Aluminide Layer Research Articles

LOW TEMPERATURE ALUMINIZATION EFFECT ON MONEL 400 ALLOY PRODUCED BY PACK CEMENTATION METHOD

In this study, aluminum coating process was performed on Monel 400 alloy at a temperature of 600°C using the low-temperature pack cementation method for durations of 2, 4, and 6 hours. The mixture for the coating consisted of metallic Al powder as the aluminum source, Al2O3 as the inert filler, and Ammonium Chloride (NH4Cl) as the activator. The formed coatings were characterized using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analyses to examine their microstructures, and phase analyses were conducted using and X-Ray Difraction Analyses (XRD). SEM analysis revealed that the coating layers were homogeneous, compact, and pore-free, demonstrating a strong bond between the coating and the matrix. The thickness of the coating layer was measured from the surface to the matrix, and it was observed to vary between 4 µm and 10 µm. It was determined that 600°C was sufficient for the accumulation of an aluminide layer and a successful coating layer was obtained. The hardness values of the alumina layer formed on the surface were measured, and an increase in hardness values was observed with increasing process duration and temperature.

Influence of pre-aluminizing on elemental diffusion behavior and fracture mechanism of thermal barrier coatings

The development of high-performance aero-engines raises the urgent requirement of coatings deposited on blades, containing both thermal barrier coatings (TBCs) on the external surface and aluminide coatings in the internal winding cooling channels. A TBC system with a low activity aluminizing process before deposition of conventional TBC was developed here to evaluate the feasibility of co-deposition technology. The thermal cyclic oxidation behavior of co-deposited “Al-modified TBC” was examined at 1100 °C and compared to that of conventional TBC. The cross-sectional microstructure evolution and elemental diffusion behavior of the modified TBC were also investigated. Even though the underlying aluminizing layer can serve abundant Al for the upper NiCoCrAlYHf layer to eliminate “Al depletion” in conventional TBC, which is a main reason for spallation, the Al-modified TBC system exhibited shorter thermal cycling life than conventional TBC. The spallation mechanism was discussed. Cracks caused by the fast growth rate of thermally grown oxide (TGO), Cr-rich precipitates resulted from the decreased γ/γ′-phase in the coating, and Re-rich precipitates originated from outward diffusion through the aluminide layer were mainly responsible for the failure.

Underlying mechanisms of enhanced plasticity in Ti/Al laminates at elevated temperatures: A molecular dynamics study

The Ti/Al laminated metal components have attracted considerable attention due to their impressive strength and lightweight properties, positioning them as promising materials for aerospace and automotive applications. Although experimental evidence has highlighted their exceptional elongation and formability at elevated temperatures, there is still limited understanding of the underlying atomic-level mechanisms governing high-temperature plastic deformation, particularly with regards to the titanium aluminide (TiAl3) layer. This study utilized molecular dynamics (MD) simulations to investigate the tensile deformation of Ti/Al laminates, emphasizing the effects of temperature and TiAl3 layer thickness on atomic structural evolutions and mechanical properties. The MD simulations confirmed the decreases in the elastic modulus and peak stress at elevated temperatures, consistent with the experimental findings. The total dislocation length displayed an increasing trend with temperature, reaching a maximum at 600 K, before decreasing at 900 K due to amorphization. Moreover, the coordinated deformation among the Ti, Al and TiAl3 layers at elevated temperatures contributed to enhanced plasticity of the Ti/Al laminates. Furthermore, the TiAl3 layer thickness positively influenced the total dislocation length. However, increasing the layer thickness also leads to more high-strain bands in the TiAl3 layer, resulting in crack nucleation and decreased ductility of the Ti/Al laminate. This study provides valuable insights into the plastic deformation of Ti/Al laminates at elevated temperatures from the molecular dynamics perspective, benefitting further improvement in their plastic forming technique and engineering applications.

