Plastic strain localization induced by microstructural gradient in laser cladding repaired structures

Guévenoux, Camille; Hallais, Simon; Balit, Yanis; Charles, Alexandre; Charkaluk, Éric; Constantinescu, Andréï

doi:10.1016/j.tafmec.2020.102520

Cited by 22 publications

(10 citation statements)

References 41 publications

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“…The repaired part shows a decrease in its UTS, 630 MPa versus 650 MPa, and a greatly reduced EAB, 46% versus 91% for the substrate. Similar results are found in the work of Guévenoux et al [102] using the same analysis techniques but with an Inconel 718 assembly. The microstructure is highly dependent on the process parameters and the variation of a single parameter locally can significantly change the properties of the zone.…”

Section: Chaptersupporting

confidence: 88%

Laser metal deposition repair of stainless steel 316L parts

Cailloux

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The nuclear and offshore wind industries are of great interest to meet the current challenges of producing carbon-free electrical energy in the context of the global energy and climate crisis. However, the structural materials used in these facilities are exposed to aggressive environments that damage components, limiting their lifespan and requiring their replacement. In the context of a circular economy, repair technologies make it possible to limit these replacements, thus reducing the time and costs associated with plant shutdowns. They also allow for minimizing the mineral resources required for the development of new components, as well as the carbon footprint associated with the manufacturing processes and transportation of the components. The objective of this thesis is to develop a process for the repair of metal parts that meets the following deposition criteria: dense, without cracks, with metallurgical bonding to the substrate, and imperceptible in terms of mechanical behavior and corrosion resistance. This process must ultimately be able to repair the initial defect with a return to the original dimensions without damaging the rest of the part. Laser Metal Deposition (LMD) technology, which is based on additive manufacturing, appears to be a promising way to meet these requirements. The LMD process has demonstrated its ability to repair metal parts while maintaining high deposition density and good mechanical properties. The energy provided by the laser allows the material to be fused without significantly affecting the substrate thermally, thereby avoiding distortion of the repaired part. Finally, the implementation of deposition heads on computer numerical control machines allows the repair process to be automated and to achieve a high level of precision compared to manual repair. The thesis, therefore focused on understanding and optimizing two main steps of the repair process: (i) the pre-machining to remove damaged material and (ii) the laser fused powder deposition to replace the material. An understanding of the synergy between these two steps is also essential to obtain a good quality deposit while machining a minimum volume of damage. For this purpose, a study was conducted to optimize the shape and dimensions of the machined defect. An ellipsoidal pre-machining with an opening angle of 120°and optimized deposition parameters were determined. The influence of substrate preheating, i interlayer dwell time, and different post-heat treatments on the repair was also studied. The results have allowed proposing a method to homogenize the characteristics of the repaired parts in terms of microstructure, mechanical properties, and corrosion resistance during the deposition of the material, aiming at the imperceptibility of the repair in the part. This work has also allowed the implementation of all these optimized steps in an additive/subtractive hybrid machine to demonstrate the feasibility and efficiency of this emerging technology. Repair times are thus reduced while maintaining a dense repair an...

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Section: Chaptersupporting

confidence: 88%

Laser metal deposition repair of stainless steel 316L parts

Cailloux

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“…Since smaller grains are located in the inter-layers, lower yield stress is expected in these regions by Hall-Petch effect [44], which could participate in strain localization. While strain localization at inter-layers has been reported on polished specimens [ 27,28], a structural effect is also expected as inter-layers correspond to the valleys in the thickness profile (thinnest regions). In addition, strain localization is clearly affected by the lack-of-fusion defects, which tend to concentrate strain around them.…”

Section: In-situ Sem Fracture Testmentioning

confidence: 93%

“…The distribution of the grain orientations, defined as the angle between the equivalent ellipse major axis and the print direction, is presented in figure 4(d). The grains exhibit a preferred orientation of 71 • , related to the direction of the temperature gradient in the process, which depends on the laser scanning direction (from left to right) [16,28]. In addition, the distribution of grain aspect ratios and grain areas are presented in figure 4(e) which shows that smaller grains tend to be spherical, while the aspect ratio increases with the grain area.…”

Section: Microstructural Analysismentioning

confidence: 98%

“…In addition, the influence of layer orientation and surface roughness on the fatigue behavior of SLM parts were addressed in [20,21]. The ability to manufacture 316L stainless steel parts using the DED additive manufacturing technology have been investigated in a number of recent works [22][23][24][25][26][27][28]. However, most of the studies related to the fracture properties of parts resulting from this specific process have focused on polished Ti-6Al-4V specimens.…”

Section: Introductionmentioning

confidence: 99%

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Tensile and ductile fracture properties of as-printed 316L stainless steel thin walls obtained by directed energy deposition

Margerit

Weisz-Patrault

Ravi‐Chandar

et al. 2021

Additive Manufacturing

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Mechanical properties of as-printed 316L stainless steel thin-walled structures obtained by directed energy deposition are investigated. In-situ tensile and fracture tests are performed on small samples obtained from a additively manufactured square section tube and extracted with three different orientations with respect to the part build direction. Despite a strongly oriented microstructure resulting from the process, as-printed specimens exhibit a reduced anisotropy in comparison with thick or polished samples commonly reported in the literature. Moreover, it is shown using a simple model that the reduced dentified anisotropy can be explained by considering the material thickness variation pattern only, resulting from the layer stacking process. Fracture tests are analyzed using an adapted digital image correlation procedure that evaluates the specimen fracture toughness from experimentally computed J-integrals. Using time reversal, strain fields in regions close to the crack path are identified. Stress fields are then computed from the constitutive behavior identified in tensile tests. A regularization procedure is proposed to enforce the stress equilibrium. Finally, the J-integral is computed using various integration contours in order to validate its path-independance. On this basis, a nearly isotropic fracture toughness is identified. Additional scanning electron microscope observations show that fracture surface features are independent from specimen orientation. This apparent isotropy is explained by the isotropic distribution of lack-of-fusion defects driving crack initiation and propagation.

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“…The tensile properties were measured using different loading directions and considering the distance to the substrate and the free edges. In order to obtain a mechanistic understanding of the observed anisotropy, in-situ tensile testing combined with digital image correlation (DIC) was also performed as this technique provides unique information about deformation and strain localization in relation to the microstructure [38,[41][42][43][44][45]. The origin of tensile anisotropy in the investigated material is finally discussed in light of the obtained data.…”

Section: Introductionmentioning

confidence: 99%