Simulation-assisted investigation on the formation of layer bands and the microstructural evolution in directed energy deposition of Ti6Al4V blocks

Lu, Xufei; Zhang, Guohao; Li, Junjie; Cervera, Miguel; Chiumenti, Michele; Chen, Jing; Lin, Xin; Huang, Weidong

doi:10.1080/17452759.2021.1942077

Cited by 21 publications

(11 citation statements)

References 49 publications

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“…3). Note that a remarkable agreement between numerical (dash lines) and experimental (solid lines) results is achieved, as reported in reference [21]. Also, the average numerical error during the entire processing is calculated, resulting in less than 3% for each thermocouple.…”

Section: Calibration Of the Thermo-mechanical Fe Modelsupporting

confidence: 76%

“…On the other hand, the homogenization of the final microstructure is also a challenge in AM because of the temperature histories experienced at any location of the AM-builds [20][21][22]. For instance, the lower part of the builds often undergoes a larger number of subsequent thermal cycles during the DED process than the top of the metal deposition.…”

Section: Introductionmentioning

confidence: 99%

“…For instance, the lower part of the builds often undergoes a larger number of subsequent thermal cycles during the DED process than the top of the metal deposition. Consequently, the microstructure initially formed is generally coarsened and the martensitic phase (α′ in AM titanium alloy) is decomposed because of an Intrinsic Heat Treatment (IHT) [21,22]. In addition, AM titanium alloys also present regularly distributed layer-bands along the building direction [23].…”

Section: Introductionmentioning

confidence: 99%

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Mitigation of residual stresses and microstructure homogenization in directed energy deposition processes

Chiumenti

Cervera

et al. 2022

Engineering with Computers

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In additive manufacturing (AM), residual stresses and microstructural inhomogeneity are detrimental to the mechanical properties of as-built AM components. In previous studies the reduction of the residual stresses and the optimization of the microstructure have been treated separately. Nevertheless, the ability to control both them at the same time is mandatory for improving the final quality of AM parts. This is the main goal of this paper. Thus, a thermo-mechanical finite element model is firstly calibrated by simulating a multi-track 40-layer Ti-6Al-4V block fabricated by Directed Energy Deposition (DED). Next, the numerical tool is used to study the effect of the baseplate dimensions and the energy density on both residual stresses and microstructure evolution. On the one hand, the results indicate that the large baseplate causes higher residual stresses but produces more uniform microstructures, and contrariwise for the smaller baseplate. On the other hand, increasing the energy density favors stress relief, but its effect fails to prevent the stress concentration at the built basement. Based on these results, two approaches are proposed to control both the stress accumulation and the metallurgical evolution during the DED processes: (i) the use of a forced cooling suitable for small baseplates and, (ii) the adoption of grooves when large baseplates are used.The numerical predictions demonstrated the effectiveness of the proposed manufacturing strategies.

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Section: Calibration Of the Thermo-mechanical Fe Modelsupporting

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mitigation of residual stresses and microstructure homogenization in directed energy deposition processes

Chiumenti

Cervera

et al. 2022

Engineering with Computers

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“…The temperature-the substrate, increasing with the distance from the printing region. The temperature-dependent mechanical and thermal properties of Ti-6Al-4V, used for both the build and the substrate, are from references [25,26].…”

Section: Fe Modelling Of Ammentioning

confidence: 99%

Residual Stresses Control in Additive Manufacturing

Cervera

Chiumenti

et al. 2021

JMMP

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Residual stresses are one of the primary causes for the failure of parts or systems in metal additive manufacturing (AM), since they easily induce crack propagation and structural distortion. Although the formation of residual stresses has been extensively studied, the core factors steering their development in AM have not been completely uncovered. To date, several strategies based on reducing the thermal gradients have been developed to mitigate the manifestation of residual stresses in AM; however, how to choose the optimal processing plan is still unclear for AM designers. In this regard, the concept of the yield temperature, related to the thermal deformation and the mechanical constraint, plays a crucial role for controlling the residual stresses, but it has not been duly investigated, and the corresponding approach to control stresses is also yet lacking. To undertake such study, a three-bar model is firstly used to illustrate the formation mechanism of the residual stress and its key causes. Next, an experimentally calibrated thermomechanical finite element model is used to analyze the sensitivity of the residual stresses to the scan pattern, preheating, energy density, and the part geometry and size, as well as the substrate constraints. Based on the numerical results obtained from this analysis, recommendations on how to minimize the residual stresses during the AM process are provided.

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“…Therefore, correctly predicting the thermal results has become one of the key steps in thermo-mechanical simulations. Various numerical methods have been proposed to solve heat transfer equations, such as analytical solutions [19][20][21][22][23] and FE models [24][25][26][27][28][29]. The comprehensive comparison of the analytical and FEM made by Promoppatum et al [30] shows that good correlations of the melt pool width have been observed between numerical results and experimental measurements, while the comparison of melt pool depth is neglected.…”

Section: Introductionmentioning

confidence: 99%

A Temperature-Dependent Heat Source for Simulating Deep Penetration in Selective Laser Melting Process

2021

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Numerical methods for simulating selective laser melting (SLM) have been widely carried out to understand the physical behaviors behind the process. Numerical simulation at the macroscale allows the relationship between input parameters (laser power, scanning speed, powder layer thickness, etc.) and output results (distortion, residual stress, etc.) to be investigated. However, the macroscale thermal models solved by the finite element method cannot predict the melt pool depth correctly as they ignore the effect of fluid flow in the melting pool, especially in the case of the presence of deep penetration. To remedy this limitation, an easy-implemented temperature-dependent heat source is proposed. This heat source can adjust its parameters during the simulation to compensate for these neglected thermal effects related to the fluid flow and keyhole, and the heat source’s parameters become fixed once the temperatures of the points of interest become stable. Contrary to the conventional heat source model, parameters of the proposed heat source do not require a calibration with experiments for each process parameter. The proposed model is validated by comparing its results with those of the anisotropic thermal conductivity method and experimental measurements.

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Simulation-assisted investigation on the formation of layer bands and the microstructural evolution in directed energy deposition of Ti6Al4V blocks

Cited by 21 publications

References 49 publications

Mitigation of residual stresses and microstructure homogenization in directed energy deposition processes

Mitigation of residual stresses and microstructure homogenization in directed energy deposition processes

Residual Stresses Control in Additive Manufacturing

A Temperature-Dependent Heat Source for Simulating Deep Penetration in Selective Laser Melting Process

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