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- Laser shock peeningFemtosecond laserNiTi alloyCorrosion behaviorLaser surface treatment (1)
- laser mode locking; polymerisation; optical waveguides; high-speed optical techniques; two-photon processes; optical pulse compression; optical saturable absorption; integrated optics; semiconductor lasers (1)
- laser nitriding; wear resistance; NiTi alloy; roughness; microhardness (1)
- laser shock peeningfemtosecond laserNiTi alloymicrohardness (1)
Laser shock peening is a new and important surface treatment technique that can enhance the mechanical properties of metal materials. Normally, the nanosecond laser with pulse-width between 5 ns and 20 ns is used to induce a high-pressure shock wave that can generate plastic deformation in the top layer of metals. The femtosecond laser shock peening in the air has been studied recently, which can induce higher pressure shock wave than that of traditional nanosecond laser shock peening in a very short time. The NiTi alloy is processed by femtosecond laser shock peening, then a nanoindentation device is used to measure its surface hardness and residual stress. The hardness results of NiTi alloy before and after treatment show that the femtosecond laser shock peening can increase the hardness of NiTi alloy, which also shows that the femtosecond laser can be used to perform laser shock peening on NiTi alloy without coating.
Laser shock peening with femtosecond laser was used to improve the corrosion resistance of biomedical NiTi alloy without protective coating in the air environment. The energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) based analysis showed that the laser ablation could produce titanium oxide layer and femtosecond laser shock peening (FsLSP) can generate residual stress in the surface layer of NiTi alloy. The FsLSP improved the corrosion resistance of NiTi in 3.5% NaCl solution and Hank’s solution and also prevented the formation of corrosion cracks and pits during corrosion testing. The reasons for the improvement of corrosion behavior may be the generation of residual stress and titanium oxide film during the laser surface treatment.
Laser shock peening with a femtosecond laser system was presented in this research work. The NiTi shape memory alloy was processed by the femtosecond laser shock peening (FsLSP) treatment without a protective layer in the air. Femtosecond laser shock peening is a new surface technology, which can induce an intense shock wave with low single laser pulse energy under atmospheric conditions. The surface topography, roughness, microhardness, and wear resistance were measured on the surface of NiTi alloy before and after femtosecond laser peening treatment. The results showed that the surface roughness and microhardness could be increased after femtosecond laser shock peening, which may be due to the laser ablation and micro-plastic deformation induced by the shock wave. The wear property of NiTi alloy was improved, which may be attributed to the FsLSPed surface texturing and …
The colourisation of metallic surface which appears due to periodic surface patterns induced by ultrashort laser pulses is studied. Ripples due to the sub-micrometer size of their period act as a diffraction grating, generating structural colours. Carefully chosen strategy of the laser spot scanning allows us to mimic the nanostructures responsible for structural colours of some flowers on the metal substrate. We investigate the correlation between the colourising effects and the artificially-induced defects in the ripples structure and show that these defects can make the colours observable in a larger range of viewing angles. Further we address the influence of the processing parameters on the spectral profile of the reflected light.
Progress in materials development is often paced by the time required to produce and evaluate a large number of alloys with different chemical compositions. This applies especially to refractory high-entropy alloys (RHEAs), which are difficult to synthesize and process by conventional methods. To evaluate a possible way to accelerate the process, high-throughput laser metal deposition was used in this work to prepare a quinary RHEA, TiZrNbHfTa, as well as its quaternary and ternary subsystems by in-situ alloying of elemental powders. Compositionally graded variants of the quinary RHEA were also analyzed. Our results show that the influence of various parameters such as powder shape and purity, alloy composition, and especially the solidification range, on the processability, microstructure, porosity, and mechanical properties can be investigated rapidly. The strength of these alloys was mainly affected by the oxygen and nitrogen contents of the starting powders, while substitutional solid solution strengthening played a minor role.
Three-dimensional porous nanostructures made of noble metals represent novel class of nanomaterials promising for nonlinear nanooptics and sensors. Such nanostructures are typically fabricated using either reproducible yet time-consuming and costly multi-step lithography protocols or less reproducible chemical synthesis that involve liquid processing with toxic compounds. Here, we combined scalable nanosecond-laser ablation with advanced engineering of the chemical composition of thin substrate-supported Au films to produce nanobumps containing multiple nanopores inside. Most of the nanopores hidden beneath the nanobump surface can be further uncapped using gentle etching of the nanobumps by an Ar-ion beam to form functional 3D plasmonic nanosponges. The nanopores 10–150 nm in diameter were found to appear via laser-induced explosive evaporation/boiling and coalescence of the randomly arranged nucleation sites formed by nitrogen-rich areas of the Au films. Density of the nanopores can be controlled by the amount of the nitrogen in the Au films regulated in the process of their magnetron sputtering assisted with nitrogen-containing discharge gas.
High strength steel has been used in the aviation industry and automotive body structural applications to reduce its mass through a reduction in thickness. Therefore, it is very important to enhance its mechanical property, such as microhardness. In the present research, the high strength steel samples were treated by laser shock peening (LSP) with different laser pulse energy and laser pulse width. The microhardness and residual stress were measured to compare the difference between laser energy of 3 J with 10 ns and 5 J with 20 ns. The results in the study show that the surface LSP treatment can increase the microhardness and the compressive residual stress can be found when the samples were tested by hole drilling testing.
The experiment study presents the influence of femtosecond laser shock peening (FsLSP) without a protective layer in the air on the surface hardness and surface mechanical property of NiTi shape memory alloy. Femtosecond laser shock peening is a new possibility of direct laser ablation without any protective layer under atmospheric conditions, which can produce intense shock waves with low pulse energy in the air. The average surface roughness values of the NiTi alloy samples were measured, because the surface roughness may affect its friction resistance. The results showed that the surface roughness of NiTi increased after femtosecond laser shock peening treatment. In comparison with the initial state, the coefficient of friction decreased and surface microhardness increased after femtosecond laser shock peening treatment with different FsLSP parameters. This improvement of wear properties may be attributed to the enhancement of surface microhardness and surface titanium oxide layer induced by the shock wave and laser ablation during FsLSP treatment.
In this Letter, the authors present the construction of three-dimensional microstructures by two-photon polymerisation induced by ultrashort pulses of a mode-locked diode laser. The ultrafast light source is based on a diode laser with segmented metallisation to realise a waveguide integrated saturable absorber. It is subsequently amplified and compressed resulting in ultrashort laser pulses of 440 fs length and average output power of 160 mW at a fundamental repetition rate of 383.1 MHz. These pulses are coupled into a customised two-photon polymerisation setup. A series of suspended lines were fabricated between support cuboids for testing the process behaviour. A 3D structure with complex features was polymerised to demonstrate the high potential for mode-locked diode lasers in the field of direct laser writing.
We experimentally study the occurrence of pattern formation during the slot-die coating of low-viscosity nearly Newtonian liquids onto Polyethylenterephthalat (PET)-substrates. In particular, it is demonstrated that with increase of the coating speed a homogeneous coating becomes unstable with respect to periodic stripe patterns. Thereby, depending on the liquid viscosity, the stripes can be oriented parallel or perpendicular with respect to the coating direction. Mixed states do also occur. The spatial period of perpendicular [parallel] stripes increases [decrease] with the coating speed. The dependence of the effect on various control parameters of slot-die coating is investigated. Finally, a simple theoretical model based on the hydrodynamics of thin films of partially wetting liquids is analysed. Comparing the results to the experiments, conclusions are drawn regarding the acting instability and pattern formation mechanisms.