High entropy alloys, as a novel alloy system, demonstrated excellent mechanical performance. However, despite its excellent mechanical performance, the strength-ductility trade-off effect still limit its performance. In recent decades, it has been found that heterogenous or gradient microstructure can efficiently solve the conflict. Cold spray is a promising method to create heterogenous microstructure with high efficiency and low cost. In this work, equiatomic FeCoNiCrMn HEA was deposited by cold spray and the microstructure was systematically investigated by transmission electron microscopy (TEM) and transmission Kikuchi diffraction (TKD). In cold spray, a gradient microstructure was formed and segregated Ni and Mn in starting particle were also redistributed. Moreover, twinning in ultra-fine nanograins were detected in the region close to the impact interface. Compared with severe deformation of other low SFE metals, for FeCoNiCrMn HEA, twinning in nanograins also highly related to the grain size.

The paper reports the results of structure examination of intermetallic Fe-Al type coatings obtained by the detonation gun spraying on a C45 plain carbon steel substrate. The structure was analysed with scanning (SEM), transmission (TEM) electron microscopy techniques and electron (SAE) and X-ray diffraction methods as well as quantitative inspection of composition in microareas (EDX). Special attention was paid to the interface between the coating and the substrate analyzing particularly the substructure of the individual grains contained up to 15μm away from the substrate surface layer. The results allowed explaining the formation mechanism of the coating morphology with a contribution of intermetallic phases Fe 3 Al, FeAl, FeAl 2 and Fe 2 Al 5 as well as the ε phase taking into consideration the influence of velocity, temperature and pressure on the powder particles during the D-gun spraying. It was established that the coating produced with the DGS method had sublayer morphology of alternate flattened and partially melted grains with wide range of Al content from 39 up to 63 at.%. Partial melting of the individual powder particles brought about the appearance of the amorphous grains and subsequently columnar crystals of the Fe-Al type phases formed sequentially at the interface area coating and cold substrate surface layer material, which was essential in the mechanism of the Fe- Al coating formation. It was established, that in the area of the polycrystalline dispersive structure formed from the highly plasticized FeAl grains during D-gun spraying, complex oxide films identified as Al 2 O 3 -γ formed, serving as specific composite reinforcement in the intermetallic Fe-Al coating. A mechanism of crystallization of partially melted Fe-Al particle containing nominally 63 at.% Al was carried out in the work in an attempt to explain the formation of different sub-layers within the Fe-Al intermetallic coating at the interface 045 steel surface layer.

The dynamic properties and thermal history of FeAl particles were estimated and assessed in this study. First, parameters of the detonation process for the investigated mixture were calculated using a thermochemical code. Next, the motion parameters and thermal history of the analyzed powder particles were assessed using computational fluid dynamics software and algorithms developed by the investigators. The appropriate models allowed for determination of melted volume (mass) fraction of a certain analyzed single particles that have diameters ranging from 10 to 160 μm. The results show that only the smallest particles melt under the investigated conditions. Moreover, the estimated radial distribution of the temperature inside the particles is almost homogeneous due to the relatively high FeAl thermal conductivity and relatively low thermal conductance of surface heat transfer. The calculated particle terminal velocity was compared to experimental data and to data from previous studies in the literature to determine the accordance of results among the data sets.

This study evaluates the effects of heat treating on the microstructure, phase composition, and friction and wear behavior of plasma sprayed FeAl coatings. Fe-40Al feedstock powder was deposited on mild steel substrates by atmospheric plasma spraying and the coatings were vacuum annealed at 500, 650, 900, and 1000 °C. An examination of coating cross-sections revealed the presence of diffusion layers in the samples treated at 900 and 1000 °C. XRD analysis indicates that annealing at 650°C facilitates the transformation of Fe(Al) solid solution into FeAl intermetallic phase, resulting in an increase in coating hardness. At higher temperatures, however, Al depletion occurs along with a reduction in hardness. Tribological testing showed that both the friction coefficient and the effects of wear increased after heat treatment.

The aim of this work is to determine whether local disordering plays a role in the bonding of FeAl intermetallic coatings produced by cold spraying. XRD analysis of the powder and coatings revealed superlattice peaks, indicative of an ordered intermetallic structure. Nevertheless, locally disordered structures were detected in the deposits by TEM imaging. This may be related to a deformation induced order-to-disorder transformation due to the high strains involved in cold spraying, which is supported by comparing the magnetic properties of the deposits with those of HVOF sprayed coatings produced using disordered ball-milled feedstock.

