scholarly journals Residual stress reduction of LPBF-processed CM247LC samples via multi laser beam strategies

2021 ◽  
Author(s):  
Marcel Gerstgrasser ◽  
Michael Cloots ◽  
Josef Stirnimann ◽  
Konrad Wegener
Keyword(s):  
Residual Stress ◽  
Laser Beam ◽  
Stress Reduction ◽  
Laser Power ◽  
Electron Backscatter Diffraction ◽  
Laser Source ◽  
Scan Speed ◽  
Lateral Offset ◽  
Solidification Cracks ◽  
Backscatter Diffraction

AbstractBased on SLM parameters from previous works, which guarantee fully dense and crack free CM247LC samples, multi laser beam strategies have been pursued to reduce residual stresses or rather distortion during LPBF processing. By using a second post heating and non-melting laser source with a defocused laser beam and lateral offset, cantilever distortion is reduced more than 7.5%, compared to the reference. Based on pre-tests with 9 different offset parameters, the optimum offset has been identified. Also, an upper limit for the laser power of 65 W is identified for the second heat laser beam with a spot diameter of 380 μm, to avoid re-melting and creating new defects. A theoretical “two bar model,” to explain the residual stress behavior and reduction with multi laser beam offset strategy during the LPBF process, is presented. Furthermore, re-melting cracks, defects, and microstructure are analyzed in conjunction with the second defocused offset laser, in case of a 200 W laser power, an increased scan speed of 1300 mms/s, and a reduced hatch distance. Secondary electron signal (SE) images of re-melting cracks are analyzed and compared to SE-image of hot cracks (solidification cracks). Based on electron backscatter diffraction (EBSD), the results of the microstructure from the last mentioned multi laser beam approach, which creates re-melting cracks, are presented and analyzed.

scholarly journals Diffracting-grain identification from electron backscatter diffraction maps during residual stress measurements: a comparison between the sin2ψ and cosα methods

2019 ◽  
Vol 52 (4) ◽  
pp. 828-843 ◽  
Author(s):  
Dorian Delbergue ◽  
Damien Texier ◽  
Martin Lévesque ◽  
Philippe Bocher
Keyword(s):  
Residual Stress ◽  
Grain Size ◽  
Tilt Angle ◽  
Measurement Errors ◽  
Electron Backscatter Diffraction ◽  
Measurement Techniques ◽  
Single Exposure ◽  
X Ray ◽  
Electron Backscatter ◽  
Backscatter Diffraction

X-ray diffraction (XRD) is a widely used technique to evaluate residual stresses in crystalline materials. Several XRD measurement methods are available. (i) The sin2ψ method, a multiple-exposure technique, uses linear detectors to capture intercepts of the Debye–Scherrer rings, losing the major portion of the diffracting signal. (ii) The cosα method, thanks to the development of compact 2D detectors allowing the entire Debye–Scherrer ring to be captured in a single exposure, is an alternative method for residual stress measurement. The present article compares the two calculation methods in a new manner, by looking at the possible measurement errors related to each method. To this end, sets of grains in diffraction condition were first identified from electron backscatter diffraction (EBSD) mapping of Inconel 718 samples for each XRD calculation method and its associated detector, as each method provides different sets owing to the detector geometry or to the method specificities (such as tilt-angle number or Debye–Scherrer ring division). The X-ray elastic constant (XEC) ½S 2, calculated from EBSD maps for the {311} lattice planes, was determined and compared for the different sets of diffracting grains. It was observed that the 2D detector captures 1.5 times more grains in a single exposure (one tilt angle) than the linear detectors for nine tilt angles. Different XEC mean values were found for the sets of grains from the two XRD techniques/detectors. Grain-size effects were simulated, as well as detector oscillations to overcome them. A bimodal grain-size distribution effect and `artificial' textures introduced by XRD measurement techniques are also discussed.

scholarly journals Effect of Tensile Deformation on Residual Stress of GH4169 Alloy

