Electron Beam Geometry Rewrites the Surface Properties of Titanium Alloy

Titanium alloys are famous for being stubborn. Ti–6Al–4V, the workhorse of the aerospace and biomedical worlds, offers an exceptional combination of strength, low density and corrosion resistance, yet its surface often fails to live up to the demands engineers place on it. Fatigue cracks begin at the surface, wear begins at the surface, and implants interact with living bone through the surface. A new comparative study published in the Journal of Materials Science by a team from the Panin Institute of Strength Physics and Materials Science, the Tomsk Scientific Center and the Institute of High Current Electronics in Russia now shows that the way an electron beam is delivered to that surface can completely change the outcome of the treatment, turning the same alloy either harder or more ductile without altering its bulk chemistry.

The research, led by L. L. Meisner together with F. A. D’yachenko, M. G. Ostapenko, S. N. Meisner, A. B. Markov, E. V. Yakovlev, P. P. Kiziridi and A. V. Solovyov, compared two fundamentally different irradiation geometries of a low-energy, high-current electron beam. In the classical axially symmetric configuration, the beam strikes the target perpendicularly, like a flashlight pointed straight at a wall. In the radially converging configuration, electrons arrive from a ring of emission sources and converge on the sample from all sides at grazing angles, wrapping the surface in a cylindrical shower of charged particles. The team deliberately held the key irradiation parameters constant: an energy density of approximately 3.7 joules per square centimetre, a pulse duration of roughly two to three microseconds, and ten pulses per treatment. Only the geometry changed.

That controlled design is what makes the result so striking. Because energy density, pulse length and pulse count were matched, any difference in the resulting surface layers could be attributed to the direction and distribution of the incoming electrons rather than to the total energy deposited. The researchers found that both treatments produced modified surface layers, but those layers differed dramatically in phase composition, crystallographic texture, residual elastic stress state, hardness and ductility. In effect, the same alloy, the same beam and the same energy budget produced two entirely different materials at the surface, depending solely on how the electrons converged.

With the axially symmetric beam, the surface layer hardened. The treatment generated high compressive residual stresses acting perpendicular to the treated surface, a state that materials engineers prize because compressive stress at the surface suppresses crack opening and thereby improves fatigue life. The perpendicular bombardment drives rapid heating and even more rapid self-quenching of a thin melt layer, and the associated phase and structural transformations leave the near-surface region in a strengthened condition. For components that must resist cyclic loading, such as turbine discs, landing gear elements or orthopaedic stems, this is exactly the kind of surface state one wants.

The radially converging geometry told the opposite story. When the beam converged on the sample from the sides, the modified layer became softer and more ductile than the original material, with hardness actually dropping below its initial value. At first glance, softening a titanium alloy surface sounds like a defect, but the authors frame it as an opportunity. A ductile surface layer can accommodate strain, delay crack initiation under contact and impact conditions, and improve the performance of parts that must deform rather than fracture. The team proposes physical explanations for this behaviour rooted in the different thermal and stress fields generated when energy arrives obliquely from all directions rather than head-on, including altered phase transformation pathways and a distinct evolution of crystallographic texture in the treated zone.

Texture, the preferred orientation of crystals, is a subtle but powerful variable in titanium alloys. Ti–6Al–4V is a two-phase alloy combining the hexagonal alpha phase with the body-centred cubic beta phase, and the mechanical response of the surface depends strongly on which crystallographic planes lie parallel to it. The investigators characterised the treated layers using X-ray diffraction and electron microscopy, quantifying phase fractions, pole figures and residual elastic stresses, and measuring hardness and ductility by instrumented indentation following the Oliver–Pharr methodology. Their analysis revealed that the two irradiation geometries select different variant populations during the rapid alpha-to-beta and back-to-alpha transformations that occur under the microsecond melt-and-quench cycle, imprinting different textures and therefore different anisotropic mechanical behaviour onto the surface.

The low-energy, high-current electron beam itself is a well-established tool with a rich history. Pioneered in Tomsk, the technique relies on a plasma-anode electron gun that delivers intense pulses of relatively low-energy electrons, typically tens of kilovolts, which deposit their energy within a micrometre-scale depth of the surface. Each pulse melts that thin layer in microseconds, and the cold bulk underneath quenches it at extraordinary cooling rates, producing refined microstructures, dissolved precipitates and dense defect populations that conventional furnace treatments cannot achieve. What the new study adds is the recognition that beam geometry is a free design parameter, one that had been largely overlooked because most installations worldwide use the conventional perpendicular configuration.

The radially converging source used in the experiments is itself a recent development. Described in earlier work by Kiziridi and Ozur, the source generates a hollow, ring-shaped beam whose energy density distribution across the cross-section was characterised in a follow-up publication in Instruments and Experimental Techniques. This apparatus allowed the team to treat samples in a configuration impossible with standard guns, opening a genuinely new processing window. The current paper builds on the group’s 2025 study in the same journal, which examined residual stress and texture evolution in Ti–6Al–4V under radially converging beams alone; the new work completes the picture by placing those results side by side with the axially symmetric case under matched conditions.

The practical implications extend across industries. Aerospace manufacturers are under constant pressure to extend the fatigue life of titanium components, and surface treatments that introduce compressive residual stress, such as shot peening and laser shock peening, are already standard practice. An electron beam process that achieves hardening with precisely controlled compressive stresses, while leaving no embedded media on the surface and treating complex shapes with a scanning beam, could compete in that space. Conversely, the ductility-enhancing radially converging treatment may suit applications where surface cracking under contact stress is the limiting failure mode, or where a compliant surface layer could improve the mechanical compatibility of implants with bone, which is stiffer than titanium and stresses the implant surface in complex ways.

What elevates the study beyond incremental process optimisation is its demonstration that surface engineering is a geometric problem, not merely an energetic one. Two beams carrying identical energy per pulse, delivered for identical durations and repeated an identical number of times, sculpted the same alloy into two different surface materials with opposite mechanical characters. As pulsed-beam sources with configurable geometries mature, designers may one day specify not just the hardness of a titanium part’s surface but the full stress-and-texture recipe, dialling in hardening or softening on demand. The Tomsk team’s comparative analysis provides the first rigorous, like-for-like evidence that the dial exists, and it points toward a future where the direction of an electron beam matters as much as its power.

Subject of Research: Surface modification of the Ti–6Al–4V titanium alloy by low-energy high-current pulsed electron beams in different irradiation geometries

Article Title: Comparative analysis of Ti–6Al–4V surface modification under axially symmetric and radially converging electron–beam irradiation configurations

Article References: Comparative analysis of Ti–6Al–4V surface modification under axially symmetric and radially converging electron–beam irradiation configurations. (n.d.). https://doi.org/10.1007/s10853-026-13825-2

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13825-2

Keywords: Ti-6Al-4V, electron beam treatment, surface modification, low-energy high-current electron beam, radially converging beam, residual stress, crystallographic texture, hardness, ductility, titanium alloys, phase transformation, materials science