Papers by Keyword: Laser Processing

Abstract: Laser beam welding (LBW) is an advanced welding technique based on keyhole welding, which makes use of a laser in order to join metals or thermoplastics. LBW is employed mainly in high volume applications which require high precision using automation, such as the automotive industry. The weldability, welding speed and penetration depth is mostly dependent on the power supplied to the laser, but the material and thickness of the workpiece also influences these parameters. This paper will present how various welding parameters such as power, frequency, the shape and size of the focal point affect different types of aluminium alloys, in an attempt to find the ideal parameters for the 5083 and 6082 aluminium alloys.

Abstract: Biodegradable magnesium alloy WE43 (Mg-4Y-3RE) has received great attention in orthopaedic applications as it can dissolve completely after bone tissue repair, eliminating the need for a second surgery to remove the WE43 implant. However, the rapid degradation of WE43 implants during bone healing remains a concern. Rapid degradation can deteriorate the mechanical strength and generate a significant amount of hydrogen gas via corrosion in physiological environments, negatively affecting bone healing and the surrounding tissues. To overcome the rapid degradation of medical implants, one commonly used method is surface modification via laser surface melting (LSM) to alter the surface microstructures and improve the corrosion resistance. This paper investigates the possibility of applying LSM technique to refine the surface microstructures of WE43 alloy and compares the microstructures induced by LSM with the extruded alloy without laser treatment. Results show significant grain refinement after LSM with average grain size decreased to 3μm as compared to 5μm before LSM, approximately 40% reduction in grain size. Different types of grain morphology are also identified at different locations in the melt pool due to different temperature gradients and cooling rates. It is observed that the depth of the melt pool increases with increasing laser power and decreasing laser scanning speed due to the higher heat input. It is also observed that grain size decreases with decreasing laser power and increasing laser scanning speed due to increased cooling rate. Results from this study show that LSM, a form of rapid solidification processing, can form a predominantly basal crystallographic texture, homogenise and refine the surface microstructures of WE43, which are beneficial for corrosion resistance.

Abstract: The micromaching of silicon carbide using femtosecond laser pulses is becoming an important field of research. High-repetition-rate sub-pulse trains, so-called pulse bursts, are a particularly promising route towards completely new process regimes. We report on the results of micro-punching n-type 4H-silicon carbide wafers using GHz pulse burst in order to systematically investigate the influence of the temporal energy distribution on laser processing. Pulse-burst experiments are performed at a laser wavelength of λ= 1030 nm using a single GHz burst containing a varying number of pulses and then compared with standard single femtosecond pulse exposures. The pulse energy is swept across the ablation threshold. For each set of parameters, the micromachining efficiency is evaluated in terms of ablation efficiency and burr characteristics. Scanning electron micrographs provide qualitative information about the machining quality. The characteristics of the laser modification are discussed in relation to an increase in the number of pulses in a burst envelope and to an increase in pulse energy. We observe that, compared to a single pulse, a GHz burst comprised of 10 lower-energy pulses leads to an increase in the ablation rate by a factor of ≤ 10.

Abstract: Icing, the phenomenon of the formation and accumulation of ice or frost on a surface due to the solidification of water droplets at low temperature can be undesirable in many applications. Surface icing can lead to increased energy consumption in aerospace and automotive applications due to increased aerodynamic drag. Ice formation can also present a mechanical and electrical safety hazard, and as such significant work has been done to produce surfaces with anti-icing properties through surface modification to decrease ice formation and adhesion to surfaces. One route toward the generation of anti-icing surfaces is through laser surface processing. Laser micro/nanostructuring of surfaces has advanced greatly in recent years due to advancements in laser source technology and reduction in capital costs for ultrafast femtosecond pulsed machining lasers. Laser material processing offers a rapid, scalable, and non-contact method for fabricating large area anti-icing surfaces. In this work, the production of anti-icing surfaces using femtosecond laser micro-and nanostructuring on aluminum alloy 7075 surfaces was examined. With an aim to optimize the anti-icing properties of the substrates, laser parameters such as pulse energy, repetition rate and beam scanning speed were varied to produce highly defined microstructures on the aluminum surface.Various functional properties such as hydrophobicity and surface roughness are examined.

