Non-vacuum Electron Beam Cladding Research Articles

Al-Co-Cr-Fe-Ni high-entropy coatings produced by non-vacuum electron beam cladding: Understanding the effect of Al by in-situ synchrotron X-ray diffraction

This study investigates the structure and properties of Al-Co-Cr-Fe-Ni high-entropy alloy (HEA) based coatings on steel substrates produced by non-vacuum electron beam cladding. Powder mixtures with Al molar ratios of 0.5, 1, and 1.5 were used for cladding, resulting in coatings with fcc, bcc + fcc, and bcc structures, respectively. The Fe content, which entered the coating from the substrate during cladding, increased from 9.9 up to 48.1 at. %. with the decrease of the Al molar fraction from 1.5 to 0.5. In-situ synchrotron X-ray diffraction analysis showed that this effect can be attributed to the higher solidus temperatures of the compositions with higher Al content. Electron backscatter diffraction showed that differences in grain morphology and crystallographic texture were related to the crystallization temperatures in different zones of the coatings. The bcc coating with an Al molar ratio of 1.5 demonstrated superior hardness and wear resistance. Fcc coating, which received more Fe from the substrate, had lower hardness and was prone to plastic flow. However, the specific wear rate of the fcc coating was close to that of the bcc + fcc one due to the hardening of the fcc phase during sliding wear.

Structure and tribological properties of “carbon steel – VC containing coating” compositions formed by non-vacuum electron-beam surfacing of vanadium-containing powder mixtures

Vanadium carbides are known as efficient reinforcing components for surface layers of steel parts. They provide good tribological characteristics of material under sliding friction conditions and against dry abrasive particles. Since wear conditions usually are quite severe, a thick coating is needed to provide the reliable protection of the part. The majority of currently used surfacing technologies ensure the coatings of insufficient thickness. For this reason, the non-vacuum electron beam cladding which is able to provide thick coatings is a reasonable alternative to other surfacing methods. This paper presents an analysis of the microstructure, micro- and nanohardness, elasticity, and tribological characteristics of coatings formed by non-vacuum electron-beam surfacing of vanadium and graphite-containing powder mixtures. In the course of the study, coatings with the average thicknesses of 1.8, 2.5, 2.6, 3.4 mm were formed on the surface of blanks made of medium‑carbon steel. Hardness of cladding layers was significantly improved compared to the low-carbon steel (by the factor of 5–7). The wear resistance of coatings under conditions of sliding friction was 5.8 times higher than the wear resistance of the base metal after quenching and tempering; the wear resistance of coatings under conditions of friction against fixed and loosely fixed abrasive particles was ∼2 and ∼4.8 times higher, respectively. Surface hardening of steel alloyed with vanadium and carbon derives from the presence of a martensitic matrix, ledeburite precipitates and a high volume fraction (14.5–29.5 vol%) of vanadium carbide particles of a dendritic form, which act as rigid barriers.

Heat Treatment Induced Structural Transformations and High-Temperature Oxidation Behavior of Al21Co22Cr22Fe13Ni22 High-Entropy Coatings Produced by Non-Vacuum Electron Beam Cladding

In this study, Al21Co22Cr22Fe13Ni22 high-entropy coatings were produced on steel substrates by non-vacuum electron beam cladding of Co, Cr, and NiAl powders. The high-temperature oxidation behavior of the coatings was studied by holding the specimens at 900 °C in air. The microstructure and phase constitution of the samples were studied both in the as-cladded state and after the heat treatment. The microstructure was characterized using light microscopy (LM) and scanning electron microscopy (SEM). Synchrotron X-ray diffraction (SXRD) and energy-dispersive X-ray spectroscopy (EDX) were used to study the phase constitution of the coatings and the “coating-substrate” interface. The coating consisted of disordered bcc (A2), ordered bcc (B2), and disordered fcc (A1) phases. Annealing the coatings for 50 h at 900 °C led to the formation of fcc precipitates in the bcc dendritic grains and a mixture of fcc and σ-phase particles in the interdendritic regions. Needle-like nanosized B2-precipitates were formed due to annealing in the fcc grains at the coating/substrate interface. The microhardness at the top of the as-cladded coating was 585 HV and gradually decreased towards the substrate. A more uniform distribution of the microhardness was obtained after the annealing. Its average value was 441 HV. Rhomboid Cr2O3, needle-like Al2O3, and spinels of a different morphology were found on the surface of the samples after oxidation at 900 °C.

