High-current Pulsed Electron Beam Irradiation Research Articles

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.

Study on Nanostructures Induced by High‐Current Pulsed Electron Beam

Four techniques using high‐current pulsed electron beam (HCPEB) were proposed to obtain surface nanostructure of metal and alloys. The first method involves the distribution of several fine Mg nanoparticles on the top surface of treated samples by evaporation of pure Mg with low boiling point. The second technique uses superfast heating, melting, and cooling induced by HCPEB irradiation to refine the primary phase or the second phase in alloys to nanosized uniform distributed phases in the matrix, such as the quasicrystal phase Mg30Zn60Y10 in the quasicrystal alloy Mg67Zn30Y3. The third technique involves the refinement of eutectic silicon phase in hypereutectic Al‐15Si alloys to fine particles with the size of several nanometers through solid solution and precipitation refinement. Finally, in the deformation zone induced by HCPEB irradiation, the grain size can be refined to several hundred nanometers, such as the grain size of the hypereutectic Al‐15Si alloys in the deformation zone, which can reach ~400 nm after HCPEB treatment for 25 pulses. Therefore, HCPEB technology is an efficient way to obtain surface nanostructure.

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.

Deformation Twinning in Pure Nickel Induced by a High-Current Pulsed Electron Beam

Recent experimental evidence has shown that face-centered-cubic materials that are not normally associated with deformation twinning will twin during moderate high-current pulsed electron beam (HCPEB) processing. In this paper, we present an experimental investigation of deformation twinning in pure multi-crystalline nickel exposed to HCPEB irradiation from a Nadezhda-2 HCPEB device. The samples, which were irradiated with various numbers of pulses, were examined. The formation of a large number of twin lamellae on the treated surface was observed in the regions without surface melting. Moreover, a large strain located at the twin lamellae deformation was found. Transmission electron microscope analysis revealed that the deformation twinning was indeed triggered during the HCPEB irradiation. This suggests that the very high stresses and superfast strain rates induced via the rapid heating and cooling caused by the HCPEB irradiation lead to deformation twinning in coarse-grained nickel.

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.

Microstructures in polycrystalline pure copper induced by high-current pulsed electron beamdeformation structures

In order to investigate the superfast deformation mechanism of metal, the high-current pulsed electron beam (HCPEB) technique is employed to irradiate the polycrystalline pure copper. The microstructure of the irradiated sublayer is investigated by using transmission electron microscopy. It is suggested that the stress with very high value and strain rate is introduced within the sublayer after HCPEB irradiation. The dislocation cell and the tangle dislocation formed by cross slip are the dominant defects after one-pulse HCPEB irradiation, whereas, dense dislocation walls and twins are the central microstructures after five- and ten-pulse irradiation. The diffusion and the climb of the atomic plane can cause the formation of the steps at the grain boundary and (or) the twin boundary. Based on the structure characteristics of the irradiated surface, the possible deformation mechanism induced by HCPEB irradiation is discussed.

Surface modification of Al–20Si alloy by high current pulsed electron beam

Hypereutectic Al–20Si (Si 20wt.%, Al balance)alloy surface was treated with high current pulsed electron beam (HCPEB) under different pulse numbers. The results indicate that HCPEB irradiation induces the formation of metastable structures on the treated surface. The coarse primary Si particle melts, producing a “halo” microstructure with primary Si as the center on the melted surface. A supersaturated solid solution of Al is formed in the melted layer caused by Si atoms dissolving into the Al matrix. Cross-section structure analysis shows that a 4μm remelted layer is formed underneath the top surface of the HCEPB-treated sample. Compared with the matrix, the Al and Si elements in the remelted layer are distributed uniformly. In addition, the grains of the Al–20Si alloy surface are refined after HCPEB treatment, as shown by TEM observation. Nano-silicon particles are dispersed on the surface of remelted layer. Polygonal subgrains, approximately 50–100nm in size, are formed in the Al matrix. The hardness test results show that the microhardness of the α(Al) and eutectic structure is increased with increasing pulse number. The hardness of the “halo” microstructure presents a gradient change after 15 pulse treatment due to the diffusion of Si atoms. Furthermore, hardness tests of the cross-section at different depths show that the microhardness of the remelted layer is higher than that of the matrix. Therefore, HCPEB technology is a good surface modification method for enhancing the surface hardness of hypereutectic Al–20Si alloy.

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.

