Fe Al Intermetallic Coatings Research Articles

Improvement of Microstructure and Sliding Wear Property of Cold-Sprayed FeAl Intermetallic Compound Coating by Annealing Treatment

Nanograin Fe(Al) solid solution alloy coating was firstly produced through cold-spraying technology using mechanically alloyed powder. Then, the above-mentioned coating was annealed at different temperatures to explore its influence on the phase constitution, microstructure, microhardness and dry sliding wear property of the coatings. Results exhibited that an FeAl phase appeared in the coatings after 500 °C treatment and remained stable with increasing annealing temperature. The annealing temperature had a considerable effect on the microstructure, microhardness and wear behavior of the FeAl coating. The existing laminated structure in the as-sprayed coating gradually faded away with increasing temperature and finally obtained a dense coating microstructure with no particle interface when annealed above 950 °C. Nanograin began to evidently grow at temperatures over 800 °C. The microhardness of the FeAl coating stayed at 400 Hv0.1 at temperatures below 800 °C, then it quickly dropped to 300 Hv0.1 at 950 °C and remained nearly unchangeable up to 1100 °C. The dry sliding wear mechanism of the FeAl coating annealed at low temperatures below 700 °C was mainly delamination of the oxide layer and showed a high wear rate within the order of magnitude range of 10−4, whereas FeAl coatings annealed at high temperatures above 950 °C were worn by microploughing and little oxidation and exhibited very low wear rates within the order of magnitude range of 10−6.

Microstructure and properties of in situ synthesized Fe-Al coating by laser cladding

To improve the hardness and wear resistance of an aluminum alloy, Fe-Al intermetallic coatings are synthesized in situ on the surface of aluminum alloys by laser cladding. An x-ray diffractometer (XRD) and a scanning electron microscope are used to characterize the phase and microstructure of the coating. The corrosion resistance, wear resistance, and hardness of the coating were measured by an electrochemical workstation, a reciprocating friction and wear tester, and a Vickers hardness tester, respectively. There are no pores but some microcracks in the coating. The coating structure is composed of a dendrite crystal, a columnar crystal, and an equiaxed crystal. The XRD results show that the Fe-Al coating is mainly composed of body-centered cubic solid solution, FeAl phase, and Fe3Al phase. At the same time, the average hardness of the coating reaches 601.54 Hv0.2, which is approximately 5.9 times that of the substrate (101.8 Hv0.2). Compared with the substrate, the self-corrosion voltage of the coating in 3.5% NaCl solution increased by 0.41 V, the self-corrosion current reaches 1.65 × 10−5 A, and the protection rate increased by 71%.

Influence of gas detonation spraying parameters on the geometrical structure of Fe-Al intermetallic protective coatings

The paper presents the results of an investigation and analysis of the geometrical structure of Fe-Al intermetallic protective coatings sprayed under specified gun detonation spraying (GDS) conditions. As GDS variable parameters there were applied two different barrel lengths and two powder injection position (PIP) at the moment of spark detonation as well as two different number of GDS shots with 6.66 Hz frequency.
 The measurements of the surface's profile were carried out through means of contact profilometry, in which case TOPO-01 system and Mitutoyo SJ 210 profilometer were applied. On the basis of the measurements conducted the analysis of in two-dimensional (2D) and spatial (3D) systems was made possible. The authors assumed that roughness can be considered as a non-stationary parameter of variance of surface amplitude, which is highly dependent on the sampling rate and length of an elementary segments. Therefore, the changes in the amplitude parameters and functional properties of the surface at different lengths of measuring segments (ln), respectively: 1.25, 4 and 12.5 mm, were analyzed. In the analysis of the degree of development of the geometric structure of the surface, the RMS (Root Mean Square) fractal method was used, with an assessment of the geometric structure of the surface stretched over several size levels, taking into account the correlation between the roughness parameter Rq, the measuring length (ln) and the fractal dimension (D). The application of the RMS method with the determination of the fractal dimension (D) allowed for the characterization of the geometric structure of intermetallic Fe-Al protective coatings detonation sprayed under specific conditions of the GDS process - based on the surface roughness profiles of different measured length (ln).
 Research undertaken within the framework of project No. 2015/19 / B / ST8 / 02000 subsidized by the National Science Center of Poland.

