A. Pérez del Pino

Depth profiling characterisation of the surface layer obtained by pulsed Nd:YAG laser irradiation of titanium in nitrogen

We investigated the composition of the surface layer obtained by pulsed Nd:YAG laser (λ=1.064 μm, τ∼120 ns, ν=1 kHz) irradiation of Ti targets in high pressure nitrogen. The surface morphology, the crystalline state, and the depth distribution of the elements were analysed by scanning electron microscopy, X-ray diffractometry, secondary ion mass spectrometry, X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy. The chemical binding states were studied by deconvolution of the XPS spectra. The layer has a uniform surface, and mainly consists of the tetragonal δ′-TiNx crystalline phase. The nitrogen concentration increases firstly in the depth until approximately 0.15 μm, and then decreases until the greatest measured depth of 2 μm. The TiNx stoichiometry changes from x≈0.8 close to the surface to x≈0.5 at a depth of approximately 0.2 μm, it remains around this value until approximately 0.5 μm, and for greater depths decreases until 0.1 at 1.6 μm. Furthermore, the oxygen concentration decreases quickly and reaches the concentration of bulk Ti at approximately 0.2 μm.

Oxidation of titanium through Nd:YAG laser irradiation

Abstract Surface oxidation of titanium was performed by irradiation in air with a Nd:YAG ( λ =1.064xa0μm) laser operating in pulsed mode. Different oxide coatings of apparently uniform colors were obtained by changing the accumulated fluence on the material. However, detailed view of the surfaces through an optical microscope showed micron-sized zones of different colors. Compositional studies performed by X-ray diffraction (XRD) showed that the coatings were mainly composed of Ti 2 O and TiO. Micro-Raman spectroscopy of the small colored zones revealed the presence of Ti 2 O 3 and TiO 2 with different ratios characteristic of each color. These results evidence that exists some correlation in the coatings between composition and color, although only the compositional changes detected by Raman do not fully account for the observed differences in color.

Surface nitridation of titanium by pulsed Nd:YAG laser irradiation

Abstract Surface nitridation of titanium is an adequate method to improve the hardness and wear resistance of the material. We report experimental results concerning the surface treatment of titanium by pulsed Nd:YAG (λ=1.064 μm ) laser irradiation in nitrogen atmosphere. Titanium foils were scanned with constant velocity by high repetition rate (1xa0kHz) laser beam pulses, and the most appropriate irradiation conditions were determined to obtain titanium nitride surface layers without defects or corrugations. The best results were obtained at laser intensities just under the transition from surface melting to ablation. The obtained layers were characterised by surface profilometry, scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and spectrophotometry. In the XRD spectra of the films the positions of the ( h k l ) reflections reproduce the standard data of the tetragonal δ′-Ti 2 N phase. In the literature films containing tetragonal Ti 2 N phases are described as having better mechanical properties, corrosion and wear resistance in comparison with cubic TiN.

Coloring of titanium by pulsed laser processing in air

Surface treatments of titanium in air were performed by scanning with a Nd:YAG (ls1.064 mm) pulsed laser beam at high repetition rate.Different colored samples were obtained depending on the laser accumulated fluence.The surface morphology and cross-sections of the coatings were studied by scanning electron microscopy, revealing the formation of a bi-layer structure consisting of a thin shallow layer covering a thicker layer.Compositional analyses performed by X-ray diffraction and Raman spectroscopy measurements revealed the presence of several oxide phases like Ti O, TiO, Ti O and TiO (rutile and anatase). 22 3 2 Although changes in the colors of the samples may be correlated with the coating composition, the influence of light interference within the thin surface layer should not be discarded. 2002 Elsevier Science B.V. All rights reserved.

