PhD proposal 2023 | CEA Paris-Saclay
Study of the monitoring and control by laser-carried ultrasound waves of laser additive manufacturing of metallic materials
Pascal Aubry1 and Jérôme Laurent2
1CEA-DEN–SEARS, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France
2CEA-LIST, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France
Abstract
Laser Powder Bed Fusion (LPBF), a process for additive manufacturing of metals, has strong and ever-growing potential for a wide range of applications. However, there is a need to develop new manufacturing strategies to adapt solidification conditions as well as online nondestructive testing (NDT) systems. Recent work at CEA-DRT has shown that it is possible to detect certain irregularities in materials through the emission and reception of ultrasound induced by a laser. In addition, based on some publications and recent work by CEA-DES and CEA-DRT, the effect of microstructural refinement by excitation of laser ultrasonic waves has been demonstrated under representative process conditions. The work proposed in the dissertation will be used to better understand the process and eventually validate on-line control of the process and microstructure by laser ultrasound under real conditions. The work will be carried out on an existing LPBF test bench at CEA-DES, which can be equipped with adapted sensors (ultrafast CMOS camera, fast thermal camera, laser vibrometer, pulsed probe laser, etc.). Following additional bibliographic analysis and the results of previous studies, the work will start with instrumentation focused on ultrasonic excitation of the melting process of the material (metal powder bed) and acquisition of signals over a wide frequency band. By varying the process and ultrasonic laser parameters, an attempt is made to control the microstructural evolution of the part. Appropriate instrumentation will be used to determine variations in the physical phenomena of fluid pooling and solidification that can be induced by the ultrasonic waves. Similarly, we will attempt to find evidence of melt defects by analyzing the signals acquired online over a broad spectral band (possible AI data mining tools). The experimental work will be supported by simulations with finite element codes of the process and the propagation of the waves in matter to propose substantiated interpretations of the observed phenomena.
Place of work : CEA Paris-Saclay, 91191 Gif-sur-Yvette
Doctoral School : Université Paris-Saclay, Ecole Doctorale SMEMAG (ED 579)
Contact :
Pascal Aubry
CEA/DES/DPC/SEARS/LISL
Tel : 06 62 60 20 29
Email :
pascal.aubry@cea.fr
Presentation
Laser additive manufacturing of metals (LAM) shows strong and ever-growing potential across a wide range of applications. However, existing systems have limitations, particularly in the ability to customize microstructures, but also in the ability to detect melt defects online [1]. To overcome these limitations, it is desirable to develop new manufacturing strategies that allow for the adaptation of solidification conditions as well as online non-destructive testing (NDT) systems.
Direct energy deposition (DED) or laser powder bed fusion (LPBF) AM processes use a locally concentrated energy source that generates strong thermal gradients, which typically results in highly oriented microstructures as well as significant surface roughness, making ultrasonic testing and measurement interpretation difficult. The resulting microstructures are out of thermodynamic equilibrium and the solidification conditions tend to produce elongated grains that are rather coarse (structural noise) compared to a microstructure normally found in materials produced by rolling or even forging. This type of microstructure affects both the mechanical behavior and the propagation of elastic waves, since the dimensions of these heterogeneities are close to the acoustic wavelengths, attenuating and scattering the waves.
Among the challenges to be overcome to expand and consolidate the use of additive manufacturing in the industry, especially in LPBF, two are of great importance:
• Controlling the quality of the material produced online and, in particular, detecting the formation of porosity or lack of fusion, which can be taken into account with the ultrasonic laser method.
• To obtain fine and equiaxed microstructures, which can consist in reducing/preventing the formation of columnar grains during the fabrication, since their presence within the microstructure is unfavorable for the use properties [2].
The manufacturing conditions and the available machines lead to the search for non-contact methods to achieve these two objectives. Recent work [3] at CEA-LIST has shown that it is possible to detect certain irregularities in materials produced by additive manufacturing through the emission and reception of ultrasound induced by a laser. As for the control of the microstructure, by controlling the thermal conditions during solidification (cooling rate, temperature gradients,...) it is possible to partially promote the formation of equiaxed grains a priori [4].
