Energy High Current Pulsed Electron Research Articles

Evolution of morphology, microstructure and phase composition of zirconia thin coating on copper as a result of low energy high current pulsed electron beam irradiation

Using X-ray diffraction, scanning and transmission electron microscopy we studied the evolution of the morphology, microstructure and phase composition in the near-surface layer of copper covered with thin (2.8 μm) ZrO2 coating induced by low-energy high-current pulsed electron beam irradiation (the surface energy density was in the interval of 5.0–18.0 J/cm2, the accelerating voltage was 30 kV, the pulse duration was 3.2 μs, the number of pulses was 10). The variation of adhesion of the coating to substrate was evaluated using scratch testing. The evaporation of the upper part of the coating during irradiation was found and the thickness of the coating nonlinearly decreased with the increase of the energy density. We discussed the reasons for the surface cracking taking into account microstructural changes in the near-surface layer of the material. The irradiation was found to transfer most of monoclinic ZrO2 phase in the as-deposited coating to tetragonal and, possibly, cubic one. The factors influencing the adhesive strength of the coating were revealed and a potential for the increase of adhesion was demonstrated. We showed that irradiation with enhanced surface energy density was required to obtain copper-based composite hardened with zirconia nanoparticles in the near-surface layer. The thickness of the composite layer may be as much as 6 μm.

Surface properties modification of magnesium alloys by low energy high current pulsed electron beam

The effects of low-energy high-current electron beam (LEHCEB) treatment on the surface properties of AZ91D and AM60B magnesium alloys were investigated. Experiments were done by controlling the beam energy, through the acceleration voltage (15 to 30 kV) and operating in two regimes: low (2 to 16) and high (20 to 100) number of pulses. The surface layers of alloys were characterized for phase and elemental composition by X-ray diffraction (XRD), Energy dispersive spectroscopy (EDS) and Glow Discharge Optical Emission Spectroscopy (GDOES). Surface modification has a significant effect on the mechanical properties evaluated by Vickers microindentation tests. The corrosion resistance behaviour was evaluated by potentiodynamic polarization tests in NaCl solution. • Low energy high current electron beam treatment allows intermetallic dissolution. • Mg selective evaporates from melted layer during the treatment. • Al 12 Mg 17 recombines after large number of pulses with higher microhardness. • AZ91D and AM60B alloys suffer microgalvanic coupling and low corrosion resistance.

Structure and Properties of Silumin Surface after Vacuum Arc Plasma-Assisted Deposition of Coatings Irradiated by Low Energy High Current Pulsed Electron Beam

The paper presents the results of modification of the silumin surface layer using a multicycle processing technique which combines the formation of the film (titanium)-substrate (silumin) system and the low energy high current pulsed electron beam (LEHCPEB) irradiation of submillisecond duration in one cycle. A KOMPLEX plasma-ion-assisted electron-beam setup (Institute of High Current Electronics SB RAS, Tomsk, Russia) is used for silumin treatment. Titanium is used as an alloying element. The thickness of the deposited film is 0.5 μm in each alloying cycle, the number of which is 1, 5 and 10. Surface alloying includes ion-bombardment cleaning and heating by hot and hollow cathodes of argon plasma discharge, with negative bias voltage supply to the specimen (initial heating up to preset temperature, surface cleaning and activation); plasma-enhanced chemical vapor deposition of metal films (argon is used as a carrier gas); and LEHCPEB irradiation of the film (titanium)-substrate (silumin) system. It is shown that multicycle alloying of the grade АK12 silumin (G-AlSi12, DIN, Germany) with titanium leads to a dissolution of silicon and intermetallic inclusions in the surface layer up to 30 μm thick, the formation of submicro- and nanocrystalline multiphase structure with the microhardness and wear resistance, which are 1.4 and 14.2 times higher than in cast silumin.