Single pulse Nd:YAG laser irradiation of titanium: influence of laser intensity on surface morphology

Abstract The interaction between single-pulse Nd:YAG (λ=1.064 μm) laser radiation and Ti target surfaces was studied by scanning electron microscopy and profilometry. The laser-assisted surface modification was analyzed and described as a function of incident laser pulse intensity. The evolution of the surface morphology was explained in terms of liquid phase material displacement, vaporization and plasma shielding. The laser intensities characteristic for the transition between these surface processes were studied for the particular laser-target system. The development of wave-like surface topography was accounted by non-linear hydrodynamic instabilities evolving on the molten target surface. The material transport and its accumulation at the border of the imprints was assigned mainly to the effect of ambient gas breakdown and vaporization plasma recoil pressure. At high laser intensities the surface morphology was influenced by the plasma shielding.

Growth of surface structures on titanium through pulsed Nd:YAG laser irradiation in vacuum

Abstract The formation of specific surface structures as a result of multi-pulse, high repetition rate Nd:YAG ( λ =1.064xa0μm, τ ∼300xa0ns, ν =30xa0kHz) laser irradiation of Ti targets in vacuum is reported. The experiments are performed at laser intensity levels below the melting threshold of Ti for single laser pulse irradiation. An analysis of the early stage of surface transformation as well as of the further structure development by cumulative laser irradiation is done. A number of consecutive laser pulses are necessary to initiate the formation of the surface micro-structures. The process continues with the next laser pulses and the surface roughness increases. However, a change to a smooth, dendritic surface morphology takes place after a certain number of pulses. The irradiated areas are analysed by profilometry and scanning electron microscopy (SEM). The main physical phenomena implied in the laser induced surface microrelief development are discussed.

Microcolumn development on titanium by multipulse laser irradiation in nitrogen

We report the growth of titanium nitride microcolumns under multipulse Nd:yttrium aluminum garnet ( 1.064 m, ∼ 300 ns, 30 kHz) laser irradiation of titanium targets in nitrogen atmosphere. The laser intensity value was chosen below the single-pulse melting threshold of titanium. The evolution with the number of laser pulses of the target morphology, crystalline state, and chemical composition at the surface as well as in depth were investigated by scanning electron microscopy, x-ray diffractometry, Raman spectroscopy, and wavelength dispersive x-ray spectroscopy. Under the action of the laser pulses, during progressive surface nitridation, an initial rippled morphology developed, which evolved with further irradiation to TiN microcolumns. In-depth investigations showed a granular zone beneath the surface consisting of rutile and anatase phase TiO2, followed by a compact needlelike layer of titanium until the interface with the unaffected target material.

Laser surface processing of titanium in air: Influence of scan traces overlapping

Laser surface treatments of titanium in air have been performed through a pulsed Nd:yttrium–aluminum–garnet (λ=1.064u2009μm) laser. Several samples have been obtained modifying the laser scan velocity and partial overlapping of consecutive traces, in order to study the influence of these parameters on the surface morphology. Scanning electron microscopy and profilometry measurements have revealed different surface morphologies depending on the physical processes involved in the treatments. The surfaces are melted in all cases and present a different crack configuration depending on the melting regime. In addition, at low scan velocities, the presence of a laser generated plasma results in a periodic groove structure that evolve to a flat and porous surface when the distance between traces is decreased.

Laser-induced growth of titanium nitride microcolumns on biased titanium targets

Titanium targets with a bias voltage ranging from −500 to +500 V were submitted to multipulse high repetition rate Nd:yttrium aluminum garnet (YAG; λ = 1.064 μm, τ ∼ 300 ns, ν = 30 kHz) laser irradiations in nitrogen at intensity values below the single-pulse melting threshold. The morphology of the TiN structures formed under the cumulative action of the laser pulses on the surface of the unbiased and biased targets was investigated by profilometry and scanning electron microscopy. Under these irradiation conditions, a specific columnar surface microrelief developed. The height of the microcolumns reached about 10–15 μm, and their diameter about 1–2 μm. The development of TiN microcolumns was enhanced by the applied bias voltage. The enhancement in the negative biased samples was stronger than that in the positive biased ones.