It is also known that the solidification process of the material is disturbed by cavitation, flow, mixing, spraying, dislocation, diffusion, and phase transformation phenomena when a molten metal is exposed to high-intensity ultrasonic waves, resulting in grain refinement [5,6,7,8]. Recent work has demonstrated the possibility of using this principle in the context of the Direct Energy Deposition process [9]. Work conducted as part of a CEA Upstream Study Program (CMFAUL project, CEA-DES and CEA-DRT partnership) has demonstrated the effect of microstructural refinement by excitation of ultrasonic laser waves under conditions representative of the LPBF process, but the process has not been clearly explained. Despite these encouraging results, many questions remain and several validation steps need to be performed to achieve the goals of inline microstructural control for the LPBF process under real conditions (typical of an industrial powder bed fusion machine), which led to proposing this topic for a dissertation.
The work is carried out on an existing powder bed laser melting system ( CEA-DES ) that can be equipped with suitable sensors (ultrafast CMOS camera, fast thermal camera, laser vibrometer, pulsed probe laser,...) available at CEA-DES and CEA-DRT. Based on additional bibliographic analysis and the results of previous studies, work will begin with instruments designed for ultrasonic excitation to melt the material (LPBF) and acquire signals in a wide frequency band. By varying the laser parameters and ultrasound exposure, we will attempt to control the microstructural evolution of the part. Using appropriate instrumentation, we will attempt to identify variations in the physical phenomena of fluid pooling and solidification that can be induced by ultrasonic waves. At the same time, we will try to find evidence of melting defects by analyzing the signals acquired online over a wide spectral band (possible AI data mining tools). The experimental work will be supported by simulations with finite element codes of the process and propagation of waves in matter to propose substantiated interpretations of the observed phenomena.
References
[1] Zhao et al, ‘Bulk-Explosion-Induced Metal Spattering During Laser Processing’, Phys. Rev. X, 9, 02052, (2019). Wolff et al, ‘In-situ high-speed X-ray imaging of piezo-driven directed energy deposition additive manufacturing’, Sci. Rep., 9, 962, (2019). Martin et al., ‘Dynamics of pore formation during laser powder bed fusion additive manufacturing’, Nat. Com., 10, 1987, (2019)
[2] Wei, Mazumder & DebRoy, ‘Evolution of solidification texture during additive manufacturing’, Sci. Rep., 5, 16446, (2015)
[3] C. Million, Contribution à l’inspection d’échantillons de fabrication additive métallique par ondes de Rayleigh au moyen d’une méthode ultrasons-laser, Thèses Doctorat, CNAM, Paris, (2018)
[4] P. Aubry et al., ‘Laser cladding and wear testing of nickel base hardfacing materials: Influence of process parameters’, J. Laser Appl., 29(2), (2017)
[5] G. I. Eskin & D. G. Eskin, ‘Ultrasonic melt treatment of light alloy melts’, 2nd edn, Boca Raton, FL, CRC Press, (2014)
[6] M. C. Flemings, ‘Solidification processing’, McGraw-HilI press, (1974)
[7] J. Campbell: ‘Effects of vibration during solidification’, Int. Met. Rev., 2, 71–108, (1981)
[8] Walter & Telschow, ‘Laser ultrasonic detection of the solidification front during casting’, QNDE, 15, (1996)
[9] C.J. Todaro & al., Nature Communications,, 11:142 (2020)
Jerome LAURENT, Researcher Engineer
Technological Research Department | DRT
Systems and Technologies Integration Laboratory | LIST
Numerical Instrumentation Department | DIN
Acoustics Laboratory for Control and Characterization | LA2C
The French Alternative Energies and Atomic Energy Commission (CEA)
DRT | LIST | DIN | LA2C - CEA Paris-Saclay Center
Building. 565 - PC120C - 91191 Gif-sur-Yvette Cedex, France
Phone. +33(0) 1 69 05 52 52 |
jerome.laurent2@cea.fr
Modifié 4 fois. Dernière modification le 24/01/23 11:33 par Jérôme LAURENT.