High-cycle fatigue behavior of a laser powder bed fusion additive manufactured Ti-6Al-4V titanium: Effect of pores and tested volume size

Abstract

This work is focused on the effect of natural defect on the fatigue resistance of a laser powder bed fusion additively manufactured Ti-6Al-4V titanium. To reveal the fatigue strength variability and its sensitivity to the defect size, push-pull fatigue tests have been undertaken on specimens with different sizes of highly loaded volume of material. In order to easily vary the size of the highly loaded volume, specimens containing different numbers of surface hemispherical shape holes of 600 µm in diameter have been tested. This method also allowed to test small volume which triggered crack initiation from microstructural features.The fatigue damage mechanisms observed and the average natural defect size measured on the failure surfaces depend on the size of the highly stressed region. A higher fatigue strength is observed for smaller stressed volumes and defect free regions. To reduce the impact lack-offusion on fatigue and increase the probability of triggering crack initiation from a microstructural feature, the specimens were built in the horizontal direction. For specimens where fatigue cracks initiated at natural discontinuities, the results reported in a Kitagawa-Takahashi diagram revealed a critical defect size ( √ area) in the range of 30 µm. In addition, a probabilistic approach based on the weakest link theory is proposed. The model describes a probabilistic Kitagawa-Takahashi diagram accounting for the size of both the highly stressed volume and the natural defect.

Effect of Platform Temperature and Post-Processing Heat Treatment on the Fatigue Life of Additively Manufactured AlSi7Mg Alloy

“…Previous publications studied the mechanical properties of metallic SLM parts, including 316 stainless steel [10,11], Ti6Al4V [12][13][14][15], Inconel 718 [16] and aluminum alloys [3][4][5][6][7][8][9][17][18][19][20][21][22][23][24][25][26][27][28].…”

Fatigue strength and life assessment of L-PBF 316L stainless steel showing process and corrosion related defects

“…This dispersion is shown in Fig. 1 and can be attributed to different sized defects at the origin of fatigue fracture and to the variation of the local microstructure at the initiation site [25][26][27]. In general, the largest defect contained in the loaded sample and close to the free surface is likely to be the critical defect responsible for the final failure in High Cycle Fatigue (HCF) [28,29].…”

“…As pointed out by several authors [21,24,25], alloys manufactured by AM are characterized by S-N data showing a large scatter in fatigue lives and fatigue strength. This dispersion is shown in Fig.…”

Machine Learning Based Predictions of Fatigue Crack Growth Rate of Additively Manufactured Ti6Al4V

“…On account of few inherent defects in additively manufacturing methods, such as poor bonding defects, porosities, and edge crack initiations, makes the components vulnerable to cyclic loading. E. Pessard et al [16] have studied the effect of pores and tested volume size on fatigue performance of additively manufactured Ti6Al4V alloy. The different number of hemispherical surface holes are introduced to locally raise the stress and change the size of highly stressed volume.…”