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Laser powder bed fusion additive manufacturing (L-PBF AM) technology holds notable advantages regarding raw material reusability. Nonetheless, a notable gap exists in extensive research assessing how the reuse of powders influences their intrinsic physicochemical traits as well as the mechanical attributes of the fabricated components. This study focuses on introducing an innovative approach to Ti6Al4V powder recycling in L-PBF AM, involving the incorporation of virgin spherical powder to maintain powder characteristics prior to printing. This results in sustained mechanical properties throughout seven cycles of printing (P7), with the fifth print (P5) showcasing the optimal mechanical performance (strength of 1185 MPa and elongation of 6.3%). Transmission electron microscopy (TEM) analysis was performed before and after the P5 tensile experiments，revealing a high amount of primary twinning {10 1 ¯ 1 } in LPBF. This study offers both theoretical insights and practical validation, thereby lending substantial support to the advancement of metal AM industrialization. [Display omitted] • Addition of new powder effectively controls the performance of reused powder. • Reused powder's low oxygen content contributes to excellent mechanical performance. • The presence of massive primary twins {10 1 ¯ 1 } in LPBF samples due to rapid cooling. • Numerous primary twins {10 1 ¯ 1 } enhance the plasticity of the LPBF samples. [ABSTRACT FROM AUTHOR]

Powder bed fusion (PBF) is a well-established method in the additive manufacturing (AM) industry. Despite its popularity, effectively managing the microstructure and mechanical properties of PBF-produced components remains a significant engineering challenge. This study aims to address this challenge by investigating the thermal accumulation effect of PBF substrate preheating on sample microstructure. The study demonstrates the graded microstructure resulting from "in-situ aging" at 630 °C at different deposition heights. The results reveal how heat accumulation and cooling rate contribute to the varying α p lamellae content and α phase selection across different regions. Notably, the bottom region, with an α p lamellae content of 53.5% and a βr content of 46.5%, exhibits the highest of fracture toughness value of 87.5 MPa.m1/2. The mechanical properties exhibit a clear grade distribution with increasing deposition height. In-situ manipulation of microstructure and mechanical properties provides theoretical and engineering guidance for future AM strategies. [ABSTRACT FROM AUTHOR]

The metal additive manufacturing (AM) technology offers a unique advantage for production of complex and unconventional parts. However, the thermal history during the AM process often leads to anisotropy in the mechanical properties and inherent porosity of the deposits, which limits their performance compared to traditional forgings. To overcome these limitations, laser powder bed fusion (LPBF) technology was employed to produce single-step die-forging preforms. This innovative approach used coarse powder with a wide distribution of particle sizes to create a variety of molten pool structures, preventing the growth of columnar β grains in AM Ti–5Al–5V–5Mo–3Cr–1Zr (Ti-55531) alloys. The subsequent die-forging process eliminated inherent defects and regulated grains to be near-equiaxed, significantly improving the mechanical properties and reducing anisotropy. With proper post-heat treatment, the strength-ductility trade-off of the Ti-55531 alloy was adjusted to meet standards. This unconventional process route produced parts with isotropic and excellent mechanical properties, overcoming the defects and anisotropic properties of AM parts. This supplement to the traditional manufacturing process of high-performance titanium alloy parts holds great promise for future applications. [ABSTRACT FROM AUTHOR]

Recently, additive manufacturing (AM) of titanium alloys has become favored by manufacturing industries. However, the obvious anisotropy of microstructure during the process of AM will be caused by the complex solidification mechanism, which will cause uncertainties in determining corrosion behavior. Two heat treatment techniques are developed to tune the microstructure of selective laser melted Ti-5Al-5Mo-5V-3Cr-1Zr (Ti-55531) alloy, i.e. , αβ phase region (αβ-STA) and supertransus triplex heat treatment (Triplex-HT). Bimodal and bi-lamellar microstructure are obtained after certain heat treatments and the corresponding corrosion resistance is systematically investigated. The columnar β grains in the vertical planes (VP) are eliminated by conducting Triplex-HT, and the corresponding corrosion anisotropy between the horizontal planes (HP) and VP is significantly reduced. While the Ti-55531 treated by αβ-STA possesses significant refinement of primary α precipitates (α p) within β grains. The size of α grains relates to the Al-rich active region, where the corrosion pits are mainly concentrated. Further immersion experiments indicate that the generation and development of pits on the passive film are determined by the occupation of oxygen vacancies by chlorine ions. The results are expected to provide a reference for the selective laser melting (SLM) Ti-55531 alloy to eliminate anisotropy and improve corrosion resistance by the adjustment of the micromorphology. • The anisotropy of the corrosion behavior of Ti-55531 is caused by columnar β. • The isotropy of Ti-55531 alloy is achieved by supertransus triplex heat treatment. • The formation of oxygen vacancies is influenced by elemental segregation. • Oxygen vacancy plays a decisive role in pitting resistance of passive film. [ABSTRACT FROM AUTHOR]

The layer-wise additive manufacturing process offers a unique approach to achieve a novel graded microstructure which can fulfill the conflicting requirement of contradictory properties. The present study investigated microstructure evolution and mechanical properties of a near β alloy Ti–5Al–5Mo–5V–3Cr–1Zr fabricated by additive manufacturing using electron beam melting. In combination, the high preheating temperature in electron beam melting, the low β transus (850 °C) in Ti–5Al–5Mo–5V–3Cr–1Zr, and the increasingly accumulated heat with build height resulted in an in-situ formed graded hierarchical microstructure from an α+β lamellar microstructure at the specimen bottom to an α p +α s bi-lamellar microstructure at the specimen top. Such a gradually changing microstructure was obtained by the same electron beam melting parameter set, and its formation was related to the controlled secondary α precipitation through manipulating the stability of metastable β-phase at different specimen heights. The resultant hardening effect in the bi-lamellar microstructure was attributed to the precipitation of fine secondary α. [ABSTRACT FROM AUTHOR]