High performance aluminized Monel coatings with prolonged corrosion resistance in saline environment

This study compares the corrosion resistance of as-sprayed and aluminized Monel 400 coatings annealed at 900 °C, and deposited on sand-blasted stainless steel. The coatings were immersed in 3.5 wt % NaCl solutions and analyzed using electrochemical impedance spectroscopy and cyclic Potentiodynamic polarization techniques for up to 100 days. Microstructural analysis showed decreased porosity as well as oxide and aluminide layer formation in annealed Monel 400 coatings. Formation of aluminides enhances the Vicker's hardness up to 4 times as compared to as-sprayed coatings. The results showed that the annealed coatings, particularly the aluminide coatings, exhibited higher corrosion resistance than the as-sprayed coatings. Additionally, the corrosion rate decreased exponentially, and the polarization resistance increased significantly as the immersion time increased. This study provides insights into cost-effective Ni-based coatings for corrosion resistance applications.

Performance Evaluation of Modified Kinetics, Deep Neural Network, and Adaptive Neuro-fuzzy Inference System (ANFIS) for Predicting Aluminide Layer Thickness on Deep-Rolled AISI 304 Stainless Steel

Performance Evaluation of Modified Kinetics, Deep Neural Network, and Adaptive Neuro-fuzzy Inference System (ANFIS) for Predicting Aluminide Layer Thickness on Deep-Rolled AISI 304 Stainless Steel

Preparation of CoCrFeMnNi-based high-entropy/aluminide laminated composites: Multielement interdiffusion reactions

CoCrFeMnNi-based high-entropy/aluminide laminate (HAL) composites were produced following the hot pressing diffusion sintering method. The microstructure of the samples was analyzed using the SEM, EDS, and EBSD techniques, and the results revealed that the diffusion reaction phases of the HAL composite consisted of a four-layer aluminide structure based on the Al13(Cr, Mn, Fe, Co, Ni)4 phase. The diffusion behavior of iron dominated the resulting phase, leading to the formation of Fe-Al compounds. Under the influence of the hysteresis diffusion effect of high entropy alloys, Al13(Cr, Mn, Fe, Co, Ni)4 phase layers (ASL I–III) with different grain sizes and growth orientations are formed due to the difference of diffusion rates at different interfaces. At the front end of the diffusion reaction, the aggregation layer of the secondary phase Al9(Fe, Co, Ni)2 appears due to the segregation of Co and Ni elements. The growth kinetics model of HAL composites was explored, and it was observed that a mixture diffusion type controlled the growth of the aluminide layer via ‘grain boundary and lattice diffusion’. The mechanical properties and failure modes of the HAL composites were investigated through quasi-static and dynamic mechanical tests. The fracture toughness reached 25 MPa·m1/2, and the main energy dissipation modes were the deformation of the ductile layer and the fracture of the hard, brittle layer. The dynamic impact failure modes were primarily deformation and 45% adiabatic shear bands, and the impact strength and energy consumption reached up to 1800 MPa and 2260 J/mm3. HAL composites with high alumina content exhibited prominent crack propagation and fragmentation properties under high-speed impact. The stress wave was significantly attenuated in the crushed aluminide layer, which significantly improved the energy absorption effect of aluminide.

„Above the Pack” Diffusion Aluminizing of Turbine Compressor Blades made of EI867 in the Aerospace Industry

In the publication, tests were conducted on compressor turbine working blades made of EI-867 material, in accordance with the TU 14-1-402-72 standard, which were subjected to the gas non-contact aluminizing process. Metallographic analyses of the produced aluminide layer were undertaken, and the phase components of the aluminide layer microstructure were identified. This identification was achieved by analyzing the chemical composition in micro-areas using the EDS attachment in a scanning electron microscope and using X-ray diffraction. Additionally, hardness and creep resistance tests of the blades, after undergoing solution and aging processes, were performed over different durations. The research was aimed at exploring the feasibility of the aluminizing process using the "above the pack" method on parts made of EI-867 material and understanding the process's impact on the creep resistance of the part. Experimental research have shown that aluminizing turbine blades with EI-867 using the "above the pack" method to obtain a layer thickness in the range of 0.03-0.06 mm is possible within 10 hours at 950ºC. Aluminizing with the analyzed method results in the formation of an aluminized layer with a three-phase structure that ensures the appropriate strength of the coating. However, it has been shown that the aluminizing process using the "above the pack" method with the applied time of 10 hours causes a significant reduction in the creep resistance of the material. Based on the obtained results, it was shown that the non-contact aluminizing method for turbine blades made of EI 867 material does not meet aviation requirements for safe operation due to a significant reduction in mechanical properties.

