High-Cycle Fatigue Performance of Laser Powder Bed Fusion Ti-6Al-4V Alloy with Inherent Internal Defects: A Critical Literature Review
Abstract
1. Introduction
Author (s) | Topics Covered | Future Direction Highlighted |
---|---|---|
Liu and Shin 2019 [21] | Overall overview of DED, EPBF and L-PBF processing and inherent defects including porosities, and residual stress, microstructure, tensile and fatigue properties and relevant influential factors in a nutshell. | Not available (NA) |
Pegues et al., 2020 [22] Molaei et al., 2020 [23] | Part I reviewed the correlation between AM processing (including post-processing) and the microstructure and defects; part II reviewed the correlation between the different types of fatigue behaviors and microstructure and defects. | NA |
Teixeira et al., 2020 [33] | Heat treatment’s role on residual stresses, microstructure, and mechanical properties including ductility, fatigue life, and hardness. |
|
Sanaei and Fatemi 2021 [24] | Different types of intrinsic AM defects and their effects on the fatigue performance. |
|
Singla et al., 2021 [26] | Overview of different types of intrinsic L-PBF defects and different types of post-processing treatments’ effects on defects and mechanical behavior. |
|
Kan et al., 2022 [28] | The effects of porosities on the mechanical properties of L-PBF metal alloys. | NA |
Nguyen et al., 2022 [30] | Microstructure of AM Ti-6Al-4V including the microstructure and the defects’ role in the fatigue properties. |
|
Jamhari et al., 2023 [29,31] | Heat treatment and HIP on the microstructure, porosities and mechanical properties of L-PBF Ti-6Al-4V alloy. |
|
Hasan Tusher and Ince 2023 [32] | Overview of the state of the art on the fatigue behavior of L-PBF Ti-6Al-4V alloy including L-PBF processing parameters, various types of defects, post-processing, and fatigue properties. |
|
Wang et al., 2024 [25] | Review of different machine learning algorithms and their application in the fatigue life of AM parts |
|
2. The Internal Defects Problem of L-PBF Ti-6Al-4V
2.1. The Role of Internal Defects on the Fatigue Performance
No. | Author (s) | Defect Type | Main Research Objective |
---|---|---|---|
1 | Günther et al., 2017 [43] | Gas pore, LOF | HCF and VHCF |
2 | Becker et al., 2020 [44] | Porosity | Crack propagation |
3 | Waddell et al., 2020 [45] | Gas pore, LOF | Crack propagation |
4 | Hu et al., 2020 [42] | Gas pore, LOF | Correlate the defect population with the fatigue life |
5 | Du et al., 2021 [38] | Gas pore, LOF | Processing parameters’ influence on the S–N curve |
6 | Pessard et al., 2021 [46] | Artificial surface defect, gas pore, LOF | Fatigue strength and critical defect size, 30 um |
7 | Xu et al., 2021 [47] | Gas pore, LOF | Microstructure, vacuum situation, microstructure |
8 | Akgun et al., 2022 [40] | Gas pore | Crack initiation and propagation |
9 | Chi et al., 2022 [48] | Artificial surface defect, gas pore, LOF | S–N curve |
10 | Gao et al., 2022 and 2023 [18,49] | Keyhole, Gas pore, LOF | S–N curve, fatigue life |
11 | Bhandari and Gaur 2023 [50] | Gas pore, LOF | Correlation between post-processing and fatigue performance |
12 | Mancisidor et al., 2023 [51] | Gas pore | Post-processing |
13 | Moquin et al., 2023 [41] | Gas pore, LOF | Microstructure, correlation of volumetric energy densities with fatigue performance |
14 | Önder et al., 2023 [52] | Gas pore, LOF | Post-processing |
15 | Qu et al., 2023 [53] | Gas pore, LOF | Coupling effects of microstructure and internal defects |
16 | Meng et al., 2023 [54] | Porosity, surface defect | Multi-crack initiation and propagation, image-based monitoring |
No. | Author | Defect Type | Material | AM Process | Numerical Approaches | Fatigue Criterion |
