Shape Deviation of Surface Structures Produced by WaveShape (Structuring by Laser Remelting) on Ti6Al4V and a Method for Deviation Reduction

Laser structuring by remelting (WaveShape) is a manufacturing process for metal surfaces in which structures are generated without material removal. The structuring principle is based on the controlled motion of the three-phase line in the area of the solidification front. The contour of the solidification front is imprinted into the remelting track during the continuous solidification process. Typically, harmonic surface structures in the form of sinusoidal oscillations are generated by means of WaveShape with virtually no material loss. However, a significant shape deviation is often observed over a wide range of process parameters. In this study, it was found that much of the shape deviation is concentrated at a spatial wavelength equal to half the spatial wavelength used for structuring. Therefore, an approach to reduce the shape deviations was specifically investigated by superimposing a compensation signal on the harmonic structuring signal. In this approach, a compensation signal with half the spatial wavelength was varied in phase and amplitude and superimposed on the structuring signal. Amplitude and phase shift of the compensation signal were further investigated for selected laser beam diameters and spatial wavelengths. This demonstrated that a shape deviation of harmonic surface structures on titanium alloy Ti6Al4V could be reduced by up to 91% by means of an adapted compensation signal.

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A brief review on the erosion-corrosion behavior of engineering materials

Corrosion Reviews ◽

10.1515/corrrev-2018-0022 ◽

2018 ◽

Vol 36 (5) ◽

pp. 435-447 ◽

Cited By ~ 9

Author(s):

Roshan Kuruvila ◽

S. Thirumalai Kumaran ◽

M. Adam Khan ◽

M. Uthayakumar

Keyword(s):

Adverse Effects ◽

Industrial Process ◽

Industrial Applications ◽

Appropriate Technology ◽

Material Loss ◽

Adverse Conditions ◽

Wide Range ◽

Erosion Corrosion ◽

The Cost ◽

Selection Of

AbstractThe efficiency of industry depends upon the working conditions of the equipment and components used in the industrial process. The biggest problems faced by the industries are the problems of erosion and corrosion. The harmful effects of corrosion will lead to material loss, which results from the degradation of the equipment. The degradation of the equipment will cause the breakdown of the plant; moreover, it is a threat to the safety of people, and also from the point of conservation, it can cause the exploitation of available resources. The cost of replacing equipment increases the expense, and it can also result in the temporary shutdown of the plant. The protection of surfaces from the adverse effects of corrosion and erosion-corrosion is a matter of great concern in most industrial applications. Advancements in technology provides a wide range of techniques to overcome adverse conditions. The selection of appropriate technology must be from the viewpoint of their interaction with the environment. This review paper addresses the adverse effects of erosion-corrosion in the present scenario.

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Effect of Laser Pulse Overlap and Scanning Line Overlap on Femtosecond Laser-Structured Ti6Al4V Surfaces

Materials ◽

10.3390/ma13040969 ◽

2020 ◽

Vol 13 (4) ◽

pp. 969 ◽

Cited By ~ 5

Author(s):

Georg Schnell ◽

Ulrike Duenow ◽

Hermann Seitz

Keyword(s):

Laser Pulse ◽

Femtosecond Laser ◽

Surface Topography ◽

Cell Attachment ◽

Surface Structures ◽

Laser Source ◽

Laser Machining ◽

Scanning Strategy ◽

Wide Range ◽

Scanning Line

Surface structuring is a key factor for the tailoring of proper cell attachment and the improvement of the bone-implant interface anchorage. Femtosecond laser machining is especially suited to the structuring of implants due to the possibility of creating surfaces with a wide variety of nano- and microstructures. To achieve a desired surface topography, different laser structuring parameters can be adjusted. The scanning strategy, or rather the laser pulse overlap and scanning line overlap, affect the surface topography in an essential way, which is demonstrated in this study. Ti6Al4V samples were structured using a 300 fs laser source with a wavelength of 1030 nm. Laser pulse overlap and scanning line overlap were varied between 40% and 90% over a wide range of fluences (F from 0.49 to 12.28 J/cm²), respectively. Four different main types of surface structures were obtained depending on the applied laser parameters: femtosecond laser-induced periodic surface structures (FLIPSS), micrometric ripples (MR), micro-craters, and pillared microstructures. It could also be demonstrated that the exceedance of the strong ablation threshold of Ti6Al4V strongly depends on the scanning strategy. The formation of microstructures can be achieved at lower levels of laser pulse overlap compared to the corresponding value of scanning line overlap due to higher heat accumulation in the irradiated area during laser machining.

