Pulsed Beam Treatment Research Articles

Surface modification of AISI 1045 steel by pseudospark based pulsed electron beam

In this paper, the surface modification of AISI 1045 steel by a hollow cathode discharge (HCD) based pulsed electron beam and the formation of the surface microstructure via a short time duration of the pulsed beam treatment are the main focus under investigation. The electron beam in our work is generated by a compact HCD electron beam device named pseudospark discharge, which is characterized by the fast plasma ignition and quenching rates. And the surface microstructure, composition and microstructure crystallographic information of AISI 1045 steel pre and post pseudospark based pulsed electron beam modification are investigated by using metallographic microscope, scanning electron microscope (SEM), X ray diffraction (XRD) and Electron Back Scatter Diffraction Patterns (EBSD). The experimental results demonstrate that a microstructure consisting of cementite and C-supersaturated austenite is formed in the near-surface region after the pseudospark based pulsed electron beam irradiation. Both the phenomenon of the metal target grain refinement and the mechanism of the grain refinement evolution are investigated by a diversity of diagnostic methods. It is also showed that the material surface modification process is highly dependent on the transient properties of the HCD-based pulsed electron beams, which offers a new and effective method to improve the performances of the metallic material surface microstructure and other properties.

Formation of large grains by epitaxial and abnormal growth at the surface of pulsed electron beam treated metallic samples

The aim of the present work was to clarify that the rapid solidification process involved during surface pulsed beam treatment does not necessarily leads to the formation of nano or ultrafine grains. To demonstrate this, two types of metallic materials (a slightly deformed 2024 aluminum alloy and nickel based single grain superalloys) have been irradiated 15 times by high current pulsed electron beam. Epitaxial growth was triggered during the re-solidification of the superalloys, leading to the formation of a deformed single grain. Thanks to the repeated combinations of epitaxial growth and solid state secondary recrystallization, the pulsed electron beam treatment has led to the formation of large (millimetric) grains, that were also 4 to 5 times thicker than the depth of the melted zone, at the surface of the aluminum alloy.

Wear resistance improvement of a commercially pure titanium by high current pulsed electron beam treatment

A commercially pure titanium was selected as target material and treated by high current pulsed electron beam. The phase and structure changes occurring in the modified surface layers were observed with optical microscopy, scanning electron microscope, and transmission electron microscope. The increase in the wear resistance was observed for the pure titanium samples after pulsed electron beam surface melting. The mechanism for wear resistance modification was discussed. The results indicated that the presence of ultrafine martensite and defects in the treated surface layer were key factors for the improvement of the wear properties of pure titanium treated by high current pulsed beam treatment.

Analysis of the evaporation and re-condensation processes induced by pulsed beam treatments

A physical model is proposed to describe the evaporation phenomena taking place at the surface of pulsed energetic beam treated samples. Samples of a NiTi alloy and a TiAl based alloy were subjected to high current pulsed electron beam (HCPEB) treatment for an increasing number of irradiation (5, 10 and 20 pulses). The results of their surface chemistry analysis have been confronted to the model. For the sample treated with 5 pulses, the experimental composition profiles revealed a selective evaporation of Ni over Ti in the NiTi alloy and Al over Ti, Cr, Nb in the TiAl based alloy, which is nicely reproduced by the simulated composition profiles. As the number of pulses increases, the results show that a part of the vapour re-condensed onto the surface. This leads to an inversion of the composition profile at the top surface of the samples, which cannot be predicted by the theoretical model. This cyclic process of evaporation and recondensation leads to the cyclic variation of compositions in the surface layer.

A review of mixing processes in Ta/Fe and Mo/Fe systems treated by high current electron beams

The review deals with a brief analysis of results on mixing in Ta/Fe and Mo/Fe systems using high current electron beams. Theoretical models of mass-transfer, which the authors used for the interpretation of experimental results obtained after pulsed beam treatment, have been considered. The formation of amorphous phase, intermetalloid phases Fe 2Ta, as well as the formation of high dislocation density up to 5×10 10 cm −2 have been shown. A non-equilibrium metastable phase Fe 4Mo(Fe 80Mo 20) and, possibly Fe 96Mo 4, is formed as a result of irradiation of Mo/Fe system. The formation of a surface complex structure and near surface layers result in an enhancement of corrosion resistance, an increased depth of the hardened layer and a higher resistance to brittle damaging.