Intermetallic Coatings Research Articles

Effect of the incorporating of refractory NbC precipitates in intermetallic iron-aluminide coatings on corrosion and high-temperature oxidation behavior

This study aims to investigate the effects of growing niobium carbide (NbC) particles into intermetallic iron-aluminide (FeAl) coatings on ductile cast iron (SGI) by thermo-reactive diffusion technique (TRD). The study compares the corrosion and oxidation behavior of the FeAl-NbC coatings with SGI, FeAl, and NbC coatings. Corrosion tests were conducted through polarization tests in a 3.5 wt% NaCl solution, while oxidation tests were performed at 900 °C for 4, 16, and 64 h. Before and after corrosion and oxidation tests, the coatings were examined using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The findings show that FeAl coatings with NbC particles had lower graphite nodules, porosity, and surface roughness values compared to FeAl coatings. FeAl-NbC composite coatings provided better corrosion and oxidation resistance compared to untreated SGI, FeAl, and NbC coatings. The results of the comparative analysis of FeAl-NbC, FeAl, NbC, and untreated SGI specimens indicate that corrosion resistance in a 3.5 wt% NaCl solution and oxidation resistance at 900 °C followed the order FeAl-NbC > FeAl > NbC > SGI.

Cermet Powders Based on TiAl Intermetallic for Thermal Spraying

The paper presents a study of the formation process of cermet powders based on TiAl intermetallic with the addition of non-metallic refractory compounds. Non-metallic refractory compounds B4C, BN, SiC, and Si3N4 were chosen as strengthening components, improving the mechanical properties and resistance to high-temperature oxidation of TiAl-type intermetallic coatings. The composition of the initial mixtures was selected based on thermodynamic analysis of the interaction between TiAl intermetallic and non-metallic refractory compounds. As a result of the mechanochemical synthesis of powder mixtures, 73TiAl-27B4C, 69TiAl-31BN, 88TiAl-12SiC, and 83TiAl-17Si3N4 (wt. %) cermet powders are formed, consisting of titanium aluminide (TiAl, Ti3Al) phases and refractory compounds of aluminium (AlB2 and AlN) and titanium (TiB2, TiC, TiN, Ti5Si3). The conglomeration technology of produced cermet powders has been developed to enhance fluidity. Using conglomerated powders will provide their constant feed to the high-temperature jet and the formation of dense coatings during thermal spraying.

Corrosion Resistance of Fe-Cr-Al Intermetallic Coatings Obtained by Aluminizing

The growing interest in intermetallic and metal–intermetallic materials and coatings is based on the number of favorable properties they possess, primarily mechanical. However, the lack of data on their corrosion resistance has largely limited their scope of application. In this study, the corrosion destruction mechanisms of coatings formed on substrates made of AISI 321 steel and Aluchrom W (fechralloy) were investigated. The coatings were created by alloying in an aluminum melt followed by diffusion annealing to form the ultimate intermetallic structure. Corrosion resistance was studied under cyclic exposure to a humid marine atmosphere simulator and potentiostatic tests in an aqueous NaCl solution. Corrosion destruction parameters were determined, and mechanisms for each type of coating were revealed. The conducted studies allowed us to determine the electrochemical parameters of the corrosion destruction process and its mechanisms. It was shown that the corrosion rates during potentiostating for coatings on substrates Cr15Al5 and 12Cr18Ni10Ti differed by almost twofold. Two different mechanisms of corrosion are proposed. The first is associated with the formation of Al2O3 and MgO oxide films, which at the initial stage protect only local areas of the coating surface on Cr15Al5. The second is determined by the diffusion of titanium atoms during annealing to the coating surface on a 12Cr18Ni10Ti steel substrate with the formation of TiC carbide at the grain boundaries.

INVESTIGATION OF CORROSION BEHAVIOR OF AISI 304 AND AISI 316L STAINLESS STEELS COATED WITH FeAL AND NiAL INTERMETALLICS USING ELECTRO-SPARK DEPOSITION METHOD

Due to their superior corrosion resistance at high temperatures, stainless steels have a wide range of applications in numerous industries (including chemistry, the petrochemical industry, the paper industry, and nuclear engineering), it is also utilized in the medical industry as an implant material. To enhance the outstanding qualities of stainless steel such as high temperature corrosion, surface coating methods are also used. Boronizing, nitriding, thermal spray coating, physical vapor deposition, chemical vapor deposition, and electro-spark deposition procedures are used to apply these coating processes to steel surfaces. The electro-spark deposition (ESD) coating technology is one of the most promising approaches in this area. Using high-frequency and high-current electric pulses, the ESD micro-welding procedure bonds electrode material to the surface of a metallic substrate. In this study, AISI 304 and AISI 316L stainless steels were coated with FeAl and NiAl intermetallics using the ESD method. First, suitable experimental parameters for ESD coating were established. Second, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the microstructures and phases that formed on the coated surfaces. Then, the surface hardness of the resulting layers was determined. Finally, the corrosion properties of intermetallic-coated stainless steels were determined using electrochemical methods and compared with each other. As a result, both the hardness values and corrosion resistances of both stainless steel sheets have increased with intermetallic coatings.

