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 alpha/beta heterointerfaces and is further facilitated by the beta-to-alpha" martensite transformation within the beta matrix. In contrast, fatigue cracks exhibit deflection within the beta matrix, located far from the alpha lamellae. Furthermore, the presence of spindle-shaped short alpha 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.