Plasma spraying of aluminum oxide is attracting great interest as a method for depositing economical coatings for use in the semiconductor equipment industry. The microstructure and mechanical properties of the sprayed aluminum oxide coatings are critical to the coating usage in the semiconductor equipment application. The influence of powder size on the coating microstructure and mechanical properties for coatings used in this industry is investigated.

The Cold Spray coatings have been sprayed from binary eutectic alloy – Al-12%Si and from the complex composition iron-based alloy. The atomized Al-Si powder had close to microcrystalline (grain size around 1micron) structure, the Fe alloy powder had amorphous-nanocrystalline structure. Aluminum-based alloy was also sprayed with addition of up to 10% of aluminum oxide powder. The coating structure and properties have been investigated using optical microscopy, scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, microcalorimetry, microhadness, tensile, bend, erosion and abrasion tests, and corrosion polarization tests. It has been shown that the Al-Si coatings have microcrystalline structure, and the Fe-based coating have amorphous-nanocrystalline structure similar but not identical to the feedstock powders. Cold Spray process has a specific mechanism to preserve the powders metastable structures. The coatings have enhanced hardness, wear and corrosion resistance. Abstract only; no full-text paper available.

The aim of this work is to produce titanium dioxide coatings doped with silicon dioxide nanoparticles. Nanoscale SiO 2 powders are prepared in an induction plasma reactor, then spray-dried to obtain a homogeneous mixture of micro- and nano-crystalline oxide powders suitable for dc plasma spraying. A test case based on conventional aluminum oxide powder is presented. Paper includes a German-language abstract.

The deposition efficiency (DE) of a particular powder for a particular thermal spray process is very important factor when coating economics is being considered. There are many coating applications, however, where it is also important to know how the deposition efficiency changes during a longer coating process. Normally the DE is determined as mass ratio of powder fed into the process and corresponding weight gain of the sample. In this work the deposition efficiency has been determined for aluminum oxide powder in atmospheric plasma spraying using different spray parameters and electrode wear states. The coating process and in-flight particles were monitored using a fast non-intensified CCD-camera. Using digital image analysis the relative hot particle concentrations and velocity distributions were calculated from images. The possibility to use a CCD camera based monitoring system for in-situ measurement of DE is discussed. Additional laser illumination and PTV measurements were performed to verify the cold particle flux unseen by the plain CCD camera.

This paper investigates the adhesion of thermally sprayed ceramic particles on metal substrates. Two aluminum oxide powders are applied to nickel-oxide coated steel substrates by detonation and vacuum plasma spraying. SEM and XRD fracture analysis is used to examine the ceramic-metal interface and the morphology of fracture surfaces. In all test samples, failure occurs in the alumina, not at the interlayer boundary, indicating a high level of adhesion between the ceramic and nickel oxide layers. Paper includes a German-language abstract.

NiAl coating can be used as bond coats for thermal barrier coatings (TBCs) with good ductility and excellent resistance against high temperature oxidation. In this study, nickel-coated aluminum composite powders were used to prepare NiAl intermetallic compound coatings on nickel-based superalloys using an air plasma spray (APS), high-velocity oxygen-fuel (HVOF) and cold spray (CS) processes. Different spraying parameters in the HVOF and CS processes were used to make different coating microstructures, and the coating prepared by the APS technique served as a control for the HVOF and CS processes. The microstructure and phase constitution of the coatings were studied using XRD, SEM and EDS. The results indicate that the deformation behavior of the NiAl powder was different under the different spraying parameters. Less defects of oxides and inclusions were observed in the CS coatings compared with the HVOF coatings.

A composite was obtained by spraying ferromagnetic powder with a plasma arc torch onto an aluminum substrate. The influences of spraying conditions (substrate temperature, plasma gas composition, powder granulometry) on the efficiency of the induction heating by the composite are investigated.

Hollow spherical (HOSP) powders of metals, metal alloys and oxide ceramics are of great interest for thermal spraying, powder metallurgy and material science. For the last decade due to constant rise of interest in HOSP powders and expansion of areas of their application, the efforts of researchers, including authors of present paper, are focused on developing methods of producing the hollow microspheres, based on processing of agglomerated powders in thermal plasma. Exists a range of methods of producing the agglomerated powders with size of dozens of microns, which particles consist of several uniformly mixed nano- submicron- and micron sized powder components: 1) spray drying, 2) processing of atomized suspensions; 3) mechanical treatment of powder mixtures in high-energy planetary mills, etc. A brief overview the results of R&D directed to production of various HOSP oxide and metallic powders (α-alumina, zirconia stabilized by yttria, quartz, nickel allow) by the use of DC torches with interelectrode inserts (cascade torches) and twin torch is presented. In particular, the theoretical approach providing the requirements to plasma flow in criterion view have been developed. A physical and mathematical model of hollow particle behavior in plasma flow is developed and discussed.