Dry Sliding Wear Behavior and Mechanism of a Hot-Dip Aluminized Steel as a Function of Sliding Velocity

Fe-Al intermetallic coatings were prepared on AISI 1045 steel by hot-dip aluminizing and subsequent high-temperature diffusion. The dry sliding wear tests were performed for the aluminized steel with various substrate hardnesses in the velocity range of 0.75-4 m/s on a pin-on-disk configuration. The dry sliding wear behavior and mechanisms of the aluminized steel under various velocities were explored. It was found that the wear rate decreased substantially with an increase in sliding velocity from 0.75 to 1.5 and then slightly varied in the velocity range of 1.5-4 m/s. The wear behavior and mechanisms of the aluminized steel were noticed to be closely related with tribo-layers. As tribo-layers contained more oxides with Fe2O3, the wear resistance of the aluminized steel was markedly improved because of their protective function. The substrate hardness also changed the wear behavior of the aluminized steel by affecting the stability of tribo-layers because the substrate hardness was inversely proportional to the thermal stability of the substrate structure. Under a low velocity of 0.75 m/s, adhesive wear and abrasive wear prevailed owing to the metal-on-metal contact, resulting in a higher wear rate. At 1.5-4 m/s, mild oxidative wear prevailed due to the stable existence of tribo-oxides layers. However, at 1.5 and 4 m/s for the substrate hardness of 45 HRC, the wear rate was slightly increased because the protection of tribo-layers was weakened by a double-layered structure or more cracks in tribo-layers and coatings.

Influence of Ni and Cr on the high-temperature wear resistance of FeNiCrAl coatings

Abstract To reduce the brittleness of Fe-Al intermetallic compound coatings, FeNiCrAl powder wire for high-speed electric arc spraying is developed by integrating Ni and Cr into an Fe-Al intermetallic compound. The corresponding FeNiCrAl coating is prepared via high-speed electric arc spraying technology. A 3Cr13 coating is selected as the material for comparison, and the friction and wear properties of the two coatings are investigated from 200 °C to 800 °C. The friction coefficient variations and friction surface topography patterns of the two coatings are analyzed via X-ray diffractometry (XRD), hardness testing, and scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS). The phase compositions of the materials on the wear surfaces are analyzed via X-ray photoelectron energy spectrometry (XPS). The results show that after the friction coefficient of the FeNiCrAl coating reaches its peak value at 400 °C, it declines with increasing temperature, and its wear volume is less than that of the 3Cr13 coating. An XPS-based wear surface composition analysis and SEM wear scar topography results show that the FeNiCrAl coating produces not only Fe, Ni and Cr oxides but also Ni-Al intermetallic compounds during high-temperature friction. After the friction coefficient of the FeNiCrAl coating reaches its peak at 800 °C, more Al2O3 is formed around the Fe3Al, and these compounds aggregate to form a protective film that effectively prevents further intrusion of O ions. A dense oxide layer covers the wear surface, and the formation of hard-phase chemical compounds improves the wear resistance and bearing capability of the coating.

Artificial neural network-based prediction technique for coating thickness in Fe-Al coatings fabricated by mechanical milling

ABSTRACTThe objective of this study was to evaluate the effect of milling time, milling speed and particle size of initial powders on the coating thickness of Fe-Al intermetallic coating by using artificial neural network (ANN). Coating morphology and cross-section microstructures were evaluated using a scanning electron microscope (SEM). It was found that an increase in the milling time provided an increase in the coating-layer thickness due to the cold welding process between particles and the steel substrate. The microstructure of the coating surface was refined by ball impacts in the milling process. As a result of this study, the ANN was found to be successful for predicting the coating thickness of Fe-Al intermetallic coatings. The correlation between the predicted values and the experimental data of the feed-forward back-propagation ANN was quite adequate. The mean absolute percentage error (MAPE) for the predicted values didn’t exceed 7.46%. The ANN model can be used for predicting the coating thickness of Fe-Al intermetallic coating produced for different milling time, milling speed and particle size.

