PSI - Issue 57

David Mellé et al. / Procedia Structural Integrity 57 (2024) 61–72 David Melle´ / Structural Integrity Procedia 00 (2023) 000–000

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(2017)). Even if most additively manufactured parts are Hot Isostatic Pressed, this treatment is not e ffi cient for closing surface connected porosities (Leuders et al. (2013); Tammas-Williams et al. (2016)). The high surface roughness they produce (Cabanettes et al. (2018)) and its e ff ect on the fatigue life has also been a large part of the studied perimeter (Kasperovich and Hausmann (2015); Kahlin et al. (2017)). Linear elastic fracture mechanics and Kitagawa-Takahashi diagrams (Kitagawa and Takahashi (1976, 1979)) are extensively used to account for the e ff ects of defects on the fatigue life of additively manufactured alloys (Wycisk et al. (2014); Le et al. (2018)). In addition, numerous processes that aim at decreasing this roughness and increase the fatigue life have also been studied (Kahlin et al. (2020); Maleki et al. (2021)). Among them, chemical etching processes are especially adapted to complex geometries (Lhuissier et al. (2016); Persenot et al. (2017); Pegues et al. (2018); Vayssette et al. (2018)). The titanium alloy Ti-6Al-4V has been widely used in all these studies. In the litterature, only a few authors have focused on the e ff ect of the chemical etching process on the population of defects, sometimes on other materials (Andreau et al. (2019)). When done on Ti-6Al-4V (Persenot et al. (2020)), Murakami’s √ area appears not to be su ffi cient to determine the critical defect from this population. The present work therefore proposes, for Ti-6Al-4V coupons manufactured by laser powder bed fusion, to investi gate thee ff ect of a chemical etching process on the fatigue life and on the population of surface features. A comparison of the di ff erent metrics of the surface micro-geometric features will be proposed to understand if the critical defect can be determined from a known population and if so which indicator should be used.

Nomenclature

EDM Electric Discharge Machining ELI Extra Low Intersticial FEA Finite Elements Analysis FFT Fast Fourier Transform HIP Hot Isostatic Pressing L-PBF Laser Powder Bed Fusion SCF Stress Concentration Factor XRD X-Ray Di ff raction

2. Material, manufacturing and testing procedures

2.1. Material

Only one material is used in this study. To avoid uncontroled variabilities, all coupons were made on the same machine with the same orientation on the building plate and using the same machine parameters. A unique powder batch is also used. This powder is a Ti-6Al-4V ELI Grade 23 powder that meets ASTM B348-13 requirements. Its chemical composition is given in Table 1.

Table 1. Manufacturing powder chemical composition.

Element

Al

V

Fe

Y

C

O

N

H

Weight (%)

6.20

4.02

0.15

< 0.001

< 0.005

0.065

0.012

0.004

The powder size distribution was comprised between 20 µ m to 53 µ m (for 94 . 4 % of the powder weight). All the coupons were verticaly built on a commercial L-PBF machine using the machine constructor recommanded param eters for Ti-6Al-4V. The loading direction is therefore coincident with the building direction. The used parametry includes a hatch strategy and the construction was made with 60 µ m thick layers. In order to relieve the residual