High Chrome Steel Modified by High-Current Pulsed Electron Beam

The paper presents the results of the structure and properties modification of 20Cr23Ni18 (AISI 310) high chrome austenitic stainless steel after the exposure to the low energy high current pulsed electron beam (LEHCPEB) irradiation. The AISI 310 is used to manufacture machine components and mechanisms operating at 1000–1050°С such as combustion chambers, turbine blades, and others. The SOLO plasma-ionassisted electron-beam setup (Institute of High Current Electronics SB RAS, Tomsk, Russia) is used for the steel treatment. The SOLO provides a low-pressure arc discharge with a grid-stabilized cathode plasma boundary and the open-boundary anode plasma. The electron-beam parameters include 18 keV energy; 20, 30 and 40 J/cm2 energy density; 50 and 200 μs pulse duration; the number of pulses – 3; 0.3 s–1 pulse frequency; ~0.02 Pa gas (argon) pressure in the process chamber. Scanning and transmission electron microscopies and the X-ray diffraction analysis are used to investigate the structure and phase composition of the steel, microhardness and wear resistance being regarded as the steel properties. It is shown that the exposure of the AISI 310 to high-current pulsed electron beam results in a high-speed melting of the surface layer, creates the crystallized cellular structure of submicron size, and enhances the wear resistance by 8 times.

The effect of phase transformations on the recovery of pulsed electron beam irradiated Ti-6Al-4V titanium alloy during scratching

The formation of martensitic α′ and α′′ phases in Ti-6Al-4V titanium alloy subjected to low energy high current pulsed electron beam (LEHCPEB) treatment with an energy density of 12–25 J/cm2 was revealed by X-ray diffraction and transmission electron microscopy. It was substantiated that the strain-induced phase transformation is the dominant mechanism underlying the deformation behavior of the melted surface layer of the titanium alloy samples during nanoindentation and scratch testing. It was found that the reverse transformation of the α′′ phase into the more close-packed α phase is responsible for the softening of the uppermost surface layer of the samples subjected to LEHCPEB treatment. The development of the direct and reverse α′′→α→α′′ martensitic transformations in the uppermost surface layer resulted in the improvement in elastic recovery of the treated Ti-6Al-4V samples after scratching.

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.

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.

Pulsed electron beam surface melting of CoCrMo alloy for biomedical applications

The use of CoCrMo alloys in biomedical applications has come under scrutiny recently due to unacceptable revision rates of certain hip resurfacing and total hip arthroplasty designs. Failure analysis has demonstrated that solid and soluble wear debris and corrosion products, released from the joints have resulted in adverse local tissue reactions (ALTR), pseudo-tumour formation and ultimately implant retrieval and replacement. In order to improve the surface properties of a wrought CoCrMo alloy, a low energy high current pulsed electron beam surface treatment process was investigated. Samples were irradiated at two cathode voltages of 15 and 35kV at pulse numbers of 1, 15 and 25. At low beam energies a polishing effect was observed as a result of surface melting. At higher beam energies a higher Ra value was the result of the formation of surface craters. Nano-indentation and scratch testing of the treated surface were carried out using a nano-indenter. Depth profiling nano-indentation was performed using a Berkovich tip in load control. Loading was performed in 8mN increments up to 160mN at a rate of 3.5mN/s, with a 60s dwell period and 40% unloading. The results demonstrated that the surface treatment process reduced both the modulus and the hardness of the surface in comparison to the control. Scratching was performed with a 20μm radius spherical diamond and loading rate of 2mN/s up to a maximum of 100mN, over a 1mm scratch length. Similar scratch depths for both control and treated surfaces were observed. However, an improvement in the dynamic friction coefficient was observed at certain beam energies. These results are discussed in the light of XRD evidence that suggested rapid cooling of the surface induced preferential formation of an ε-martensite HCP phase which may be beneficial for biomedical applications.

Formation of ultrafine twinned austenite on a cold rolled 316L stainless steel induced by pulsed electron beam treatment under heating mode

The formation of highly-twinned ultrafine austenite on a cold rolled AISI 316L steel induced by low energy high current pulsed electron beam (LEHCPEB) treatment has been investigated. It is shown that rapid phase transformation, recrystallization and recovery can be achieved simultaneously through pulsed electron beam treatments under heating mode without melting the surface. The extremely fast thermo-mechanical cycles induced by the LEHCPEB account for the surface austenization and the formation of ultrafine twins. The results demonstrated that pre-deformation combined with LEHCPEB treatment under heating mode can be used to create ultrafine microstructures with special boundary characteristics in the surface layer.