Fabrication of FeAl(Cu) intermetallic coatings by plasma spraying of vacuum annealed powders

50Al-25Cu-25Fe (at.%) powders were milled for 0.5 h and subsequently annealed at 600, 750 and 900 °C for 0.5 h in a vacuum furnace. X-ray diffractometery (XRD) results revealed that FeAl(Cu) phase and unreacted Fe were seen after annealing at 600 and 750 °C while at 900 °C only FeAl(Cu) was formed. FeAl(Cu) powders were consolidated using air plasma spraying (APS) process. With increase of plasma power, the porosity content of the coating decreased from 33 to 8%. The FeAl(Cu) phase was stable during spraying while small amount of oxides were also formed. The coatings showed microhardness up to 487 HV and fracture toughness up to 4 MPa m0.5. The corrosion rate of the coatings in 0.5 M H2SO4 solution was lower than that of binary Fe-Al coatings reported in the literature.

Wear Behavior and Mechanism of Fe-Al Intermetallic Coating Prepared by Hot-Dip Aluminizing and Diffusion

A Fe-Al intermetallic compound coating was prepared on AISI H13 steel by hot-dip aluminizing and subsequent high-temperature diffusion. Dry sliding wear tests of the Fe-Al intermetallic coating were performed at 298 K to 873 K (25 °C to 600 °C). The wear behavior of the Fe-Al intermetallic coating was noticed to vary markedly with the temperature and load. At 298 K (25 °C), the wear rate rapidly increased with an increase of the load. As the temperature was elevated, the wear rate dramatically decreased except for the cases under 300 N at 473 K and 673 K (200 °C and 400 °C). The Fe-Al intermetallic coating possessed an excellent elevated-temperature wear performance, especially at 673 K to 873 K (400 °C to 600 °C), but worse room-temperature one, which were noticed to be attributed to the existence and inexistence of thin tribo-oxide layers, respectively. Such a thin tribo-oxide layer was considered to provide a protection for the intermetallic compound. When the tribo-oxide layer did not form at room temperature or the formed one was massively delaminated above the critical load at elevated temperatures, Fe-Al intermetallic coating possessed poor wear resistance.

Microstructure and properties of Fe–Al intermetallic coatings on the low carbon steel synthesized by mechanical alloying

Fe–Al coating was obtained on low carbon steel substrates using mechanical alloying and subsequent heat treatment. Light optical microscopy and a scanning electron microscope equipped with energy dispersive spectroscopy were used to conduct the microstructure characterization. Mechanical properties of the coatings were evaluated by microhardness measurements and wear tests. The corrosion behavior was determined by potentiodynamic polarization measurements in 3.5 % NaCl solution. The results of the mechanical and corrosion tests showed that the hardness and wear resistance of the coatings decreased with increasing the milling time, while increase in the milling time resulted in a significant increase in the thickness, porosity level, and corrosion resistance.

Nanocomposite Fe-Al Intermetallic Coating Obtained by Gas Detonation Spraying of Milled Self-Decomposing Powder

The nanocomposite structure of Fe-Al intermetallic coating, created in situ during gas detonation spraying (GDS) of as-milled self-decomposing powder and containing disordered 8 nm FeAl nanocrystals, was analyzed using scanning electron microscopy (SEM) with energy-dispersive x-ray (EDX) spectroscopy, transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and x-ray diffraction methods. It is found that the Fe-Al coating is characterized by a sublayer morphology consisting of flattened and partially melted splats containing a wide Al range from about 26 to 52 at.%, as well as Al2O3 oxides, created in situ at the internal interfaces of splats during the GDS process. The complex oxide films, identified as amorphous Al2O3, which are formed in the nanocrystalline Fe-Al matrix of the GDS coating behave like a composite reinforcement in the intermetallic Fe-Al coating. The combined presence of nanosized subgrains in the Fe-Al matrix and the Al2O3 nanoceramic dispersoids significantly increases the microhardness of the coating.

Corrosion Performance of Fe-Al Intermetallic Coatings in 1.0 M NaOH Solution

Corrosion Performance of Fe-Al Intermetallic Coatings in 1.0 M NaOH Solution

Microstructure and Mechanical Properties of FeAl Coating Deposited by Low Pressure Plasma Spray

The FeAl intermetallic compound coatings were deposited by low pressure plasma spray, air plasma spray and high velocity oxy-fuel spray. The influence of three kinds of thermal spraying processes on the microstructure, microhardness, elastic modulus and fracture toughness of coatings was investigated. The results show that the FeAl coating deposited by low pressure plasma spray presents special mechanical properties such as higher microhardness and elastic modulus as well as lower fracture toughness, when compared with those by atmospheric plasma spray or high velocity oxy-fuel spray.

