Multi-scale fatigue failure analysis and deformation-cracking-strengthening mechanisms of LPBF TiC/Ti6Al4V composites at service temperature

Additive manufacturing of nanoparticle-reinforced metal matrix composites has emerged as a key load-bearing structural material for hot-section components in aerospace engines. However, the mechanisms involving high-temperature performance, reinforcement content, microstructural evolution, and fatigue behavior remain insufficiently understood. In this study, low content TiC/Ti6Al4V composite fabricated by laser powder bed fusion (LPBF) is investigated to clarify the mechanical response and multi-scale failure mechanisms at a service temperature of 450 °C. Experimental characterization, including SEM, EBSD, high-cycle fatigue testing, and TEM, reveals that under monotonic tension, the fracture surface is mainly ductile fracture, alongside localized brittle fracture from interface debonding, while fatigue cracks primarily initiate from internal defects, with stress-dependent fracture modes. Quantitative analysis demonstrates that the composite is strengthened by multiple mechanisms, with dislocation strengthening being dominant (63.5 %). Complementary molecular dynamics (MD) simulations validate these deformation mechanisms at the atomic scale and extend the analysis beyond the single experimentally tested composition. Predictions from an idealized MD model, which was mechanistically validated against a single experimental composition, suggest that a moderate TiC content (C1-C5 range) may offer a promising route to achieving an optimal balance of strength and toughness. However, this theoretical prediction urgently requires systematic experimental validation. These findings provide engineering guidelines for process optimization to mitigate premature failure and enhance service reliability in aerospace and energy applications.