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Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of Ti6Al4V: High-fidelity modelling and experimental validation

Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of Ti6Al4V: High-fidelity modelling and experimental validation
Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of Ti6Al4V: High-fidelity modelling and experimental validation
Metal additive manufacturing, despite of offering unique capabilities e.g. unlimited design freedom, short manufacturing time, etc., suffers from raft of intrinsic defects. Porosity is of the defects which can badly deteriorate a part’s performance. In this respect, enabling one to observe and predict the porosity during this process is of high importance. To this end, in this work a combined numerical and experimental approach has been used to analyze the formation, evolution and disappearance of keyhole and keyhole-induced porosities along with their initiating mechanisms, during single track L-PBF of a Ti6Al4V alloy. In this respect, a high-fidelity numerical model based on the Finite Volume Method (FVM) and accomplished in the commercial software Flow-3D is developed. The model accounts for the major physics taking place during the laser-scanning step of the L-PBF process. To better simulate the actual laser-material interaction, multiple reflection with the ray-tracing method has been implemented along with the Fresnel absorption function. The results show that during the keyhole regime, the heating rises dramatically compared to the shallow-depth melt pool regime due to the large entrapment of laser rays in the keyhole cavities. Also a detailed parametric study is performed to investigate the effect of input power on thermal absorptivity, heat transfer and melt pool anatomy. Furthermore, an X-ray Computed Tomography (X-CT) analysis is carried out to visualize the pores formed during the L-PBF process. It is shown, that the predicted shape, size and depth of the pores are in very good agreement with those found by either X-CT or optical and 3D digital microscopic images.
Multiphysics model, The L-PBF process, Keyhole formation, Porosity, X-CT analysis, Multiple reflection
2214-8604
Bayat, Mohamad
11377ea9-8478-413d-b99c-55a37cf7bf6c
Thanki, Aditi
1fb66672-7672-41fd-81e7-0e346567475b
Mohanty, Sankhya
76faf486-a0df-40da-a61c-908247ed407a
Witvrouw, Ann
b54ae80f-b9f9-4466-87a9-90f0c5368465
Yang, Shoufeng
e0018adf-8123-4a54-b8dd-306c10ca48f1
Thorborg, Jesper
0582a134-2d43-4e62-a7ad-04d67f71d258
Tiedje, Niels Skat
59d8d78a-8587-463c-8c31-1a3e8e91360c
Hattel, Jesper Henri
541e1a4b-9415-4583-b865-2d332c7b0106
Bayat, Mohamad
11377ea9-8478-413d-b99c-55a37cf7bf6c
Thanki, Aditi
1fb66672-7672-41fd-81e7-0e346567475b
Mohanty, Sankhya
76faf486-a0df-40da-a61c-908247ed407a
Witvrouw, Ann
b54ae80f-b9f9-4466-87a9-90f0c5368465
Yang, Shoufeng
e0018adf-8123-4a54-b8dd-306c10ca48f1
Thorborg, Jesper
0582a134-2d43-4e62-a7ad-04d67f71d258
Tiedje, Niels Skat
59d8d78a-8587-463c-8c31-1a3e8e91360c
Hattel, Jesper Henri
541e1a4b-9415-4583-b865-2d332c7b0106

Bayat, Mohamad, Thanki, Aditi, Mohanty, Sankhya, Witvrouw, Ann, Yang, Shoufeng, Thorborg, Jesper, Tiedje, Niels Skat and Hattel, Jesper Henri (2019) Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of Ti6Al4V: High-fidelity modelling and experimental validation. Additive Manufacturing, 30, [100835]. (doi:10.1016/j.addma.2019.100835).

Record type: Article

Abstract

Metal additive manufacturing, despite of offering unique capabilities e.g. unlimited design freedom, short manufacturing time, etc., suffers from raft of intrinsic defects. Porosity is of the defects which can badly deteriorate a part’s performance. In this respect, enabling one to observe and predict the porosity during this process is of high importance. To this end, in this work a combined numerical and experimental approach has been used to analyze the formation, evolution and disappearance of keyhole and keyhole-induced porosities along with their initiating mechanisms, during single track L-PBF of a Ti6Al4V alloy. In this respect, a high-fidelity numerical model based on the Finite Volume Method (FVM) and accomplished in the commercial software Flow-3D is developed. The model accounts for the major physics taking place during the laser-scanning step of the L-PBF process. To better simulate the actual laser-material interaction, multiple reflection with the ray-tracing method has been implemented along with the Fresnel absorption function. The results show that during the keyhole regime, the heating rises dramatically compared to the shallow-depth melt pool regime due to the large entrapment of laser rays in the keyhole cavities. Also a detailed parametric study is performed to investigate the effect of input power on thermal absorptivity, heat transfer and melt pool anatomy. Furthermore, an X-ray Computed Tomography (X-CT) analysis is carried out to visualize the pores formed during the L-PBF process. It is shown, that the predicted shape, size and depth of the pores are in very good agreement with those found by either X-CT or optical and 3D digital microscopic images.

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More information

Accepted/In Press date: 16 August 2019
e-pub ahead of print date: 17 August 2019
Published date: December 2019
Keywords: Multiphysics model, The L-PBF process, Keyhole formation, Porosity, X-CT analysis, Multiple reflection

Identifiers

Local EPrints ID: 439470
URI: http://eprints.soton.ac.uk/id/eprint/439470
ISSN: 2214-8604
PURE UUID: b8027991-ca93-46a7-b057-f243222cb151
ORCID for Shoufeng Yang: ORCID iD orcid.org/0000-0002-3888-3211

Catalogue record

Date deposited: 23 Apr 2020 16:54
Last modified: 21 Nov 2021 20:17

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Contributors

Author: Mohamad Bayat
Author: Aditi Thanki
Author: Sankhya Mohanty
Author: Ann Witvrouw
Author: Shoufeng Yang ORCID iD
Author: Jesper Thorborg
Author: Niels Skat Tiedje
Author: Jesper Henri Hattel

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