High Current Pulsed Electron Beam Research Articles

Microstructure Analysis of HPb59-1 Brass Induced by High Current Pulsed Electron Beam

Abstract In this paper, the effects of high current pulsed electron beam (HCPEB) on the microstructure evolution of casting HPb59-1 (Cu 57.1 mass%, Pb 1.7 mass% and Zn balance) alloy were investigated. The results showed a “wavy” surface which was formed with Pb element existing in the forms of stacking block and microparticles on the top surface layer after treatment. Nanocrystalline structures including Pb grains and two phases (α and β) were formed on the top remelted layer and their sizes were all less than 100 nm. The disordered β phase was generated in the surface layer after HCPEB treatment, which is beneficial for the improvement of surface properties. Meanwhile, there was a large residual stress on the alloy surface, along with the appearance of microcracks, and the preferred orientations of grains also changed.

The Special Features of the Phase Formation and Distribution in the Titanium Nickelide Surface Layers Treated by Electron Beams

The special features inherent in the formation of the structural-phase states on the surface of titanium nickelide samples subjected to multiple low-energy high-current variable energy density pulsed electron beam irradiation are investigated. The parameters of the electron beam operated in the fivefold surface melting regime are as follows: pulse duration τ = 150 μs, current I = 70 А, and energy densities Е 1, Е 2, and E 3 = 15, 20, and 30 J/сm2, respectively. The surface layer structure was examined by methods of the x-ray diffraction analysis and transmission electron microscopy. It is found that in the irradiated TiNi samples with Е ≤ 20 J/сm2, the layer containing a martensite phase lies at a certain depth below the surface rather than on the surface. In the irradiated TiNi sample with E 3 = 30 J/сm2, the subsurface region is in a two-phase state (B2 + B19′), with the В19′ phase being predominant. It appears that the lower is the energy density, the smaller is the amount of the martensite phase.

Microstructure changes in Zr–1Nb alloy after pulsed electron beam surface modification and hydrogenation

Abstract In this paper the results of experimental study of microstructure changes in Zr–1Nb alloy after low energy high current pulsed electron beam surface modification and hydrogenation are discussed. Surface treatment was carried out with energy density equal from 5 to 25 J/cm 2 and impulses number equal from 1 to 5. Subsequent hydrogenation was carried out at temperature equal to 350 °C until reaching the hydrogen concentration of 0.05 wt.%. The structure was analyzed by X-ray diffraction, transmission electron microscopy and by means of electron–positron techniques.

Surface modification of YW2 cemented carbide cutting tool by high current pulsed electron beam

Surface modification of YW2 cemented carbide cutting tool was carried out through high current pulsed electron beam with different pulsed times, and the microstructural, mechanical properties and cutting performance is also investigate in this work. The evolution of phase composition and morphology of tool were tested by means of XRD and SEM, and the microhardness was measured. The results showed that, metastable new phase (Co 3 W 3 C) is presented in tool surface after beam irradiation. The metastable phase and residual compressive stress induced by HCPEB treatment modified the microhardness of YW2 turning insert dramatically. The cutting performance of YW2 turning insert with 40times irradiation was examined and compared with original one by machining Ti-6Al-4V alloy bar. It is found that the irradiated YW2 tool increased cutting speed than that of un-irradiated one along with serious wear. DOI: http://dx.doi.org/10.5755/j01.ms.21.2.6748

Microstructures and properties of zirconium-702 irradiated by high current pulsed electron beam

The microstructure, hardness and corrosion resistance of zirconium-702 before and after high-current pulsed electron beam (HCPEB) irradiation have been investigated. The microstructure evolution and surface morphologies of the samples were characterized by using X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The experimental results indicate that the sample surface was melted after HCPEB irradiation, and martensitic phase transformation occurred. Besides, two kinds of craters as well as ultrafine structures were obtained in the melted layer. TEM observations suggest that high density dislocations and deformation twins were formed after HCPEB irradiation. With the increasing of pulses, microhardness of the irradiated samples was increased from the initial 178Hv to 254Hv. The corrosion resistance was tested by using electrode impedance spectroscopy (EIS) and potentiodynamic polarization curves. Electrochemical results show that, after HCPEB irradiation, all the samples had better corrosion resistance in 1mol HNO3 solution compared to the initial one, among which the 5-pulsed sample owned the best corrosion resistance. Ultrafine structures, martensitic phase transformation, surface porosities, dislocations and deformation twins are believed to be the dominant reasons for the improvement of the hardness and corrosion resistance.