Abstract: The effect of thermo-metallurgical factors, such as heat input and welding configuration, on solidification cracking driving forces nearby dendrite tip, such as solidification temperature range and columnar/equiaxed transition (CET) was thermodynamically and kinetically discussed with aid of comprehensive numerical analysis for multicomponent melt-pool solidification during laser processing under non-equilibrium solidification conditions to better understand problematical solidification cracking phenomena. By using (001)/[100] welding configuration, axisymmetrical distributions of columnar/equiaxed transition and solidification temperature range alongside solidification interface are homogeneously produced on both sides of weld pool. By using (001)/[110] welding configuration, nonaxisymmetrical distributions are heterogeneously produced, and are able to bring about infelicitous microstructure degradation. Unidirectional region of [001] columnar dendrite is more prone to epitaxial growth without morphology transition to conservatively better crystallography-assisted single-crystal growth. Unidirectional epitaxial growth is collapsed, and onset of stray grain nucleation and solidification cracking eventuates in [100] region of equiaxed dendrite growth. Low heat input relatively broadens portion of unidirectional columnar dendrite, where stray grain is infrequently nucleated and grown, and thus morphology transition seldom happens, as long as undercooling and solidification temperature range alongside dendrite tip are sufficient low to challengingly develop crackless dendrite growth and high-quality weld by thermometallurgy-aided single-crystallinity control. Auspicious (001)/[100] welding configuration simultaneously abates overall stray grain nucleation and constricts solidification temperature range nearby fusion boundary to wane microstructure heterogeneity. Conversely, plenteous stray grain formation is kinetically attained and extensive solidification temperature range nearby fusion boundary is thermodynamically obtained by problematical (001)/[110] welding configuration to metallurgically induce pernicious equiaxed dendrite and disintegrate dendrite growth. Moreover, the mechanism of solidification cracking diminution as consequence of appropriate optimization of thermo-metallurgical determinants during multicomponent nickel-based single-crystal superalloy melt-pool non-equilibrium solidification is also proposed. The potent consistency between the predicted and experimented results is exceedingly tenable.

Abstract: Amorphous metal alloys have unique properties and are widely used. The unique properties of such materials are accompanied by problems of mechanical strength. The existing methods of their processing are not unambiguous and require a certain approach. In practice, laser technologies allow us to optimize the complex properties of such materials. The selection of optimal processing modes, including the influence of the gas phase, allows you to locally affect the material, increase the microhardness in certain areas. The absence of the influence of the processing medium on the mechanical properties is confirmed. Local impact on the surface sample also leads to an increase in crack resistance. In general, nanosecond laser exposure can be an effective tool for controlling the mechanical characteristics of an amorphous nanocrystalline material.

Abstract: In this paper, a composite micromachining process is introduced. By adjusting the surface microstructure, a composite coating with two kinds of materials with different characteristics was fabricated. Carbon steel is used as the substrate material, and laser processing is used to obtain the micro morphology on the substrate surface. nanoSiC particles were selected as one of the coating materials, and the SiC coating was added through the process of micropore induced nanoparticles self-assembly. Ni was selected as another coating material and added by electrodeposition. This processing method can be used to prepare multifunctional surface coating, combining the characteristics of different materials. This work can provide an idea to create more excellent multifunctional surfaces.

Abstract: A picosecond laser in spin-cutting mode was used to drill 500μm diameter microholes on 150μm thick aluminium nitride ceramic. The effects of laser processing parameters such as the laser power, scanning speed, and defocus amount on the microhole quality were studied. The results show that as the laser power increases, the inlet and outlet diameters of the holes increase, the taper decreases slightly, and the thickness of the recast layer decreases evidently. The scanning speed has no obvious effect on the diameter and taper of the hole; however, the hole can not be drilled through when the speed is too large. Positive defocus can effectively reduce the taper of the hole. Under 28.5W laser power, 400Hz frequency, 200mm/s scanning speed, and zero defocus amount conditions, high-quality microholes with a taper of 0.85° were obtained.

Abstract: Direct femtosecond laser printing was used to fabricate circular-and coaxial-shaped hole arrays at ultrafast printing rate up to 10⁶ elements per second. To achieve such fast printing rate, we implemented a spatial multiplexing of either a single Gaussian or cylindrical vector beams into linear array of identical laser spots. Being compared to ordinary microholes, the coaxial openings arranged at the same periodicity demonstrate enhanced transmission in the mid-IR spectral range resulted from coupling between localized electromagnetic mode supported by coaxial unit cell and the lattice-type surface plasmon resonance. At optimized geometry of the coaxial openings and their arrangement we demonstrated resonant transmission as high as 92% at wavelengths ranging from 7.5 to 9 μm. This makes the coaxial microhole arrays with tailored spectral properties produced with ultrafast and inexpensive direct laser printing promising for sensing applications based on surface enhanced infrared absorption.

Abstract: Due to the increasing of the price of different materials and resource saving it is very promising to develop technology of creation cheap coatings with specified properties. We developed a diffusion-doped powder based on austenitic steels for producing plasma-sprayed coatings. In comparison with Ni-based powders our materials have better adhesion, they are cheaper, they have better mechanical machinability, it is possible to produce coatings with required properties. In our work, the features of diffusion doping of microparticles of powder, the behavior of the powder in the plasma jet were studied. The significant decreasing of porosity, increasing of adhesion of the plasma-sprayed coatings after laser processing were marked. The substantial increase of wear-resistance in 2,5-3,0 times in comparison with untreated coatings when working in conditions of abrasive wear and atmospheric precipitation was revealed.