Numerical investigation of the change of dislocation density and microhardness in surface layer of iron targets under the high power ion- and electron-beam treatment

The effect of the Low Energy High Current Pulsed Electron Beam (LEHCPEB) and High Power Pulsed Ion Beam (HPPIB) surface treatment on the dislocation density in iron target has been numerically investigated. At typical technological irradiation parameters the major factors for modification of dislocation density are the thermo-stresses in the heat affected zone. Irradiation regimes, within the process of which there is no melting, generate one maximum of dislocation density, at the same time the regimes resulting in melting produce two maximums of dislocation density: one of them is localized inside the layer which has crystallized from melt, and the other one at the melt–solid interface. The increase of enclosed energy density and the reduction of pulse duration make the excited stress wave even more significant for the dislocation modification. This wave causes hardening of the material in deeper layers which may eventually result in the influence on the whole volume of the target.

Evolution of residual stress states in surface layers of an AISI D2 steel treated by low energy high current pulsed electron beam

The quantitative evolution of the residual stress states in the surface layers of an AISI D2 steel after Low Energy High Current Pulsed Electron Beam (LEHCPEB) treatment has been investigated by using X-ray diffraction technique. The initial material contained mainly ferrite plus carbides and the ferrite had a compressive stress of about 560 MPa. After the LEHCPEB treatment, the residual stress of the ferrite in the surface layers became tensile in nature, reaching values as high as 730 MPa. A residual tensile stress also existed in the austenite formed at the surface. The stress increased from 170 MPa after 5 pulses to 700 MPa after 25 pulses of treatment. The evolution of the residual stress state in the surface layers can be explained by taking into account the fast thermal cycle, deformations induced by the dynamic thermal stress at the surface together with melting and phase transformations generated by the LEHCPEB treatment.

Crater-formation-induced metastable structure in an AISI D2 steel treated with a pulsed electron beam

A detailed investigation concerning the microstructure and phase formations in the crater-erupted areas formed under low energy high current pulsed electron beam bombardment has been carried out for a treated AISI D2 steel. The crater formations are initiated at carbides. Such carbide eruption events change the composition, phase selection and grain growth behaviour inside the craters. Under these extremely non-equilibrium conditions, amorphous patches and feathery type structures containing twinned nano-grains are retained.

Microstructure and property modifications in a near α Ti alloy induced by pulsed electron beam surface treatment

The effect of the low energy high current pulsed electron beam (LEHCPEB) surface treatment on the microstructure and properties of a near α Ti alloy have been investigated. Both the melted layer and solid state transformation layer of the LEHCPEB treated samples contained α’ martensite. The size of the former β grains suggests a cooling rate of about 107Ks−1. Selective Al evaporation occurred at the top surface of the melted layer and affected both surface hardness and corrosion properties.

Surface modification of TA2 pure titanium by low energy high current pulsed electron beam treatments

Surface integrity changes of TA2 pure titanium including surface topography, microstructure and nanohardness distribution along surface layer were investigated by different techniques of low energy high current pulsed electron beam treatments (LEHCPEBTs). The surface topography was characterized by SEM. Moreover, the TEM observation and X-ray diffraction analysis were performed to reveal the surface modification mechanism of TA2 pure titanium by LEHCPEBTs. The surface roughness was modified by electron beam treatment and the polishing mechanism was analyzed by studying the cross section microstructure of electron beam treated specimens by SEM and TEM. The results show that the surface finish obtains good polishing quality and there is no phase transformation but the dislocations by LEHCPEBT. Furthermore, the nanohardness in the surface modified layer is improved. The remelt and fine-grain microstructure of surface layer caused by LEHCPEBTs are the main polishing mechanism and the reason of modification of surface topography and the increment in nanohardness is mainly due to the dislocations and fine grains in the modified layer induced by LEHCPEBT.

