High-current Pulsed Electron Beam Technique Research Articles

Evolution of Microstructure and Mechanical Properties of NiCoCrAlY Coatings After High-Current Pulsed Electron Beam Irradiation

In this paper, the NiCoCrAlY coating prepared by laser cladding was modified by a high-current pulsed electron beam technique. Scanning electron microscopy and X-ray diffraction analysis were used to characterize the microstructure and composition of the coatings before and after irradiation, and then the changes in mechanical properties were revealed by comparing the hardness and friction properties of the two coatings. The results showed that the pulsed irradiation purified the coating surface, formed an evaporative recondensation layer and a plastic deformation layer, and produced a dense remelting layer with a thickness of 3-4 µm. The remelted layer led to an increase in the hardness of the irradiated coating and a decrease in the friction coefficient and wear. The pulsed irradiation effectively improved the mechanical properties of the coatings.

Microstructures and high-temperature oxidation behavior of laser cladded NiCoCrAlYSi coating on Inconel 625 Ni-based superalloy modified via high current pulsed Electron beam

NiCoCrAlYSi coatings were prepared on the surface of nickel-based high-temperature alloys (Inconel 625) by laser cladding (LC) technique, and then the surface was modified by high current pulsed electron beam (HCPEB). The microstructural results indicate that metallurgical defects on the original surface, including micropores and elemental segregations were eliminated, and a remelted layer consisting of high density of cross slips and nanostructures was obtained. High-temperature oxidation resistance at 900 °C, 1000 °C and 1100 °C of the original coatings was investigated. When oxidized at 900 °C for 100 h, the original coating followed the linear growth law, and the TGO was mainly consisted of Al 2 O 3 . When oxidized at 1000 °C and 1100 °C for 100 h, the original coating followed the parabola law, and the TGO existed in a double-layer structure. After HCPEB irradiation, a rather stable, continuous, and slow-growing α-Al 2 O 3 was formed on the surface after oxidation for 100 h at 1100 °C. The kinetic curves show that the growth rate of the TGO of the irradiated coatings was reduced by 43.9%, and the thickness was effectively decreased compared with the original sample. Thus, HCPEB technique is proved to be an effective method to improve the service life of laser cladding coatings. • Microstructures and oxidation behavior of NiCoCrAlYSi laser cladding coating was investigated. • Cladding coatings presented different oxidation rate and growth behavior at different temperatures. • HCPEB technique was used to further improve the microstructures and properties of cladding coating. • Restructured surface promoted the formation of a protective α-Al 2 O 3 layer at 1100 °C. • HCPEB technology is an effective way to improve the high-temperature service life of cladding coatings.

Microstructure and transient oxidation behavior of NiCoCrAlYSiHf coating modified via high-current pulsed electron beam

In this study, NiCoCrAlYSiHf coatings deposited via arc ion plating technique were modified by high-current pulsed electron beam (HCPEB) irradiation with different pulses. The coarse surface of the original coating was completely modified, and the modification effects of HCPEB irradiation, including surface finishing, composition optimization, and microstructural adjustment were obtained. The transient oxidation behavior of original and irradiated coatings was comparatively investigated under 1100 °C for 10 h. Experiment and characterization results showed that the remelting effects induced by HCPEB irradiation could greatly influence the growth behavior of the thermally grown oxides (TGO), presenting as the rapid formation of a complete and dense α-Al 2 O 3 layer in the transient oxidation stage, which guaranteed the protective effect of the AIP- M CrAlY X type coatings in subsequent oxidation stages. • NiCoCrAlYSiHf arc ion plated coating was modified via HCPEB technique with different parameters. • HCPEB irradiation led to a complete surface remelting, and eliminates original surface defects. • Nano-scale grains and deformation structures were obtained. • A stable, continuous and uniform α-Al 2 O 3 scale can be expected for all of treated coatings. • HCPEB technique is an effective approach to improve the performance of M CrAlY X -type coatings.

Microstructural modifications and high-temperature oxidation resistance of arc ion plated NiCoCrAlYSiHf coating via high-current pulsed electron beam

A NiCoCrAlYSiHf coating prepared via arc ion plating was irradiated using a high-current pulsed electron beam (HCPEB) technique. The self-quenching and polishing effect induced by HCPEB treatment normalized the defects, re-melted the surface, refined the grains, introduced the dislocations, and changed the elemental distributions. After oxidation for 200 h, severe spalling of the oxide scale and internal oxidation occurred in the original coating. The restructuring of the remelted layer contributed to a very stable, continuous, slow-growing, and uniform α-Al2O3 scale during the entire oxidation stage. HCPEB technique is an effective way to dramatically improve the service life of an MCrAlYX-type coating.