ENHANCEMENT OF MARINE CORROSION AND TRIBOCORROSION RESISTANCE OF OFFSHORE MOORING CHAIN STEEL BY ALUMINIZING PROCESS

The safety of mooring systems and accessories is one of the most critical issues in the structural integrity of floating oil/gas and renewable offshore structures. Mooring chains and accessories operate under dynamic conditions in harsh marine environments. They are subject to severe wear and corrosion between their links due to relative movement from waves, wind, and ocean currents that disrupt structural integrity. To cope with this problem, the pack-aluminizing process was applied on the R4 grade offshore mooring chain steel for 2 h at 850 °C to improve corrosion and wear-corrosion (tribocorrosion) resistance in 3.5% NaCl. The tribocorrosion behaviour of untreated and aluminized samples was investigated by a tribo-electrochemical setup that simultaneously allows for collecting the wear and corrosion data. Potentiodynamic and potentiostatic corrosion and tribocorrosion tests were carried out to understand corrosion kinetics. Optical, SEM, XRD and EDS analyses were performed to characterize the aluminide layer and surface morphologies before and after tribocorrosion investigations. In polarization scans under corrosion and tribocorrosion conditions, the current showed a significant activation stretch of several orders of magnitude, with minor potential changes in the anodic region. Due to the galvanic effects of sliding under natural electrochemical conditions, the untreated R4 alloy exhibited cathodic properties in the wear track, while the aluminium coating was out of the wear track due to its oxide-forming ability. At the cathodic potential, two hard Al2O3 materials under pure mechanical effects and third bodies emerging from cracks on the coating surface increase the friction coefficient (COF), while the oxide product film, which has a lubricating ability and pits which reduces the contact area, caused a decrease in COF at the high anodic potential. The study revealed that while the aluminide layer improved the corrosion and tribological character of R4 alloy, material loss from wear track increased due to micro fractures and cracks in the coating layer during sliding tribocorrosion conditions.

Linear growth of reaction layer during in-situ TEM annealing of thin film Al/Ni diffusion couples

During reactive layer growth in binary diffusion couples new phases can nucleate and grow. In the present work we perform in- and ex-situ interdiffusion studies in the system Ni-Al using X-ray diffraction (XRD) and analytical transmission electron microscopy (TEM). We investigate the reaction between 270 °C and 500 °C. We show that in the early stages of the solid-state reaction a small polycrystalline aluminide layer forms, while preferential grain growth follows in the later stage. In the reaction layer we detect the presence of Al3Ni by XRD and electron diffraction. Local chemical analysis by EDX in the TEM suggests that a second aluminide phase forms simultaneously. An in-situ TEM study at 380 °C shows layer growth of about 0.042 nm/s with a linear time dependence. We interpret this rate law on the basis of an interface-controlled reaction and discuss our results in the light of what is known about layer growth in thin film diffusion couples (presence/absence of predicted phases, linear/parabolic rate laws) and in view of results from the Ni-Al system published in the literature. Areas in need of further work are identified.

Hot dip aluminization of 304L SS and P91 ferritic-martensitic steel – Comparison of interface morphology and growth kinetics of reaction zones