The Preparation and Properties of Ni2Al3 Intermetallic Compound Coating

In this work, a Ni2Al3 intermetallic compound coating was prepared on 45 # steel by combining methods of low-pressure cold spray and heat treatment. Firstly, powders mixed with Ni powders, Al powders, and Al2O3 powders as a mass ratio of 20:6:4 were sprayed on surface of 45 # steel by low-pressure cold spraying technology to prepare a Ni-Al pre-coating. Subsequently, the pre-coating was annealed at 570 °C in an argon atmosphere for 12 h to obtain the Ni2Al3 intermetallic compound coating. The composite coating was characterized using TEM, SEM, and XRD. High temperature oxidation performance of the composite coating was analyzed by isothermal oxidation tests conducted at 600 °C in air atmosphere for 96 h. The results show that the composite coating is composed of Ni2Al3 phase. Under a high-temperature oxidation environment, a protective oxide film composed by Al2O3 and NiO was formed on the coating surface, which resulting in a superior high-temperature oxidation resistance compared to 15CrMo heat-resistant steel. The mechanism of the Ni2Al3 coating resistance to high-temperature oxidation is that an oxide film mainly composed of Al2O3 and NiO formed on the surface during the high-temperature oxidation process; this oxide film can effectively resist oxidation and protect the substrate material from oxidation at a high temperature of 600 °C.

Perspectives on Developing Burn Resistant Titanium Based Coatings-An Opportunity for Cold Spraying.

Titanium alloys are crucial lightweight materials; however, they are susceptible to spontaneous combustion under high-temperature and high-pressure conditions, limiting their widespread use in aerospace engines. Improving the burn resistance of Ti alloys is essential for the structural safety and lightweight of aerospace equipment. Burn-resistant Ti alloys, such as Ti-V-Cr and Ti-Cu, however, face limitations such as high cost and low specific strength. Surface coatings provide a cost-effective solution while maintaining the high specific strength and good processability of the base material. Conventional surface treatments, such as laser cladding, result in defects and deformation of thin-walled parts. Cold spray technology offers a promising solution, as it uses kinetic energy to deposit coatings at low temperatures, avoiding defects and deformation. In this paper, we review the current research on burn-resistant surface technologies of Ti alloys and propose a new method of bimetallic coating by cold spraying and low-temperature heat treatment, which has the potential to solve the problem of spontaneous combustion of aerospace engine parts. The strategy presented can also guide the development of high-performance intermetallic compound-strengthened metal matrix composite coatings.

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.

Raman Spectroscopic Analysis of the Reaction between Al-Si Coatings and Steel.

Hot-stamped ultrahigh strength steel components are pivotal to automotive light-weighting. Steel blanks, often coated with an aluminum-silicon (Al-Si) layer to protect them from oxidation and decarburization, are austenitized within a furnace and then simultaneously quenched and formed into shape. The Al-Si coating melts within the furnace and reacts with iron from the steel to yield an intermetallic phase that provides some long-term corrosion protection. During the intermediate liquid phase, some of the coating may transfer to the furnace components, leading to maintenance costs and operational downtime. A detailed understanding of the coating transformation mechanism is needed to avoid such production issues while ensuring that final intermetallic coatings conform to specifications. We introduce cross-sectional Raman microscopic mapping as a method to rapidly elucidate the coating transformation mechanism. Raman spectroscopic fingerprints for relevant intermetallic compounds were determined using synthesized Al-Fe-Si ternary and Al-Fe binary compounds. These fingerprints were used to map the spatial distribution of intermetallic compounds through cross sections of Al-Si-coated 22MnB5 specimens that were heated at temperatures between 570 and 900 °C. These chemical maps show that the intermetallic fraction of the coating does not grow significantly until formation of η (Al5Fe2) at the steel interface, suggesting that η facilitates extraction of iron from the steel and subsequent diffusion through the coating. Under the heating conditions used here, a series of reactions ultimately lead to a silicon-rich τ2 (Al3FeSi) phase on top of the binary η phase. The technique presented here simplifies structural analysis of intermetallic compounds, which will facilitate prototyping of strategies to optimize hot stamping.