Obtaining of composite coatings by non-vacuum electron-beam cladding of WC on AMg6: microstructure, phase composition and properties

Obtaining of composite coatings by non-vacuum electron-beam cladding of WC on AMg6: microstructure, phase composition and properties

Synthesis of Al–Mg–WC composite coating by relativistic electron beam

The composite coating with a thickness of 5.2 ± 0.3 mm was obtained by non-vacuum electron-beam cladding of WC powder on an Al–6 % Mg alloy. A highly concentrated relativistic electron beam exposure to the alloying system leads to partial dissolution of tungsten carbide in the melt pool, causing interfacial interactions and new phases formation. The microstructure and phase composition of composite coating was studied using scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction analysis. The microhardness of the composite coating is 1.3 times higher than substrate material and wear resistance is 1.13 times higher than Al–6 % Mg alloy.

Structural characterization of layers fabricated by non-vacuum electron beam cladding of Ni-Cr-Si-B self-fluxing alloy with additions of niobium and boron

This paper is devoted to characterization of microstructure and phase constituion of coatings produced by non-vacuum electron beam cladding of Ni-Cr-Si-B self-fluxing alloy with Nb and amorphous B additions on mild steel substrates. The main purpose of this study was to form niobium diborides (NbB 2 ) belonging to AlB 2 structural family directly during the cladding process. For this reason we carried out a series of experiments with different ratios of (Nb+B (Am) ) and Ni-Cr-Si-B powders. When the starting material contained 15-40 wt.% of (Nb+B (Am) ) powder the NbC and (Cr, Fe) 23 C 6 carbides, as well as NbB 2 particles distributed in γ-(Ni-Fe) solid solution, were formed. When the starting powders contained 30-40 wt.% of (Nb+B (Am) ), NbB 2 formed shells around the NbC particles. The mechamism of shells formation, the ordering of γ-(Ni-Fe)-matrix and other structural peculiarities of the samples are discussed in the paper. Microhardness of the samples materials ranged from 450 to 950 HV 0.1 . • Ni-Cr-Si-B protective layers reinforced with NbB2 were fabricated on steel. • High-power electron beam accelerator was used to completely melt the alloy. • «NbB2 shell – NbC core» complex particles form at high concentrations of Nb and B. • Complex precipitates provide 2-fold improvement of Ni-Cr-Si-B-alloy microhardness. • The CuAuI type ordering of γ-(Ni-Fe)-matrix occurs in the cladding layer

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 <100> 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.

Structure and oxidation behavior of CoCrFeNiX (where X is Al, Cu, or Mn) coatings obtained by electron beam cladding in air atmosphere

High-entropy alloys (HEAs) are currently considered as promising materials for a wide range of applications, including high-temperature use. Since HEAs contain a large number of expensive elements, producing HEA-based coatings seems to be a reasonable approach from an economic point of view. In this study, non-vacuum electron beam cladding was used for the first time to produce CoCrFeNiX layers (where X = Al, Cu or Mn) on a surface of low-carbon steel. As-received coatings had a columnar grain structure with a 〈100〉 fiber texture. The CoCrFeNiCu cladding layer consisted of two fcc phases: Cu-enriched phase was observed in the interdendritic regions, and the Cu-depleted phase was found in dendrites. The CoCrFeNiMn coating had a single-phase fcc structure. CoCrFeNiAl alloy consisted of bcc and B2 phases. The hardness of the Cu and Mn-containing coatings was 190 and 186 HV, respectively. The hardness of the CoCrFeNiAl coating was 570 HV, which is 3.4 times higher compared to the material of the substrate. High-temperature oxidation tests carried out at 850 °C for 45 h revealed that oxide layers formed on the tested samples had a gradient structure that consisted of several different sublayers. The total mass gain due to high temperature oxidation was 2.29 mg/cm2, 2.04 mg/cm2, and 0.60 mg/cm2 for the CoCrFeNiCu, CoCrFeNiMn, and CoCrFeNiAl samples, respectively. The mass gain of the base material over the same period of time was 41.01 mg/cm2. The CoCrFeNiAl coating had the best oxidation resistance due to the formation of a dense Al2O3 scale. We show that non-vacuum electron beam cladding can be used to produce an HEA-based coating with a different chemical composition. The thickness of coatings in a single pass cladding can be as high as 1.8 mm. CoCrFeNiAl is a suitable coating for low-carbon steel in applications where high hardness and oxidation resistance are required.

