TEM analysis of quasi in-situ formed tensile and fatigue cracks in a dual-phase Ti alloy

Designing dual-phase titanium (Ti) alloys with exceptional damage tolerance holds profound scientific and engineering significance. A comprehensive understanding of microstructure evolution around cracks under diverse loading conditions is pivotal in advancing this pursuit. Here, tensile and fatigue cracks were formed quasi in-situ in a dual-phase Ti alloy, and the microstructures around the cracks were systematically analyzed and compared using TEM. Our findings reveal that the deflection of tensile cracks is primarily influenced by the hindrance posed by the straight α/β heterointerfaces and is further facilitated by the β-to-α" martensite transformation within the β matrix. In contrast, fatigue cracks exhibit deflection within the β matrix, located far from the α lamellae. Furthermore, the presence of spindle-shaped short α lamellae holds promise for enhancing resistance to fatigue crack nucleation. These results contribute to fundamental comprehension of the crack nucleation and propagation in dual-phase Ti alloys and provide valuable guidance for materials design. © 2023 Acta Materialia Inc.