Various categories of defects after surface alloying induced by high current pulsed electron beam irradiation

High current pulsed electron beam (HCPEB) is an attractive advanced materials processing method which could highly increase the mechanical properties and corrosion resistance. However, how to eliminate different kinds of defects during irradiation by HCPEB especially in condition of adding new elements is a challenging task. In the present research, the titanium and TaNb-TiW composite films was deposited on the carburizing steel (SAE9310 steel) by DC magnetron sputtering before irradiation. The process of surface alloying was induced by HCPEB with pulse duration of 2.5μs and energy density ranging from 3 to 9J/cm2. Investigation of the microstructure indicated that there were several forms of defects after irradiation, such as surface unwetting, surface eruption, micro-cracks and layering. How the defects formed was explained by the results of electron microscopy and energy dispersive spectroscopy. The results also revealed that proper energy density (∼6J/cm2) and multi-number of irradiation (≥50 times) contributed to high quality of alloyed layers after irradiation.

Surface modification of Cu–25Cr alloy induced by high current pulsed electron beam

A Cu–25Cr alloy prepared by vacuum induction melting method was treated by the high current pulsed electron beam (HCPEB) with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of the alloy before and after the treatment were investigated by scanning electron microscopy and X-ray diffraction. The results show that significant surface modification can be induced by HCPEB with the pulse number reaching 10. Craters with typical morphologies on the Cu–25Cr alloy surface are formed due to the dynamic thermal field induced by the HCPEB. Micro-cracks, as a unique feature, are well revealed in the irradiated Cu–25Cr specimens and attributed to quasi-static thermal stresses accumulated along the specimen surface. The amount of cracks is found to increase with the pulse number and a preference of these cracks to Cr phases rather than Cu phases is also noted. Another 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–25Cr alloy. In addition, an examination on surface roughness of all specimens reveals that more pulses will produce a roughened surface, as a result of compromising the above features.

Phase and Structural States Formed in Titanium Nickelide Subsurface Layers Exposed to High-Current Pulsed Electron Beams

The behavior of the non-equilibrium states formed in the subsurface layers of a titanium nickelide-based alloy exposed to electron beams operated in the pulsed surface layer melting mode is investigated experimentally. Using methods of an x-ray diffraction analysis, and optical, scanning, and transmission electron microscopies, an 8–10 μm thick surface layer is shown to exhibit В2 phase-based structure undergoing inhomogeneous lattice microstrain. The core layer located at a depth of 10–20 μm below the irradiated surface contains a small amount (up to 5 vol.%) of a phase with В19′ martensite structure along with a slightly distorted lattice and unmelted Ti2Ni phase particles. Electron beam treatment brings about changes in the chemical composition of the surface-modified layer which becomes enriched in titanium owing to the dissolution of the Ti2Ni phase particles therein. Transmission electron microscopy has not revealed martensite phases in the modified layer. The electron beam exposure of the titanium nickelide surface is assumed to give rise to nonequilibrium highly distorted bcc structure.

Improving corrosion and wear resistance of FV520B steel by high current pulsed electron beam surface treatment

High current pulsed electron beam (HCPEB) surface treatment was conducted on FV520B steel with accelerating voltage 27kV, pulse duration 2.5μs, energy density 5J/cm2 and 1–25 pulses. The surface microstructure and element distribution were examined by using scanning electron microscope (SEM), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) methods. After HCPEB treatments, the surface microstructure became refined and uniform with an average grain size less than 2μm and a preferential solidification orientation in 〈200〉 direction. The thickness of surface remelted layer was ∼4μm. The initial precipitated particles in surface layer of depth ∼10μm were dissolved into the base matrix and gave a homogenous element distribution. The HCPEB modified surface exhibited an effective improvement in corrosion and wear resistance. The corrosion potential shifted towards positive and the corrosion rate decreased nearly one order of magnitude, while the wear resistance after 25 pulses of HCPEB treatment increased by 3 times as compared with the initial FV520B steel.