P91 ferritic/martensitic and AISI 304L austenitic stainless steels were hot dip aluminized (HDA) in 99.9% pure aluminum in a pit type vertical furnace at three different temperatures i.e. 750, 800 and 850 °C for 1 to 10 min. Evolution of interface morphology, type and distribution of phases and growth kinetics of the reaction zones were studied using a variety of experimental techniques. Though similar intermetallic compounds formed in both steels, their distribution, morphology and growth kinetics were distinctly different. In P91 F/M steel, aluminized surface adjacent to the substrate had wide Fe2Al5 layer with serrated morphology containing high volume fraction of 2–3 μm sized Cr rich intermetallic phases. Width of FeAl3 phase present adjacent to this layer did not show much variation with HDA conditions. Above FeAl3, on the surface, the pure Al top coat contained nonequilibrium phases. Compared to P91 steel, width of the aluminized layer in 304L SS was less (35 ± 5 μm vs 120 ± 15 μm at 800 °C-10 min) and the Fe2Al5 layer had a planar interface with the substrate. Optimum temperature-time combination to get thin, uniform, defect free surface aluminide layer in P91 F/M and 304L steels were found to be 750 °C-2 min and 800 °C-1 min respectively. Growth kinetics of surface aluminide layers in both steels were studied, kinetic parameters were determined and compared with information available in literature.

Increase in Oxidation Resistance of MAR M-509 via LA-CVD Aluminizing

Due to their excellent mechanical properties, Co-based alloys are one of the main candidates to replace Ni-based alloys in high temperature application. Knowledge about oxidation resistance of Co-based alloy MAR M-509 and the extent of its aluminizing on its oxidation resistance is limited. Therefore, in the present study, an aluminide layer was manufactured by low activity chemical vapor deposition (LA-CVD) on MAR M-509. Aluminized and uncoated alloys were investigated in terms of oxidation kinetics and oxidation resistance during isothermal and cyclic oxidation at 1000 and 1100 °C. Material in the as-cast and after exposure was analyzed using scanning electron microscopy (SEM), thermogravimetry (TG) and glow-discharge optical emission spectrometry (GD-OES). Obtained results allowed for elucidating of degradation mechanism including nitridation process of carbides for MAR M-509. It was found that aluminizing of MAR M-509 significantly decreases its oxidation kinetics by the factor of 2.5 and 1.5 at 1000 and 1100 °C respectively. Moreover, the suppression of identified degradation mechanism in case of aluminized alloy was found until occurrence of breakaway oxidation of the aluminide layer. It was also proposed that further increase in oxidation resistance can be successively achieved by an increase in aluminide layer thickness.

Nondestructive Methodology for Identification of Local Discontinuities in Aluminide Layer-Coated MAR 247 during Its Fatigue Performance.

In this paper, the fatigue performance of the aluminide layer-coated and as-received MAR 247 nickel superalloy with three different initial microstructures (fine grain, coarse grain and column-structured grain) was monitored using nondestructive, eddy current methods. The aluminide layers of 20 and 40 µm were obtained through the chemical vapor deposition (CVD) process in the hydrogen protective atmosphere for 8 and 12 h at the temperature of 1040 °C and internal pressure of 150 mbar. A microstructure of MAR 247 nickel superalloy and the coating were characterized using light optical microscopy (LOM), scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). It was found that fatigue performance was mainly driven by the initial microstructure of MAR 247 nickel superalloy and the thickness of the aluminide layer. Furthermore, the elaborated methodology allowed in situ eddy current measurements that enabled us to localize the area with potential crack initiation and its propagation during 60,000 loading cycles.

Low-temperature aluminizing influence on degradation of nimonic 80A surface: Microstructure, wear and high temperature oxidation behaviors

Nimonic 80A alloy has been subjected to aluminizing process to improve its high temperature oxidation and wear properties. Pack aluminizing process was carried out for 3 and 5 h at 650 and 700 °C temperatures without using a protective atmosphere. Aluminising treatment was carried out using metallic aluminium, ammonium chloride (NH4Cl) and alumina as a filler. The morphology and structure of aluminide layers was analysed by SEM-EDS. It was observed that there was a super bonding between matrix and coating layers which are smooth, dense and porosity free. Dominant phases of Ni2Al3 and Al80Cr20 were detected by XRD analysis. Layer thickness was measured from the surface to the matrix and changed from 20 to 70 μm which was increased with increasing process duration and temperature. The matrix hardness is 400 HVN while the hardness of coating layer raised to 1025 HVN with the process time and temperature. Wear losses decreased with the increase in coating temperature and time in both high temperature and room temperature tests. After isothermal oxidation tests at 1000 °C up to 75 h, all aluminized samples consist of alumina scale while Nimonic 80A consist of Cr2O3 and TiO2 mixed oxides with high thickness. The increased aluminizing temperature and time provide better protection against high temperature oxidation.