---|---|---|---|---|---|---|
1 | Siddique et al., 2015 [59] | Gas pores | AlSi12 | L-PBF | FEA | SCF |
2 | Wan et al., 2016 [60] | Gas pores | Ti-6Al-4V | - | Multiscale, FEA | Stiffness, S–N curve |
3 | Biswal et al., 2018 [56] | Gas pores | Ti-6Al-4V | L-PBF | FEA | SCF, SWT |
4 | Lukhi et al., 2018 [61] | Micro void | Nodular cast iron | - | Micromechanical, FEA | Stress, strain |
5 | Biswal et al., 2019 [57] | Gas pores | Ti-6Al-4V | WAAM | Graphic analysis, FEA | SCF, S–N curve |
6 | Dinh et al., 2020 [62] | Gas porosity and surface roughness | Ti-6Al-4V | L-PBF | FEA | nlSWT |
7 | Hu et al., 2020 [39] | Gas pores, LOF | Ti-6Al-4V | L-PBF | FEA, EXP | NASGRO method |
8 | Wang and Su 2021 [63] | Gas pores | 316L steel | L-PBF | FEA | SCF |
9 | Lauterbach et al., 2021 [58] | Gas pores | Metal | - | Immersed-Boundary-FEA | Von Mises stress |
10 | Pessard et al., 2021 [46] | Surface defects, sub-surface defect | Ti-6Al-4V | L-PBF | FEA | SCF |
11 | Li et al., 2022 [64] | LOF | Ti-6Al-4V | L-PBF | FEA | SCF |
12 | Xie et al., 2021 [65] | Gas pores, LOF | Al-Mg4.5 Mn | WAAM | FEA | Von Mises stress, SCF |
13 | Shao et al., 2023 [66] | Crack from pore | Ti-6Al-4V | L-PBF | FEA | Crack propagation |
14 | Li et al., 2024 [55] | LOF | Ti-6Al-4V | L-PBF | Individual analysis | 3D average SWT, SIF, irregular crack propagation |
2.2. Crack Initiation and Micro-Short Crack (MSC) Propagation
2.3. Crack Propagation
3. Microstructure
3.1. Microstructure in Different States
3.1.1. As-Built Alloys
3.1.2. After Post Heat Treatments
3.1.3. After HIP
3.2. Microstructure’s Role in High-Cycle Fatigue Performance
4. Post Processing Treatments
4.1. Machining
4.2. Heat Treatment
4.3. HIP
5. Machine Learning Models of Predicting Fatigue Life
6. Conclusions and Perspective for Future Research
- Research on different types of internal defects was extremely uneven, partially due to the occurrence frequency, detriment level, and difficulty of analysis for each defect type. As a result, gas porosity has been extensively and quantitatively investigated, recently followed by LOF defects. However, studies on other internal defect types, such as keyholes, balling, and α-phase facets, were rare. There is an urgent need for detailed research on these types of defects.
- Quantitatively correlating LOFs with fatigue life performance is challenging due to their complex topology. Recent studies suggested that LOFs can be simplified based on their main profile and most critical embedded features, using an adapted SWT method to evaluate fatigue life. Comprehensive investigations are needed to further digitalize the geometric features of LOFs with a validated analytical approach. Additionally, the influence of un-melted powders embedded in LOFs needs to be investigated and clarified.
- The microstructure composition of L-PBF Ti-6Al-4V alloy, especially in the as-built state, is distinct from conventionally manufactured Ti-6Al-4V alloy. Additionally, L-PBF Ti-6Al-4V alloy have more microstructural imperfections, such as dislocations, which introduce uncertainties in quantifying the microstructure’s role in early-stage crack evolution. To address this, the microstructures of L-PBF Ti-6Al-4V alloy under various conditions need to be standardized. Subsequently, the quantification of the microstructure’s role in fatigue life performance should be progressively investigated, starting with simple cases and advancing to more complex scenarios. This could begin with the fine α + β structure after heat treatment, progress to the α′ in the β phase of the as-built condition, and eventually include the coupling effects with internal defects.
