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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 thin-walled Al-5Si-1Cu-Mg aluminum alloy plate was fabricated by laser melting deposition additive manufacture technique followed by heat treatments. The microstructure and mechanical properties of the alloy are investigated considering the effects of solution/solution and artificial aging. Results show that due to the high cooling rate, a fine microstructure is formed with distinct grain structures and eutectic Si network embedded in the Al matrix, which gives rise to significantly better tensile properties (yield strength: 99 MPa, ultimate tensile strength: 223 MPa, elongation: 12.1%) as compared to as-cast Al-5Si-1Cu-Mg counterpart. After solution treatment, a superior ductility of approximately 22.4% can be achieved due to the increased mean distance and globularization of Si phases, and the appearance of nano-metric β〞and C phases during subsequent aging treatment gives a remarkable comprehensive mechanical behavior: The specimens show yield strength of 316 MPa, ultimate tensile strength of 416 MPa along with fracture strain of 15.2%. The combined effect of laser melting deposition and post-process heat treatments can yield parts with excellent mechanical properties, promoting the material for a wider range of applications. [ABSTRACT FROM AUTHOR]

Ultrahigh-strength AerMet100 steel plate was fabricated by laser additive manufacturing process (LAM) followed by subsequent heat treatments. Microstructures and tensile mechanical properties of the steel were examined using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and universal mechanical testing machine. The results indicate that post-LAM heat treatments greatly change alloy carbide characteristics, decrease austenite content and prompt the formation of fine equiaxed prior-austenite grains for LAM AerMet100 steel. Compared to fine short rod-like Nb-rich MC carbides and needle-like M 3 C carbides in as-deposited specimens, alloy carbides in tempered specimens have the large changes, which include fine spherical Nb-rich MC carbides, fine rod-like M 2 C carbides, large-size spherical Mo-rich M 6 C carbides and Cr-rich M 23 C 6 carbides. And the fine rod-like M 2 C carbides are dispersive distribution and coherency with the martix martensite, resulting in strong coherent strain strengthening. After proper post homogeneity heat treatment processes, tensile mechanical properties of LAM AerMet100 steel have the comprehensive improvement, which are comparable to those of the forged ones. In comparison with low ductility of as-deposited specimen, the higher ductility of tempered specimen is mainly related to its extremely strong strain-strengthening capability achieved by dispersive precipitation of M 2 C carbides. With the increase of homogenization, the further improved ductility of tempered specimen mainly ascribe to the decreased amount and size of large-size alloy carbides (especially Mo-rich M 6 C carbide). [ABSTRACT FROM AUTHOR]

Highly-dense Al-5Si-1Cu-Mg alloy bulk was firstly produced by laser additive manufacture (LAM) technique. LAM involves extraordinary thermal cycles and will therefore significantly affect the microstructure. In this research, the phase evolution of LAMed Al-5Si-1Cu-Mg alloy was studied in detail by characterization along the deposition direction. The rapid solidification of LAM encourages the generation of various unstable phases of vermicular Si, fishbone shaped θ-Al 2 Cu, blocky π-Al 8 Mg 3 FeSi 6 and irregular Q-Al 5 Mg 8 Cu 2 Si 6 . As the increasing times of thermal cycling, phase evolution takes place by spheroidization of Si phases, transformation of π-Fe to plate-like β-Al 5 FeSi with dissolution of θ and Q phases. In particular, after certain times of thermal excursions, many micron-sized and nano-sized Q′ phases precipitate out from matrix, and the stabilized microstructure consists of α-Al, Q′, Si and β. [ABSTRACT FROM AUTHOR]

Gas tungsten arc welding was used to repair the laser additive manufactured Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy with a subsequent triplex annealing treatment. The tensile properties of heat treated specimens containing of different proportions of weld zone were designed to evaluate the influence of weld zone on tensile properties of the alloy. Microstructures, microhardness and tensile tests were performed to study the mechanical properties and fracture behaviors of the specimens. Results show that dissolved oxygen in the weld zone has a strong influence on increasing the number of α phase nucleation sites that can lead to different α p morphologies in the base metal and weld zone. These different α p can lead to distinct microstructures after triplex annealing treatment but with similar α volume fractions. Besides, plasticity deterioration of the repaired tensile specimens is mainly attributed to the formation of columnar grain boundary α phases in the weld zone which are considered to be the earliest nucleation sites of microcracks and confirmed by in situ tensile test. With the increase of WZ proportions in the cross section of tensile specimens, the plasticity of the alloy gradually decreases. [ABSTRACT FROM AUTHOR]