Papers by Keyword: Laser Processing

Abstract: Slurry jet impingement test was carried out on a laser processed nickel aluminium bronze (NAB) and the results are compared with the as-cast NAB. It is observed that the invariably, erosion corrosion rate is increasing with the jet velocity. Also, as the slurry impact angle is increased, the erosion corrosion rate of laser processed and as-cast NAB decreased. The erosion corrosion rate of laser processed sample exhibited 28 % higher erosion resistance as compared to the as-cast NAB. Enhanced surface hardness and fine grain formation due to laser processed are the main reasons for the improvement in the erosion corrosion resistance.

Abstract: The superficial microstructure, received by laser processing, is characterized by a high density of defects of a crystal structure and incompleteness of thermal phase and structural transformations. The degree of a neravnovesnost of such a structure can be estimated by means of multifractal ranges. As a measure for calculation of multifractals, it is possible to use any quantitative structural index, in particular, the area of microstructural objects, their perimeter and density of borders. The most informative is density of borders, which considers the area and perimeter of structural object. Microstructures of stainless steel 12kh18n10t in an initial state, after laser processing and a local laser alloying by hard-alloy powder from BK8 were investigated. Calculations of complex indicators of the structural organization of material, which showed, are executed on the basis of the multifratalnykh of ranges, that laser processing leads to, increase of orderliness and frequency. It indicates high degree of a neravnovesnost with which increase hardening increases.

Abstract: To increase product quality injection molding tools are equipped with innovative tempering technologies. The customers strive for the technology with the lowest energy consumption. Ceramic materials like yttria-stabilized zirconia (YSZ) are able to thermally insulate tool surfaces providing a more precise temperature regulation with intent to shorten cycle times as well as to decrease energy demands during the molding process. High quality ceramic thin films could be applied by metalorganic chemical vapor deposition (MOCVD). Laser machining technologies have been developed for machining the ceramic materials. In this work we demonstrate the fabrication of zirconia based thin films on steel tools via MOCVD using solid metalorganic precursors. Shorter coating times and a solvent free process are some of the advantages of our new developed coating process. The ultrashort pulse laser processing (USPLP) was used to structure the developed MOCVD coating. Using this technology the ceramic material undergoes no thermal stress cracks, because USPLP is characterized by the preference of cold material removal. The laser processing procedure was developed by working out machining parameters for the different materials. The difference between steel and ceramic in the removal behavior was determined immediately so that a machining strategy for the ceramic CVD coating could be designed successfully. The implementation of defined roughness and a carbon fiber like structure in the coating were realized. Coated and laser-structured injection molding tools were tested regarding their desired properties under production conditions.

Abstract: In the nuclear field, efforts are made to find substitutes to cobalt hardfacing alloys since these alloys have a principal drawback, the transmutation from stable ⁵⁹Co to ⁶⁰Co under neutron irradiation. In case of wear, fragments could be deposed on the surface of primary circuit and thus contaminate it, causing a real issue for deconstruction.

Abstract: In recent years, the performance and miniaturization of portable information devices have rapidly advanced. The build-up process is often used in the manufacturing of printed wiring boards (PWBs) for high-density circuits. At present, CO2 laser beams are generally used in the build-up process to drill blind via holes (BVHs) that connect copper foils. However, Cu direct drilling is problematic in that it produces a copper overhang as a result of copper and resin, with different decomposition points, being melted simultaneously. Overhang could cause an adverse effect in plating the hole for connectivity. However, only few studies have investigated Cu direct processing for drilling BVHs. At an actual production site of PWBs, the number of processing holes is enormous, which leads to neglecting the quality of each processed hole. Therefore, we focused on pulse drilling, which involves laser irradiation using short multiple pulses to reduce the thermal effect. Pulse drilling could reduce overhang compared to single pulse irradiation; however, it lengthens the total processing time. Pulse irradiation after BVH formation would be unnecessary, since it could cause thermal damage to the hole and lengthen the processing time. Therefore, during pulse irradiation, it is essential to distinguish whether a BVH is formed. We observed the value of the motion graph, which was acquired from the high-speed camera images. The motion graph shows the luminance value of an image at a given time of the video. Based on the peak time of the motion graph during each pulse, we proposed a method to distinguish BVH formation during multiple pulse drilling.

Abstract: The performed studies of the application features of the cutting tool, hardened by laser pulsed radiation are based on the comprehensive cutting process analysis. In this approach, the modeling results of the cutting process with hardened tool allowing to define the area of the effective use of laser treatment (LT). In particular, the increase in the tool life only for the certain values of the cut depth at the fixed irradiation energy was observed. The causes of the observed phenomena were determined based on durometric researches and studies of the microstructure in the contact zone. The measurements were performed for the cutters (steel R18) after turning structural steel 12Kh2N4A under various cutting modes. It was found that the processes of tool material softening, observed at turning with high feed values, limits the scope of cutting conditions by hardened tool. It is shown that LT leads to increased tool life, operating at the cutting conditions when the growth of tension thermodynamic in the cutting zone does not result in the development of softening processes. It is established that the area cutting modes are restricted to the values of cut depth not exceeding 1.5 mm (V=42.5 m/min, s=0.2 mm/rev) for the investigated pair of tool-workpiece (R18-12Kh2N4A). Tool life increases by more than 4 times compared to the durability of the non-irradiated tool provided the optimal combination of laser processing and hardened tool cutting modes is achieved.

Abstract: Al doping of 4H-SiC with high surface concentration and deep depth profile is found to be realized by irradiating single-pulse excimer laser to an Al film deposited on the surface. Optical emission spectra suggest that high-temperature molten Al is produced behind the laser-generated high-density Al plasma and Al is diffused from the molten Al into 4H-SiC. The Al doping depth reaches to ~200 nm by irradiating a single laser pulse. A pn junction diode fabricated by the doping with the molten Al shows on/off ratio over 10 orders of magnitude.

Abstract: The formation of layered ripples covered pyramid structure is reported on 316L stainless steel surface with femtosecond laser pulses in this paper. These unique structures form though a combination of preferential ablation of flat regions around the pyramids and extension of layered ripples created during the ablation process. The cause of the formation about these structure is investigated using multi-means and the results show that these structures are derived from an inhomogeneous distribution of laser fluence, which is caused through a combination of the redeposition of nanoparticles and the local oxidation as well as the geometric factors.

Abstract: Phase transformations in laser processed metallic materials usually occur under very high temperature gradients and during a short time. Therefore, laser materials processing has been usually associated to high heating and cooling rates. However, before understanding the temperature evolution of the target, the absorptivity and the optical penetration must be considered. This paper presents some conjectures about the how the metal absorbs the laser radiation and how rapid phase transformations take place. It would be proposed that the interface response functions could be a possible way to understand phase transformations from liquid or high temperature solid solution conditions. Finally, it will be presented some results about laser processed materials of aerospace interest: steels, titanium and aluminium, which will illustrate the practical applications of the theories.

Abstract: Quasiperiodic microstructures are formed on the surfaces of metals under irradiation with high-power femtosecond laser pulses. Interpretation of microstructures as a result of interference of the incident plane wave and surface waves leads to the logical conclusion about the relationship of dislocations in the interference fringes with optical vortices in surface wave. Other peculiarities observed in these structures contain different periods and nanogranular fine structure. It is demonstrated that such laser-induced structures can find applications for surface plasmon excitation and surface enhanced Raman scattering.