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%.

Fabrication of In Situ rGO Reinforced Ni-Al Intermetallic Composite Coatings by Low Pressure Cold Spraying with Desired High Temperature Wear Characteristics.

In this study, the surface of aluminum powder was uniformly coated with in situ reduced graphene oxide (r-GO) sheets (Al/r-GO). The Ni powder, Al2O3 powder, and Al/r-GO powders were mixed uniformly in a mass ratio of 20:6:4. In situ rGO-reinforced Ni-Al intermetallic composite coatings were successfully prepared using low-pressure cold spraying and subsequent heat treatment. The microstructure and phase of the composite coatings were characterized using X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The high-temperature wear test was conducted at 200 °C, 400 °C, and 600 °C to understand the mechanism. The results indicate that the in situ rGO-reinforced Ni-Al intermetallic composite coatings exhibit a 33.3% lower friction coefficient and 26% lower wear rate in comparison to pure Ni-Al intermetallic coatings, which could be attributed to the generation of an easy-shearing transferred film between the coating and grinding ball.

Investigation of Aluminized Intermetallic Coatings on Fe–Cr–Al System Alloy Corrosion Resistance

Investigation of Aluminized Intermetallic Coatings on Fe–Cr–Al System Alloy Corrosion Resistance

Effective time of a diffusion source in a pack cementation process on the AZ91D magnesium alloy

The powder thermal diffusion alloying method is an important method to fabricate intermetallic coatings on magnesium alloy substrates. The diffusion source, the diffusion time and the diffusion temperature are key parameters for a diffusion alloying process. While the effective time of an active diffusion source at the diffusion temperature is still unclear. Clarification of the effective time of a diffusion source is important, as the diffusion source could be utilized effectively and economically only if the effective time of the active diffusion source is known. Here, the effective time of a diffusion source at 400 °C was investigated. Results show that, the effective time of the diffusion source which contains 10 g ZnO and 1 g NH4Cl is around 150 h at 400 °C. For a more compact diffusion source, the effective time is relatively shorter. Then, chemical reactions in the diffusion source at elevated temperature were analyzed. The failure of the diffusion source is related to the reduction in the number of active metal ions, while an ineffective diffusion source can be reactivated by addition of new halide powder. These results could deepen the understanding of the role of the diffusion source in a powder thermal diffusion alloying process and indicate a limit under which the diffusion source could be utilized effectively.

Formation of a Ni3Al Intermetallic Coating by Cold Spray Deposition of a Ni–Al Powder Mixture Mechanically Processed in a Planetary Mill

Formation of a Ni3Al Intermetallic Coating by Cold Spray Deposition of a Ni–Al Powder Mixture Mechanically Processed in a Planetary Mill

Biocompatible Ti3Au–Ag/Cu thin film coatings with enhanced mechanical and antimicrobial functionality

BackgroundBiofilm formation on medical device surfaces is a persistent problem that shelters bacteria and encourages infections and implant rejection. One promising approach to tackle this problem is to coat the medical device with an antimicrobial material. In this work, for the first time, we impart antimicrobial functionality to Ti3Au intermetallic alloy thin film coatings, while maintaining their superior mechanical hardness and biocompatibility.MethodsA mosaic Ti sputtering target is developed to dope controlled amounts of antimicrobial elements of Ag and Cu into a Ti3Au coating matrix by precise control of individual target power levels. The resulting Ti3Au-Ag/Cu thin film coatings are then systematically characterised for their structural, chemical, morphological, mechanical, corrosion, biocompatibility-cytotoxicity and antimicrobial properties.ResultsX-ray diffraction patterns reveal the formation of a super hard β-Ti3Au phase, but the thin films undergo a transition in crystal orientation from (200) to (211) with increasing Ag concentration, whereas introduction of Cu brings no observable changes in crystal orientation. Scanning and transmission electron microscopy analysis show the polyhedral shape of the Ti3Au crystal but agglomeration of Ag particles between crystal grains begins at 1.2 at% Ag and develops into large granules with increasing Ag concentration up to 4.1 at%. The smallest doping concentration of 0.2 at% Ag raises the hardness of the thin film to 14.7 GPa, a 360% improvement compared to the ∼4 GPa hardness of the standard Ti6Al4V base alloy. On the other hand, addition of Cu brings a 315—330% improvement in mechanical hardness of films throughout the entire concentration range of 0.5—7.1 at%. The thin films also show good electrochemical corrosion resistance and a > tenfold reduction in wear rate compared to Ti6Al4V alloy. All thin film samples exhibit very safe cytotoxic profiles towards L929 mouse fibroblast cells when analysed with Alamar blue assay, with ion leaching concentrations lower than 0.2 ppm for Ag and 0.08 ppm for Cu and conductivity tests reveal the positive effect of increased conductivity on myogenic differentiation. Antimicrobial tests show a drastic reduction in microbial survival over a short test period of < 20 min for Ti3Au films doped with Ag or Cu concentrations as low as 0.2—0.5 at%.ConclusionTherefore, according to these results, this work presents a new antimicrobial Ti3Au-Ag/Cu coating material with excellent mechanical performance with the potential to develop wear resistant medical implant devices with resistance to biofilm formation and bacterial infection.Graphical