Surface modification of pure titanium by pulsed electron beam

The microstructure, hardness and corrosion resistance of commercially pure Ti treated by low energy high current pulsed electron beam (LEHCPEB) have been investigated. The thin near-surface melted layer rapidly solidified into β and subsequently transformed into ultrafine α′ martensite. This has led to a drastic improvement of the corrosion properties and a significant increase (more than 60%) in hardness of the top surface.

Microstructure Modifications Induced by Pulsed Electron Beam in Steels

The present paper presents the first results of an ongoing research dedicated to the analysis of microstructure in steels surfaces treated by Low Energy High Current Pulsed Electron Beam (LEHCPEB). Various steels - 316L (a stainless steel), D2 (a cold-worked die steel) and 4Cr13 (a martensitic steel) - have been treated by LEHCPEB in order to improve the understanding of the surface microstructure modifications induced by this treatment. The microstructures in the modified surface were characterized by microscopy and diffraction techniques.

Microstructure, Texture and Residual Stresses Induced by Surface Thermo-Mechanical Treatments

This paper reviews some recent results concerning surface integrity of materials processed with two important developing techniques: high speed machining (HSM) – here applied to the difficult case of Ti alloys – and low energy high current pulsed electron beam (LEHCPEB) surface treatment of steels. The effect of the processing parameters on the development of microstructure, texture and residual stresses is detailed for modifications occurring both at the surfaces and sub-surfaces.

Grain Refinement and Hardening Induced by Heavy Deformation Using Low Energy High Current Pulsed Electron Beam Surface Treatment

The low energy high current pulse electron beam (LEHCPEB) irradiation induces ultra fast dynamic temperature fields in the surface of the material to which is associated dynamic stress fields that causes intense deformation at the material surface and sub-surface. Improved surface properties (hardness, corrosion resistance) can be obtained using the LEHCPEB treatment. Under the “Melting” mode, the top surface (few µm) which is melted and rapidly solidified (107 K/s), can solidify has nano-domains formed from the highly under-cooled melt. The thermal stress wave that propagates in the sub-surface imposes strain hardening and grain size refinement. This induces a sub-surface hardening that can extent over about 100 µm. The use of the “Heating” mode is less conventional. This mode can promote grain size refinement, hardening as well as texture modification without modification of the sample geometry.

Microstructure and property modifications of an AISI H13 (4Cr5MoSiV) steel induced by pulsed electron beam treatment

In the present work, surface modifications generated by the low energy high current pulsed electron beam (LEHCPEB) treatments have been investigated on an AISI H13 (4Cr5MoSiV) steel. From the observations of scanning electron microscopy, x-ray diffraction, and electron back scattering diffraction determinations, it could be established that the final structure in the melted layer is a mixture of ultrafine δ phase, martensite, and residual austenite. The formation of the heterogeneous microstructures on the surface layer is related to the very rapid heating, melting, solidification, and cooling induced by the LEHCPEB irradiation. After the LEHCPEB treatment, the wear resistance of the steel effectively improved. This can be mainly attributed to the higher hardness of the ultrafine structures formed on the top surface and the hardened subsurface layers after the treatment.

Mechanisms of hardening, wear and corrosion improvement of 316 L stainless steel by low energy high current pulsed electron beam surface treatment

The mechanisms of corrosion and wear improvements by low energy high current pulsed electron beam (LEHCPEB) have been investigated for an AISI 316 L steel. Selective purification followed by epitaxial growth occurred in the top surface melted layer (2–3 μm thick) that was softened by tensile stresses and, to a much lower extent, by lower efficiency of MnS precipitation hardening. Electrochemical impedance spectroscopy and potentiodynamic polarization analyses used to model the corrosion behavior revealed that, while craters initiated at MnS inclusions initially served as pitting sites, the resistance was increased by 3 orders of magnitude after sufficient number of pulses by the formation of a homogeneous covering layer. The wear resistance was effectively improved by sub-surface (over 100 μm) work hardening associated with the combine effect of the quasi-static thermal stress and the thermal stress waves. The overall results demonstrate the potential of the LEHCPEB technique for improving concomitantly the corrosion and wear performances of metallic materials.