Fatigue Performance of Additively Manufactured Metallic Alloys

Additive manufacturing of metallic alloys has transformed component design by enabling complex geometries, graded compositions and lightweight lattice structures. However, the inherent thermal cycles and layer-by-layer deposition introduce characteristic features—such as porosity, anisotropic microstructures, residual stresses and surface roughness—that markedly influence fatigue performance. Fatigue life in these materials is governed by crack initiation at process-related defects and subsequent crack propagation under cyclic loading. Variability in defect size, shape and location leads to scatter in fatigue strength, complicating reliable life prediction. Strategies to mitigate fatigue degradation include optimisation of build parameters, heat treatments to refine microstructure, surface enhancement to induce compressive residual stress, and advanced modelling to correlate defect populations with endurance limits. These efforts target critical applications in aerospace, automotive and biomedical sectors, where safety and weight reduction are paramount. Establishing robust design protocols demands a nuanced understanding of multiaxial stress responses, probabilistic defect assessments and interplay between microstructural features and service-loading conditions.

Research from Nature Portfolio

Seminal investigations using X-ray computed tomography have demonstrated that porosity characteristics decisively determine fatigue crack initiation in electron beam-melted Ti-6Al-4V. It was shown that not only the size but also the proximity of pores to the surface and their aspect ratio govern the onset of crack growth, with initiating defects often among the smaller subset of pores when surface proximity is high. Complementary in situ fatigue testing with synchrotron tomography on cast components revealed that surface defects up to ten times smaller than internal pores dominate crack initiation, indicating that surface quality control can substantially enhance fatigue life even when internal defects remain.

Fatigue Performance of Additively Manufactured Metallic Alloys publication trend

The graph below shows the total number of articles in fatigue performance of additively manufactured metallic alloys across all publications each year (not limited to Nature Index journals).

Technical terms

Additive manufacturing: A layer-wise fabrication process enabling complex metallic components through selective melting or deposition of powder or wire feedstock.

Fatigue life: The number of load cycles a component endures before crack initiation or failure under cyclic stresses.

Porosity: Void defects introduced during printing, arising from incomplete fusion or gas entrapment, which act as stress concentrators.

Residual stress: Locked-in stresses within a component resulting from rapid thermal gradients during fabrication or post-processing.

Multiaxial fatigue: Fatigue behaviour under combined stress states (e.g. tension, torsion and bending) that more closely mimic service conditions.

Endurance limit: The stress amplitude below which a material can theoretically withstand an infinite number of cycles without failure.

References

1. Multiaxial fatigue of additively manufactured metallic components: A review of the failure mechanisms and fatigue life prediction methodologies. Progress in Materials Science (2023).
2. The Influence of Porosity on Fatigue Crack Initiation in Additively Manufactured Titanium Components. Scientific Reports (2017).
3. Location, location & size: defects close to surfaces dominate fatigue crack initiation. Scientific Reports (2017).
4. A Bayesian defect-based physics-guided neural network model for probabilistic fatigue endurance limit evaluation. Computer Methods in Applied Mechanics and Engineering (2024).
5. Fatigue behaviour of PBF additive manufactured TI6AL4V alloy after shot and laser peening. International Journal of Fatigue (2022).
6. Effect of Various Peening Methods on the Fatigue Properties of Titanium Alloy Ti6Al4V Manufactured by Direct Metal Laser Sintering and Electron Beam Melting. Materials (2020).