Ti-xNb alloys produced by laser powder bed fusion (LPBF) from mixed powder usually exhibit an inhomogeneous elemental distribution, leading to a deterioration in mechanical properties. To address this issue, we proposed a strategy to achieve heterostructure in laser powder bed fused Ti-xNb alloys from mixed powders through precipitation of ω within β. Moreover, the effect of Nb content on the microstructure and mechanical behavior of Ti-xNb alloys was studied. The results indicated that in-situ laser re-melting can realize the homogeneous elemental distribution in Ti-xNb alloys. When the Nb content increases from 30 wt%, 35 wt% to 40 wt%, Ti-xNb alloys experience a transformation from β + α′ to β + ω and monolithic β. Specifically, ω nano-precipitates in Ti-35Nb alloy are only distributed in some β grains, forming a heterostructure with “soft β” and “hard β + ω” grains. As a result, LPBF-produced Ti-35Nb alloy demonstrates excellent mechanical properties, with yield strength of ~(792 ± 6) MPa, tensile strength of ~(806 ± 7) MPa, Young’s modulus of ~(68 ± 6) GPa, and uniform elongation of ~(18.0 ± 1.1)%. The Frank-Read mechanism induces dislocation proliferation and dislocation cross-slip, and the geometrically necessary dislocations (GNDs) are induced at the heterogeneous interface of “soft β” and “hard β + ω” grains, resulting in an enhancement in the strength-ductility synergy of Ti-35Nb alloy produced by LPBF. This work provides an innovative strategy to improve the strength-ductility synergy of LPBF-produced Ti-xNb alloys from mixed powders by tailoring ω nano-precipitates.

Four-dimensional (4D) printing technology is a revolutionary development that produces structures that can adapt in response to external stimuli. However, the responsiveness and printability of smart materials with shape memory properties, which are necessary for 4D printing, remain limited. Biomass materials derived from nature have offered an effective solution due to their various excellent and unique properties. Biomass materials have been abundant in resources and low in carbon content, contributing to the then-current global green energy-saving goals, including carbon peaking and carbon neutrality. This review focused on different sources of biomass materials used in 4D printing, including plant-based, animal-based, and microbial-based biomass materials. It systematically outlined the responsive deformation mechanisms of printed objects that contained biomass materials and delved into the roles and unique advantages of biomass materials in those printed objects. Leveraging these advantages, the review discussed the potential applications of biomass materials in biomedicine, food printing, and other fields to support ongoing development and application efforts. Additionally, it emphasized the crucial role played by bio-fabrication technologies utilizing biomass materials in the integration of biomass materials with 4D printing. Finally, this paper discussed the then-current challenges and potential future directions of biomass materials in 4D printing, aiming to promote the effective development of biomass materials in 4D printing applications.