Connecting Diffraction-Based Strain with Macroscopic Stresses in Laser Powder Bed Fused Ti-6Al-4V

Mishurova, Tatiana; Artzt, Katia; Haubrich, Jan; Evsevleev, Sergei; Evans, Alexander; Meixner, M.; Munoz, Itziar Serrano; Sevostianov, Igor; Requena, Guillermo; Bruno, Giovanni

doi:10.1007/s11661-020-05711-6

Cited by 15 publications

(10 citation statements)

References 45 publications

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“…The AM Ti6Al4V alloy seems to deviate from this behavior: Mishurova et al [156] showed, that for low H 2 (prismatic planes) the model predictions by Kröner agreed better with experimental data than other schemes (Figure 12c). In contrast, for higher H 2 (basal planes) the model prediction of Reuss better matched with the data [156]. This can be explained by the transverse isotropy of the single crystal elastic tensor, exhibiting an isotropic behavior in the basal directions but a strong anisotropy along its c-axis.…”

Section: Experimental Determination Of Diffraction Elastic Constantsmentioning

confidence: 86%

“…When, on the contrary, the columnar as-built microstructure (exhibiting relatively strong crystallographic texture) was retained, the model prediction of Reuss best fit the experimental data for Inconel 718 and 625 (Figure 12a,b) [39,131]. The AM Ti6Al4V alloy seems to deviate from this behavior: Mishurova et al [156] showed, that for low H 2 (prismatic planes) the model predictions by Kröner agreed better with experimental data than other schemes (Figure 12c). In contrast, for higher H 2 (basal planes) the model prediction of Reuss better matched with the data [156].…”

Section: Experimental Determination Of Diffraction Elastic Constantsmentioning

confidence: 91%

“…As Mishurova et al [45,156] argue, it is mandatory to report the DECs used to obtain stress values if one wants to compare own data with literature. Severe differences in the RS magnitude are the consequence if different model predictions considered for the determination of DEC.…”

Section: Experimental Determination Of Diffraction Elastic Constantsmentioning

confidence: 99%

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Diffraction-Based Residual Stress Characterization in Laser Additive Manufacturing of Metals

Schröder

Evans

Mishurova

et al. 2021

Metals

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Laser-based additive manufacturing methods allow the production of complex metal structures within a single manufacturing step. However, the localized heat input and the layer-wise manufacturing manner give rise to large thermal gradients. Therefore, large internal stress (IS) during the process (and consequently residual stress (RS) at the end of production) is generated within the parts. This IS or RS can either lead to distortion or cracking during fabrication or in-service part failure, respectively. With this in view, the knowledge on the magnitude and spatial distribution of RS is important to develop strategies for its mitigation. Specifically, diffraction-based methods allow the spatial resolved determination of RS in a non-destructive fashion. In this review, common diffraction-based methods to determine RS in laser-based additive manufactured parts are presented. In fact, the unique microstructures and textures associated to laser-based additive manufacturing processes pose metrological challenges. Based on the literature review, it is recommended to (a) use mechanically relaxed samples measured in several orientations as appropriate strain-free lattice spacing, instead of powder, (b) consider that an appropriate grain-interaction model to calculate diffraction-elastic constants is both material- and texture-dependent and may differ from the conventionally manufactured variant. Further metrological challenges are critically reviewed and future demands in this research field are discussed.

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Section: Experimental Determination Of Diffraction Elastic Constantsmentioning

confidence: 86%

Section: Experimental Determination Of Diffraction Elastic Constantsmentioning

confidence: 91%

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Diffraction-Based Residual Stress Characterization in Laser Additive Manufacturing of Metals

Schröder

Evans

Mishurova

et al. 2021

Metals

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“…The correct determination of the magnitude of residual stresses is expected to be crucial for the understanding of the mechanical performance of components. In this regard, the DEC measured in a LPBF Ti-6Al-4V alloy have been already reported to deviate from the DEC values of conventionally produced Ti-6Al-4V [27]. Note that the need to assess the validity of conventional DEC is not exclusive to AM materials, since this requirement is valid for any new material exhibiting unconventional microstructures.…”

Section: Introductionmentioning

confidence: 99%

On the interplay of microstructure and residual stress in LPBF IN718

et al. 2020

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The 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.

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“…By adapting the scan strategy during the production of the AM samples, the impact of texture on the residual stress measurements can be minimized, at least within the near-surface region. [43][44][45] Other issues encountered in XSA analysis of AM samples include surface roughness and internal flaws, such as porosity and lack of fusion, as addressed in several recent studies. [46][47][48] In the case of laboratory measurements in reflection mode, the influence of such aspects is much more pronounced due to the lower information depth (penetration depth) of the beam and the resulting smaller gauge volume (e.g., depending on the wavelength of the beam, the angle of incidence, and the material under investigation).…”

Section: Challenges For Diffraction Experimentsmentioning

confidence: 99%

A Novel Approach to Robustly Determine Residual Stress in Additively Manufactured Microstructures Using Synchrotron Radiation

et al. 2021

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Introduction 1.1. Microstructure of Additively Manufactured MaterialsAdditive manufacturing (AM) is the subject of many recent publications. [1][2][3] Typical representatives of AM methods for the processing of metallic metals are mainly divided into three categories: wire feeding, powder feeding, and powder bed fusion systems. [3] The latter technique enables the production of metallic structures by layer-wise melting of a thin metal powder bed only using AM equipment and a sliced model generated by a computeraided design (CAD) program. The application of a powder bed in powder-based AM technology facilitates the selective processing of individual layers in complex geometry. The most commonly used powder bed fusion techniques are selective electron beam powder bed fusion (EPBF) and laser powder bed fusion (LPBF). [3,4] EPBF structures are produced in a vacuum atmosphere and at a high temperature, eventually leading to a relatively low residual stress level. In contrast, LPBF processes usually take place at temperatures up to 200 C. The localized energy input and the small melt pool sizes, respectively, in combination with low build chamber temperatures result in high temperature gradients, whereby residual stresses are favored. [5] Generally, the influence of scan vectors and related strategies is a complex topic, which crucially has to be dealt with. Scan vector lengths, orientations, the order of rotation within a specific layer, and its subsequent layers are variables in every building process. Only a very limited number of comprehensive studies have reported on the effect of the scan strategy on the density, microstructure, mechanical properties, and residual stresses of LPBF parts, as clearly stated in previous studies. [5][6][7][8] Already an increased scan path length, e.g., due to a change of cross-section of a part, can result in a severely decreased relative density as well as fundamentally changed microstructure. [9,10] The influence of parameters on the evolution of residual stresses was already numerously studied. [11,12] The authors showed that the residual stresses are mainly influenced by cooling rates, temperature gradients, and melt pool sizes. Also, a minimization of the temperature gradient by powder bed preheating is an option to reduce process-induced stresses. [1,13] The high influence of the laser power and the effect of scan strategies have been characterized.

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Connecting Diffraction-Based Strain with Macroscopic Stresses in Laser Powder Bed Fused Ti-6Al-4V

Cited by 15 publications

References 45 publications

Diffraction-Based Residual Stress Characterization in Laser Additive Manufacturing of Metals

Diffraction-Based Residual Stress Characterization in Laser Additive Manufacturing of Metals

On the interplay of microstructure and residual stress in LPBF IN718

A Novel Approach to Robustly Determine Residual Stress in Additively Manufactured Microstructures Using Synchrotron Radiation

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