Structure and Properties of Surface Layers Obtained Via Nonvacuum Electron-Beam Cladding with Copper and Boron Powder Mixtures

Structure and Properties of Surface Layers Obtained Via Nonvacuum Electron-Beam Cladding with Copper and Boron Powder Mixtures

Use of Non-Vacuum Electron Beam Cladding for Creating a Combined Joint of High-Carbon and Chromium-Nickel Steels

Use of Non-Vacuum Electron Beam Cladding for Creating a Combined Joint of High-Carbon and Chromium-Nickel Steels

Structural Features of Ni-Based Self-Fluxing Alloy Protective Layers, Produced by Non-Vacuum Electron Beam Cladding, Reinforced with Titanium-Based Particles

The aim of this research was to establish influence of Ti-enriched powder mixtures on structure and microhardness level of protective layers based on Ni-Cr-Si-B-alloy, produced with non-vacuum electron beam cladding technology. The fabricated protective layers possessed the complex structure, consisting of matrix phase (γ-(Ni, Fe)) combined with hard phases such as Fe2B, CrB and TiC. Addition of titanium with boron in amount of 15 wt. % leads to significant increasing of microhardness level. In this case, level of microhardness increases up to 700 HV.

Oxidation Resistance of “Ni-Cr-Si-B-Alloy + Nb + B” Protective Layers, Produced by Non-Vacuum Electron Beam Cladding Technique

The aim of this investigation was to study the influence of Nb-enriched powder mixtures on structure and oxidation resistance of protective layers based on Ni-based self-fluxing alloy, produced by non-vacuum electron beam cladding technique on low-carbon steel substrates. The oxidation resistance of coatings was studied by thermogravimetric analysis (TGA). The samples held at 900°C for two hours in air atmosphere. TGA results indicate that the highest oxidation resistance has the material, obtained by cladding of pure Ni-based self-fluxing alloy. Samples, produced by cladding of Ni-based self-fluxing alloy in combination with Nb-enriched powder mixtures demonstrate lower level of oxidation resistance. Structure of the coatings was characterized by optical and scanning electron microscopy combined with electron microprobe analysis as well as X-ray diffraction.

Microstructure and properties of WC-Ni3Al composite coatings fabricated by non-vacuum electron beam cladding

The non-vacuum electron beam cladding technique was used to fabricate composite coatings with WC on the surface of Ni3Al intermetallic. The microstructure and phase composition of composite coatings were studied using scanning electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction analysis. The results showed a good metallurgical bond of WC particles with the Ni3Al intermetallic matrix. Addition of CaF + LiF flux mixtures in the initial cladding powder reduces the loss of tungsten carbide powder compared to MgF2 flux during electron-beam processing. Effect of tungsten carbide volume fraction, particle size and shape on the microhardness, wear mechanism of composite coatings was demonstrated. The microhardness of produced composite coatings was 1.3–1.5 times higher than substrate material and wear resistance was 2.2 times higher than Ni3Al.

Structure and Properties of Ti-Al-Ta and Ti-Al-Cr Cladding Layers Fabricated on Titanium

Being one of the most high-demand structural materials, titanium has several disadvantages, including low resistance to high-temperature oxidation and wear. The properties of titanium and its alloys can be improved by applying protective intermetallic coatings. In this study, 2 mm thick Ti-Al-Ta and Ti-Al-Cr layers were obtained on titanium workpieces by a non-vacuum electron-beam cladding. The microstructure and phase compositions of the samples were different for various alloying elements. The Cr-containing layer consisted of α2, γ, and B2 phases, while the Ta-containing layer additionally consisted of ω′ phase (P3¯m1). At the same atomic concentrations of aluminum and an alloying element in both layers, the volume fraction of the B2/ω phase in the Ti-41Al-7Ta alloy was significantly lower than in the Ti-41Al-7Cr alloy, and the amount of γ phase was higher. The Ti-41Al-7Cr layer had the highest wear resistance (2.1 times higher than that of titanium). The maximum oxidation resistance (8 times higher compared to titanium) was observed for the Ti-41Al-7Ta layer.

Effect of refractory modifiers on the structure of coatings based on chromium carbide

Chromium carbide-based coatings with and without TiC and TiB2 modifiers were fabricated by non-vacuum electron-beam cladding. Addition of the modifiers to the initial Cr3C2 powder mixture led to a change in the phase composition, microhardness and wear resistance of the composite coatings and the α → γ transformation of Fe. TiC and TiB2 particles formed the many crystallization centers in composite coatings, which led to a refinement of their microstructure. Larger TiC particles compared to the TiB2 particles were formed in the coatings as a result of melt crystallization. TiC modifier caused a decrease in the size of dendrites, while TiB2 led to a transition from a coarse dendritic structure to an equiaxed one. The coatings with TiC modifier demonstrated the maximum microhardness, and TiB2 coating had increased wear resistance.

