prices.

Relationships between the properties of thermally sprayed nickel based alloys and their microstructure (density, porosity, oxide phase content) are investigated. Cross-property- correlation of physical properties such as electrical conductivity and elasticity were examined. The experimental results of the structures and properties of the different coatings are discussed with respect to their pore surface area obtained by small angle neutron scattering (SANS) measurements. As wide as possible range of thermally sprayed microstructures of NiCr and NiCrAlY was produced by vacuum - and atmospheric plasma spraying, flame spraying, HVOF and water stabilized plasma spraying. Commercially available powders with process specific grain size distributions were used as feedstock materials resulting in a wide range of microstructures of the coatings depending on the spraying technique and, to much less extent, on the variation of the process parameters. In this work the examination of the pore structure was carried out by optical microscopy on metallographic cross sections. Phase composition and distribution were investigated by hot gas extraction for oxygen and nitrogen determination and by Scanning Auger Microscopy on polished cross sections and fracture surfaces. The properties of the coatings were characterized by their wear (ASTM G75) behavior, reflecting application-oriented properties. Significant and varying amount of anisotropy of the coating properties - electrical conductivity and elastic modulus - was found in the sprayed microstructures. This anisotropy could be directly linked to microstructure anisotropy as characterized by Small-Angle Neutron Scattering.

Technological properties of thermally sprayed deposits are to a great extent related to the underlying microstructure. The present project aims to relate macroscopic properties of metallic coatings to their microstructure. For this purpose, thermally sprayed deposits of nickel based alloys (NiCr, NiCrAlY) were manufactured by various spraying techniques - atmospheric and vacuum plasma spraying, flame spraying, high velocity oxygen fuel and water-stabilized plasma spraying. One of the key microstructural features is the void system. This system is usually characterized by the total volume of voids, the so called porosity. An additional characteristic parameter of the void system is the specific surface area. The method of anisotropic Small Angle Neutron Scattering (SANS) in the "Porod Regime" allows the determination of the anisotropic specific surface area of the complex void system that consists of intralamellar cracks and interlamellar pores. In contrast to optical microscopy, the SANS technique is capable of resolving the pore structure down to the nanometer scale, and the measured specific surface area represents a statistically relevant average value for the whole illuminated sample volume which is usually a few mm 3 . Besides the presence of voids and cracks the performance of thermally sprayed coatings is also significantly influenced by residual stresses. In the present work residual strains were determined by the technique of neutron diffraction as well as by bending tests, i.e. laser profilometry of the substrate before and after the spraying process. The specific surface area and the residual stresses are discussed with respect to total porosity, the presence of secondary phases like oxides and wear behavior. Special attention is drawn to the anisotropy of the apparent surface area, which is discussed with respect to the anisotropy of macroscopic properties like electrical resistance.

Improved understanding of microstructure-property relationship can help to shift from experiment-based to science-based development of thermally spray deposits. This should result in shorter and less expensive development as well as in higher functionality and reliability of the deposits. Significant amount of work has been done, however, nearly always studying deposits manufactured by only one of the thermal spray techniques. Results are therefore often spray technique specific. A broad study with samples manufactured by a number of different thermal spray techniques seems to be missing yet. Relationships valid across different techniques should provide better understanding of the generic relationships. This research employs number of different techniques - flame, HVOF, plasma (APS, VPS, WSP), to generate a wide range of microstructures. Various Ni-based alloys are studied starting from a simple chemistry (Ni) and ending with complex NiCrAlY alloys. Presented results were obtained with NiCr (80% Ni, 20% Cr) feedstock. Microstructures are characterized by various techniques-OM, SEM, XRD, small-angle neutron scattering (SANS) and others - to obtain the most comprehensive set of macro to micro structural parameters available today. The wear and corrosion properties of these deposits are measured together with internal coating stresses and the most generic microstructure-property relationships are sought.

Three iron-base alloys with different chemical compositions were developed and sprayed in these investigations. The effect of different process parameters (primarily a reactive APS and VPS process) on the attainable nitrogen concentrations and on the resulting coating structure is demonstrated. Furthermore, the metallurgical interaction between the selected alloys as a result of the spraying process is described and the properties (such as hardness, porosity and bond strength) are discussed. The objective of this development is to form nanostructured deposits of the vanadium-nitride type with a crystal structure similar to that of the austenitic lattice. The formation, appearance and type of deposits are described as functions of the process parameters. Paper text in German.

This paper investigates a hypothesis for understanding how the substrate texture influences the adhesive strength. A surface-scale fractal analysis is carried out on measured surface textures obtained from various metallic substrate materials. The results of these area-scale analyzes are correlated with the adhesive tensile strength of the finished coating. The results show that scale-considering fractal parameters predict bond strength better than average roughness, and that they support a hypothesis that relates bond to available surface area at a given scale. Paper includes a German-language abstract.

For quality control in the coating sector, coat thicknesses are measured either destructively or non-destructively. Many European and internationally applicable testing possibilities are available for this purpose, e.g. [1-13]. One common feature in all the procedures is the retraceability of the length or length differences measured using various methods to national or international units. In the range of the thin coats (< 10 µm), various coat standards exist today according to which, for example, device manufacturers or users can adjust their measuring devices. However, there are no such certifiable standards for the thick-coat range. The objective of this project was to manufacture standard coat thicknesses of approx. 50 - 1,000 µm using vacuum plasma spraying consisting of non-conductive, non-magnetic coats with the highest possible precision with regard to coat ho¬mogeneity and final-contour fabrication and then to certify them. This article describes the requirements concerning the material selection, spraying process and subsequent machining. Paper text in German.

In the present project, the widest possible variety of coats applied by means of high-speed flame spraying are investigated with regard to their applicability to components of hydroelectric power stations. The investigations concentrate on protective coats for the wear surfaces of turbine wheels and various guide vanes. The structural shapes and specific features of different turbine wheels, forms of wear phenomena and their causes as well as experience with different materials and coatings are described. The resulting planning and stipulation of suitable testing conditions for the targeted investigations with high-speed flame- sprayed coats are also described. Paper text in German.

In thermal spraying, Fe-based alloys are often applied for relatively thick and inexpensive coatings. The main advantage of the Fe-based alloy coatings is their high ductility as compared to ceramic and hardmetal coatings. Other advantages such as high toughness, easy machineability and satisfactory corrosion resistance are characteristic of Fe-based alloys. The wear resistance is not outstanding, but nevertheless acceptable for a large number of applications. A further improvement of the wear resistance can be achieved by reinforcing the Fe-based alloy coatings, e.g. by addition of nitrogen to the spraying powder.