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Analytical Study of the Solidification of a Phase Change Material in an Annular Space

Energies ◽

10.3390/en13215561 ◽

2020 ◽

Vol 13 (21) ◽

pp. 5561

Author(s):

Zygmunt Lipnicki ◽

Tomasz Małolepszy

Keyword(s):

Heat Transfer ◽

Phase Change ◽

Phase Change Material ◽

Solidification Front ◽

Solidification Process ◽

Theoretical Research ◽

Graphical Form ◽

Annular Space ◽

Conjugate System ◽

Change Material

In this study, the process of the solidification of a PCM (phase change material) liquid in an annular space was analytically investigated with the use of a simplified quasi-steady-state model. This model described the phase change phenomenon with the cylindrical solidification front and with the solidification liquid overheated above the solidification temperature. One of the important novelties of the applied model was the determination of the coefficient of the heat transfer between the liquid and the solidified layer on the solidification surface, which was calculated as a function of the location of the solidification front. A method for calculating the variable coefficient of heat transfer on the surface of the solidification front during the solidification process is presented. The contact layer between the cold wall and the solidified layer was incorporated into the model and played an important role. The theoretical analytical method describing the solidification process based on the quasi-steady model was used in the study. Moreover, the main problem considered in this work could be reduced to a conjugate system of differential equations, allowing it to be solved numerically. From this perspective, the influence of various dimensionless parameters on the solidification process could be clearly seen. The obtained numerical results are presented in graphical form. The results of the theoretical research were compared with the experimental research of one of the author’s earlier works and they showed a significant agreement. Finally, the simple analytical approach presented in this work can be used for designing annular heat accumulators.

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The tsunami triggered by the 21 May 2003 Boumerdès-Zemmouri (Algeria) earthquake: field investigations on the French Mediterranean coast and tsunami modelling

Natural Hazards and Earth System Science ◽

10.5194/nhess-9-1823-2009 ◽

2009 ◽

Vol 9 (6) ◽

pp. 1823-1834 ◽

Cited By ~ 41

Author(s):

A. Sahal ◽

J. Roger ◽

S. Allgeyer ◽

B. Lemaire ◽

H. Hébert ◽

...

Keyword(s):

High Resolution ◽

Sea Level ◽

Sampling Rate ◽

Signal Amplitude ◽

Field Studies ◽

Mediterranean Coast ◽

Material Loss ◽

Virtual Sensors ◽

Tsunami Modelling ◽

Wave Amplification

Abstract. A field survey was organized on the French Mediterranean coasts to investigate the effects of the tsunami induced by the 21 May 2003 Boumerdès-Zemmouri (Algeria) earthquake (Mw=6.9). The results show that eight harbours were affected by important sea level disturbances that caused material loss. Unfortunately, the low sampling rate of the French tide gage records (10 min) does not allow for a proper evaluation of the tsunami wave amplitudes since these amplitudes were probably underestimated in the harbours where these sensors are installed. The survey brings to light regional and local contrasts among the harbours' hydrological responses to the tsunami. To better understand these contrasts, a numerical simulation of the sea level elevations induced by the tsunami was conducted. The simulation showed a certain correlation between the field results and the wave amplification along the coast; however it underestimated the observed phenomena. Another simulation was then conducted using high resolution bathymetric grids (space step of 3 m) centred more specifically on 3 neighbouring harbours, however, again the simulation results did not match the amplitudes recorded through the observations. In order to better understand the wave amplification mechanisms inside each grid, a Gaussian signal was virtually broadcasted from the source to the harbours. Virtual sensors identified the periods which are stimulated – or not – by the arrival of the signal in each grid. Comparing these periods with those previously recorded emphasizes the proper period of each waterbody. This paper evaluates the limitations of such a study, focusing specifically on (1) the importance of having accurate and precise data about the source (the lack of information about the signal amplitude leads to an underestimation of the tsunami, thus reproducing only a fourth to a third of the observed phenomenon), (2) the need for networked tide gages with high resolution records and short sampling rates, and (3) the importance of conducting field studies immediately after a tsunami occurs.