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1773
Author(s):  
Wenxiang Zhu ◽  
Fei Zhao ◽  
Sheng Yin ◽  
Yuan Liu ◽  
Ronggui Yang
Keyword(s):  
Residual Stress ◽  
Tensile Deformation ◽  
Electron Backscatter Diffraction ◽  
Reduction Rate ◽  
Stress Relief ◽  
X Ray ◽  
Dislocation Movement ◽  
Dislocation Group ◽  
Backscatter Diffraction ◽  
Gh4169 Alloy

In order to reduce the residual stress of the GH4169 alloy, the effect and micro-mechanism of the tensile deformation were studied. The residual stress, dislocation density, and distribution of the GH4169 alloy were analyzed by X-ray residual stress tester, X-ray diffractometer (XRD), and electron backscatter diffraction (EBSD). The results show that: with the increase of tensile deformation, the residual stress relief first increases and then decreases. When the tensile deformation is 3%, the reduction rate of residual stress reaches the maximum, which is 90%. The mechanism of residual stress relief by the tensile treatment is that the dislocation group in the alloy is activated by tensile treatment, and the dislocation distribution in the alloy is more uniform by dislocation movement, multiplication, and annihilation so that the residual stress can be eliminated.

scholarly journals Effects of Pulsed Magnetic Fields of Different Intensities on Dislocation Density, Residual Stress, and Hardness of Cr4Mo4V Steel

Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 115 ◽  
Author(s):  
Mingdong Hou ◽  
Kejian Li ◽  
Xiaogang Li ◽  
Xu Zhang ◽  
Shaoshi Rui ◽  
...  
Keyword(s):  
Residual Stress ◽  
Magnetic Fields ◽  
Dislocation Density ◽  
Compressive Residual Stress ◽  
Electron Backscatter Diffraction ◽  
Dislocation Motion ◽  
Pulsed Magnetic Fields ◽  
X Ray ◽  
Average Value ◽  
Backscatter Diffraction

To study the effects of pulsed magnetic fields of different intensities on the dislocation density, residual stress, and hardness of Cr4Mo4V steel, magnetic treatment is conducted at 0, 1.0, 1.3, 1.5, 2.0, and 2.5 T. The dislocation density and residual stress are measured using Electron Backscatter Diffraction (EBSD) and X-ray technique, respectively. The results reveal the dislocation density and compressive residual stress decrease at lower magnetic fields such as 1.0 T and 1.3 T, while they increase at higher magnetic fields such as 2.0 T and 2.5 T. The average value of kernel averaged misorientation (KAM) and compressive residual stress decrease about 10.4% and 15.8%, respectively, at 1.0 T, while they increase about 5.88% and 18.2%, respectively, at 2.5 T. The average value of hardness decreases about 3.5% at 1.0 T, from 817 HV to 787 HV. With the increments of intensities, the hardness of the treated samples increases. The hardness essentially remains unchanged at 2.0 T and 2.5 T. The reason for the dislocation motion under the action of pulsed magnetic fields is discussed.

Melt Pool and Single Track Formation in Selective Laser Sintering/Selective Laser Melting

2014 ◽  
Vol 933 ◽  
pp. 196-201 ◽  
Author(s):  
Mohd Rizal Alkahari ◽  
Tatsuaki Furumoto ◽  
Takashi Ueda ◽  
Akira Hosokawa
Keyword(s):  
Laser Beam ◽  
Layer Thickness ◽  
Laser Power ◽  
Selective Laser Sintering ◽  
Single Track ◽  
Laser Melting ◽  
Consolidation Process ◽  
Melt Pool ◽  
Track Formation ◽  
Scan Speed

