Exploring the Correlation between Subsurface Residual Stresses and Manufacturing Parameters in Laser Powder Bed Fused Ti-6Al-4V

Mishurova, Tatiana; Artzt, Katia; Haubrich, Jan; Requena, Guillermo; Bruno, Giovanni

doi:10.3390/met9020261

Cited by 41 publications

(26 citation statements)

References 39 publications

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“…In this case, the plateau starts from τ 0 = 30 µm and σ z values vary between 800 and 900 MPa. These results are in good agreement with a previous study by the authors, where the impact of surface roughness was investigated using a LPBF Ti6Al4V material 57 . In this previous study, the effect of surface roughness on the relaxation of RS is also reported to vanish once the plateau is reached.…”

Section: Lpbfsupporting

confidence: 93%

The residual stress in as-built Laser Powder Bed Fusion IN718 alloy as a consequence of the scanning strategy induced microstructure

Serrano-Muñoz¹,

Mishurova²,

Thiede³

et al. 2020

Sci Rep

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The effect of two types of scanning strategies on the grain structure and build-up of Residual Stress (RS) has been investigated in an as-built IN718 alloy produced by Laser Powder Bed Fusion (LPBF). The RS state has been investigated by X-ray diffraction techniques. The microstructural characterization was performed principally by Electron Backscatter Diffraction (EBSD), where the application of a post-measurement refinement technique enables small misorientations (< 2°) to be resolved. Kernel average misorientation (KAM) distributions indicate that preferably oriented columnar grains contain higher levels of misorientation, when compared to elongated grains with lower texture. The KAM distributions combined with X-ray diffraction stress maps infer that the increased misorientation is induced via plastic deformation driven by the thermal stresses, acting to self-relieve stress. The possibility of obtaining lower RS states in the build direction as a consequence of the influence of the microstructure should be considered when envisaging scanning strategies aimed at the mitigation of RS. IN718 is a Ni-based superalloy widely used in aviation (e.g., aircraft engines) and energy industries (e.g., power generation turbines) due to its exceptional combination of high-temperature mechanical stability (up to 650 °C), good fatigue life and high resistance to degradation in corrosive or oxidizing environments 1. Nonetheless, nickel alloys are also known for their poor machinability 2. Compared to conventional subtractive routes, Additive Manufacturing (AM) permits the production of 3D complex near-net-shape components with greatly reduced machining, buy-to-fly ratios close to 1 and shorter production times, while also providing comparable material performances 3. Among AM techniques, Laser Powder Bed Fusion (LPBF) consists of a layer-by-layer selective melt of a powder bed using a focused energy source. Unfortunately, one important shortcoming of LPBF is the formation of complex Residual Stress (RS) states, with values in the range of the yield strength of a material when connected to the baseplate. This RS state results from the steep spatial and temporal thermal gradients, locally induced by the laser during processing 4,5. RS is defined as the stress in a body with uniform temperature that is in equilibrium in the absence of external forces 6. In general, RS is undesirable, especially if tensile, as they can negatively affect mechanical properties, distort the design geometry, and induce cracking or delamination 5,7. Considerable amount of work (both experimental and numerical) has been reported to elucidate and mitigate macroscopic RS in AM 3. In general, the RS tends to be tensile towards the surfaces of the sample and compressive at the centre of LPBF parts 5,8-22. Moreover, the largest tensile values tend to occur near the top (last added layers) of the sample, when it remains connected to the baseplate. The magnitude and trend of RS have been shown to vary depending on parameters such as the geometry of the part, ...

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Section: Lpbfsupporting

confidence: 93%

The residual stress in as-built Laser Powder Bed Fusion IN718 alloy as a consequence of the scanning strategy induced microstructure

Serrano-Muñoz¹,

Mishurova²,

Thiede³

et al. 2020

Sci Rep

Self Cite

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“…It should be noted that a linear interpolation was applied to combine the surface measurement positions and the neutron data in Figure 9. Therefore, any possible sub-surface tensile peaks that had been reported by Mishurova et al [11,34] in LPBF Ti-6Al-4V were not be taken into account in this study.…”