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Dendritic Growth in Si1−xGex Melts

Crystals ◽

10.3390/cryst11070761 ◽

2021 ◽

Vol 11 (7) ◽

pp. 761

Author(s):

Genki Takakura ◽

Mukannan Arivanandhan ◽

Kensaku Maeda ◽

Lu-Chung Chuang ◽

Keiji Shiga ◽

...

Keyword(s):

Dendritic Growth ◽

Elevated Temperatures ◽

Electronic Devices ◽

Solidification Process ◽

Dendrite Growth ◽

In Situ Observation ◽

Wide Range ◽

Solidification Processes ◽

Semiconductor Alloy

We investigated the types of dendrites grown in Si1−xGex (0 < x < 1) melts, and also investigated the initiation of dendrite growth during unidirectional growth of Si1-xGex alloys. Si1−xGex (0 < x < 1) is a semiconductor alloy with a completely miscible-type binary phase diagram. Therefore, Si1−xGex alloys are promising for use as epitaxial substrates for electronic devices owing to the fact that their band gap and lattice constant can be tuned by selecting the proper composition, and also for thermoelectric applications at elevated temperatures. On the other hand, regarding the fundamentals of solidification, some phenomena during the solidification process have not been clarified completely. Dendrite growth is a well-known phenomenon, which appears during the solidification processes of various materials. However, the details of dendrite growth in Si1−xGex (0 < x < 1) melts have not yet been reported. We attempted to observe dendritic growth in Si1−xGex (0 < x < 1) melts over a wide range of composition by an in situ observation technique. It was found that twin-related dendrites appear in Si1−xGex (0 < x < 1) melts. It was also found that faceted dendrites can be grown in directional solidification before instability of the crystal/melt interface occurs, when a growing crystal contains parallel twin boundaries.

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Towards an Alternative to Time of Flight Diffraction Using Instantaneous Phase Coherence Imaging for Characterization of Crack-Like Defects

Sensors ◽

10.3390/s21030730 ◽

2021 ◽

Vol 21 (3) ◽

pp. 730

Author(s):

Baptiste Gauthier ◽

Guillaume Painchaud-April ◽

Alain Le Duff ◽

Pierre Bélanger

Keyword(s):

Imaging Techniques ◽

Time Of Flight ◽

Experimental Tests ◽

Signal Amplitude ◽

Steel Sample ◽

Single Element ◽

Time Of Flight Diffraction ◽

Instantaneous Phase ◽

Similar Characterization ◽

Wide Range

Time of flight diffraction (TOFD) is considered a reliable non-destructive testing method for the inspection of welds using a pair of single-element probes. On the other hand, ultrasonic phased array imaging has been continuously developed over the last couple of decades, and now features powerful algorithms, such as the total focusing method (TFM) and its multi-view approach to rendering detailed images of inspected parts. This article focuses on a different implementation of the TFM algorithm, relying on the coherent summation of the instantaneous signal phase. This approach presents a wide range of benefits, such as removing the need for calibration, and is highly sensitive to defect tips. This study compares the sizing and localization capabilities of the proposed method with the well-known TOFD. Both instantaneous phase algorithm and TOFD do not take advantage of the signal amplitude. Experimental tests were performed on a ¾″-thick steel sample with crack-like defects at different angles. Phase-based imaging techniques showed similar characterization capabilities as the standard TOFD method. However, the proposed method adds the benefit of generating an easy-to-interpret image that can help in localizing the defect. These results pave the way for a new characterization approach, especially in the field of automated ultrasonic testing (AUT).