Selective Laser Sintering/Selective Laser Melting (SLS/SLM) is one of Additive Manufacturing (AM) processes that utilize layer by layer powder deposition technique and successive laser beam irradiation based on Computer Aided Design (CAD) data. During laser irradiation on metal powders, melt pool was formed, which then solidified to consolidated structure. Therefore, melt pool is an important behavior that affects the final quality of track formation. The study investigates the melt pool behavior through visualization of the consolidation process during the single track formation on the first layer. In order to understand the transformation process of metal powder to consolidated structure and mechanism involved, high speed camera was used to monitor the process. Yb:fiber laser beam was irradiated on metal powder at maximum power of 150W. The laser processing parameters such as laser power, scan speed and layer thickness were varied in order to investigate their influence on the consolidation process. The result shows the size of melt pool increased with laser power and decreasing with increment in scan speed. Furthermore, with the increase of layer thickness, melt pool formation was unstable with chaotic movement. Significant amount of molten powder splattering was recorded from the melt pool. At high layer thickness also, the molten powder formed spherical shaped and the solidified molten powder failed to wet with the substrate.

scholarly journals On the interplay of microstructure and residual stress in LPBF IN718

2020 ◽  
Vol 56 (9) ◽  
pp. 5845-5867
Author(s):  
Itziar Serrano-Munoz ◽  
Tobias Fritsch ◽  
Tatiana Mishurova ◽  
Anton Trofimov ◽  
Daniel Apel ◽  
...  
Keyword(s):  
Residual Stress ◽  
Electron Backscatter Diffraction ◽  
Microstructural Characterization ◽  
Theoretical Models ◽  
Near Surface ◽  
Powder Bed ◽  
Rs Analysis ◽  
Scanning Strategies ◽  
Backscatter Diffraction

AbstractThe relationship between residual stresses and microstructure associated with a laser powder bed fusion (LPBF) IN718 alloy has been investigated on specimens produced with three different scanning strategies (unidirectional Y-scan, 90° XY-scan, and 67° Rot-scan). Synchrotron X-ray energy-dispersive diffraction (EDXRD) combined with optical profilometry was used to study residual stress (RS) distribution and distortion upon removal of the specimens from the baseplate. The microstructural characterization of both the bulk and the near-surface regions was conducted using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). On the top surfaces of the specimens, the highest RS values are observed in the Y-scan specimen and the lowest in the Rot-scan specimen, while the tendency is inversed on the side lateral surfaces. A considerable amount of RS remains in the specimens after their removal from the baseplate, especially in the Y- and Z-direction (short specimen dimension and building direction (BD), respectively). The distortion measured on the top surface following baseplate thinning and subsequent removal is mainly attributed to the amount of RS released in the build direction. Importantly, it is observed that the additive manufacturing microstructures challenge the use of classic theoretical models for the calculation of diffraction elastic constants (DEC) required for diffraction-based RS analysis. It is found that when the Reuß model is used for the calculation of RS for different crystal planes, as opposed to the conventionally used Kröner model, the results exhibit lower scatter. This is discussed in context of experimental measurements of DEC available in the literature for conventional and additively manufactured Ni-base alloys.

scholarly journals Rainbow Archimedean spiral emission from optical fibres

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
F. Mangini ◽  
M. Ferraro ◽  
M. Zitelli ◽  
V. Kalashnikov ◽  
A. Niang ◽  
...  
Keyword(s):  
Laser Beam ◽  
Optical Tweezers ◽  
Laser Power ◽  
Near Infrared ◽  
Laser Source ◽  
Optical Fibres ◽  
Far Field ◽  
Archimedean Spiral ◽  
Spiral Shape ◽  
Helical Beam

AbstractWe demonstrate a new practical approach for generating multicolour spiral-shaped beams. It makes use of a standard silica optical fibre, combined with a tilted input laser beam. The resulting breaking of the fibre axial symmetry leads to the propagation of a helical beam. The associated output far-field has a spiral shape, independently of the input laser power value. Whereas, with a high-power near-infrared femtosecond laser, a visible supercontinuum spiral emission is generated. With appropriate control of the input laser coupling conditions, the colours of the spiral spatially self-organize in a rainbow distribution. Our method is independent of the laser source wavelength and polarization. Therefore, standard optical fibres may be used for generating spiral beams in many applications, ranging from communications to optical tweezers and quantum optics.

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