The metastable structure of hypereutectic Al–17·5Si alloy surface induced by high current pulsed electron beam

For this study, several types of metastable structures were investigated for the high current pulsed electronic beam treated hypereutectic Al–17·5Si alloy. Metastable structures that were studied included nano-silicon particles, aluminium (Al)-based supersaturated solid solution, dislocation tangle and amorphous structure. One of the goals of this research was to provide a better understanding of the high current pulsed electronic beam induced formation of metastable structures’ super-rapid melting and solidification processes, as well as plastic deformation. Furthermore, the phase composition of modified layer remained unchanged and the majority of the aluminium and silicon (Si) diffraction peaks escalated after high current pulsed electronic beam treatment. The result of the microhardness test revealed that the microhardness of the Al matrix had improved markedly after high current pulsed electronic beam treatment, increasing by 56·2%. On the contrary, the microhardness of primary Si decreased slightly, reducing by 54%.

Application of high-current pulsed electron beams for the restoration of operational properties of the blades of gas-turbine engines

The experimental data on the influence of irradiation modes by high-current pulsed electron beams (HEBs) on the ablation kinetics of the surface layer of a compressor blade made of steel EP866Sh and NiCrAlY protective coating on turbine blades of the gas-turbine engine made of ZhS26NK alloy are analyzed. It is shown that microsecond HEB is a highly efficient tool for repairing compressor and turbine blades. The application of HEB offers the opportunity to remove surface layers of coatings on turbine blades from 5 to 10 μm thick which were damaged during operation for one pulse at an energy density of 50–55 J/cm2. The thickness of surface layers of compressor blades made of steel EP866Sh removed for the pulse at energy density of 48–50 J/cm2 is 7 μm.

Adhesion Strength of Thermal Barrier Coatings with Thermal-Sprayed Bondcoat Treated by Compound Method of High-Current Pulsed Electron Beam and Grit Blasting

Microstructural characteristics and adhesion properties of air plasma spraying, thermal barrier coatings (TBCs) having thermally sprayed bond coats treated by high-current pulsed electron beam (HCPEB) irradiation, and a combination treatment of HCPEB and grit blasting were investigated. Microstructure observations revealed that the original coarse surface of thermally sprayed bond coat was significantly changed to interconnected bulged nodules with a compact appearance after HCPEB irradiation. With further grit blasting treatment, these series of bulged nodules appeared with successive and uniform jagged edges. Surface roughness of the bond coat after compound treatment became higher due to these bulged nodules with jagged edges, which was conducive to ceramic deposition. The results of the tensile test revealed that the adhesion strength of thermally sprayed TBCs with the bond coats conducted by a compound treatment was obviously increased. The combination treatment of HCPEB and grit blasting improved the interfacial bonding strength as well as the interfacial homogeneity.

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.

High Current Pulsed Electron Beam Effect on Micro-Arc Oxidation Film of Ti Alloy

High Current Pulsed Electron Beam (HCPEB) was employed to treat Ti-6Al-4V alloy subjected to micro-arc oxidation. The surface morphology and phase composition of surface film were investigated, as well as the wear and corrosion resistance. The results show that the coarse porous ceramic coating becomes smooth and compact after electron beam treatment. High temperature stable rutile phase increases, and low temperature stable anatase phase reduces. The friction coefficient of composite coating reduces obviously and stabilizes at 0.2, and the wear resistance is improved. The increased corrosion potential and decreased corrosion rate exhibits an enhanced corrosion resistance.

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.

Microstructure Modifications and Associated Corrosion Improvements in GH4169 Superalloy Treated by High Current Pulsed Electron Beam

The surface of the nickel‐based superalloy GH4169 was subjected to high‐current pulsed electron beam (HCPEB) treatment. The microstructural morphologies of the material were analysed by means of optical microscope (OP), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results reveal that the irradiated surface was remelted and many craters were formed. The density of craters decreased with the increment of HCPEB pulses. After 20‐pulsed HCPEB irradiation, nanostructures were formed in the melted region of the surface. Furthermore, slipping bands and high density of dislocations were also formed due to the severe plastic deformation. The selective purification effect, homogenized composition, nanostructures, and dislocation slips introduced by HCPEB irradiation bring a significant improvement of corrosion resistance of GH4169 superalloy.

