A wide range of properties can be achieved in intermetallic coatings applied by gas detonation spraying (GDS). The properties of Fe-40at%Al GDS layers, however, may change when exposed to temperatures exceeding a threshold level. To characterize such changes, Fe-40at%Al GDS coatings were subjected to systematic dilatometric studies in which temperatures were cycled from room temperature to 1180 °C. The investigation revealed both irreversible and reversible phase transitions as described in the paper. Dilatometry measurements obtained from sintered samples made from the same powder are presented for comparison.

The main goal of the combined Cold Spray – Sintering technology development is to obtain high density ductile Fe- Al intermetallics based thermal barrier coatings as an alternative to conventional ZrO 2 coatings widely applied in industry. The task of this paper is to examine the structural changes of cold sprayed Al-AISI 316L composite coatings due to synthesis of Fe-Al intermetallics during annealing and find the conditions of high density composite formation. A dense Fe/Al intermetallic-Al composite coating is obtained. Three factors are found to play the main role in the structure formation of dense Fe-Al intermetallic composite coating: i) layered structure, ii) particle size and thickness of Fe and Al layers, iii) annealing temperature.

Protective coatings with high wear, erosion and corrosion resistance are of great importance in many fields of application and in particular, in the electric power generation sector. In this paper, the HP-HVOF (high-pressure high velocity oxy-fuel) technique is used to produce dense rapidly quenched metal-ceramic nanocomposite protective coatings. The powders for the thermal spray process are produced by high energy ball milling using mechanochemical displacement reactions to synthesize ceramic components in-situ at the nanometric scale. Boron nitride solid lubricant is used as a source of nitrogen and boron to precipitate nitride and boride phases in a corrosion resistant iron aluminide metal matrix. The formation of the hard phases during milling and/or thermal treatments is investigated using various analytical methods. The tribological properties of the coatings with and without ceramic additives are reported.

This study evaluates the effect of annealing on the microstructure, hardness, and wear resistance of FeAl-WC coatings obtained by cold spraying. As-sprayed deposits exhibited a dense microstructure with uniformly dispersed WC particles in the iron matrix. The Fe(Al) solid solution was transformed to an FeAl intermetallic compound at around 650 °C. Further increases in temperature were found to improve the composite microstructure with a slight decrease in microhardness. Wear resistance peaked at 750 °C, and at 950 °C, a diffusion layer appeared at the bottom of the coating close to the substrate.

This paper presents the results of metallographic investigations of electric arc sprayed composite coatings for the manufacture or refurbishment of bearing components. The materials studied include iron aluminide and aluminum bronze, and their interface microstructure was examined by optical and environmental scanning electron microscopy (ESEM).

Thick Fe-Al deposits were produced by low-pressure cold spraying using heated air as the working gas. The coatings were isothermally annealed for two hours in Ar at temperatures from 250 °C to 750 °C. Changes in fracture behavior and microhardness were evaluated along with the microstructure and composition of newly formed phases. The results show that the evolution of intermetallic phases was driven by diffusion at temperatures above 550 °C. The new phases formed a hard skeleton that preserved the general shape of the samples during treatment despite the growth of external dimensions and porosity.

This study investigates the impact behavior and consequences for coating formation in cold spraying of FeAl intermetallic compound powder. A range of spraying conditions was used to process single impacts in so-called wipe tests and for processing spray layers. In order to avoid brittle failure, high process gas temperatures and varied traverse speeds were used to account for thermal softening of spray particles and already adhering layers. Morphologies of as-impacted particles and partially removed single splats were subsequently investigated by SEM. The study of spray lines indicates that secondary impacts are only successful within an extremely narrow range of impact conditions. Within this narrow parameter regime, thicker and dense coatings are obtained. Hardness testing shows that the properties of the powders were retained.

This study deals with two new material deposition processes in which raw materials are in the form of a thixotropic slurry. In one case, the slurry (Al 2 O 3 nanoparticles in an acrylic resin) is misted into an arc plasma jet and sprayed on a stainless steel substrate. By varying the volume content of nanoparticles and slurry supply rates, investigators were able to achieve uniform droplets, resulting in fine Al2O3 layers free of microcracks and pores. In the other process evaluated, pure aluminum particles were dispersed in a photosensitive resin, producing a slurry that was spread on stainless steel substrates then patterned with a UV laser. The patterned metal particles were heat treated, creating iron-aluminide intermetallic phases through reaction diffusions. The microstructure and composition of the patterned lines are analyzed by SEM and XRD and surface stress distributions associated with a Hilbert fractal pattern are simulated via finite element analysis.

In the present study, Fe-Al 2 O 3 -FeAl 2 O 4 and FeAl coatings were synthesized in situ by reactive plasma spraying of Al-Fe 2 O 3 composite powder under atmosphere and low-pressure conditions. Coating microstructure and phase composition are examined and coating formation mechanisms are discussed. It was found that FeAl 2 O 4 hercynite phase is always synthesized as an intermediate product under low oxygen partial pressure conditions. In the APS process, such a phase can be retained in the final coating by extremely fast cooling. It can also be continuously reduced to FeAl by deoxidation in an oxygen-free H/H 2 atmosphere.

In this work, Fe-40Al coatings are produced by atmospheric plasma spraying using a nanostructured feedstock exhibiting a very low degree of order. The as-sprayed deposits consist of fundamental FeAl phases, Fe3Al phases, and oxides and are found to be ferromagnetic due to the low degree of order and the presence of unmelted nanoparticles retained from the feedstock. The magnetic properties of the coatings are shown to be heterogeneous in the parallel and vertical direction.

