Pulsed Electron Beam Processing Research Articles

Metallurgical patterns of the formation of W–Zr surface alloys via pulsed electron-beam processing

In this study, W–Zr surface alloys (SAs) were synthesized by low-energy high-current electron beam (LEHCEB) processing of preliminary deposited tungsten films on zirconium substrates in a single vacuum cycle. Then, their microstructure, as well as both chemical and phase compositions were investigated. Also, computer simulation of the dynamics of temperature fields was carried out. After LEHCEB processing of the Zr substrate with the preliminary deposited W film, the constituent element distributions were non-uniform over the surface of the W–Zr SA at the energy density of 3.5 J/cm2. Rising the energy density up to 5.5 J/cm2 resulted in a smoother and more homogeneous W–Zr SA. At the energy density of 3.5 J/cm2, the average tungsten content over the surface was 53 ± 39 at.%, while it was only 26 ± 2 at.% at 5.5 J/cm2. All W–Zr SAs consisted of the W phase (in different proportions), tungsten-rich solid solutions in the stabilized β-Zr phase, and the W2Zr intermetallic compound. The contents of the β-Zr and W2Zr phases enhanced with rising the energy density due to a greater amount of dissolved tungsten. Based on the obtained results, a scheme was proposed describing the formation of the SAs upon LEHCEB processing.

Модификация поверхности карбидовольфрамового композиционного материала методами электронно-ионно-плазменного воздействия

The surface of a porous tungsten carbide pseudoalloy of the WC-WCoNiFe system has been modified by a pulsed electron beam and the method of combined electron-ion-plasma, which includes vacuum arc deposition of a film from VT1-0 titanium alloy (1 μm) and subsequent pulsed electron-beam processing of the"coating/substrate" system. Optimal modes of pulsed electron-beam processing were found depending on the energy density in the pulse (40-65 J/cm2) and the pulse duration (150-200 µs). It is shown that electron-beam surface treatment of a material of this class under optimal conditions of electron-beam processing makes it possible to increase the microhardness of the surface layer by 15% relative to the initial material. Using the methods of X-ray phase analysis, it was revealed that the increase in microhardness is due to the formation of the W2C phase in the surface layer and a decrease in the amount of the binder (WCoNiFe). It is concluded that the combined electron-ion-plasma treatment of a porous tungsten carbide pseudoalloy of the WC-WCoNiFe system makes it possible to form a modified layer with a minimum number of pores and cracks on the surface.

Technical Note: Effect of High-Current Pulsed Electron Beam Processing of Zr-1%Nb Alloy on Its Oxidation Kinetics at 1,200°C in Air and Steam

The paper reports the effect of high-current pulsed electron beam (HCPEB) processing of the Zr-1%Nb alloy as one of the most widely used in water-cooled nuclear reactors, based on the kinetics of its oxidation at 1,200°C in air and steam (these conditions are typical for potential loss-of-coolant accidents). It was shown that HCPEB processing caused a change in the surface morphology of the samples. In particular, craters with diameters of about 100 μm were found on the modified surfaces. They had initiated at an energy density of 5 J/cm2 and were characterized by relevant reliefs with microcracks. After HCPEB processing at 10 J/cm2, the craters were deeper with fractured surface layers. In addition, a pronounced surface relief corresponding to quenched martensitic microstructures was observed on the modified sample surfaces that had formed due to high heating and cooling rates. Due to sufficient degradation of the sample surfaces after HCPEB processing at 10 J/cm2, the kinetics of high-temperature oxidation was estimated only for the as-received samples and ones treated at 5 J/cm2. It was found that the as-received samples showed slightly greater weight gain levels in both air and steam environments, which fully correlated with the thickness ratio of the oxide, α-Zr(O), and prior-β layers. These phenomena and further research directions were discussed.

Structure and mechanical properties of stainless-steel specimens, made by additive method, after pulsed electron beam treatment

The article presents a method for finishing the surface of metal products made by sequential electron-beam surfacing, which consists in modifying the surface with an intense low-energy electron beam of submillisecond duration. On the example of 308LSi stainless steel, the results of such processing are demonstrated, the optimal modes of exposure are determined. It is shown that as a result of pulsed electron-beam processing, a homogeneous polycrystalline structure without cracks is formed on the surface with unchanged, relative to the initial material, elemental composition, strength (microhardness) and tribological (wear rate) properties. In this case, the surface roughness is reduced to 2.1 times in the longitudinal direction relative to the surfacing plane, to 5.2 times in the transverse direction. Tensile tests of specimens showed anisotropy of mechanical properties depending on the direction of tension relative to the surfacing plane, which decreases after surface pulse electron-beam processing.