In this study, plain carbon steel wire and pure iron powder are deposited on grit-blasted Fe-Si alloy substrates using thermal (electric arc, plasma, and HVOF) and kinetic spraying techniques. The coatings obtained were then heat treated. Coating microstructures and mechanical properties were investigated and compared focusing on oxidation, delamination, and Si dilution from the substrate to the coating.

In this study, ceramic-matrix composites consisting of elongated metal (CoNbZr) particles in a cordierite (MgAlSiO) matrix were produced by plasma spraying. The metal powder was injected into the plasma jet downstream of the ceramic powder to minimize metal decomposition and oxidation. The microstructure and composition of cermet coatings containing 5, 10, and 20 vol% metal were analyzed by SEM and XRD and their electromagnetic properties were evaluated via saturation magnetization, permittivity, and permeability measurements. As expected, flake-shaped metallic particles were obtained and all coatings exhibited soft ferromagnetic behavior.

With the purpose of elaborating high-quality FeAl coatings, a so-called very low pressure reactive plasma spray technique that combines VLPPS and SHS processes was used in the present study. A dense and homogeneous FeAl coating was thus successfully in situ synthesized by reactive plasma spraying of an Al/Fe 2 O 3 composite powder under 1 mbar. The phase composition and microstructural features of the coating were characterized by XRD and SEM. Results indicated that the B2 ordered FeAl phase was synthesized, and the coating featured a dense and defect-free microstructure. The fracture mechanism of the coating remains mainly a brittle failure but the appearance of some dimples in local zones suggests some unexpected toughness.

In the present study, a nanostructured FeAl coating was prepared by cold spraying of ball milled powder. Annealing treatment was applied to the coating to investigate its effect on the phase structure, grain size and microhardness of the cold-sprayed nanostructured FeAl coating. The results showed that the FeAl phase was kept unchangeable when the coating annealed at the temperature above 500°C. Annealing temperature significantly influenced the microstructure and microhardness of cold-sprayed FeAl coating. With raising annealing temperature, the lamellar structure in the as-sprayed coating disappeared and a dense coating microstructure with fully bonding of deposited particles at their interfaces was achieved after annealing at 950°C. Nanograin growth of the FeAl phase occurred at an annealing temperature higher than 800°C. The microhardness of cold-sprayed FeAl coating remained about 400 Hv 0.1 at the annealing temperature below 800°C and decreased to 300 Hv 0.1 at 1100°C.

The FeAl intermetallic compound offers a combination of attractive properties such as thermal barrier, good strength at intermediate temperatures and an excellent corrosion resistance at elevated temperatures under oxidizing, carburizing and sulfidizing atmospheres. So they have attracted considerable attention as potential candidates for structural and coatings applications at elevated temperatures. However, the application of these intermetallics has been limited due to lack of deposition techniques and their low ductility at room temperature. To overcome the drawbacks we apply Low Pressure Cold Spray (LPCS) with following sintering for improving coating ductility and structure. The aim of this paper is to present the first results of FeAl intermetallic compound synthesis with this technique. A CS deposit is built up by the successive impact of individual powder particles that are the ‘‘building blocks’’ of the deposit. Sintering is applied to utilize reactions between the particles and obtain complex intermetallic compound. The microstructures and properties of the coatings were characterized by SEM, EDX and thermal diffusivity tests to define the structure formation mechanisms.

The FeAl intermetallic compound coatings were sprayed by low pressure plasma spraying (LPPS), air plasma spraying (APS) and high velocity oxy-fuel spraying (HVOF). The influence of three kinds of thermal spraying processes on the microstructure, microhardness, elastic modulus and fracture toughness of coatings were investigated. The results showed that the APS and HVOF coatings exhibited similar microhardness, about 540HV 0.3 , which is much lower than that of LPPS coatings, 860HV 0.3 . The elastic modulus measured for APS, HVOF and LPPS coatings using Knoop indentation were 96, 84, 176GPa, respectively. The APS coatings were also observed to have lower elastic modulus values in the in-plane direction than those in the perpendicular direction, as a result of microcracks scattered within the coatings. In fracture toughness tests, the LPPS coatings revealed the lowest fracture toughness, as compared with other two spraying processes, indicating low porosity and crack levels are related to low fracture toughness. From these results, it appeared that potential improvements to certain mechanical properties can be achieved using low pressure plasma spraying process.