- The surrounding microstructures around internal defects significantly influence fatigue crack initiation and MSC propagation. However, relevant research on AM Ti-6Al-4V alloy was very limited. While similar investigations on other types of metal alloys can be referenced, their findings cannot be directly applied due to distinct microstructures and properties. The CPFE approach may be an ideal solution to clarify the role of microstructures in fatigue life performance and reveal the mechanisms and behaviors of MSC propagation.
- The distribution of residual stresses in L-PBF Ti-6Al-4V alloy, in both as-built and post-treated states (e.g., machining, heat treatments, and HIP), has been investigated and visualized in recent years. Understanding the mechanism by which fatigue life performance is altered is straightforward: residual stresses superpose the remote stresses. However, there is an urgent need to quantitatively correlate residual stresses in different states with fatigue crack evolution. Numerical analysis of residual stress formation during L-PBF processing and post-processing treatments, as well as its impact on fatigue crack evolution, can be both necessary and valuable.
- Post-processing techniques have a considerable impact on the fatigue life performance of L-PBF Ti-6Al-4V alloy. There have been in-depth investigations into various post-processing parameters (e.g., heat treatment at different temperatures, HIP) and studies combining different post-processing treatments (e.g., machining, heat treatment, and HIP), as suggested by previous review papers. Further research in this direction is needed to establish standardized post-processing treatments and combinations to achieve an optimal balance of mechanical properties for various application purposes.
- Data-driven ML models seriously rely on the quantity and quality of dataset, and their contribution to the physical mechanism might be limited. Physics-informed ML models are more promising as they improve the prediction accuracy while requiring less data. In addition, they provide a deeper understanding of the physical mechanism than the pure data-driven models. FEA is an efficient solution for enlarging the dataset, on the premise of being validated.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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No. | Method | Pros | Cons | References |
---|---|---|---|---|
1 | Natural internal defects | Conform to reality | Difficult to control the initiation site | [45,90] |
2 | Artificial defect by computer aid design (CAD) | Size, morphology, and location are controlled, regarded as an internal defect | (1) Defects are usually much larger than natural defects; (2) residual stress is not natural; (3) unfused powders inside | [91,92] |
3 | Manual notch | Crack initiation site is controlled | (1) Not desirable for crack propagation at early stages; (2) cracks do not initiate from internal defects | [45] |
4 | CT specimen | Standardized crack propagation approach | Only to study crack propagation | [44] |
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Li, Z.; Affolter, C. High-Cycle Fatigue Performance of Laser Powder Bed Fusion Ti-6Al-4V Alloy with Inherent Internal Defects: A Critical Literature Review. Metals 2024, 14, 972. https://doi.org/10.3390/met14090972
Li Z, Affolter C. High-Cycle Fatigue Performance of Laser Powder Bed Fusion Ti-6Al-4V Alloy with Inherent Internal Defects: A Critical Literature Review. Metals. 2024; 14(9):972. https://doi.org/10.3390/met14090972
Chicago/Turabian StyleLi, Zongchen, and Christian Affolter. 2024. "High-Cycle Fatigue Performance of Laser Powder Bed Fusion Ti-6Al-4V Alloy with Inherent Internal Defects: A Critical Literature Review" Metals 14, no. 9: 972. https://doi.org/10.3390/met14090972
APA StyleLi, Z., & Affolter, C. (2024). High-Cycle Fatigue Performance of Laser Powder Bed Fusion Ti-6Al-4V Alloy with Inherent Internal Defects: A Critical Literature Review. Metals, 14(9), 972. https://doi.org/10.3390/met14090972