Differentiated mechanical properties between additively manufactured and as-cast TC4 titanium alloy subject to deep cryogenic treatment regulation

To address the challenge of synergizing strength and ductility in laser-additively manufactured TC4 titanium alloy (Ti-6Al-4V), which forms non-equilibrium high-energy metastable structures due to rapid solidification, this study focuses on the modification effects of deep cryogenic treatment (DCT) on additive-manufactured TC4 (AM-TC4) and systematically compares it with conventional cast specimens (CF-TC4). The key findings demonstrate that DCT synergistically enhances both strength and ductility in AM-TC4: tensile strength, yield strength, and elongation increase by 3.5%, 5.0%, and 33.9%, respectively. In contrast, while cast TC4 exhibits more pronounced plasticity improvement (elongation +58.7%), its strengthening effect is limited and mechanistically distinct, primarily relying on severe grain refinement induced by DCT. Mechanistic analysis reveals that for the high dislocation density and high internal stress microstructure characteristic of additive manufacturing, DCT triggers a “defect restructuring” effect. This promotes β→α′ phase transformation, induces nano-precipitation (precipitation strengthening), and drives dislocation rearrangement. Consequently, an optimized grain boundary structure of “intragranular low-angle grain boundary (LAGB) dispersion + stabilized high-angle grain boundary (HAGB) network” is formed, constituting the fundamental mechanism for achieving its strength-toughness synergy. This study provides a theoretical basis for utilizing deep cryogenic treatment to enhance the comprehensive properties of additive-manufactured titanium alloy components, highlighting its distinct mechanism compared to conventional cast materials. • Experiments on deep cryogenic treatment (DCT) of both additive-manufactured and as-cast TC4 titanium alloy were conducted. • It reveals the distinct microstructural evolution and "defect restructuring" mechanism in additive-manufactured TC4 induced by DCT. • The strength and ductility of additive-manufactured TC4 are synergistically improved after DCT treatment. • It clarifies the differential strengthening mechanisms between additive-manufactured and cast TC4 subjected to DCT.