Surface Nanostructure Formations in an AISI 316L Stainless Steel Induced by Pulsed Electron Beam Treatment

High current pulsed electron beam (HCPEB) is an efficient technique for surface modifications of metallic materials. In the present work, the formations of surface nanostructures in an AISI 316L stainless steel induced by direct HCPEB treatment and HCPEB alloying have been investigated. After HCPEB Ti alloying, the sample surface contained a mixture of the ferrite and austenite phases with an average grain size of about 90 nm, because the addition of Ti favors the formation of ferrite. In contrast, electron backscattered diffraction (EBSD) analyses revealed no structural refinement on the direct HCPEB treated sample. However, transmission electron microscope (TEM) observations showed that fine cells having an average size of 150 nm without misorientations, as well as nanosized carbide particles, were formed in the surface layer after the direct HCPEB treatment. The formation of nanostructures in the 316L stainless steel is therefore attributed to the rapid solidification and the generation of different phases other than the steel substrate in the melted layer.

Halo Evolution of Hypereutectic Al‐17.5Si Alloy Treated with High‐Current Pulsed Electron Beam

Halo evolution of an Al‐17.5Si alloy surface after treatment with increasing pulse numbers of a high‐current pulsed electron beam (HCPEB) was investigated. A halo is a ring microstructure resembling a bull’s eye. SEM results indicate that the nanocrystallization of halo induced by HCPEB treatment leads to gradual diffusion of the Si phase. Multiple pulses numbers cause the Si phase to be significantly refined and uniformly distributed. In addition, nanosilicon particles with a grain size of 30~100 nm were formed after HCPEB treatment, as shown by TEM observation. XRD results indicate that Si diffraction peaks broadened after HCPEB treatment. The microhardness tests demonstrate that the microhardness at the midpoint from the halo edge to center decreased sharply from 9770.7 MPa at 5 pulses to 2664.14 MPa at 25 pulses. The relative wear resistance of a 15‐pulse sample is effectively improved by a factor of 6.5, exhibiting optimal wear resistance.

X-ray Analysis of the Structure-phase States of the Tantalum Coating on NiTi Substrate Treated by Electron Beams

The evolution of the structural phase states in the Tantalum coatings formed on the NiTi substrate and their change before and after low energy high current pulsed electron beam treatment has been investigated by using X-ray diffraction technique. It was found that in the Tantalum coating reflections of cubic α-Ta and β-Ta tetragonal phases, with a predominance of α-Ta phase (∼ 65 vol.%) were observed. The layer between the coating and the NiTi substrate composed of the phase with a bcc structure based on Ta-O with an oxygen concentration of CO ≈ 13 atm.%. After LEHCPEB at E = 15J/cm2 of coated samples in addition to the B2, α-Ta and -Ta phases the martensite phase B19’ was detected in the surface layer. It was revealed that after the treatment of samples a uniform layer consisting mainly of Tantalum with no clearly defined boundaries between the coating and the NiTi substrate was formed on the surface.

Formation of Ultrafine‐Grained Ti3Al on a Ti48Al2Cr2Nb Intermetallic Alloy Induced by Pulsed Electron Beam Treatment

The microstructure modifications, phase, and texture formations encountered in a TiAl based Ti48Al2Cr2Nb intermetallic alloy induced by the high current pulsed electron beam (HCPEB) treatment were carefully investigated using scanning electron microscope (SEM), X‐ray diffraction (XRD), and electron backscattered diffraction (EBSD) techniques. The initial material contains the majority γ‐TiAl phase and the minority α‐Ti3Al phase. After the HCPEB treatment, the initial α‐Ti3Al was dissolved into the melted layer and the very top surface is covered by ultrafine‐grained α‐Ti3Al phase having thermal stress induced cracks. EBSD analyses showed that α‐Ti3Al phase on the very top surface has a 〈001〉//ND fiber texture and its texture intensity increases with the number of pulses. The superfast thermal stress cycles and the selective evaporation induced by the HCPEB treatment account for the microstructure modifications and formations of ultrafine α‐Ti3Al in the TiAl based intermetallic alloy.