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Improvement of images by using graduate transformations of their Fourier depictions

Technology audit and production reserves ◽

10.15587/2706-5448.2021.230079 ◽

2021 ◽

Vol 2 (2(58)) ◽

pp. 16-19

Author(s):

Ihor Polovynko ◽

Lubomyr Kniazevich

Keyword(s):

Fourier Transform ◽

Image Enhancement ◽

Data Science ◽

Visual Analysis ◽

Inverse Fourier Transform ◽

Signal Amplitude ◽

Initial Image ◽

Data Set ◽

Space Images ◽

Wide Range

The object of research is low-quality digital images. The presented work is devoted to the problem of digital processing of low quality images, which is one of the most important tasks of data science in the field of extracting useful information from a large data set. It is proposed to carry out the process of image enhancement by means of tonal processing of their Fourier images. The basis for this approach is the fact that Fourier images are described by brightness values in a wide range of values, which can be significantly reduced by gradation transformations. The work carried out the Fourier transform of the image with the separation of the amplitude and phase. The important role of the phase in the process of forming the image obtained after the implementation of the inverse Fourier transform is shown. Although the information about the signal amplitude is lost during the phase analysis, nevertheless all the main details correspond accurately to the initial image. This suggests that when modifying the Fourier spectra of images, it is necessary to take into account the effect on both the amplitude and the phase of the object under study. The effectiveness of the proposed method is demonstrated by the example of space images of the Earth's surface. It is shown that after the gradation logarithmic Fourier transform of the image and the inverse Fourier transform, an image is obtained that is more contrasting than the original one, will certainly facilitate the work with it in the process of visual analysis. To explain the results obtained, the schedule of the obtained gradation transformation into the Mercator series was carried out. It is shown that the resulting image consists of two parts. The first of them corresponds to the reproduction of the original image obtained by the inverse Fourier transform, and the second performs smoothing of its brightness, similar to the action of the combined method of spatial image enhancement. When using the proposed method, preprocessing is also necessary, which, as a rule, includes operations necessary for centering the Fourier image, as well as converting the original data into floating point format.

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Thermochemical Laser-Induced Periodic Surface Structures Formation by Femtosecond Laser on Hf Thin Films in Air and Vacuum

Materials ◽

10.3390/ma14216714 ◽

2021 ◽

Vol 14 (21) ◽

pp. 6714

Author(s):

Dmitrij A. Belousov ◽

Kirill A. Bronnikov ◽

Konstantin A. Okotrub ◽

Sergey L. Mikerin ◽

Victor P. Korolkov ◽

...

Keyword(s):

Laser Radiation ◽

Orientation Angle ◽

Ambient Air ◽

Chemical Oxidation ◽

Surface Structures ◽

Large Area ◽

Temperature Oxidation ◽

Periodic Surface ◽

High Regularity ◽

Wide Range

Thermochemical laser-induced periodic surface structures (TLIPSS) are a relatively new type of periodic structures formed in the focal area of linear polarized laser radiation by the thermally stimulated reaction of oxidation. The high regularity of the structures and the possibility of forming high-ordered structures over a large area open up possibilities for the practical application for changing the optical and physical properties of materials surface. Since the mechanism of formation of these structures is based on a chemical oxidation reaction, an intriguing question involves the influence of air pressure on the quality of structure formation. This paper presents the results on the TLIPSS formation on a thin hafnium film with fs IR laser radiation at various ambient air pressures from 4 Torr to 760 Torr. Despite the decrease in the oxygen content in the ambient environment by two orders of magnitude, the formation of high-ordered TLIPSS (dispersion in the LIPSS orientation angle δθ < 5°) with a period of ≈700 nm occurs within a wide range of parameters variation (laser power, scanning speed). This behavior of TLIPSS formation is in agreement with experimental data obtained earlier on the study of the kinetics of high-temperature oxidation of hafnium at various oxygen pressures.