Aluminide Thermal Barrier Coating for High Temperature Performance of MAR 247 Nickel Based Superalloy

In this paper, mechanical properties of the as-received and aluminide layer coated MAR 247 nickel based superalloy were examined through creep and fatigue tests. The aluminide layer of 20 µm was obtained through the chemical vapor deposition (CVD) process in the hydrogen protective atmosphere for 8 h at the temperature of 1040 °C and internal pressure of 150 mbar. A microstructure of the layer was characterized using the scanning electron microscopy (SEM) and X-ray Energy Dispersive Spectroscopy (EDS). It was found that aluminide coating improve the high temperature fatigue performance of MAR247 nickel based superalloy at 900 °C significantly. The coated MAR 247 nickel based superalloy was characterized by the stress amplitude response ranging from 350 MPa to 520 MPa, which is twice as large as that for the uncoated alloy.

Development and characterization of an iron aluminide coating on mild steel substrate obtained by friction surfacing and heat treatment

Iron aluminides are intermetallic Fe–Al alloys known for their high temperature corrosion and oxidation resistance, which makes them candidate materials for high temperature applications. In the present work, the formation of an iron aluminide layer on a mild steel substrate by friction stir surfacing of aluminium alloy AA6351 followed by isothermal heat treatment is reported. After Al-alloy deposition, the samples were subjected to annealing at temperature of 500, 550, 600 and 650 °C for various times up to 120 h. Microstructure analyses conducted by XRD and SEM/EDS indicated the formation of a homogenous layer of Fe2Al5 with average hardness value of 1070 HV for a 72-h treatment at 650 °C. The electrochemical corrosion behaviour of the developed coatings was analysed, and it was possible to show that friction stir surfacing followed by heat treatment constitutes an effective processing route for obtaining iron aluminide coatings on conventional steel substrates.

High Temperature Corrosion Behaviour of Aluminide-Coated Cast Iron for an Exhaust Manifold Application

To reduce the pollution emission from vehicles, an improvement on the combustion process is expected, leading to increased exhaust gas temperature. As a result, the development of new materials for an exhaust manifold used at higher temperatures is required. A cost-effective cast iron exhaust manifold treated by aluminising pack cementation was developed in the present work to combat the high temperature corrosion. Its kinetics under cyclic oxidation in N2–12%O2–10%H2O at 850 °C was parabolic with the rate constant (kp) of 5.66 × 10−12 g2 cm–4 s–1, about two orders of magnitude lower than that of the bare cast iron, which indicated the protectiveness of the applied coating. These results relate to the protective alumina formation for the aluminised cast iron and the formation of the less protective iron oxides for the bare cast iron after oxidation, as evidenced by the XRD and Raman spectroscopy results. The addition of 10% water vapour to N2–12%O2 thickened the aluminide layer from 344 μm for the sample oxidised in dry atmosphere to 409 μm for the sample oxidised humidified one. It accelerated the oxidation rate of the aluminised cast iron as the kp value increased by 8.5 times, and also increased the hardness of the aluminised surface, as it was 364 HV for the sample exposed to dry atmosphere and 420 HV for the sample exposed to humidified one. The latter result implied the possibility of the hydrogen dissolution into the metal surface. The roles of hydroxyl ion and dissolved hydrogen on the oxidation and evolution of the aluminide layer after exposure to water vapour were proposed.

Electron Microscopy Characterization of the High Temperature Degradation of the Aluminide Layer on Turbine Blades Made of a Nickel Superalloy.