Hot corrosion behaviour of thermally sprayed CoCrAlY coating irradiated by high-current pulsed electron beam

Microstructural modifications and hot corrosion behaviour of plasma spraying CoCrAlY coatings before and after high-current pulsed electron beam (HCPEB) irradiation were investigated. The microstructural observations revealed that the coarse surface of plasma spraying CoCrAlY was remelted and changed as a wavy aspect with a compact appearance. The fast heating and melting, and self-quenching effects induced by HCPEB treatment normalized the thermal spraying defects, refined the grains, and changed the elemental distributions. Cyclic hot corrosion test of two kinds of coatings in Na2SO4/K2SO4 (75:25, wt.%/wt.%) eutectic salt was performed at 900 °C in air. After 80 h hot corrosion, the relatively loose and non-protective scale was formed with poor adherence on the initial porous surface, which made the initial coating highly susceptible to hot corrosion. Comparatively, the irradiated coating displayed a stable and slow-growing kinetic curve of very small mass change, revealing that resistance to hot corrosion was superior to that of the initial one. The irradiating effects promoted the formation and self-healing of a dense and adherent Al2O3 scale in the initial stage, which effectively suppressed the formation of internal oxides and sulfides. The results demonstrated that HCPEB technique is an effective way to prolong the service life of MCrAlY coatings.

Study on the nanostructure formation mechanism of hypereutectic Al–17.5Si alloy induced by high current pulsed electron beam

This work investigates the nanostructure forming mechanism of hypereutectic Al–17.5Si alloy associated with the high current pulsed electron beam (HCPEB) treatment with increasing number of pulses by electron backscatter diffraction (EBSD) and SEM. The surface layers were melted and resolidified rapidly. The treated surfaces show different structural characteristics in different compositions and distribution zones. The top melted-layer zone can be divided into three zones: Si-rich, Ai-rich, and intermediate zone. The Al-rich zone has a nano-cellular microstructure with a diameter of ∼100nm. The microstructure in the Si-rich zone consists of fine, dispersive, and spherical nano-sized Si crystals surrounded by α(Al) cells. Some superfine eutectic structures form in the boundary of the two zones. With the increase of number of pulses, the proportion of Si-rich zone to the whole top surface increases, and more cellular substructures are transformed to fine equiaxed grain. In other words, with increasing number of pulses, more Si elements diffuse to the Al-rich zone and provide heterogeneous nucleation sites, and Al grains are refined dramatically. Moreover, the relationship between the substrate Si phase and crystalline phase is determined by EBSD; that is, (111)Al//(001)Si with a value of disregistry δ at approximately 5%. The HCPEB technique is a versatile technique for refining the surface microstructure of hypereutectic Al–Si alloys.

Evolution of surface microstructure of Cu-50Cr alloy treated by high current pulsed electron beam

A Cu-50Cr alloy was treated by the high current pulsed electron beam (HCPEB) at 20 and 30 keV with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of specimens before and after the treatments were investigated by employing scanning electron microscopy and X-ray diffraction. Results show that the HCPEB technique is able to induce remarkable surface modifications for the Cu-50Cr alloy. Cracks in Cr phases appear even after one-pulse treatment and their density always increases with the pulse number. Formation reason for these cracks is attributed to quasi-static thermal stresses accumulated along the specimen surface. Craters with typical morphologies are formed due to the dynamic thermal field induced by the HCPEB and they are found to prefer the sites near cracks or boundaries between neighboring Cr phases. Another microstructural characteristic produced by the HCPEB is the fine Cr spheroids, which are determined to be due to occurrence of liquid phase separation in the Cu-50Cr alloy. Finally, a general microstructural evolution profile that incorporates various HCPEB-induced surface features is tentatively outlined.