The aim of this work is to fabricate a particle-reinforced FeAl composite coating by cold spraying. Fe, Al, and WC powders were placed in a ball mill and mechanically alloyed for up to 36 h in order to obtain a nanostructured Fe(Al) solid solution reinforced with a high volume fraction of WC particles. The powder was examined and then cold sprayed on stainless steel substrates using N 2 as the accelerating gas. The as-sprayed deposits exhibited rough surface morphology and dense cross-sectional microstructure with dual-scale WC dispersoids distributed uniformly in the Fe(Al) matrix. The coatings were annealed at 650 °C and subsequently reexamined. In-situ phase transformation from the solid solution to an intermetallic compound occurred after the post-spray treatment along with an improvement in microstructure.

Atmospheric plasma spray is considered as one of the most efficient methods for forming FeAl intermetallic coatings. But the performance of plasma-sprayed FeAl coatings was remarkably limited because of oxidation and phase transformation during the preparation. In the present work, FeAl intermetallic coatings were prepared by atmospheric plasma spray combined with dry-ice blasting. The microstructure, oxidation and porosity of FeAl intermetallic coatings were investigated. In addition, XRD measurements were also employed to illustrate the lattice-scale performance, e.g., dislocation density. The temperatures during plasma spray were also measured using an infrared pyrometer system. The results show that a denser B2-FeAl coating with a lower content of oxide and lower phase transformation can be achieved because of the cryogenic effect and the mechanical effect of dry-ice blasting. Moreover, the microhardness of FeAl coating was nearly increased by 72%, due to the lower porosity and higher dislocation density.

Solid-particle erosion of metals and alloys at elevated temperatures is one of the main reasons of the damage of components used in the energy production and utilization industries. Application of protective coating systems can be an attractive and economically reasonable solution for preventing the failure and increasing the durability of the components working in severe conditions of high-temperature corrosion and erosion. However, thermal spraying of intermetallic materials that have excellent high-temperature corrosion resistance is limited because of their low ductility. Present work reports the results of the investigation of abrasion wear resistance at elevated temperatures of combined coatings, which include the intermetallic layer. Such iron aluminide layers have been formed as a result of diffusion during the heat post-treatment of arc-prayed metallic coatings combining Fe- and Al-based layers. Post-treatment of arc-sprayed coatings was carried out by means of infrared radiation and induction heating. It was shown that the abrasion resistance of the developed coating tested at elevated temperatures (T > 500 °C) is considerably higher than that of low-alloyed steel and some nickel-based alloys and depends on the test load condition. The high performance of intermetallic-based graded coatings at elevated temperatures makes them interesting for applications as a low-cost erosion-corrosion-resistant material.

The aim of this work is to analyze the morphology and composition of iron-aluminide (FeAl) powders produced by liquid metal atomization using a de Laval nozzle. The variables studied are atomization gas pressure and melt nozzle diameter. Different sized powders were characterized via SEM, XRD, and EDS analysis and were found to be similar in composition and shape (spherical) regardless of their size. The paper provides a detailed description of how the powders were produced, classified, and tested, and presents and interprets the results.

Iron aluminides have been lately proposed as promising materials for wear applications. Many authors have focused their investigations on the friction behaviour of FeAl coatings emphasizing the role of this intermetallic as a new matrix to embed ceramic particles and replace for high temperature the extensively studied WC-Co cermet system. However, few works deal with the evaluation of the different tribological properties and their relationship with the coating microstructure. Thus, in the present study, the near stoichometric Fe40Al was successfully sprayed by means of HVOF using different spraying parameters and the tribological behaviour was assessed through solid particle erosion, abrasive and dry sliding tests. The wear mechanisms that took place in the produced coatings are discussed with regard to the obtained results. The friction coefficient versus sliding distance was obtained. In addition, isothermally treated samples in air were tested showing both lower friction coefficient and lower wear rate.

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.

This study examines the oxidation performance of two different iron aluminide coatings obtained by means of High Velocity Oxygen Fuel spraying starting from the same feedstock powder but using propylene and hydrogen as fuels. The isothermal oxidation tests were carried out at 900°C for 4, 36 and 72 hours. After detailed observation a more rapid oxide scale growth is obtained for that coating obtained under hydrogen conditions. It leads to the assertion that propylene-coatings would perform better under high temperature environments.

Coatings of Metal-Matrix-Composite (MMC) with enhanced wear resistance were created by thermal spraying. The used powders composed of iron and nickel aluminides reinforced with alumina, Cr- and Ti-carbides were produced before by self-propagating high temperature synthesis (SHS). The fused and crushed composite powders were sprayed by atmosphere plasma spraying (APS) and gas detonation spraying (D-Gun). Spray powder and coating properties like morphology, structure, microhardness, porosity, bond strength, wear and corrosion resistance are examined using optical and scanning electron microscopy, XRD analysis, pin-on-disc (wear resistance). The produced MMC coatings are compared to commercially used wear resistant coatings, e.g. high velocity oxyfuel flame sprayed Cr 3 C 2 -NiCr. The properties of a special coating type depend on the used spraying method. Plasma sprayed MMCs show a slightly higher porosity than D-Gun sprayed coatings. The chemical composition of used powders has a big influence on the coating properties. Fe- and Ni-aluminide matrix coatings reinforced additionally with carbides, especially Cr 3 C 2 , show a better wear resistance compared to coatings containing just oxides as hard material.

Iron aluminides show great potential for use in high-temperature oxygen and sulfur environments, but the intermetallic phases of the Fe-Al system tend to be brittle. This paper describes a powder making process in which FeAl phases are reinforced with inclusions from other intermetallic phases that arrest cracks and prevent them from spreading. Thermally sprayed coatings produced from these SHS powders are analyzed with regard to their composition and structure. Paper includes a German-language abstract.

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.