Fatigue Crack Growth Phenomena in Additively Manufactured Ti-6Al-4V

Ti-6Al-4V(Ti64), widely used in aerospace structures for its high specific strength and corrosion resistance, is increasingly produced by additive manufacturing (AM) to enhance material efficiency and design flexibility. However, its fatigue performance remains highly variable due to process-induced microstructural heterogeneities and inherent defects. Since aerospace components are designed under damage-tolerant principles, understanding fatigue crack growth (FCG) behavior in AM Ti64 is essential for reliable life prediction. This short review critically examines FCG in Ti64, focusing on the influence of build orientation, processing routes, heat treatment, mean stress, defects, and environmental conditions. These factors, through their effect on the microstructure, govern crack propagation. Achieving consistent and predictable FCG behavior requires standardized test reporting, high-resolution microstructural and defect characterization, and data-driven approaches, that link processing, microstructure, and mechanical response. To complement this mechanistic perspective, a meta-analysis of 67 studies was conducted to assess how FCG research in AM Ti64 is reported. The results showed that only 66 percent of studies included details on manufacturing processes and specimen preparation, and just 68 percent documented feedstock characteristics and material properties, whereas 99 percent reported testing conditions. These gaps highlight the need for more consistent and harmonized reporting. To address this, a reporting benchmark grounded in established testing standards and domain expertise is proposed. Such standardization will enhance reproducibility, enable meaningful data comparisons, and advance data-driven FCG research in AM.