The effects of exposure to overheating (temperature above 1000 °C) on the degradation (modification) of layers of coatings (coatings based on aluminum) of uncooled polycrystalline rotor blades of aircraft turbine jet engines were investigated under laboratory conditions. In order to determine the nature of the changes as well as the structural changes in the various zones, a multi-factor analysis of the layers of the coating, including the observation of the surface of the blades, using, among others, electron microscopy, structural tests, surface morphology, and chemical composition testing, was carried out. As a result of the possibility of strengthening the physical foundations of the non-destructive testing of blades, the undertaken research mainly focused on the characteristics of the changes occurring in the outermost layers of the coatings. The obtained results indicate the structural degradation of the coatings, particularly the unfavorable changes, become visible after heating to 1050 °C. The main, strongly interacting, negative phenomena include pore formation, external diffusion of Fe and Cr to the surface, and the formation and subsequent thickening of Fe-Cr particles on the surface of the alumina layer.

Preparation of Cyclic Oxidation Resistant Coating Consisting of Ni Aluminide and Ni-Hf Alloy Layers on Ni-Cr-Al Alloy by Electrodeposition

Preparation of Cyclic Oxidation Resistant Coating Consisting of Ni Aluminide and Ni-Hf Alloy Layers on Ni-Cr-Al Alloy by Electrodeposition

Effect of Si addition on the microstructure and oxidation behaviour of formed aluminide coating on HH309 steel by cast-aluminizing

Cast-aluminizing (CA) of HH309 stainless steel by Al-alloy sheets containing various amounts of silicon was studied in this research. To do this, the Al-alloy sheets were inserted at the bottom of a copper mould. Then, molten HH309SS was cast into the mould. The heat transfer from the steel melt enabled the melting of Al-alloy and the high-temperature reactions with the substrate elements to result in the intermetallic compounds (IMCs) at the HH309/Al interface. FE-SEM and XRD results indicated that the (Fe,Cr,Ni)2Al5 and (Fe,Cr,Ni)Al3 phases were detectable when pure Al sheet was used. In contrast, when the sheet contained silicon, a new intermetallic layer Al7(Fe,Cr)2Si appeared at the interface. To create the aluminide coating on the cast-aluminized specimens, they were annealed at 1000 °C for 2h. The multilayer coating was formed by inter-diffusion between aluminum and substrate elements during the heat treatment. This multilayer coating included (Fe,Cr,Ni)2Al5 + (Fe,Cr,Ni)Al2, (Fe,Cr,Ni)Al and α-Fe,Cr,Ni(Al) sub-layers. To investigate the oxidation behaviour of the CA specimens with various Si contents, the isothermal oxidation tests were conducted at 1000 °C for 75 h. The oxidation rate constant, kp, was inversely proportional to the Si content in the aluminide layers. The kp values for CA samples with pure Al, 5, 8 and 12 wt% Si sheets were 1.5 × 10−11, 1.175 × 10−11, 6.39 × 10−12 and 4.36 × 10−12 g2 cm−4 s−1, respectively. The addition of Si significantly improved the high-temperature oxidation resistance of CA samples due to the formation of a combined Al2O3-SiO2 scale on the surface.

The Role of Substrate Surface Roughness on in-Pack Aluminization Kinetics of Ni-Base Superalloy

The Ni-base superalloys facing high temperature require further protection against high temperature oxidation. One of the most common methods providing high temperature oxidation resistance is the production of aluminide layers (NiAl-coatings). It is known that the thickness of produced diffusion layer can be controlled by the temperature and time of aluminization process. However, no research on the effect of surface roughness on aluminization kinetics was conducted so far. Then, to elucidate the effect of surface roughness on aluminization kinetics, diffusion layers were obtained by an in-pack aluminization method on the IN 617 alloy with differently prepared surfaces, namely polished, ground using 220 grit SiC paper and 80 grit SiC paper. The obtained results revealed that different surface preparation does not affect the chemical and phase composition of produced layers. However, a strong influence of surface preparation method on aluminide layers thicknesses was observed. Namely, it was found that the increase in substrate surface roughness results in an increase of aluminization kinetics. The dependence between surface roughness and thickness of aluminide layers was found to be logarithmic. Moreover, it was found that the aluminization kinetics is influenced, especially at early stages of the aluminization process.