Fatigue prediction through quantification of critical defects and crack growth behaviour in additively manufactured Ti-6Al-4V alloy

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Naab, Bryan and Ramachandran, Saranarayanan and Mirihanage, Wajira and Celikin, Mert (2024) Fatigue prediction through quantification of critical defects and crack growth behaviour in additively manufactured Ti-6Al-4V alloy. Materials Science and Engineering: A, 903. 146658. ISSN 0921-5093 (https://doi.org/10.1016/j.msea.2024.146658)

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Abstract

The study presents a methodology for predicting the fatigue life and identifying critical defects in additively manufactured (AM) Ti-6Al-4V alloy processed via laser powder bed fusion (L-PBF). Predictions were made on L-PBF Ti-6Al-4V alloy in two conditions: as-built and heat-treated by using X-ray μ-Computed Tomography (μ-CT) for the quantification of the defects and fatigue crack growth (FCG) data. For validation, fatigue life predictions were made on the same specimens on which μ-CT was conducted prior to fatigue testing. FCG and fatigue tests (S-N) highlighted differences in the performance between the as-built and heat-treated conditions: the as-built condition had a lower threshold stress intensity factor range (ΔKth) of 2.16 MPa m1/2 than that of the heat-treated condition, 4.96 MPa m1/2. Differences in fatigue limit were attributed to differences in ΔKth in as-built and heat-treated specimens. To gain mechanistic understanding of these differences near ΔKth cracks were examined using Electron Backscatter Diffraction - Kernel Average Misorientation (EBSD-KAM). It was found that upon heat treatment, the dislocation density increased around near threshold fatigue cracks. Increases in ΔKth are attributed to the increases in β-phase content and α-lath thickness caused by heat treatment.

ORCID iDs

Naab, Bryan, Ramachandran, Saranarayanan ORCID logoORCID: https://orcid.org/0000-0002-6881-2940, Mirihanage, Wajira and Celikin, Mert;
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