Structural transformation and residual stresses in surface layers of a + b titanium alloys nanotextured by femtosecond laser pulses Yu. R. Kolobov • E. V. Golosov • T. N. Vershinina • M. V. Zhidkov • A. A. Ionin • S. I. Kudryashov • S. V. Makarov • L. V. Seleznev • D. V. Sinitsyn • A. E. Ligachev Received: 25 August 2014 / Accepted: 15 December 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract Surface topography, phase composition and compressive residual stresses were characterized in surface layers of a ? b titanium alloys VT6 (Ti–6Al–4V) and VT16 (Ti–3Al–4.5V–5Mo) nanotextured by 744-nm, 120-fs-laser pulses. The relative content of b-phase, along with the residual compressive stresses, increases signifi- cantly in both these materials over the depth *0.2 l in the nanotextured surface layer comprised by nanograins and remains almost unchanged at higher depths of 1–2 l in bulk. The laser-driven a ? b phase transformation is related to the combined effect of ultrafast heating/cooling, strong (multi-GPa) shock waves, chemical segregation and nanograin formation induced during the ablative surface nanotexturing. 1 Introduction Femtosecond (fs) laser multi-scale ablative texturing of materials surfaces, broadly varying their optical, electrical and other physicochemical properties is attracting rapidly increasing interest as an advanced prototyping method in contemporary material research [1–4]. Following the pio- neering fs-laser ablation studies [5–9], this approach employs the key advantage of fs-laser pulses—their high peak power at the minute pulse duration, enabling high- temperature [10, 11] and high-pressure shock-wave [10– 12] material processing within the minimal—submicron or micron-wide—heat-affected zone [13] at extremely high isochoric heating (10 15 –10 16 K/s) and cooling (10 12 K/s) rates. Moreover, such fs-laser-driven high-temperature processing of compound materials accompanied by intense sub-ablative subsurface boiling [14] may also result in pronounced chemical segregation, yielding in depleted surface concentration of more volatile components [2]. As a result, non-equilibrium phase transformations may occur on laser-treated surfaces [11, 15–18], resulting in signifi- cant internal residual stresses, as demonstrated presumably for semiconducting materials. However, such fundamental structural studies are still missing for fs-laser-generated textures of important con- struction metals and alloys, as compared to their topo- graphic or chemical studies. For titanium, being the basic construction and biomedical material, multi-scale surface relief [1, 19–25] and related chemical (oxidation [26, 27] or segregation [2, 14]) nano- and micro-scale modifications induced by fs lasers were actively investigated during the Yu. R. Kolobov (&) Á E. V. Golosov Á T. N. Vershinina Á M. V. Zhidkov REC Nanostructured Materials and Nanotechnologies, Belgorod State National Research University, 308015 Belgorod, Russia e-mail: kolobov@bsu.edu.ru Yu. R. Kolobov Á E. V. Golosov The Institute of Problems of Chemical Physics, RAS, 142432 Chernogolovka, Russia M. V. Zhidkov Institute of Structural Macrokinetics and Materials Science, RAS, 142432 Chernogolovka, Russia A. A. Ionin Á S. I. Kudryashov (&) Á S. V. Makarov Á L. V. Seleznev Á D. V. Sinitsyn Lebedev Physical Institute, 119991 Moscow, Russia e-mail: sikudr@lebedev.ru S. I. Kudryashov National Research Nuclear University ‘‘MEPhI’’ (Moscow Engineering Physics Institute), 115409 Moscow, Russia A. E. Ligachev A.M. Prokhorov General Physics Institute, RAS, 119991 Moscow, Russia 123 Appl. Phys. A DOI 10.1007/s00339-014-8954-6