FeAl intermetallics matrix composites reinforced by ceramics particles such as titanium carbide have attracted much attention in recent years. In this study, shrouded plasma spraying with nitrogen as a protective gas was employed to deposit TiC particles dispersed FeAl/TiC composite coatings. Fe-35Al powder and Fe-35Al/TiC composite powders containing 35 vol.% and 45 vol.% TiC prepared by mechanical alloying were used as feedstock powders. The microstructure of the ball-milled powders and the as-sprayed coatings was characterized by scanning electron microscopy and X-ray diffraction. The mean coefficient of thermal expansion (CTE) of FeAl and FeAl/TiC was measured. The results showed that dense FeAl and FeAl/TiC coatings with low oxide inclusions were deposited by shrouded plasma spraying. The mean CTEs calculated based on the Reuss formula are reasonably consistent with those measured in the present study. As a result, the CTE of FeAl-based composite coating can be properly controlled by adjusting TiC content in the composite coating to match with that of the substrate.

As compared to thermal spray techniques, cold spraying allows to retain metastable phases of the feedstock material like amorphous structures, due to lower process gas temperatures. Compared to crystalline metals, metallic glasses are brittle at ambient temperature but viscous at higher temperatures. Therefore, cold spray parameters must be optimized for conditions that allow softening of the amorphous spray material for successfully producing coatings. For this study, a FeCoCrMoBC metallic glass was used that in comparison to others offers advantages with respect to higher hardness, less costly feedstock powder and minimum reactivity with the environment. Necessary impact conditions were investigated to meet the window of deposition. According to calculations and cold spray experiments, neither the glass transition temperature Tg nor the melting temperature Tm can describe required conditions for bonding. Thus, a so called softening temperature between the glass temperature and the melting temperature had to be defined to calculate the critical velocity of metallic glasses. With respect to the bonding mechanism, impact morphologies could prove that a transition to viscous flow gets more prominent for harsher spray conditions. By sufficiently exceeding critical condition for bonding, coatings with rather dense microstructures can be processed at deposition efficiencies of about 70 %. The coatings have a hardness of 1100 HV 0.3, but the results also demonstrate that further work is still needed to explore the full potential for bulk metallic glasses.

FeAl intermetallic compound coating was prepared by cold spraying a mechanically alloyed Fe(Al) alloy powder followed by post-spray annealing at 950°C. The high-temperature abrasive wear test was carried out for the annealed cold-sprayed FeAl at a temperature range from room temperature to 800°C. The high temperature abrasive wear of a heat-resistant stainless steel 2520 was performed for comparison. The results showed that the annealing treatment of the as-sprayed Fe(Al) alloy coating at a temperature of 950°C results in the formation of dense FeAl intermetallic compound coating with no particle boundaries. It was found that with the increase of the test temperature the wear rate of the stainless steel increased at the temperature higher than 400°C, while the wear rate of cold sprayed FeAl coating tended to decrease at the temperature higher than 400°C. The high temperature abrasive wear resistance of the cold-sprayed FeAl intermetallic compound coating increased with the increase of the abrasive wear temperature in a temperature range from 400°C to 600°C and changed little in the temperature range from 600°C up to 800°C. The wear resistance of cold-sprayed FeAl coating was higher than that of heat-resistant 2520 stainless steel under 800°C by a factor of 3.

The cold gas dynamic spray process, or cold spraying (CS), represents a radical departure from conventional thermal spray (TS) methods in that the deposition process relies purely on kinetic energy rather than on a combination of thermal and kinetic components. A potential advantage of this process over TS is the ability to generate dense coatings retaining initial material chemistry and phase composition with a very little oxidation. Also, low temperature process (no bulk particle melting) eliminates solidification stresses and enables thicker coatings. However, hard brittle materials like ceramics can not be sprayed without using ductile binders. In this study, magnetic alloys such as FeSiBNbCu also called Finemet and FeSiBNbCu-Al with various percentages of Aluminum coatings were synthesized using cold spray technique in order to produce ferromagnetic materials. Ultra-fine grain coatings were obtained using FINEMET nanostructured powders mixed with Aluminum as ductile binder in order to improve adherence. Magnetic measurements revealed a soft magnetic character for all the powders and the coatings. 25% of Al was considered as ideal to produce a homogenous coating with suitable magnetic properties.

