Abstract The unique combination of the properties of iron aluminides opens up a multitude of novel applications at elevated temperatures in oxygen and sulphurous atmospheres. FeAl composites have excellent wear and corrosion resistance paired with the intermetallic phases of the Fe-Al system, which, however, tend to hydrogen embrittlement. In this paper, intermetallic phases are produced from FeAl using the self-propagating high-temperature synthesis process, which is reinforced with inclusions from other intermetallic phases, which prevent cracks from spreading. In addition, layers are deposited by means of thermal spraying, which are analyzed with regard to their composition and structure. Paper includes a German-language abstract.

Abstract In this paper, a novel coated wire is developed for the production of a layer of iron aluminide/WC intermetallic matrix composite material (IMC) with the thermal spraying process. The microstructure and phases of the layer are examined with an energy dispersive analysis, an X-ray phase analysis, a scanning electron microscope, and an image analysis. The results show that the main phase of the coated wire-sprayed iron-aluminum layer consists of iron aluminide and the reinforcement phase consists of approx. 20% WC, W2C, and alpha-aluminum oxide. The erosion-corrosion behavior of the iron aluminide/WC-IMC layer is determined at different particle beam angles and temperatures and is compared with that of AISI 1018 steel. The iron aluminide/ WC-IMC layer showed a higher erosion-corrosion resistance at high temperatures than the steel AISI 1018. The erosion-corrosion mechanism of the iron aluminide/WC-IMC layer at high temperatures is discussed. Paper includes a German-language abstract.

Abstract Thick thermal spray coatings are used to repair worn parts during aircraft overhaul. The thermal spray coating is used to restore a part to its original dimensions. Characteristics of the as-applied coating that affect the performance of thermal sprayed parts are the residual stress in the coating, the tensile bond strength, the amount of porosity, oxides and impurities near the coating/substrate interface, and the hardness of the coating. An understanding of the relation of these coating characteristics to process variables such as the material used for the coating, spray process, spray angle, and thickness of the applied material is needed. In this paper, four thermal spray coatings, Ni5Al, Ni5Al-atomized, (NiCr)6Al, and Inco 718, on a substrate of Hastelloy X are investigated. These materials are applied using two different thermal spray application processes: plasma spray and High Velocity Oxy-Fuel (HVOF). Spray angles of 90° and 45° are used during spraying. The nominal thickness of the applied coatings ranges from 0.4 mm to 1.8 mm. The thermal spray coatings are evaluated in four types of tests. Residual stresses in the coatings and substrate are evaluated using the modified layer removal method. A tensile bond strength test is performed. Metallographic examination is used to determine the porosity and content of oxides and bond zone impurities (percent) of the applied materials. In addition, the hardness of the coating is measured. For the materials and conditions investigated, it is found that residual stress varies with each of the four process parameters. The bond strength for plasma sprayed coatings is related to the type of material and possibly to the coating thickness. The percent porosity varies with coating material, but, for Ni5Al, it does not depend on application process. Oxide content, as a percentage, varies with material and process, but not with spray angle and thickness. The percentage of impurities near the coating/substrate interface varies with process and, for the specimens that were coated using the HVOF process, with thickness. The hardness of the coating was found to vary with material and spray process. For three of the four coatings, hardness increases with thickness but, for Inco 718, hardness decreases as thickness increases.

Abstract Properties of thermally sprayed coatings, including residual stress, are controlled by various parameters of the spraying process. This study is focused on three thermal spraying techniques with significantly different particle temperatures and velocities. These are plasma spraying, twin wire arc spraying and high velocity oxy-fuel spraying. For each method, in-flight particle diagnostics was performed. Through-thickness residual stress profiles in Ni+5%A1 coatings on steel substrates were determined nondestructively by neutron diffraction. The stresses range from high tensile in the plasma sprayed coating to compressive in the HVOF one. Various stress generation mechanisms, including splat quenching, peening, and thermal mismatch, are discussed with respect to process parameters and material properties.

Abstract 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.

Abstract In many industrial processes, metallic materials are subjected to high temperature corrosion and aggressive forms of erosion. Such conditions occur especially in thermal energy advanced systems using tube bundles of fluidised bed boilers. For these types of plants, availability and low costs determine the choice of materials and in most cases this choice is not optimised for middle or long-term behaviour. Moreover, few data exist to estimate material lifetime under such aggressive conditions. Such is the case for low carbon steel grades which constitute the basic materials for these plants. New FeAl intermetallic alloys have been developed in the framework of a European collaboration, and it has been seen that these materials have good corrosion and erosion resistance properties at high temperature. Heat exchanger tubes in low carbon steel have been coated by thermal-spray then tested in a new industrial plant burning a very poor fuel (coal residues). After 5000 hours of operation in a rich erosive high temperature environment (850-900°C), no significant wear was observed on coated tubes whereas the other tubes, without protection, showed an appreciable diameter reduction.

Abstract This paper presents a novel process that uses RF plasma spraying and premixed elemental powders to produce intermetallic matrix composites in situ without having to add reinforcement fibers or particles. Splats were collected on a stainless steel substrate and were analyzed to determine if nitrides had formed in metal droplets during flight and how it affected splat morphology. The typical splat morphology of impinged Ti droplets is disk-type with an outer peripheral fringe. Aluminum splats, on the other hand, are classified into two categories: a disk-type with an irregular outer periphery and a semi-massive-type. Other composites produced and examined include TiAl, AlN, and Ti2AlN.

Abstract Current HVOF systems available on the world market are relatively complicated to operate and expensive. At the Bauman State Technical University in Moscow (BMSTU) a new portable HVOF spraying and cutting system MiniJet-30 has been developed. This rugged system offers the ease of operation of conventional gas welding equipment and produces high quality HVOF coatings. In this paper, the results of numerical simulation calculations of supersonic gas/powder flows, with and without a particle mask, are presented and compared with experimental outcomes. Additionally, typical HVOF coatings were sprayed and evaluated for bond strength, porosity, microhardness, abrasive wear, and phase composition (OM, XRD). The results are compared to those of other HVOF systems. Lastly, the cutting efficiencies for stainless steel, cast iron, and non-ferrous metals are discussed.

Abstract 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.

Abstract Magnesium alloys are widely used as lightweight metals in cars and trucks, but they require special surface treatments to offset corrosion and wear limitations. One such treatment, electron beam remelting, is the focus of this present work. As described in the paper, copper and nickel powders were plasma sprayed onto magnesium in a vacuum chamber, then heated to melting temperatures with a swept electron beam. Copper and nickel were chosen because they form hard intermetallic compounds when melted with magnesium. The structure and properties of the remelted Cu- or Ni-alloyed surface layer were found to be dependent on the properties of the plasma sprayed coating and the parameters of the e-beam treatment. In the course of the investigation, the coatings were assessed based on their microstructure, the thickness of the remelting zone, occurring phases, and the determination of hardness and abrasive wear resistance.