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The influence of prior-β-grain (PBG) size on the tensile behavior of a laser-deposited α/β Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy was investigated to reveal the strengthening mechanism of PBGs. Results show that the strength increases with increasing PBG size. This special coarse-PBG strengthening predominantly depends on the strong constraints resulting from the strain incompatibility among PBGs rather than PBG boundary resistance to dislocation motion. With increasing PBG size, increasing constraints are developed in the adjacent PBGs, and thus the applied stress needed to maintain the compatible deformation among these PBGs increases. In particular, the strengthening effect is not significantly affected by increasing temperature, which reveals a potential strengthening method that can strengthen a laser-deposited α/β Ti alloy at room and elevated temperatures simultaneously by controlling its PBG size. [ABSTRACT FROM AUTHOR]

Abstract: The compositional variation and the microstructural evolution in laser additive manufactured Ti/Ti–6Al–2Zr–1Mo–1V graded structural material were investigated. An anomalous compositional variation and its good correlation with hardness were found. Although, during the forming process, the ratio of Ti–6Al–2Zr–1Mo–1V in feeded powders abruptly changes from 0% to 100%, all the elements exhibit a gradual variation, which is preferred to a graded material because such gradient change can decrease the discontinuity of its microstructures and properties and can remarkably reduce the costs due to the simplified manufacturing process and the rational distribution of materials. [Copyright &y& Elsevier]

The mechanical behavior of commercial purity Ti (CP-Ti)/Ti–6Al–2Zr–1Mo–1V structurally graded materials (SGMs) fabricated by laser additive manufacturing was investigated via uniaxial tensile experiments. Although the strength of all SGM specimens is higher than that of the monolithic CP-Ti specimens, only the SGM specimen of Ø10mm gauge diameter with bulky α-grains exhibits excellent plasticity comparable to the CP-Ti specimen under the same conditions. The SGM presents a potential for use as load-bearing components due to its good strength–ductility balance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Proposing a solid-state transformation control solution to additive manufacturing of fine-grain alloys. • Developing a high-scanning-speed laser deposition technique to prepare fine-grain fully lamellar TiAl. • The fine-grain fully lamellar TiAl overcome the conflict between room-temperature properties and creep resistance. • The fine-grain fully lamellar TiAl can be applied to a high temperature up to 900 °C. Additive manufacturing (AM), or 3D printing, has attracted increased attention in producing metallic parts with complex geometries, but it has proved difficult to prepare equiaxed fine-grain parts because the high thermal gradient in solidification commonly conduces the formation of coarse columnar grains. This work shows a solution to fine-grain titanium aluminide (TiAl) alloys by designing a high-frequency thermal cycling to control the solid-state phase transformations in layer-by-layer AM. After solidification, the specially-designed high-frequency thermal cycling can significantly refine the microstructure by repeatedly inducing the nucleation of new grains and suppressing the growth of these newborn fine grains. Therefore, even if solidification leads to coarse columnar grains, equiaxed fine-grain microstructure can still be obtained by solid-state phase transformations. The resulting TiAl alloys have fine heteromorphic grains (∼50 μm) and a fully lamellar microstructure. These fine grains contribute to good strength-ductility balance at room temperature, and their irregular shape and fully lamellar microstructure restrict the flow and distortion of grains at high temperatures, which stands a chance to significantly increase the operating temperature of TiAl parts. [ABSTRACT FROM AUTHOR]