High cycle fatigue in selective laser melted Ti-6Al-4V

A major drawback of additively manufactured metallic components is their poor high cycle fatigue (HCF) resistance, which is primarily due to the presence of porosity in them. Keeping this in view, the effect of process parameters such as laser power (w), layer thickness (t), and scan rotation (ϕ) on...

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Main Authors: Kumar, Punit, Ramamurty, Upadrasta
Other Authors: School of Mechanical and Aerospace Engineering
Format: Article
Language:English
Published: 2022
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Online Access:https://hdl.handle.net/10356/160890
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Institution: Nanyang Technological University
Language: English
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spelling sg-ntu-dr.10356-1608902022-08-05T05:16:27Z High cycle fatigue in selective laser melted Ti-6Al-4V Kumar, Punit Ramamurty, Upadrasta School of Mechanical and Aerospace Engineering Engineering::Mechanical engineering High Cycle Fatigue Porosity A major drawback of additively manufactured metallic components is their poor high cycle fatigue (HCF) resistance, which is primarily due to the presence of porosity in them. Keeping this in view, the effect of process parameters such as laser power (w), layer thickness (t), and scan rotation (ϕ) on pore size, shape and distribution in selectively laser melted (SLM) Ti-6Al-4V alloy specimens and the influence of such pore characteristics on the HCF life under rotating bending fatigue conditions were investigated in this work. X-ray tomography was used to characterize the porosity in coupons produced using four different w-t-ϕ combinations. The possibility of enhancing the fatigue strength (σf) of the as-fabricated alloy through microstructural modification, via a post-fabrication heat-treatment that substantially improves the threshold for fatigue crack initiation, and subsequent shot peening were explored. Results show that the pore sizes and distribution are sensitive to the process parameters utilized; pores align in the build direction for ϕ = 90° whereas they are randomly distributed for ϕ = 67°, and a higher t results in denser parts. These observations are rationalized by recourse to the combined effect of the Marangoni convection and the Rayleigh instability in adjoining melt-pools. Only a marginal improvement in σf upon heat treatment was noted, whereas shot peening enhances it substantially such that σf is up to 55% of the tensile strength. These results are analyzed using the fracture mechanics-based K-T (Kitagawa-Takahashi) approach that is based on the El-Haddad formula. Agency for Science, Technology and Research (A*STAR) This work at NTU was conducted under the Structural Metals and Alloys Programme, which was funded by A*STAR, Singapore. 2022-08-05T05:16:27Z 2022-08-05T05:16:27Z 2020 Journal Article Kumar, P. & Ramamurty, U. (2020). High cycle fatigue in selective laser melted Ti-6Al-4V. Acta Materialia, 194, 305-320. https://dx.doi.org/10.1016/j.actamat.2020.05.041 1359-6454 https://hdl.handle.net/10356/160890 10.1016/j.actamat.2020.05.041 2-s2.0-85085727247 194 305 320 en Acta Materialia © 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic Engineering::Mechanical engineering
High Cycle Fatigue
Porosity
spellingShingle Engineering::Mechanical engineering
High Cycle Fatigue
Porosity
Kumar, Punit
Ramamurty, Upadrasta
High cycle fatigue in selective laser melted Ti-6Al-4V
description A major drawback of additively manufactured metallic components is their poor high cycle fatigue (HCF) resistance, which is primarily due to the presence of porosity in them. Keeping this in view, the effect of process parameters such as laser power (w), layer thickness (t), and scan rotation (ϕ) on pore size, shape and distribution in selectively laser melted (SLM) Ti-6Al-4V alloy specimens and the influence of such pore characteristics on the HCF life under rotating bending fatigue conditions were investigated in this work. X-ray tomography was used to characterize the porosity in coupons produced using four different w-t-ϕ combinations. The possibility of enhancing the fatigue strength (σf) of the as-fabricated alloy through microstructural modification, via a post-fabrication heat-treatment that substantially improves the threshold for fatigue crack initiation, and subsequent shot peening were explored. Results show that the pore sizes and distribution are sensitive to the process parameters utilized; pores align in the build direction for ϕ = 90° whereas they are randomly distributed for ϕ = 67°, and a higher t results in denser parts. These observations are rationalized by recourse to the combined effect of the Marangoni convection and the Rayleigh instability in adjoining melt-pools. Only a marginal improvement in σf upon heat treatment was noted, whereas shot peening enhances it substantially such that σf is up to 55% of the tensile strength. These results are analyzed using the fracture mechanics-based K-T (Kitagawa-Takahashi) approach that is based on the El-Haddad formula.
author2 School of Mechanical and Aerospace Engineering
author_facet School of Mechanical and Aerospace Engineering
Kumar, Punit
Ramamurty, Upadrasta
format Article
author Kumar, Punit
Ramamurty, Upadrasta
author_sort Kumar, Punit
title High cycle fatigue in selective laser melted Ti-6Al-4V
title_short High cycle fatigue in selective laser melted Ti-6Al-4V
title_full High cycle fatigue in selective laser melted Ti-6Al-4V
title_fullStr High cycle fatigue in selective laser melted Ti-6Al-4V
title_full_unstemmed High cycle fatigue in selective laser melted Ti-6Al-4V
title_sort high cycle fatigue in selective laser melted ti-6al-4v
publishDate 2022
url https://hdl.handle.net/10356/160890
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