Effect of Internal Defects on the Fatigue Behavior of Additive Manufactured Metal Components: A Comparison between Ti6Al4V and Inconel 718

Abstract

In order to obtain a widespread application of Additive Manufactured (AM) technology in the aircraft industry for fatigue critical parts, a detailed characterization of the Fatigue and Damage Tolerance (F&DT) behavior of structural components is required. Metal AM techniques in particular are prone to internal defects inherently present due to the nature of the process, which have a detrimental effect on fatigue properties. In the present work, Ti6Al4V and Inconel 718 coupons with artificially induced defects of different dimensions were produced by the Laser Powder Bed Fusion (LPBF) technique. Fatigue tests were performed, and a different defect sensitiveness was observed between the two materials with Inconel being more defect tolerant compared to Titanium. The environmental role at the crack tip of internal defects was discussed, and based on a purely fracture mechanics approach, a simplified stress–life–defect size model was finally devised. The experimental test results together with the information obtained from the fracture surface analysis of tested samples are used to validate the model predictions. The proposed approach could be adopted to define a critical defect size map to be used for tailored Non-Destructive Testing (NDT) evaluation.

Recent developments and future trends in fatigue life assessment of additively manufactured metals with particular emphasis on machine learning modeling

“…[189][190][191] Based on this consideration, the defect-based fracture mechanics methods have been successfully employed to predict the fatigue life of AM materials and achieved good results. 37,46,55,[191][192][193][194][195][196][197][198] Many fatigue crack propagation models have been adopted to predict the fatigue life of AM metals. A simply modified version of the Paris equation is as follows:…”

“…There are many defects in AM metals, and the cracks usually initiate from the critical defects 189–191 . Based on this consideration, the defect‐based fracture mechanics methods have been successfully employed to predict the fatigue life of AM materials and achieved good results 37,46,55,191–198 …”

“…C and m are material parameters. This form was adopted in the work of Cersullo et al 192 and Molina et al 195 Cersullo et al 192 determined initial crack size as parameter while the final crack size was obtained from the fracture surface observations. In the work of Molina et al, 195 was calculated by the following equation considering the effect of defect and hardness: where is the Vickers hardness of materials.…”

An Investigation of Anisotropic Fatigue Properties of Laser Additively Manufactured Ti-6Al-4V under Vibration Loading

“…Laser additive manufacturing technology (LAM) is becoming an increasingly popular manufacturing technology in aerospace industry. In LAM process, high-energy laser deposit metallic wires or powders, layer-by-layer, to build components [1][2][3][4]. The high-efficiency and fast-forming process does not require subsquent expensive tooling and machining, enabling the directly fabrication of near-net-shaped components.…”

Point Defects Stability, Hydrogen Diffusion, Electronic Structure, and Mechanical Properties of Defected Equiatomic γ(U,Zr) from First-Principles

“…During the fission neutron irradiation, or even at the fabrication stage, some point defects, such as vacancies and hydrogen (H) atoms, are generated in the material [ 17 , 18 , 19 , 20 , 21 ]. These point defects can further form clusters and lead to adverse mechanical degradation [ 22 , 23 , 24 ] or even change the phase of nuclear fuel [ 25 ]. It is found that voids or dislocation loops formed in α-U can lead to the hardening of the material [ 26 , 27 ].…”