Электронно-ионно-плазменная модификация поверхности магниевого сплава MA-2 для формирования легированных слоев с улучшенными механическими свойствами

The surface alloying of MA-2 magnesium alloy with aluminum was carried out by the method of combined electron-ion-plasma exposure, which consists in deposition of a thin (1 μm) film of aluminum from an arc discharge plasma and subsequent pulsed electron-beam processing of the "film/substrate" system. The optimal modes of surface Al-Mg alloy formation by the method of electron-ion-plasma exposure were revealed as a result of temperature measurements carried out on the surface of the specimens during irradiation with a pulsed electron beam and depends on energy density and pulse duration. It is shown that the combined surface treatment in optimal modes makes it possible to increase microhardness of the alloyed layer by up to 1.7 times due to alloying of the magnesium alloy surface with aluminum and formation of particles of Mg17Al12 intermetallic phase.

Effect of electron-beam processing on structure of electroexplosive electroerosion resistant coatings of CuO-Ag system

The application of electron-beam processing enabled to obtain the mirror luster of electroexplosive coating surface of CuO-Ag system, to reduce the roughness without the loss of the composite material, to homogenize the surface layer of the coatings to the whole thickness of the coating being equal to 40 μm. The utilization of the selected regimes of pulsed electron—beam processing results in the realization of the processes of surface layer structurization of electroexplosive coating of CuO-Ag system. The phase composition of electroexplosive coating of CuO-Ag system after electron—beam processing presents the following phases: Ag, Cu2O, Cu64O and Cu. The electroexplosive coating of CuO-Ag system fail after 3000 cycles of switching on / switching off in the course of the accelerated electroerosion resistance tests. During the accelerated electroerosion resistance tests the electrical resistance is acceptable to the weak—current electrical contacts and is within the interval from 5.8 to 14.8 μOhm. The wear resistance tests have shown that EES of copper is accompanied by ≈3.3-fold increase in wear resistance of the modified layer; in this case, ≈1.3-fold increase in the fiction coefficient is observed. Nanohardness of coating layer varies within 280 MPa to 290 MPa at the average hardness value being 866.5 MPa. Young modulus varies within 24.3 GPa to 71.7 GPa at the average value of the modulus of 49.6 GPa.

NOx removal with multiple pulsed electron beam free of catalysts or reagents

A catalyst free approach for nitrogen oxides (NOx) removal has been developed at the United States Naval Research Laboratory. Our goals were to assess the ability of pulsed electron beam to enhance NOx removal at potential lower capital cost with greater efficiency than other large scale NOx removal methods. Removal efficiency over 95% has been attained for NOx concentrations of 1000 parts per million (ppm), 500 ppm and 200 ppm in nitrogen atmosphere. The NOx concentration dropped from 204 ppm to below 4.8 ppm after 10 shots supplying a total dose of 65 kGy. The resultant chemicals after catalyst free pulsed electron beam processing of NOx are nitrogen and oxygen, same as components of air. Pulsed electron beams in a catalyst free approach remove a larger percentage of NOx than continuous wave electron beam with a catalyst. Catalyst free approach removes issues of handling, collecting, transporting and efficiently distributing chemical byproducts. Pulsed electron beams are as efficient as continuous wave electron beams for small removal percentages and have a significant advantage at higher fractional removal percentages of NOx. Preferential destruction of NO species relative to the removal of NO2 species is observed in the pulsed electron beam reaction chamber. The energy required to remove a kilogram of NOx is nearly the same at pressures of 1.16 atmospheres and 1.02 atmospheres.

Nanocrystalline and amorphous surface structure of 0.45%C steel produced by high current pulsed electron beam

We study in this article the microstructure and phase transformation on the near-surface of 0.45% C carbon steel during the high current pulsed electron beam processing by using electron microscopy. Based on a physical model, the temperature profile is simulated for carbon steel. The depth of heat-affected zone, the initial melting position, heating rate and quenching rate are computed. The original crystalline structure was changed to a different degree that grew with the numbers of bombardment, and in the near-surface layer amorphous states and nanocrystaline structures consisting of grains of γ-phase and cementite were formed after multiple pulses.