Oxidation Control of Atmospheric Plasma Sprayed FeAl Intermetallic Coatings Using Dry-Ice Blasting

The performance of atmospheric plasma sprayed FeAl coatings has been remarkably limited because of oxidation and phase transformation during the high-temperature process of preparation. In the present work, FeAl intermetallic coatings were prepared by atmospheric plasma spraying combined with dry-ice blasting. The microstructure, oxidation, porosity, and surface roughness of FeAl intermetallic coatings were investigated. The results show that a denser FeAl coating with a lower content of oxide and lower degree of phase transformation can be achieved because of the cryogenic, the cleaning, and the mechanical effects of dry-ice blasting. The surface roughness value decreased, and the adhesive strength of FeAl coating increased after the application of dry-ice blasting during the atmospheric plasma spraying process. Moreover, the microhardness of the FeAl coating increased by 72%, due to the lower porosity and higher dislocation density.

Effect of annealing on the microstructure and erosion performance of cold-sprayed FeAl intermetallic coatings

FeAl intermetallic coatings were prepared by cold spraying of mechanically alloyed metastable Fe(Al) powder assisted with post-spray annealing treatment. The microstructure evolution and erosion performance of the coatings annealed at different temperatures were investigated and the erosion mechanism of the intermetallic coatings was examined through the surface morphology and cross-sectional microstructure of the eroded coatings. After annealing at 650 °C, the heterogeneous feature in the as-sprayed coating was evidently modified. With annealing temperature rising to 950 °C and 1100 °C, the interfaces between the particles in the coating completely disappeared. The erosion rate of the coating at the erosion angles of both 30 o and 90 o decreased with the increase in the annealing temperature. It was found that the erosion resistance of the intermetallic coating annealed at 1100 °C was three times higher than that of the as-sprayed coating. The weight loss of the as-sprayed coating with low cohesion at erosion angle of 90° was attributed to particle spalling off. The weight loss of the annealed intermetallic coatings with enhanced cohesion was attributed to microcutting and ploughing of erosive particles.

Detonation Deposited Fe-Al Coatings Part II: Transmission Electron Microscopy of Interlayers and Fe-Al Intermetallic Coating Detonation Sprayed onto the 045 Steel Substrate

Detonation Deposited Fe-Al Coatings Part II: Transmission Electron Microscopy of Interlayers and Fe-Al Intermetallic Coating Detonation Sprayed onto the 045 Steel Substrate The microstructure of detonation gaseous sprayed (DGS) transition layers of Ni(Al), Ni(Cr) and subsequent coating of Fe-Al intermetallic phases deposited on the 045 steel were studied in the paper using transmission electron microscopy. In order to identify phases in the particular interlayers the selected area electron diffraction (SAED) and an energy dispersive X-ray microanalysis (EDX) were applied. It was found that the Ni(Al) interlayer contained basically pure nickel with a small fraction of NiAl phase. The Al based amorphous phase was also observed its area in the form of bands. The Ni(Cr) interlayer basically contained Ni-rich small grains. Pure chromium in the Ni matrix appeared in the vicinity of Fe-Al coating in the shape of bow-like bands, parallel to the coating. The boundary between the Ni(Cr) layer and the Fe-Al coating revealed abrupt decrease of the Ni content in the coating at simultaneous rapid increase of the Fe amount. Improper Al/Cr ratio within the Ni matrix seems to be responsible for the formation of Al-oxides and the bands of almost pure Cr and Ni(Cr) layers and resulting decrease of interlayer adherence.

Characterization of High-Temperature Abrasive Wear of Cold-Sprayed FeAl Intermetallic Compound Coating

FeAl intermetallic compound coating was prepared by cold spraying using 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 FeAl coating 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. It was observed that the abrasive wear weight loss of FeAl coating was proportional to wear cycles in terms of sample revolutions at the tested temperatures. It was found that with the increase of the test temperature higher than 400 °C, the wear rate of cold-sprayed FeAl coating decreased with the increase of test temperature, while the wear rate of the heat-resistant steel increased significantly. The results indicate that the high-temperature abrasive wear resistance of the cold-sprayed FeAl intermetallic coating increased with the increase of the wear temperature in a temperature range from 400 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.