This paper examines plasma-sprayed alumina and chromia coatings, with and without aluminum phosphate sealing, in order to assess the stability of the as-sprayed layers and phosphate reaction as a function of temperature during the sealing process. Thermogravimetric analysis showed no changes in mass in the alumina layers, an increase of 1.7% in the mass of the chromia layers due to oxidation, and a 14% loss of mass in the sealed layers, which agrees well with the evaporation behavior of a pure seal. Paper includes a German-language abstract.

FeAl Intermetallic compounds have excellent wear resistance and high temperature oxidation resistances. The low temperature brittleness makes intermetallic compound materials more suitable to be applied in the form of coating to protect materials from high temperature oxidation and wear. In the present study, a iron/aluminum composite coating was produced by cold spraying of iron and aluminum powder mixtures and then was annealed at different temperatures to aim at forming an iron aluminide intermetallic based coating. The deposition behavior of iron and aluminum powder mixtures and microstructural characteristics of the as-sprayed deposit were examined by scanning electron microscopy (SEM). The kinetics of the phase transformation of the as-sprayed iron/aluminum composite deposit to iron aluminide was characterized by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that after heat treatment at a temperature of 600°C, intermediate phase Al 5 Fe 2 coexisted in the deposit with remaining Fe and Al. With increasing heat treatment temperature to 900°C, the deposits consisted of mainly FeAl phase and a trace of remaining Fe phase.

Oxygen present in the High Velocity Air-Fuel (HVAF) process can react with the in-flight metallic particles and cause their oxidation. A grown brittle oxide shell on metallic microsize particles can reduce their deposition efficiency and impair the coating final deposited properties/microstructure. In the current study, the oxide growth of MCrAlY particles, where M stands for Ni and Co, during their flight in the HVAF process has been modeled using the particle tracking scheme. A comprehensive theoretical oxide layer growth background is presented and used to track the particle oxidation process. The oxidation development includes the Mott-Cabrera theory for very thin films, which is function of the particle surrounding temperature and oxygen partial pressure. The very thin film regime, applicable under a limiting thickness, is defined based on the electric field present across the growing oxide layer. As the electric field decreases with oxide thickness, the oxidation rate is determined by thermal diffusion. The obtained results provide a correlation between HVAF system design and surface oxidation phenomena while offering a clear description of different oxidation stages.

To understand the adhesion mechanism of cold spraying, the characteristics of a newly formed cold spray surface are essential. This surface is formed by the dynamic plastic deformation of the substrate and particles during cold spray impact. Over the surface, the amount of newly generated surface, bonding state, and strength can differ. Even within an individual attached particle, the amount of plastic deformation also differs. To determine the relationship between the coating deposition mechanism, microstructure, and adhesion strength, tensile adhesion strength tests of cold sprayed copper coatings on an aluminum substrate were carried out. Then, using an Auger electron spectroscopic analyzer, the remained oxide film at the fracture surface, which is the bonding interface, was analyzed. The natural oxide film that covers the surface of the substrate before the impact, which is broken by plastic deformation during the spray process. However, the results show that it is not broken at the center of the collision crater, where the amount of plastic deformation of the substrate material is small. Hence, at the center of the collision crater, the oxide film still covers the substrate. Moreover, the results reveal that the adhesion strength is not uniform but is strong at the edge of the crater, where the oxide film has been removed by the colliding particle. These results reveal insights that will be valuable for future improvements in the adhesion strength of cold spray coatings.

This paper presents a way of processing cold-sprayed Ti-Al to produce titanium aluminum nitride coatings. These coatings are meant to serve as a durable protective layer on tools exposed to molten aluminum alloys. A Ti-Al powder mixture with a weight ratio of 70/30 was cold sprayed onto specially prepared substrates using nitrogen as a process and powder delivery gas. The resulting coatings were alloyed at different temperatures to obtain a stabilized Ti-Al intermetallic phase for further nitriding treatment. The nitriding process was carried out in an ammonia-nitrogen atmosphere at 900 °C. The final product had a web-shaped microstructure with the same thickness as the cold-sprayed Ti-Al. Test samples were placed in molten aluminum for 1200 hours without notable chemical reaction.