Surface microstructure and stress characteristics in pure zirconium after high current pulsed electron beam irradiation

High-current pulsed electron beam (HCPEB) technique was applied to irradiate the samples of pure zirconium. The microstructures and defects of the irradiated surface are investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD results show that the high value of stress (GPa order) is introduced within the irradiated surface layer, while the formation of {0002}, {1012}, {1120} and {1013} textures are present after HCPEB irradiation. Microstructure observations demonstrate that the surface craters are rarer, and almost no craters are present after multiple pulses HCPEB irradiation, which is evidently different from the case of other metal materials irradiated by HCPEB. Moreover, a large number of ultrafine grains are formed on the irradiated surface. Martensitic transformation occurs and severe plastic deformation is also induced due to the superfast melting and cooling processes. After one- pulse irradiation, the dislocations are the dominant defects, while the amount of twins is less. After five pulses, the dislocation density and the number of deformation twins increase evidently, whereas dense deformation twins are the central microstructures after ten-pulse irradiation, coupled with the appearance of secondary twins occasionally. The formation of these deformed structures results in a significant effect both on the evolution of surface textures and on grain refinement. It is suggested that HCPEB technique provides an impactful approach for hardening of zirconium and zirconium alloys.

Surface Nanocrystallization of Nickel Produced by High-Current Pulsed Electron Beam Irradiation

The nanocrystalline surface was obtained on bulk pure nickel by using high-current pulsed electron beam (HCPEB) technique. The temperature field induced by HCPEB was numerically simulated. The structures of the nanocrystallized surface were characterized by scanning electron beam (SEM), which showed that after HCPEB irradiation, the initial coarse-grained structure on the surface was refined into fine grains with sizes of about 70nm. It was revealed that melting surface caused by HCPEB irradiation and subsequently rapid cooling was the dominant mechanism of the surface nanocrystallization of bulk nickel. The HCPEB technique provides a new method for rapid fabricating surface-nanocrystallized materials.

Rapid Fabrication and Characterization of Micropores on Pure Nickel Surface by High-Current Pulsed Electron Beams Irradiation

The Mechanism of Micropores Formed on the Surface of Polycrystalline Pure Nickel under High-current Pulsed Electron Beam (HCPEB) Irradiation Is Explained. it Is Discovered that Dispersed Micropores with Sizes of 0.1-2.0 µm on the Irradiated Surface of Pure Nickel Can Be Successfully Fabricated after HCPEB Irradiation. the Dominant Formation Mechanism of the Surface Micropores Should Be Attributed to the Formation of Supersaturation Vacancies within the near Surface during the HCPEB Irradiation and the Migration of Vacancies along Grain Boundaries and/or Dislocations towards the Irradiated Surface. it Is Expected that the HCPEB Technique Will Become a New Method for the Rapid Synthesis of Surface Porous Materials.

Surface Modification of Pure Titanium by High Current Pulsed Electron Beam

Polycrystalline pure titanium was irradiated by high-current pulsed electron beam (HCPEB). The microstructure changes and material strength were investigated by using microhardness tester, optical microscope, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) technique. The experimental results indicate that many craters are inevitably formed on the irradiated surface. The eruption of the craters makes the material surface cleaned, which can improve the corrosion resistance of materials. Furthermore, martensitic structure, ultra-fine grains and high-density dislocations are formed on the irradiated surface, which increase the hardness of the treated samples. The microhardness of 20-pulsed sample reaches 286Hv, which is 71% higher than the initial sample. Martensitic transformation, grain refinement and dislocation strengthening induced by HCPEB treatment are the dominating mechanism for the improvements of material strength. It is suggested that HCPEB technique is becoming an effective approach to surface modification for pure titanium and titanium alloy.

Synthesis and Characterization of Micropores on Nanocrystalline Pure Copper Surface by High-Current Pulsed Electron Beam Irradiation

In this paper, we studied the formations of surface micropores in nanocrystalline pure copper under the action of high-current pulsed electron beam (HCPEB) surface irradiation. It was established that surface porous metal can be successfully fabricated using HCPEB technique. After HCPEB irradiation, a mass of rounded micropores are formed on the irradiated surface. The size and distribution of the micropores can be effectually controlled by adjusting HCPEB processing parameters. The number density of surface micropores decreased but their size increased with increasing HCPEB energy density. The present results indicate that HCPEB technique can provide a new approach for surface porous materials synthesis.