The vacancy defect clusters in polycrystalline pure nickle induced by high-current pulsed electron beam

High-current pulsed electron beam (HCPEB) technique is employed to irradiate the samples of polycrystalline pure nickel. The microstructures of the irradiated surface layers are investigated by using transmission electron microscopy (TEM). After HCPEB irradiation, very high value of residual stress is induced in the irradiated surface layer, which leads to the formation of dense dislocation walls and twins. Furthermore, a larger number of vacancy defect clusters including dislocation loops, stacking fault tetrahedra (SFT) and voids are also formed. Among three vacancy defect clusters, the number of SFT is much more than that of two other vacancy defect clusters. The lower dislocation density near the regions with dense SFT is observed and voids are likely to be present in these regions. It suggests that the stress with very high value and strain rate induced by rapid heating and cooling due to HCPEB irradiation could cause the shifting of the whole atomic plane synchronously.

The vacancy defect clusters in polycrystalline pure aluminum induced by high-current pulsed electron beam

The specimens of polycrystalline pure aluminum were irradiated with high-current pulsed electron beam （HCPEB）. The microstructure of vacancy defect clusters has been investigated in detail by using transmission electron microscopy （TEM）. The results reveal that large numbers of vacancy cells including dislocation loop and even stacking fault tetrahedra （SFT） can be formed in the specimens of polycrystalline pure aluminum irradiated with HCPEB. For the specimen irradiated with one pulse, vacancy dislocation loops were formed in the vacancy cells. SFTs became the dominating structures after five pulses. For the specimen irradiated with ten pulses, dislocation loops were frequently present and SFTs were only formed in some local zones of vacancy cells. In the vicinity of SFT formation, dislocation-free or very low dislocation densities were observed. It is suggested that high stress and strain rate induced by rapid heating and cooling due to HCPEB irradiation could cause the shifting of whole atomic planes synchronously. This is the more probable mechanism of the formation of SFTs.

Physical Model of Stress and Deformation Microstructures in AISI 304L Austenitic Stainless Steel Induced by High-current Pulsed Electron Beam Surface Irradiation

AISI 304L austenite stainless steel was irradiated by a high-current pulsed electron beam (HCPEB) source in different process. The deformation microstructures were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The relationship between stress characteristic and the microstructures has been established. The current numerical simulations of the thermal-mechanical process of HCPEB treatment were also reviewed comparing with the present experimental results. Our experimental results suggest that the value of the stress induced by HCPEB is between 102–103 MPa or even larger. This stress results in the change of microstructure of the irradiated material in deeper region beneath the surface. According to the experimental results, a new physical model of the thermal-stress process and related modification mechanism as a result of HCPEB irradiation has been developed.

Orientation-dependent deformation on 316L stainless steel induced by high-current pulsed electron beam irradiation

Electron backscatter diffraction has been used to study the severe plastic deformation occurring in the surface layer of an AISI 316L stainless steel treated by high-current pulsed electron beam (HCPEB). The exact nature of the triggered mechanisms was orientation-dependent. In particular, twinning was activated in grains having 〈1 1 1〉 orientation close to the sample normal direction while high misorientation deformation gradients were created by intense crystallograplic slip in some other grains. The nature of the different deformation mechanisms and their orientation dependence are discussed both from theoretical and experimental points of views by considering the biaxial quasi-static thermal stresses generated during the HCPEB bombardment.

Effect of high-current pulsed electron beam irradiation on the structure of La0.7Sr0.3CoO3 powder

The effect of pulsed electron irradiation on the long- and short-range order in the La0.7Sr0.3CoO3 ceramics is reported. Neutron and X-ray powder diffraction reveal that the unit cell symmetry and single-phase state of single and multiple irradiated La0.7Sr0.3CoO3 are preserved, while the oxygen atoms coordination changes towards the La0.5Sr0.5CoO3 structure. X-ray absorption data confirm this observation and further reveal the details of the shift and splitting of the Co 3+ t2g and eg atomic orbitals. Possible mechanisms of pulsed electron irradiation effect in La0.7Sr0.3CoO3 are discussed.

Effect of ‘duplex’ treatment on changes of physical and mechanical properties of steel (0.3wt% C)

Abstract After electrochemical deposition, subsequent thermal annealing and high-current pulsed electron beam (HCEB) treatment with melting and partial evaporation, the binary systems Cr–Fe, Ni–Fe and Al–Fe have been analyzed. Depending on the treatment regime, the formation of FeAl, Fe2Al5, FeAl3, Cr2O3, CrO and FeNi phases has been found. The HCEB irradiation resulted in a decrease or a total disappearance of oxides from the surfaces, an increase in microhardness and a decrease in the friction coefficient against steel.

Neutron Diffraction Investigation of Effects Induced in Materials by High-Current Pulsed Electron Beam Irradiation

Neutron Diffraction Investigation of Effects Induced in Materials by High-Current Pulsed Electron Beam Irradiation