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Efficient Way for Chemicals Identification Using Hexagonal Fiber with the Terahertz (THz) Band

10.21203/rs.3.rs-865031/v1 ◽

2021 ◽

Author(s):

Md. Selim Hossain ◽

Shuvo Sen

Keyword(s):

Finite Element ◽

Photonic Crystal ◽

Optical Parameters ◽

Perfectly Matched Layers ◽

Material Loss ◽

Crystal Fiber ◽

Wide Range ◽

Real World Applications ◽

Medical Signals ◽

Matched Layers

Abstract To detect chemicals, we proposed a photonic crystal fiber (PCF) with hexagonal cladding and a hexahedron core (THz). Circular air holes (CAHs) in the vestibule provide the basis of the suggested sensor. To develop and evaluate our suggested hexahedron PCF sensor, we employed the finite element (FEM) technique and perfectly matched layers (PML), which utilized the optical parameters numerically. Here, 92.65%, 95.25%, and 90.70% are relatively sensitive, and confining losses are low. the value 5.40×10− 08, 6.70×10− 08 dB/m, and 5.75×10− 08 dB/m for three chemicals such as Ethanol (n = 1.354), Benzene (n = 1.366) and Water (n = 1.330) and effective material loss (EML) of 0.00694 cm− 1. The suggested Hx-PCF sensor has been successfully tested at 1 THz. We are certain that the suggested sensor's optimal geometric structure can be manufactured and that it can contribute to real-world applications in biomedicine and industry. In terahertz areas, our suggested PCF fiber is also suited for a wide range of medical signals and applications (THz).

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Adiabatic pulses enhance surface nuclear magnetic resonance measurement and survey speed for groundwater investigations

Geophysics ◽

10.1190/geo2015-0527.1 ◽

2016 ◽

Vol 81 (4) ◽

pp. WB85-WB96 ◽

Cited By ~ 27

Author(s):

Elliot Grunewald ◽

Denys Grombacher ◽

David Walsh

Keyword(s):

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Field Experiments ◽

Signal Amplitude ◽

Pulse Frequency ◽

Adiabatic Pulse ◽

Adiabatic Pulses ◽

Wide Range ◽

Measurement Efficiency ◽

Nuclear Magnetic

Surface nuclear magnetic resonance (surface NMR) is an extremely powerful tool for groundwater resource investigations. However, the technique suffers from an inherently low signal-to-noise ratio (S/N), which commonly necessitates extensive signal averaging, resulting in very long measurement times. Previous approaches to improve S/N and measurement efficiency have focused primarily on reducing noise, through hardware and processing advancements. We introduce a new and divergent approach to actually increase the signal amplitude by modifying the form of the transmitted pulse used to excite the groundwater signals. An on-resonance pulse, the only form of excitation pulse previously used in surface NMR, has a fixed frequency and induces coherent excitation over a narrow range of transmit field strengths. Given spatially inhomogeneous fields underlying the surface coil, an on-resonance pulse excites water, a limited volume of water, producing a similarly limited signal amplitude. An adiabatic pulse, one of many pulse forms used for medical imaging and chemical spectroscopy, modulates pulse frequency and provides excitation over a much larger range of transmit field amplitudes. Numerical simulations of surface NMR with adiabatic pulses demonstrate almost a factor of three improvement in the peak signal amplitude compared to an on-resonance pulse. Simulations also show that a single measurement using an adiabatic pulse with high transmit current provides sensitivity to water over a wide range of depth. In contrast, multiple on-resonance measurements using a range of transmit currents are required to span sensitivity over a similar range of depths. Numerical simulation results are validated by the first field experiments comparing on-resonance and adiabatic pulses. We have considered how improvements in S/N can be used for dramatically improved measurement speed and how other advantages of adiabatic pulses may more generally be used to enhance surface NMR measurements.

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