Section: Discussionmentioning

confidence: 99%

Separation of the Formation Mechanisms of Residual Stresses in LPBF 316L

Ulbricht

Altenburg

Sprengel

et al. 2020

Metals

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Rapid cooling rates and steep temperature gradients are characteristic of additively manufactured parts and important factors for the residual stress formation. This study examined the influence of heat accumulation on the distribution of residual stress in two prisms produced by Laser Powder Bed Fusion (LPBF) of austenitic stainless steel 316L. The layers of the prisms were exposed using two different border fill scan strategies: one scanned from the centre to the perimeter and the other from the perimeter to the centre. The goal was to reveal the effect of different heat inputs on samples featuring the same solidification shrinkage. Residual stress was characterised in one plane perpendicular to the building direction at the mid height using Neutron and Lab X-ray diffraction. Thermography data obtained during the build process were analysed in order to correlate the cooling rates and apparent surface temperatures with the residual stress results. Optical microscopy and micro computed tomography were used to correlate defect populations with the residual stress distribution. The two scanning strategies led to residual stress distributions that were typical for additively manufactured components: compressive stresses in the bulk and tensile stresses at the surface. However, due to the different heat accumulation, the maximum residual stress levels differed. We concluded that solidification shrinkage plays a major role in determining the shape of the residual stress distribution, while the temperature gradient mechanism appears to determine the magnitude of peak residual stresses.

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“…The chosen setup was identical to the one used in previous measurements [ 12 , 13 , 16 ]. All measurements were conducted in reflection at a diffraction angle of 2θ = 8°.…”

Section: Methodsmentioning

confidence: 99%

“…The scan strategies and laser parameters in LPBF also strongly influence the formation of residual stresses (RSs) [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. The origins of the RS in AM are the steep and local thermal gradients developing during melting, remelting, reheating, solidification, and cool-down (see further Refs.…”

Section: Introductionmentioning

confidence: 99%

“…Despite the growing number of experimental and simulation studies on the formation of residual stresses in LPBF of titanium alloys (e.g., [ 8 , 9 , 11 , 12 , 13 , 15 , 16 , 17 , 18 , 21 ]), the role of contour strategies for tackling subsurface residual stresses, as well as their interplay with the surface qualities, has received little attention so far. Hence, the present study was conducted to provide new insights for the optimization of contour scan strategies and contour laser parameters based on surface qualities and subsurface residual stress formation.…”

Section: Introductionmentioning

confidence: 99%

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Pandora’s Box–Influence of Contour Parameters on Roughness and Subsurface Residual Stresses in Laser Powder Bed Fusion of Ti-6Al-4V

et al. 2020

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The contour scan strategies in laser powder bed fusion (LPBF) of Ti-6Al-4V were studied at the coupon level. These scan strategies determined the surface qualities and subsurface residual stresses. The correlations to these properties were identified for an optimization of the LPBF processing. The surface roughness and the residual stresses in build direction were linked: combining high laser power and high scan velocities with at least two contour lines substantially reduced the surface roughness, expressed by the arithmetic mean height, from values as high as 30 µm to 13 µm, while the residual stresses rose from ~340 to about 800 MPa. At this stress level, manufactured rocket fuel injector components evidenced macroscopic cracking. A scan strategy completing the contour region at 100 W and 1050 mm/s is recommended as a compromise between residual stresses (625 MPa) and surface quality (14.2 µm). The LPBF builds were monitored with an in-line twin-photodiode-based melt pool monitoring (MPM) system, which revealed a correlation between the intensity quotient I2/I1, the surface roughness, and the residual stresses. Thus, this MPM system can provide a predictive estimate of the surface quality of the samples and resulting residual stresses in the material generated during LPBF.

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Exploring the Correlation between Subsurface Residual Stresses and Manufacturing Parameters in Laser Powder Bed Fused Ti-6Al-4V

Cited by 41 publications

References 39 publications

The residual stress in as-built Laser Powder Bed Fusion IN718 alloy as a consequence of the scanning strategy induced microstructure

The residual stress in as-built Laser Powder Bed Fusion IN718 alloy as a consequence of the scanning strategy induced microstructure

Separation of the Formation Mechanisms of Residual Stresses in LPBF 316L

Pandora’s Box–Influence of Contour Parameters on Roughness and Subsurface Residual Stresses in Laser Powder Bed Fusion of Ti-6Al-4V

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