Formation of the CoCrCuFeNi high entropy cladding layer by non-vacuum electron beam treatment

Non-vacuum electron beam cladding was applied to obtain CoCrCuFeNi cladding layers with thicknesses of 0.89 and 1.24 mm on a surface of mild steel. The cladding layers possessed the dendritic structure. Interdendritic space was filled with a Cu-rich phase. It was found by X-ray diffraction analysis that FCC solid solution phases were formed during crystallization. The lattice parameter of the dendritic phase was a=3.59 Å, while that of the interdendritic phase was equal to a=3.60 Å. The average microhardness values of the cladding layers were lower compared to the base material and equaled 156 HV and 190 HV.

Energy Parameters of an Electron Beam and Structure and Mechanical Properties of Composite Coatings

An important parameter of non-vacuum electron-beam cladding is the surface density of the input energy that depends on the beam current and the specimen travel speed. The paper presents results of investigation of the effect of the heat input on the structure and properties of composite coatings fabricated by electron beam cladding. The modes of cladding with beam currents of 25 and 40 mA and specimen travel speed varying within 0.5–2.0 cm/s have been studied. It was revealed that the thickness, the dendrite grain size, and the microhardness of the coatings increased, and the volume fraction of the eutectic decreased with increasing specific electron beam power. It is shown that for a low heat input, an austenitic-martensitic structure is formed with carbides in the eutectic and martensite needles. For a large heat input, an austenitic structure with eutectic carbide network is formed. The martensitic structure is formed only along the coating-substrate interface as a result of intense heat removal deep into the substrate material.

Fabrication of Cr-Ti-C composite coating by non-vacuum electron beam cladding

TiC reinforced composite coatings were fabricated by the non-vacuum electron beam cladding of Cr3C2-TiC powder mixture on the steel surface. The structure of coatings consisted mainly of γ-Fe dendrites and eutectics. The dissolution of Cr3C2 in the melted binder metal led to precipitation of Cr7C3, Cr23C6, (Cr, Fe)C carbides in the eutectic during electron beam exposure. The results showed that the value of beam power density influences on an arrangement of TiC particles in the cladded layers. TiC particles were found to be crystallization centers at the power density of 8.8 kJ/cm2. The microhardness values of coatings were found to correlate with the volume fraction of the eutectic phase, chromium and titanium content in the coatings.

Formation of wear-resistant copper-bearing layers on the surfaces of steel substrates by non-vacuum electron beam acladding using powder mixtures

By using the method of non-vacuum electron beam cladding, copper-bearing surface layers have been obtained on mild steel substrates. These layers possessed enhanced wear resistance under sliding friction compared to the substrate material. Metallographic and TEM investigations revealed that copper in cladding layers was in the form of nanoscale inclusions distributed in the ferrite matrix as well as in the form of large precipitates in the interdendritic space. The latter is an undesirable effect that significantly reduces the reliability of the material. Technological experiments aimed at dilution of the cladding material with aluminium or carbon in order to reduce the amount of copper precipitate in the interdendritic space and, consequently, to improve the quality of the cladding layers have established that the latter approach is the most efficient. The addition of aluminium, which increases the solubility of copper in the iron, contributes to the formation of the embrittling intermetallic phase (AlFe) in the ferrite matrix. When applying cladding using a mixture containing copper, iron, and carbon, the structure of hypoeutectic cast iron with nanoscale precipitates of copper in ferrite and cement forms in the surface layer. The wear resistance of such layers is one order of magnitude higher than that of the base material.

Influence of the Ti/Al/Nb ratio on the structure and properties on intermetallic layers obtained on titanium by non-vacuum electron beam cladding

Ti-Al-Nb based intermetallic layers of sufficient quality and thickness were obtained by non-vacuum electron beam cladding on the surfaces of Ti workpieces. Optical microscopy and X-ray tomography did not reveal any dramatical defects in the structure of cladded layers. X-ray diffraction as well as scanning and transmission electron microscopy were applied to thoroughly investigate the structure and phase composition of coatings. It was found that non-equilibrium cooling conditions of coatings provided by fast removal of heat to untreated Ti substrate after the electron beam cladding was terminated induced the proceeding of metastable phase transformations. For example, γ-phase formation was suppressed in these coatings. In coatings with 8 and 20 at.% Nb (46 and 43% Al respectively) along with ordered with α2, formation of disordered solution of the alloying elements in α-Ti took place. In high-Nb alloys β(B2) phase has undergone the diffusionless transformation to ω’, which is the intermediate phase in β → ω and the coating with the maximum Nb content characterized by appearance of γ1 as a main phase. ω-phase had negative influence to hardness and wear resistance of coatings, however, generally this paremeter increased in 1.3–1.75 times compared to cp-Ti. The high temperature creep and oxidation properties decreased proportionally with increasing Nb and decreasing Al content in the cladded layers.