Abstract
Enhancing both strength and ductility in commercially pure titanium (CP-Ti) still poses significant technical challenges. Here, a micro-laser powder bed fusion (micro-LPBF) followed by annealing strategy was developed to achieve an exceptional strength-ductility combination in CP-Ti. The resulting microstructure consists of fine rod-like α/α′ crystallographic units, a dense network of Burgers orientation relationship (BOR)-related α/α′ inter-variant boundaries, and abundant dislocations. These features arise from preferential formation and retention of α/α′ variant during the non-equilibrium β → α/α′ transformation under the highly localised and rapid heating–cooling cycling inherent to micro-LPBF. The CP-Ti achieves an excellent yield strength of 793 MPa together with a uniform elongation of 8.7%. The high strength originates primarily from the reduced effective dislocation mean free path provided by the fine α/α′ units, with grain-boundary (GB) strengthening contributing approximately 507 MPa. The exceptional ductility is enabled by heterogeneous deformation accommodation among α/α′ crystallographic units with different characteristic sizes, geometrically necessary dislocation (GND) accumulation, and progressive activation of dislocations, which provide additional c-axis strain accommodation and sustain strain hardening during plastic deformation. This work offers novel perspectives on the regulation of transformation crystallography and deformation mechanisms in additively manufactured CP-Ti for developing high-performance Ti materials.