Resultant physical properties of as-built nitinol processed at specific volumetric energy densities and correlation with in-situ melt pool temperatures

Monu, Medad C.C.; Ekoi, Emmanuel J.; Hughes, Cian; Kumar, Sanjeev; Brabazon, Dermot

doi:10.1016/j.jmrt.2022.10.073

Cited by 11 publications

(4 citation statements)

References 74 publications

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“…This narrowing is seen especially at vlat > 30 mm/s. The increasing cracking tendency for elevated EA and vlat was also found for the selective laser melting process (SLM) [10,32].…”

Section: Efficient and Sustainable Pbf-eb Niti Process Window Generat...mentioning

confidence: 67%

“…In addition, the material has a high potential in terms of new sustainable technologies, e.g., heating and cooling using the elastocaloric effect [5], newly designed actuators [6] or heat engines without the usage of fossil fuels [7]. The combination of NiTi and additive manufacturing (AM), especially powder bed fusion (PBF), has gained significant interest over the last years [8][9][10][11][12]. Conventional processes such as casting can have a higher probability of impurity pick-up compared to electron beam powder bed fusion (PBF-EB), which operates under high vacuum [8].…”

Section: Introductionmentioning

confidence: 99%

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Anisotropic Superelastic and Shape Memory Effect of Nitinol Manufactured by Electron Beam Powder Bed Fusion

Fink,

Wahlmann,

K鰎ner

2024

Advanced Materials &Amp; Sustainable Manufacturing

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This study explores the impact of energy input and build orientation on the anisotropic mechanical and functional properties of Ti-rich Nitinol (NiTi) produced via electron beam powder bed fusion (PBF-EB), integrated with layerwise in-situ monitoring of the melted surface via backscatter electron detection (ELO). NiTi, a binary alloy of nickel and titanium, exhibits shape memory and superelasticity, making it widely used in biomedical applications and sustainable technologies. PBF-EB, particularly with ELO, is highlighted for its advantages in producing crack-free NiTi with tailored microstructures. The investigation reveals that energy input significantly influences microstructure phases, with higher energy promoting increased evaporation of Ni and enhancing Ti-rich Ti2Ni precipitates, allowing for tailored material properties. Build orientation also proves crucial, impacting mechanical responses and functional properties. The 0° orientation yields the hardest mechanical response with the highest ultimate tensile strength (UTS) and the highest strain recovery ratio while the 45° orientation shows improved ductility but lower UTS. The influencing factors towards the formation of the anisotropic material properties are explained and the potential of tailoring the NiTi properties for specific applications by controlling energy input and build orientation in the PBF-EB process are underlined. These insights offer valuable criteria for designing innovative NiTi parts.

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“…This narrowing is seen especially at vlat > 30 mm/s. The increasing cracking tendency for elevated EA and vlat was also found for the selective laser melting process (SLM) [10,32].…”

Section: Efficient and Sustainable Pbf-eb Niti Process Window Generat...mentioning

confidence: 67%

Section: Introductionmentioning

confidence: 99%

Anisotropic Superelastic and Shape Memory Effect of Nitinol Manufactured by Electron Beam Powder Bed Fusion

Fink,

Wahlmann,

K鰎ner

2024

Advanced Materials &Amp; Sustainable Manufacturing

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show abstract

“…In the context of this study, the presented thermograms are only suitable in explaining the TGM of residual stress formation in single layers and few micron-layer components. However, the thermal gradients and ensuing thermally induced residual stresses across the build height in PBF-LB processed ‘bulk’ NiTi can be deduced by in-depth quantitative (statistical) analysis of the collated in situ melt pool thermal radiation data, as demonstrated by Monu et al [ 70 ].…”

Section: Resultsmentioning

confidence: 99%

“…The studies by Refs. [ 32 , 70 , 71 ] have demonstrated that indeed, a few micron layers from the build substrate is required to attain homogeneous temperature distribution during PBF-LB processing of NiTi parts/components. This typifies the onset of the cooling phase and shrinkage mechanism (CPSM) predominance over TGM, in the formation of residual stresses as build height increases.…”

Section: Resultsmentioning

confidence: 99%

Bi-directional Scan Pattern Effects on Residual Stresses and Distortion in As-built Nitinol Parts: A Trend Analysis Simulation Study

Monu

Afkham

Chekotu

et al. 2023

Integr Mater Manuf Innov

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In this paper, a part-scale simulation study on the effects of bi-directional scanning patterns (BDSP) on residual stress and distortion formation in additively manufactured Nitinol (NiTi) parts is presented. The additive manufacturing technique of focus is powder bed fusion using a laser beam (PBF-LB), and simulation was performed using Ansys Additive Print software. The numerical approach adopted in the simulation was based on the isotropic inherent strain model, due to prohibitive material property requirements and computational limitations of full-fledged part-scale 3D thermomechanical finite element approaches. In this work, reconstructed 2D and 3D thermograms (heat maps) from in situ melt pool thermal radiation data, the predicted residual stresses, and distortions from the simulation study were correlated for PBF-LB processed NiTi samples using selected BDSPs. The distortion and residual stress distribution were found to vary greatly between BDSPs with no laser scan vector rotations per new layer, whereas negligible variations were observed for BDSPs with laser scan vector rotations per new layer. The striking similarities between the reconstructed thermograms of the first few layers and the simulated stress contours of the first lumped layer provide a practical understanding of the temperature gradient mechanism of residual stress formation in PBF-LB processed NiTi. This study provides a qualitative, yet practical insight towards understanding the trends of formation and evolution of residual stress and distortion, due to scanning patterns.

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Steady-state and transient mechanical response analysis of superelastic nitinol lattice structures prior to additive manufacturing: An in-silico study

Khan

Ayub

Chekotu

et al. 2023

Journal of Materials Research and Technology

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Resultant physical properties of as-built nitinol processed at specific volumetric energy densities and correlation with in-situ melt pool temperatures

Cited by 11 publications

References 74 publications

Anisotropic Superelastic and Shape Memory Effect of Nitinol Manufactured by Electron Beam Powder Bed Fusion

Anisotropic Superelastic and Shape Memory Effect of Nitinol Manufactured by Electron Beam Powder Bed Fusion

Bi-directional Scan Pattern Effects on Residual Stresses and Distortion in As-built Nitinol Parts: A Trend Analysis Simulation Study

Steady-state and transient mechanical response analysis of superelastic nitinol lattice structures prior to additive manufacturing: An in-silico study

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