Due to their attractive combination of properties (high resistance to oxidation and wear, high melting point, and lower density) iron and nickel aluminides show promise for the development of advanced materials and coatings However, poor room temperature ductility and susceptibility to intergranular cracking restrict their commercial application. To provide the structure required composite materials produced by the self-propagating high-temperature synthesis (SHS) are promising. In this paper, the potential of thermally sprayed NiAl/aluminum oxide and FeAl/aluminum oxide composite powders produced using the SHS method is evaluated. The results of the structure and property investigations for the synthesized powders as well as for the resulting plasma coatings are presented. Paper includes a German-language abstract.

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.

Cold spray is a promising potential material deposition process of which the main advantage is that the material to be sprayed is not heated to high temperatures. But one problem encountered is that the coatings for some powders are not well bonded to the substrate. The mechanisms of bonding of cold-sprayed coating to substrates are not at present clearly understood. This work considers the deposition of aluminum bronze by cold spray process onto stainless steel. The micro diffusion along the interface between the substrate and coating as well as the beta-phase depletion of the cold-sprayed coating is observed. Results obtained are important not only for understanding the interaction of the particles with the substrate but also for optimizing the spray parameters for the cold spray process.

In this paper the development of thermal sprayed, hard phase reinforced aluminum based layers, in particular for coating light metal substrates is described. The aim of the project was to obtain wear resistant coatings for applications on light metal surfaces combined with other advantageous characteristics, especially good thermal conductivity. One possible application for these coatings can be seen in automotive light weight constructions as wear protection for brake discs or drums. Flame shock spraying as well as high velocity oxyfuel flame spraying (HVOF) were used as coating processes. As consumables mechanically alloyed powders consisting of aluminum and ferric oxide were used. Due to the high kinetic process energy developed by the selected procedures in connection with the exothermically reacting spraying material, a new light metal matrix composite was produced. One major advantage of this coating material is the in-situ synthesis of the hard particles in the aluminum matrix during the spray process resulting in good adhesion/cohesion properties. This research project includes an extensive analysis of the consumables including differential thermal analysis, SEM, and EDX. Furthermore, process parameters were optimized. This includes a characterization of the HVOF process using modern particle diagnostics. Besides good bonding properties proven coating characteristics are high thermal conductivity and thermal shock resistance as well as good wear behavior even at elevated temperatures. The results show that the developed coating system is a promising alternative for cast aluminum matrix composite materials used for wear stressed parts even at elevated temperatures.

High temperature alloy powder CoCrAlYTa made by vacuum-atomized technology has satisfied properties such as spherical degree, fluidity and low oxygen quantity etc. Compact and steady high temperature properties coating was prepared when CoCrAlYTa was blast sprayed onto stainless steel. In this paper, several high temperature working performance like hot shocking, high temperature oxidation and high temperature corrosion of CoCrAlYTa coating got was studied, the micro-structure of coating was analyzed with metallographical analysis, SEM and XRD. Experiments results indicated that, with the added of Y and Ta, the structure and toughness of chromium and aluminum oxidation membrane in the coating was improved, overall, blast spraying coating has excellent high temperature characteristics. Abstract only; no full-text paper available.

Ni+Al, Ti+Al, NiCr+AI, and Cr+Al powders react exothermically in the heat zone of thermal spraying systems. Whether such reactions occur between aluminum and superalloy powders is the underlying question of this study. This paper describes composites of this nature and their sprayability to form adherent, metallurgically bonded deposits. Through parametric manipulation, coatings can be produced with a range of properties from dense to open (porous/abradable) structures. The paper also shows how seed particles can be clad with aluminum and sprayed to predictable property limits.

The deposition of MCrAlX coatings (where M is Ni, Co, Fe, or a combination of these, and X is Y, Si, Ta, Hf, or a combination of these) via thermal spraying has acquired significant importance in industries such as aerospace, power plants, oil, and gas, etc. Among various thermal spray deposition techniques, high-velocity air fuel (HVAF) has shown a growing potential for the deposition of metallic powders which are sensitive to high-temperature oxidation during spraying. Thus, it is essential to understand the in-flight behavior of these metallic particles in the high-velocity, low-temperature HVAF flame. In this work, a NiCoCrAlY powder was sprayed using two sets of HVAF deposition parameters onto stainless steel substrates. In-flight particle diagnostic tools such as AccuraSpray were employed to understand the behavior of these spray particles. The deposited particles were comprised of partially molten particles and fully deformed splats. Samples with higher powder feed rates showed a primary coating buildup on the substrate surface. EDS plots revealed no traces of inflight particle oxidation but contained carbon residue due to the presence of unburnt hydrocarbons from the fuel-rich HVAF-M3 torch. This study provides a preliminary understanding towards the significance of deposition parameters on the in-flight particle oxidation behavior and splat deformation characteristics by HVAF spraying.