The effect of beam scan strategies on microstructural variations in Ti-6Al-4V fabricated by electron beam powder bed fusion

Shao, Meiyue; Vijayan, Sriram; Nandwana, Peeyush; Jinschek, Joerg R.

doi:10.1016/j.matdes.2020.109165

Cited by 39 publications

(28 citation statements)

References 54 publications

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“…3D analysis of the microstructure of the E-PBF samples reveal that changing the printing strategy changes the microstructural evolution and variant selection behavior of the material significantly. While the limitations of 3D data make it difficult to generalize the observations, previously published 2D studies of different locations in each build [66,67], as well as analysis of similar samples from different locations on the same build plate support the relevance and repeatability of these results [68,72]. The relatively small changes in texture within a given E-PBF build further support the assumption that the scan strategy is the primary reason for the different behaviors observed [73].…”

Section: Discussionmentioning

confidence: 57%

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3D characterization of microstructural evolution and variant selection in additively manufactured Ti-6Al-4 V

et al. 2021

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Ti-6Al-4 V is a popular alloy in additive manufacturing (AM) due to its applications in the biomedical implants and aerospace industries where the complex part geometries allowed by AM provide cost and performance benefits. Ti-6Al-4 V goes through a b ? a' transformation after solidification which is known to experience variant selection, e.g., through the formation of clusters of variants which, when situated together, partially accommodate the strain of the phase transformation. During electron beam powder bed fusion AM, an in situ decomposition of a' martensite occurs during the cyclic reheating caused by melting successive layers, resulting in a ? b microstructures. How variant selection influences the evolution beyond the initial rapid cooling remains an open question. Using 3D electron backscatter diffraction, we provide a clearer understanding without ambiguity from sectioning effects of how a' decomposes into microstructures with distinct morphologies and variant/intervariant distributions. We extract quantitative 3D information on the various intervariant boundaries networks formed in samples printed using three different electron beam scanning strategies. This shows that differing mechanisms during the decomposition result in a shift from self-accommodating clusters in an acicular microstructure, to either the preferred growth of six variants in a basketweave microstructure, or to a colony microstructure where variant selection is determined by prior-b grain boundaries. We propose a new representation of the misorientations arising from the Burgers orientation relationship, which we refer to as intervariant network diagram, to reveal how variant selection during the martensitic transformation and subsequent decomposition leads to the intervariant boundary networks observed. This holistic understanding of the microstructural evolution has the potential to allow tailoring of microstructures and properties for specific applications.

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Section: Discussionmentioning

confidence: 57%

“…A detailed 2D analysis of the a and reconstructed prior b microstructures resulting from these scan strategies has recently been reported [66][67][68]. Each scan strategy was found to produce variations in microstructure and corresponding variant selection behavior.…”

Section: D-ebsdmentioning

confidence: 99%

3D characterization of microstructural evolution and variant selection in additively manufactured Ti-6Al-4 V

et al. 2021

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“…An acicular α/α' is observed in the optical micrograph taken in the plane parallel to the building direction (Figure 3b). Since the heat treatment was carried out at the temperature above the β to α transformation point of 900-950 • C [26,27], the traces of primary β-grains elongated along the building direction (Z-axis), which have been frequently observed in PBF-fabricated specimens [28][29][30], disappeared. Heat treatment resulted in the formation of necks between the powder particles (Figure 4), and powder particles construct a three-dimensional network through the necks.…”

Section: Densities and Microstructures Of Specimensmentioning

confidence: 99%

Fabrication of Ti-Alloy Powder/Solid Composite with Uniaxial Anisotropy by Introducing Unidirectional Honeycomb Structure via Electron Beam Powder Bed Fusion

et al. 2021

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In this study, a Ti–6Al–4V alloy composite with uniaxial anisotropy and a hierarchical structure is fabricated using electron beam powder bed fusion, one of the additive manufacturing techniques that enable arbitrary fabrication, and subsequent heat treatment. The uniaxial anisotropic deformation behavior and mechanical properties such as Young’s modulus are obtained by introducing a unidirectional honeycomb structure. The main feature of this structure is that the unmelted powder retained in the pores of the honeycomb structure. After appropriate heat treatment at 1020 °C, necks are formed between the powder particles and between the powder particles and the honeycomb wall, enabling a stress transmission through the necks when the composite is loaded. This means that the powder part has been mechanically functionalized by the neck formation. As a result, a plateau region appears in the stress–strain curve. The stress transfer among the powder particles leads to the cooperative deformation of the composites, contributing to the excellent energy absorption capacity. Therefore, it is expected that the composite can be applied to bone plates on uniaxially oriented microstructures such as long bones owing to its excellent energy absorption capacity and low elasticity to unidirectionally suppress stress shielding.

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“…Their valuable research showed that the relative amount of six α variants could account for the anisotropy in the mechanical properties. Many factors such as process parameters [13][14][15], scanning strategies [16][17][18], build orientation [13,[19][20][21][22][23][24], heat treatments [25][26][27][28][29] and hot isostatic pressing [28,[30][31][32][33] affect the microstructure and mechanical properties of EBM Ti-6Al-4V. Besides, columnar prior β-grains were found to epitaxially grow through a few layers and their major axis was found to orient parallel to the build direction [2,11,12,23,26,[34][35][36].…”

Section: Introductionmentioning

confidence: 99%

Spatial and Direction-Based Characterization of Microstructures and Microhardness of TA15 Titanium Alloy Produced by Electron Beam Melting

et al. 2021

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The extracted position and characterization direction of specimens have an unignorable effect on the microstructural characteristics of materials produced by electron beam melting (EBM). This study focused on the effects of extracted position and characterization direction on the microstructure, defect distribution and Vickers hardness of TA15 titanium alloy fabricated by electron beam melting. Results show that the microstructure at the bottom end of TA15 specimens is coarser and hot cracks are visible at this end. Grain morphology in longitudinal direction is columnar while that in transversal direction is chessboard-like. The results of defect analysis show that gas pores are visible in transversal direction while lack of fusion exists in longitudinal direction. The average relative density of TA15 specimens in transversal direction is higher than that in longitudinal direction. The results of energy spectrum analysis show that there is evaporation of Al during the forming process, but no elements segregation and enrichment are observed. This study provides important insights on the microstructure analysis and defect evaluation of materials made by EBM technology.

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The effect of beam scan strategies on microstructural variations in Ti-6Al-4V fabricated by electron beam powder bed fusion

Cited by 39 publications

References 54 publications

3D characterization of microstructural evolution and variant selection in additively manufactured Ti-6Al-4 V

3D characterization of microstructural evolution and variant selection in additively manufactured Ti-6Al-4 V

Fabrication of Ti-Alloy Powder/Solid Composite with Uniaxial Anisotropy by Introducing Unidirectional Honeycomb Structure via Electron Beam Powder Bed Fusion

Spatial and Direction-Based Characterization of Microstructures and Microhardness of TA15 Titanium Alloy Produced by Electron Beam Melting

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