Impact of the Loading Conditions and the Building Directions on the Mechanical Behavior of Biomedical β-Titanium Alloy Produced In Situ by Laser-Based Powder Bed Fusion

In order to simulate micromachining of Ti-Nb medical devices produced in situ by selective laser melting, it is necessary to use constitutive models that allow one to reproduce accurately the material behavior under extreme loading conditions. The identification of these models is often performed using experimental tension or compression data. In this work, compression tests are conducted to investigate the impact of the loading conditions and the laser-based powder bed fusion (LB-PBF) building directions on the mechanical behavior of β-Ti42Nb alloy. Compression tests are performed under two strain rates (1 s−1 and 10 s−1) and four temperatures (298 K, 673 K, 873 K and 1073 K). Two LB-PBF building directions are used for manufacturing the compression specimens. Therefore, different metallographic analyses (i.e., optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), electron backscatter diffraction (EBSD) and X-ray diffraction) have been carried out on the deformed specimens to gain insight into the impact of the loading conditions on microstucture alterations. According to the results, whatever the loading conditions are, specimens manufactured with a building direction of 45∘ exhibit higher flow stress than those produced with a building direction of 90∘, highlighting the anisotropy of the as-LB-PBFed alloy. Additionally, the deformed alloy exhibits at room temperature a yielding strength of 1180 ± 40 MPa and a micro-hardness of 310 ± 7 HV0.1. Experimental observations demonstrated two strain localization modes: a highly deformed region corresponding to the localization of the plastic deformation in the central region of specimens and perpendicular to the compression direction and an adiabatic shear band oriented with an angle of ±45 with respect to same direction.

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Effect of Build Orientation on the Microstructure, Mechanical and Corrosion Properties of a Biodegradable High Manganese Steel Processed by Laser Powder Bed Fusion

Metals ◽

10.3390/met11060944 ◽

2021 ◽

Vol 11 (6) ◽

pp. 944

Author(s):

Martin Otto ◽

Stefan Pilz ◽

Annett Gebert ◽

Uta Kühn ◽

Julia Hufenbach

Keyword(s):

Electron Backscatter Diffraction ◽

Longitudinal Axis ◽

Manganese Steel ◽

Compressive Yield Strength ◽

Powder Bed Fusion ◽

Compression Tests ◽

Laser Powder Bed Fusion ◽

Corrosion Properties ◽

Powder Bed ◽

Manufacturing Technologies

In the last decade, additive manufacturing technologies like laser powder bed fusion (LPBF) have emerged strongly. However, the process characteristics involving layer-wise build-up of the part and the occurring high, directional thermal gradient result in significant changes of the microstructure and the related properties compared to traditionally fabricated materials. This study presents the influence of the build direction (BD) on the microstructure and resulting properties of a novel austenitic Fe‑30Mn‑1C‑0.02S alloy processed via LPBF. The fabricated samples display a {011} texture in BD which was detected by electron backscatter diffraction. Furthermore, isolated binding defects could be observed between the layers. Quasi-static tensile and compression tests displayed that the yield, ultimate tensile as well as the compressive yield strength are significantly higher for samples which were built with their longitudinal axis perpendicular to BD compared to their parallel counterparts. This was predominantly ascribed to the less severe effects of the sharp-edged binding defects loaded perpendicular to BD. Additionally, a change of the Young’s modulus in dependence of BD could be demonstrated, which is explained by the respective texture. Potentiodynamic polarization tests conducted in a simulated body fluid revealed only slight differences of the corrosion properties in dependence of the build design.

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In Situ Analysis of Laser Powder Bed Fusion Using Simultaneous High-Speed Infrared and X-ray Imaging

JOM ◽

10.1007/s11837-020-04291-5 ◽

2020 ◽

Vol 73 (1) ◽

pp. 201-211 ◽

Cited By ~ 3

Author(s):

Benjamin Gould ◽

Sarah Wolff ◽

Niranjan Parab ◽

Cang Zhao ◽

Maria Cinta Lorenzo-Martin ◽

...

Keyword(s):

High Speed ◽

In Situ Analysis ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

X Ray ◽

X Ray Imaging

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Synchrotron Characterisation of Ultra-Fine Grain TiB2/Al-Cu Composite Fabricated by Laser Powder Bed Fusion

Acta Metallurgica Sinica (English Letters) ◽

10.1007/s40195-021-01317-y ◽

2021 ◽

Author(s):

Sheng Li ◽

Biao Cai ◽

Ranxi Duan ◽

Lei Tang ◽

Zihan Song ◽

...

Keyword(s):

Electron Microscopy ◽

Tensile Loading ◽

Fusion Pore ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

X Ray ◽

Random Texture ◽

Average Grain Size

AbstractIsotropy in microstructure and mechanical properties remains a challenge for laser powder bed fusion (LPBF) processed materials due to the epitaxial growth and rapid cooling in LPBF. In this study, a high-strength TiB2/Al-Cu composite with random texture was successfully fabricated by laser powder bed fusion (LPBF) using pre-doped TiB2/Al-Cu composite powder. A series of advanced characterisation techniques, including synchrotron X-ray tomography, correlative focussed ion beam–scanning electron microscopy (FIB-SEM), scanning transmission electron microscopy (STEM), and synchrotron in situ X-ray diffraction, were applied to investigate the defects and microstructure of the as-fabricated TiB2/Al-Cu composite across multiple length scales. The study showed ultra-fine grains with an average grain size of about 0.86 μm, and a random texture was formed in the as-fabricated condition due to rapid solidification and the TiB2 particles promoting heterogeneous nucleation. The yield strength and total elongation of the as-fabricated composite were 317 MPa and 10%, respectively. The contributions of fine grains, solid solutions, dislocations, particles, and Guinier–Preston (GP) zones were calculated. Failure was found to be initiated from the largest lack-of-fusion pore, as revealed by in situ synchrotron tomography during tensile loading. In situ synchrotron diffraction was used to characterise the lattice strain evolution during tensile loading, providing important data for the development of crystal-plasticity models.

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Constitutive Modelling of Laser Based Powder Bed Fusion Melted Inconel 718 Superalloy over a Wide Range of Strain Rates

10.3233/atde210036 ◽

2021 ◽

Author(s):

Laura Delcuse ◽

Slim Bahi ◽

Urvashi Gunputh ◽

Paul Wood ◽

Alexis Rusinek

Keyword(s):

Inconel 718 ◽

Bulk Material ◽

Constitutive Modelling ◽

Material Behavior ◽

Vertical Position ◽

Strain Rates ◽

Powder Bed Fusion ◽

Compression Tests ◽

Powder Bed ◽

The Difference

The aim of this paper is to determine the material parameters of the Inconel 718 manufactured by Laser Powder Bed Fusion, using the Johnson-Cook model. Different compression tests in quasi-static and dynamic domains were performed under various strain rates, in range of 10-3 s-1 to 2500 s-1 at the room temperature. The difference between the two building directions XY and ZX, horizontal and vertical position from the substrate, was investigated to highlight the influence of the process parameter on the bulk material behavior. Finally, the identified parameters were implemented into a numerical model, describing the behavior of auxetic structure under compression test, and validated using experimental data.

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