The role of lattice defects, element partitioning and intrinsic heat effects on the microstructure in selective laser melted Ti-6Al-4V

Haubrich, Jan; Gussone, Joachim; Barriobero-Vila, Pere; Kürnsteiner, Philipp; Jägle, Eric Aimé; Raabe, Dierk; Schell, Norbert; Requena, Guillermo

doi:10.1016/j.actamat.2019.01.039

Cited by 169 publications

(48 citation statements)

References 36 publications

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“…However, they also observed an anomaly decreased expansion of the β phase at around 500–600 °C that attributed to an increase of the V concentration. The same effect is reported in the paper by Huabrich et al [31] in a sample annealed at 400 °C for 2 h.…”

Section: Discussionsupporting

confidence: 88%

“…Thermally treating the highly defective microstructure observed in sample #AP induces elements diffusion and defects annealing. Diffusion of elements is strongly favored by defects, which therefore have a role in the solid-state phase transformations, as already shown by Haubrich et al [31]. Nevertheless, diffusion induces element partitioning that is substantially the basics of martensite decomposition: Al and O are accumulated in the α/α’ phase, while V and Fe accumulate in the β phase [31,32].…”

Section: Discussionmentioning

confidence: 92%

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Solid-State Phase Transformations in Thermally Treated Ti–6Al–4V Alloy Fabricated via Laser Powder Bed Fusion

et al. 2019

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Laser Powder Bed Fusion (LPBF) technology was used to produce samples based on the Ti–6Al–4V alloy for biomedical applications. Solid-state phase transformations induced by thermal treatments were studied by neutron diffraction (ND), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). Although, ND analysis is rather uncommon in such studies, this technique allowed evidencing the presence of retained β in α’ martensite of the as-produced (#AP) sample. The retained β was not detectable by XRD analysis, nor by STEM observations. Martensite contains a high number of defects, mainly dislocations, that anneal during the thermal treatment. Element diffusion and partitioning are the main mechanisms in the α ↔ β transformation that causes lattice expansion during heating and determines the final shape and size of phases. The retained β phase plays a key role in the α’ → β transformation kinetics.

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Section: Discussionsupporting

confidence: 88%

Section: Discussionmentioning

confidence: 92%

Solid-State Phase Transformations in Thermally Treated Ti–6Al–4V Alloy Fabricated via Laser Powder Bed Fusion

et al. 2019

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“…This cyclic re-heating consists of short temperature spikes with decreasing intensity and is referred to as intrinsic heat treatment (IHT). [549][550][551] Additionally, the substrate onto which material is deposited may be heated, allowing to change the base temperature of the temperature spikes. The high cooling rates typically lead to a fine (sub-lm diameter) cellular/dendritic solidification structure with pronounced micro-segregation, which can stabilize non-equilibrium phases such as retained austenite in the interdendritic regions.…”

Section: A Additive Manufacturing Of Advanced Steelsmentioning

confidence: 99%

Current Challenges and Opportunities in Microstructure-Related Properties of Advanced High-Strength Steels

Raabe

Sun

Silva

et al. 2020

Metall Mater Trans A

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125

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This is a viewpoint paper on recent progress in the understanding of the microstructure–property relations of advanced high-strength steels (AHSS). These alloys constitute a class of high-strength, formable steels that are designed mainly as sheet products for the transportation sector. AHSS have often very complex and hierarchical microstructures consisting of ferrite, austenite, bainite, or martensite matrix or of duplex or even multiphase mixtures of these constituents, sometimes enriched with precipitates. This complexity makes it challenging to establish reliable and mechanism-based microstructure–property relationships. A number of excellent studies already exist about the different types of AHSS (such as dual-phase steels, complex phase steels, transformation-induced plasticity steels, twinning-induced plasticity steels, bainitic steels, quenching and partitioning steels, press hardening steels, etc.) and several overviews appeared in which their engineering features related to mechanical properties and forming were discussed. This article reviews recent progress in the understanding of microstructures and alloy design in this field, placing particular attention on the deformation and strain hardening mechanisms of Mn-containing steels that utilize complex dislocation substructures, nanoscale precipitation patterns, deformation-driven transformation, and twinning effects. Recent developments on microalloyed nanoprecipitation hardened and press hardening steels are also reviewed. Besides providing a critical discussion of their microstructures and properties, vital features such as their resistance to hydrogen embrittlement and damage formation are also evaluated. We also present latest progress in advanced characterization and modeling techniques applied to AHSS. Finally, emerging topics such as machine learning, through-process simulation, and additive manufacturing of AHSS are discussed. The aim of this viewpoint is to identify similarities in the deformation and damage mechanisms among these various types of advanced steels and to use these observations for their further development and maturation.

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“…After the PWHT, the microstructure decomposes into in α + β structure, with a fine α-lamellar structure ( Figure 7 b). Precipitation of fine β within the fine α lamella detected in the Figure 7 d can be probably due to an heterogeneous enrichment of β-stabilizer elements [ 60 ].…”

Section: Resultsmentioning

confidence: 99%

Wire-Based Additive Manufacturing of Ti-6Al-4V Using Electron Beam Technique

et al. 2020

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Electron beam freeform fabrication is a wire feed direct energy deposition additive manufacturing process, where the vacuum condition ensures excellent shielding against the atmosphere and enables processing of highly reactive materials. In this work, this technique is applied for the α + β-titanium alloy Ti-6Al-4V to determine suitable process parameter for robust building. The correlation between dimensions and the dilution of single beads based on selected process parameters, leads to an overlapping distance in the range of 70–75% of the bead width, resulting in a multi-bead layer with a uniform height and with a linear build-up rate. Moreover, the stacking of layers with different numbers of tracks using an alternating symmetric welding sequence allows the manufacturing of simple structures like walls and blocks. Microscopy investigations reveal that the primary structure consists of epitaxial grown columnar prior β-grains, with some randomly scattered macro and micropores. The developed microstructure consists of a mixture of martensitic and finer α-lamellar structure with a moderate and uniform hardness of 334 HV, an ultimate tensile strength of 953 MPa and rather low fracture elongation of 4.5%. A subsequent stress relief heat treatment leads to a uniform hardness distribution and an extended fracture elongation of 9.5%, with a decrease of the ultimate strength to 881 MPa due to the fine α-lamellar structure produced during the heat treatment. Residual stresses measured by energy dispersive X-ray diffraction shows after deposition 200–450 MPa in tension in the longitudinal direction, while the stresses reach almost zero when the stress relief treatment is carried out.

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The role of lattice defects, element partitioning and intrinsic heat effects on the microstructure in selective laser melted Ti-6Al-4V

Cited by 169 publications

References 36 publications

Solid-State Phase Transformations in Thermally Treated Ti–6Al–4V Alloy Fabricated via Laser Powder Bed Fusion

Solid-State Phase Transformations in Thermally Treated Ti–6Al–4V Alloy Fabricated via Laser Powder Bed Fusion

Current Challenges and Opportunities in Microstructure-Related Properties of Advanced High-Strength Steels

Wire-Based Additive Manufacturing of Ti-6Al-4V Using Electron Beam Technique

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