Formation and oxidation resistance of MoSi2 coating for Nb-Si based alloy prepared by slurry sintering method

The high-temperature oxidation resistant MoSi2 intermetallic coatings have been successfully prepared on the Nb-Si based alloy by slurry sintering method. The heating rate before the sintering temperature is reached has an obvious influence on the density and interface structure of the coatings. The coating prepared at a heating rate of 10 °C/min is the densest, with a porosity about 18.4 area%, and has a good adhesion strength of 22.5 MPa. After oxidation at 1250 ℃ for 10 h, the coating exhibits multi-layer structure consisted of an SiO2 scale, an MoSi2 layer, an inner oxidation layer and an (Nb,X)5Si3 transitional layer from the outer to the inner.

Enhanced mechanical and biocompatibility performance of Ti(1-)Ag(x) coatings through intermetallic phase modification

Advanced materials combining superior mechanical and biocompatibility performance are of significant interest to extend the lifetime of biomedical devices. In this work, Ag is alloyed with Ti to investigate the role of emerging Ti Ag intermetallic coatings with high mechanical hardness and exceptional biocompatibility. Thin films of Ti (1- x ) Ag (x) were deposited on 316 L steel and glass substrates using magnetron sputtering and subsequently heat-treated to aid Ti Ag intermetallic development. Mechanical properties were then measured and correlated to microstructural and morphological changes in the Ti Ag films. In the as-grown state, the Ti Ag matrix developed different intermetallic structures which increased the hardness of pure Ti films from 5 to >7 GPa. After heat treatment, a peak hardness of 7.39 GPa and elastic modulus of 105 GPa was achieved for a 43 at.% Ag film due to formation of the tetragonal Ti Ag phase and increase of upper surface oxides which act as dislocation barriers. However, at higher Ag concentrations, heat treatment leads to agglomeration of Ag around grain boundaries and decreases the crystallite size, leading to reduction in hardness to <3 GPa. The Ti rich films also depict better cytotoxicity performance following exposure to the L929 cell line, though excellent cell viability values >98% are observed for the entire Ti Ag range. While leached ion concentrations lower than 100 ppb demonstrate excellent biocompatibility of this Ti Ag alloy system. This work demonstrates the first successful attempt to develop biocompatible Ti Ag thin film coatings with high mechanical hardness with the potential to extend the lifetime of medical implants. • First study on biomechanical performance of Ti (1-x) -Ag (x) intermetallic films. • First report on external heat treatment to develop Ti Ag intermetallic thin films. • Ag addition causes transition to tetragonal Ti Ag structure with enhanced hardness. • Heat treatment leads to improved crystallinity and mechanical performance. • Ti Ag films exhibit excellent biocompatibility before and after heat treatment.

Study of the composition and properties of the intermetallic layer of Al–Ti and Ni–Ti obtained on a titanium alloy for laser processing

The results of a study of intermetallic coatings of the Al–Ti and Ni–Ti systems obtained using the method of cold gas-dynamic spraying on a titanium alloy substrate and laser processing are presented. The precursor coating was obtained by cold spray deposition of aluminum and nickel and then it was processed by a laser. The change in the composition and properties of the coating under different laser processing modes is shown. The structure and microhardness of the coating are investigated, and the results of X-ray phase analysis are presented.