Intermetallic materials have excellent high temperature oxidation resistance and erosion, cavitation resistances and are promising coating materials with many potential industrial applications. In this study, the formation of Fe-Al intermetallic compound-based coating was performed by cold spraying assisted by a post-annealing treatment. Fe-Al alloy composite powder containing 20wt% WC-Co was produced by ball milling process. Nano-structured Fe-Al alloy coating was deposited through cold spraying. The coating was annealed at different temperatures. The microstructure of the coating was characterized by scanning electron microscopy, optical microscopy and x-ray diffraction analysis. It was found that the microstructure of the as-sprayed coating depended significantly on the microstructure of the powder. A Fe-Al intermetallic phase was formed during the annealing at a temperature higher than 500°C. Moreover, grain growth occurred with the increase of the annealing temperature. The results showed that the microhardness of the as-sprayed coating reached 600HV and more. The effect of the annealing treatment on the coating microstructure and hardness was examined.

Fe-Al based composite coatings were deposited on Grade 20 steel substrates by High Velocity Arc Spraying (HVAS) technology. Hot salt corrosion properties of the coatings were studied at the temperatures of 450 °C,650 °C and 800 °C . Results showed that the corrosion resistance of the Fe- Al/Cr 3 C 2 composite coatings changed little with the increase of temperature, contrasted to the substrate and Fe-Al coatings. The excellent corrosion resistance of the Fe-Al/Cr 3 C 2 composite coatings was attributed to the oxidation of the iron, aluminum and chromium to form protective scales. In hot salt, there are mainly iron oxides at the outer corrosion surface; aluminum and chromium oxides are found at the inner corrosion surface, which can effectively protect the Fe- Al/Cr 3 C 2 composite coatings from corrosion.

The microstructure and sliding wear behavior from room temperature up to 650°C of Fe-Al intermetallic coating produced by cored wire and high velocity arc spraying (HVAS) have been investigated. X-ray diffraction (XRD), energy dispersion spectroscope (EDS), optical microscopy (OM) and scanning electron microscopy (SEM) were used to analyze the microstructure and sliding friction and wear mechanism of the coatings. Chemical analysis of the coating indicated the composition to be Fe-20.0Al-14.1O (at.%). The microstructure was found to consist of Fe 3 Al, FeAl and α-Fe regions mainly, together with fine oxide (Al 2 O 3 ) layers and a little Al. The results of sliding wear indicated that the Fe-Al coating exhibited low friction coefficient and low wear rate at elevated temperatures. The reason of the friction coefficient decreasing at elevated temperatures is that protective oxide film formed on the worn surface during sliding wear process. And delamination is the predominant wear mechanism of the coatings. The Fe 3 Al and FeAl intermetallics which have higher strength and hardness at elevated temperatures can effectively resist crack initiation, propagation and splat fracture, thus resulting in excellent high temperature wear resistance of the Fe-Al coating.

In this investigation, binary FeAl layers are produced by detonation spraying and examined by means of microscopy and X-ray diffractometry. The examinations show that the layers have a lamellar structure consisting of FeAl and Fe 4 Al 13 phases with a small amount of alumina. It is observed that with increasing amounts of fuel gas and decreasing detonation frequency, the proportion of FeAl phases decreases and variations in microhardness throughout the coating become irregular. Paper includes a German-language abstract.

A continuous galvanizing line (CGL) has a zinc pot, which is filled with molten zinc for zinc coating. In a zinc pot there are pot rolls to guide steel strip. Usually WC-Co thermal sprayed coatings are used for protection of the pot rolls from severe corrosion by molten zinc. Authors analyzed WC-Co coatings used in a zinc pot of a CGL for 33 and 56 days. On the surface of a WC-Co coated roll, many kinds of deposits were observed including top dross, Fe2Al5 inter-metallic compound, which might induce dross defect on the surface of galvanized steel. Diffusion depth of zinc into the WC-Co coating used for 33 days was only within 10µm but some areas were severely attacked along cracks within the coating layer. Usually molten zinc contains small amount of aluminum about 0.12 - 0.2%. Through SEM study, we observed that not only zinc but also aluminum diffused into the WC-Co coating after service in the zinc pot for 56 days. Al-Fe rich layers were observed on the surface of the spray coating for some cases. The phase of those layers might be Fe2Al5 since their chemical compositions are similar to Fe2Al5 top dross.