A facile route to produce Fe–Al intermetallic coatings by laser surface alloying

This work studies the feasibility of obtaining iron aluminide coatings on pure iron substrate by means of laser surface alloying (LSA). Pure Al was plasma spray coated on pure Fe substrate and subsequently laser alloyed by using multi mode continuous wave Nd-YAG laser at different output power and scanning rates. The aluminum content of the alloyed layer shows gradual change from surface to the inside of substrate. Detailed optical, SEM–EDX and XRD investigations were performed to characterize the phases formed during laser alloying. At 300 W laser output power, Al rich intermetallic phases mainly FeAl3, Fe2Al5 had formed with scanning rate in the range of 100–400 mm/min. However, at high power outputs (500 W) Fe–Al intermetallic phase had formed, which was found to have sound and crack free interface with the substrate.

Fatigue properties of Fe–Al intermetallic coatings prepared by plasma spraying

In this research, FeAl based coatings were deposited on low carbon steel using two different plasma spraying technologies – gas stabilized plasma gun (GSP) and water stabilized plasma gun (WSP) – resulting in different deposition conditions. Significant changes in local chemical composition compared to feedstock material were observed due to uneven evaporation of Fe and Al from the molten material during the interaction of feedstock with plasma. Influence of coatings on substrate fatigue properties was characterized at room temperature using special testing device “SF-Test”. Fatigue lifetimes of specimens with different coatings were compared with those of uncoated specimens. Fractographic analysis of failed specimens revealed that substrate fatigue cracks initiated at coating–substrate interface and grew by striation mechanism. The coatings failed due to intrasplat cracking and intersplat decohesion.

Microstructure characterization of D-gun sprayed Fe–Al intermetallic coatings

Intermetallic Fe–Al type coatings about 100 μm thick were deposited on a plain carbon steel substrate by D-gun spraying technique. The 40–75 μm size fraction of the feedstock powder was obtained by self-propagating high-temperature synthesis and sieved prior to D-gun spraying. This powder contained a mixture of Fe–Al type intermetallic phases conventionally appointed Fe x Al y . The Fe–Al coatings were analysed by transmission electron microscopy, selected area electron diffraction, and semi-quantitative energy-dispersive X-ray analysis in micro-areas. Particular attention was paid to the substructure of the individual grains in the coating zone abutting the steel substrate. The Fe–Al coatings have a multi-layer composite structure. The results explain the formation mechanism of the coating microstructure. The powder particles, which were heterogeneous in chemical composition and structure, were heated, highly softened or even partially melted and oxidised while flying from the gun barrel to the substrate. After impacting the substrate or previously deposited material and being shot peened by the following powder particles, they were rapidly cooled and plastically deformed, creating overlapping splats. In the zone adjacent to the substrate, alternating FeAl and Fe 2Al 5 intermetallic phases formed columnar crystals. The columnar crystal areas were separated by elongated amorphous oxide layers. Areas of mixed equiaxed subgrains of FeAl and Fe 3Al phases, fine grains of Fe-rich Fe(Al) solid solution, and micro- and nano-pores were also present.

Influence of Detonation Gun Spraying Conditions on the Quality of Fe-Al Intermetallic Protective Coatings in the Presence of NiAl and NiCr Interlayers

The paper presents results of detailed research of the application of detonation gun (D-gun) spraying process for deposition of Fe-Al intermetallic coatings in the presence of NiAl and NiCr interlayers. A number of D-gun experiments have been carried out with significant changes in spraying parameters which define the process energy levels (changes in volumes of the working and fuel gases, and the distance and frequency of spraying). These changes directly influenced the quality of the coatings. The initial results underlay the choice of the process parameters with the view to obtain the most advantageous of geometric and physical-mechanical properties of the coating material, interlayer and substrate. The metallurgical quality of the coatings was considered by taking into account grain morphology, the inhomogeneity of chemical content and phase structure, the cohesive porosity in the coating volume, and adhesive porosity in the substrate/interlayer/coating boundaries. The surface roughness level was also considered. It was found that the D-gun sprayed coatings are in all cases built with flat lamellar splats. The splats develop from powder particles which are D-gun transformed in their plasticity and geometry. A significant result of the optimization of D-gun spraying parameters is the lack of signs of melting of the material (even in microareas) while the geometry of the subsequently deposited grains is considerably changed and the adhesivity and cohesion of the layers proves to be high. This is considered as an undeniable proof of high plasticity of the D-gun formed Fe-Al intermetallic coating.