Surface microstructure and stress characteristics in pure titanium after high-current pulsed electron beam irradiation

The specimens of polycrystalline pure titanium are irradiated by high-current pulsed electron beam (HCPEB). Surface microstructures and defects induced by HCPEB irradiation are investigated by using X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy technique. The XRD results show that the high value of stress (GPa order) is introduced into the irradiated surface layer, and the characteristics of preferential orientations (100), (102) and (103) are present after HCPEB treatment. The surface microstructure observations indicate that martensitic transformation occurs in the irradiated surface and a large number of plate martensite structures are formed in the irradiated surface. Moreover, strong plastic deformation is triggered by HCPEB treatment. After one pulse, (100) type slip bands are formed in the interior of grain, which leads to the increase of dislocation density. After multi- pulses, deformation microstructures change significantly, and the number of deformation twins increases evidently. The formation of these deformation structures produces a significant effect both on the evolution of surface textures and on grain refinement, which improves the mechanical performance of irradiated surface. It is suggested that HCPEB technique is an effective approach to surface hardening for pure titanium.

Formation Mechanism of Micropores on the Surface of Pure Aluminum Induced by High-Current Pulsed Electron Beam Irradiation

The mechanism of micropores formed on the surface of polycrystalline pure aluminum under high-current pulsed electron beam (HCPEB) irradiation is explained. It is discovered that dispersed micropores with sizes of 0.1–1 μm on the irradiated surface of pure aluminum can be successfully fabricated after HCPEB irradiation. The dominant formation mechanism of the surface micropores should be attributed to the formation of supersaturation vacancies within the near surface during the HCPEB irradiation and the migration of vacancies along grain boundaries and/or dislocations towards the irradiated surface. It is expected that the HCPEB technique will become a new method for the rapid synthesis of surface porous materials.

Defects and Microstructures in the Surface Layer of Single-crystal Silicon In-duced by High-current Pulsed Electron Beam

In order to investigate the microstructures of nonmetallic material induced by high-speed deformation, the high-current pulsed electron beam (HCPEB) technique was used to irradiate the single-crystal silicon. The surface microstructures induced by electron beam were studied by transmission electron microscope (TEM). The experimental results showed that a large number of defect structures were formed by the HCPEB irradiation. Among them, the typical defect structures were the parallel screw dislocations and the extrinsic stacking faults. In the meantime, the HCPEB irradiation induced high density of vacancy cluster defects. The surface stress with very high value and strain rate led to the integral shift of (111) crystal plane, which might be the dominating reason of the formation of the massive vacancy cluster defects. In addition, the mixtures of nanocrystal and amorphous in the surface of single-crystal silicon can be formed by HCPEB technique.

Defect microstructures in polycrystalline pure copper induced by high-current pulsed electron beam——the vacancy defect clusters and surface micropores

In this paper, high-current pulsed electron beam (HCPEB) was used to irradiate the polycrystalline pure copper. The vacancy defect clusters of the irradiated surface layer have been investigated by using transmission electron microscopy. Very dense vacancy defect clusters involving square cells, vacancy dislocation loops and stacking fault tetrahedra were formed after HCPEB irradiation. It suggests that the very high stress and high strain rate induced by rapid heating and cooling due to HCPEB irradiation could cause the shifting of whole atomic planes synchronously, which is the probable mechanism of the formation of the vacancy defect clusters. Additionally, it was established by scanning electron microscopy investigations that dense, fine and dispersed micropores on the irradiated surface of pure copper can be successfully fabricated by using HCPEB irradiation. The dominating formation mechanism of surface micropores should be attributed to the formation of supersaturation vacancies within the near-surface introduced during HCPEB irradiation and vacancy migration along grain boundaries and (or) dislocations towards the irradiated surface. The present results indicate that HCPEB technique may become a new method for rapid synthesis of surface porous materials.

Mechanisms of nanostructure and metastable phase formations in the surface melted layers of a HCPEB-treated D2 steel

This work investigates the mechanism of surface modification associated with the high-current pulsed electron beam (HCPEB) treatment of a D2 steel with increasing numbers of pulses. The surface layers were melted and resolidified but the treated surfaces showed very different features. This variation is essentially due to the different levels of homogeneity and carbide dissolution. It is demonstrated that the presence of carbides served as nucleation sites for the surface eruption phenomenon that creates craters on the surface. After a sufficient number of pulses, most of the carbides in the surface layer were dissolved and an almost crater-free homogeneous melted layer consisting of a very stable nano-austenite structure was formed. The HCPEB technique is thus demonstrated to be a versatile technique for surface microstructure modification involving, in the case of steels, austenite stabilization and ultrafine grain formation.