Temperature profile and crater formation induced in high-current pulsed electron beam processing

We study in this article the formation mechanism of craters on a metal surface during the high current pulsed electron beam processing. Based on experimental investigations and a physical model, the melting process and their temperature profiles are simulated for substrates of aluminum and steels. Initial melting positions, crater depths, and melting layer thickness are computed, the results being in a good agreement with experimental data. It is also confirmed that the temperature rises faster at a subsurface layer instead of at the outermost surface due to the maximum energy deposition located at about 1/3 of the total penetration depth of the beam. Such a subsurface layer heating and melting mechanism causes eruptions of the subsurface layer liquid matters through the outermost surface and produces the typical surface crater morphology.

Simultaneous Removal of NOx and SO2 from Combustion Flue Gas by Pulsed Electron Beams

This paper presents the results of plasma chemistry calculations to study the effect of dose rate, pulse length and pulse repetition rate on pulsed electron beam processing of NOx and SO2 in combustion flue gases. The main objective is to determine if the proposed combinations of dose rate, pulse length and pulse repetition rate would have any deleterious effect on the utilization of radicals for pollutant removal. For a dose rate of 2 × 106 kGy per second and a pulse length of 30 nanoseconds, the average dose per pulse is sufficiently low to prevent any deleterious effect on process efficiency because of radical-radical recombination reactions. During each post-pulse period, the radicals are utilized in the oxidation of NOx and SO2 in a timescale of around 200 microseconds; thus, with pulse frequencies of around 5 kilohertz or less, the radical concentrations remain sufficiently low to prevent any significant competition between radical -pollutant and radical - radical reactions. The main conclusion is that a pulsed electron beam reactor, operating with a dose rate of 2 × 106kGy per second, pulse length of 30 ns and pulse repetition rate of up to around 5 kHz, will have the same plasma chemistry efficiency as an electron beam reactor operating with a very low dose rate in continuous mode

Soft Vacuum, Pulsed Electron Beam Processing of Polyimides

ABSTRACTWe report on the successful patterning of polyamic acid over wide areas using 28 kV pulsed electron beams produced in 30 mTorr air. The pattern degradation during the 350°C, 1/2 hr, imidizing thermal cure is prevented by pulsed, flood electron beam hardening of the developed polyamic acid patterns using the same soft vacuum, pulsed electron beam apparatus. It is also shown that a CW, low voltage, 1 to 3 kV electron beam sustained oxygen discharge can be used to completely strip the hardened, imidized material which is difficult to remove by wet methods. We also present, dose versus thickness remaining characteristics as a function of electron source to substrate distance and some examples of polyimide patterning.

Pulsed Electron Beam Processing of Silicon

ABSTRACTContinued study [1] of pulsed electron beam annealing (PEBA) of thin silicon films deposited by LPCVD on silicon substrates has shown that a thin SiO2 interface remains intact during melt. PEBA of ion-implant damage in silicon has been shown to correlate dopant activation with melt depth. Also, PEBA was superior to thermal annealing of ion-implant damage in processing solar cells in some types of polycrystalline silicon material.

Pulsed Electron Beam Processing of Silicon Devices

ABSTRACTPulsed electron beams [1] were used to anneal ion-implanted diodes, transistors, and resistors. Devices were fabricated by patterning a thermal oxide on a silicon wafer, ion-implanting and pulse processing with the oxide in place, and then applying contacts. Oxide films over 0.3 micron thick were not damaged, and the silicon below these films was not melted by the pulsed electron beam. Low-dose (101311B+/cm2), implanted, pulse-annealed resistors showed no change in sheet resistance for oxide windows 2.5 to 50.0 microns wide. Diodes were fashioned with good forward and reverse I-V characteristics, with m=1.09 and IO=2.7×10−10 A/cm2 for I=IO exp(qV.mkT)−1 , when a low-temperature (550˚C, 1 hr), postpulse anneal was included in the process sequence. Both bipolar and FET types of transistors were fabricated. Results compare favorably with thermal annealing cycles.