Structure and Oxidation Behavior of NiAl-Based Coatings Produced by Non-Vacuum Electron Beam Cladding on Low-Carbon Steel

NiAl-based intermetallic coatings were obtained using non-vacuum electron beam cladding on low-carbon steel. The structure of the coatings was investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). The coatings mostly consisted of grains elongated perpendicular to the substrates, with a strong &lt;100&gt; texture along the grain growth direction. The coatings contained about 14 at. % Fe, which appeared due to the partial melting of the steel substrate. At the bottom of the coatings, an inhomogeneous mixing zone with an increased concentration of Fe was formed; at the “substrate–coating” interface, a thick layer with a Fe50-Ni25-Al25 at. % composition was observed. The samples exhibited weight gains of 0.1, 0.8, 2.14, and 3.4 mg/cm2 after 100 h of oxidation at 700, 800, 900, and 1000 °C, respectively. The oxide layer contained α-Al2O3 and θ-Al2O3, and the presence of iron atoms contributed to the formation of a small amount of spinel. During the oxidation process, a layer with a high Fe content (~60 at. %) formed along the boundary between the oxide film and the NiAl-based material, which had a positive effect on the formation of a non-porous “oxide–coating” interface.

Development of hydrophilic NbCuSi(N) &TiAlNb(N) coatings as a new strategy for medical implants modification

Herein we report the results of multi-element nitride and intermetallic coatings obtained by the arc-PVD method based on non-trivial elements combinations (Nb - 75.5, Si - 9.65, Cu - 14.85 at% and Ti - 81.8, Nb - 11.8, Al - 6.4 at%). Our experiments examine the development and evolution of biocompatible coatings for metal implants and medical devices. The elemental composition of the surface, microstructure, contact angle and biocompatibility of the coatings were studied. XRD results demonstrated that in the intermetallic TiAlNb samples, a multiphase state is formed between γ-TiAl, TiAl2, and α-Nb5Si3, since only a small part of Nb atoms occupy the same lattice sites as Ti atoms, which leads to the formation of a competing phase α-Nb5Si3. The NbCuSi coatings predominantly consist of Nbss with inclusions of silicon silicide. The human umbilical cord mesenchymal stem cells (MSC) were used for biocompatibility assessment using resazurin reduction assay and fluorescent DAPI staining. We show the high biocompatibility and ability to stimulate cell proliferation and distribution over the intermetallic coatings, especially when compared to nitrides ones. Although intermetallic coatings exhibit a higher surface contact angle due to uneven morphology, all samples exhibit hydrophilic properties, which favourably affect cell adhesion and proliferation.

Hydrothermal deposition of MoS2 on electrospark Ti – Al coatings on Ti6Al4V alloy and their characteristics

Antifriction layers on titanium alloy Ti6Al4V can be obtained by creating a developed structure of lubricant pockets, followed by the application of dry self-lubricating substances. The structure and tribological behavior of Ti &ndash; Al intermetallic coatings after hydrothermal deposition of molybdenum disulfide (MoS2) have been studied. Titanium aluminide coatings with a regular network of cracks were obtained by electrospark treatment of the Ti6Al4V alloy in an equimolar mixture of titanium and aluminum granules. To fill the lubricant voidnesses in the MoS2 coatings, the hydrothermal synthesis method was used in a solution of thiourea and sodium molybdate at 220 oC. The structure of the coatings was studied by X-ray diffraction analysis, scanning electron microscopy, X-ray microanalysis, and Raman spectroscopy. The wear resistance of the coatings was studied according to the ASTM G99 standard with dry sliding friction using counterbodies in the form of discs made of high-speed steel P6M5 at a speed of 0.47 m/s under a load of 25 N. It was found that intermetallic compounds Ti3Al, TiAl, TiAl3 and TiAl2 were overwhelming. In the structure of Ti &ndash; Al coatings, a regular network of cracks with a thickness of 0.77 &plusmn; 0.3 &mu;m and a specific area on the coating surface of 2.2 &plusmn; 0.35% was established. It was shown that as a result of hydrothermal synthesis, a MoS2 layer is formed on the surface of the samples, consisting of spherical particles with a diameter of 3.09 &plusmn; 0.63 &mu;m. Based on the data of energy dispersive spectroscopy (EDS) mapping, it was concluded that cracks in Ti &ndash; Al coatings are also filled with MoS2. According to the results of tribological tests, it was found that the hydrothermal deposition of MoS2 on Ti &ndash; Al coatings enables to reduce their friction coefficient by 30%, and the reduced wear in dry sliding friction by 2 times. The conducted studies show the promise of hydrothermal deposition of MoS2 on Ti &ndash; Al coatings in order to study tribotechnical properties.The study was supported by the Russian Science Foundation (No. 19-73-00031).