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• A gradient TiAl specimen whose chemical composition varied greatly along the building direction was fabricated by high-power direct laser deposition. • The microstructure transforms from basket-weave microstructure into acicular martensite microstructure as the height increases, and the mechanical properties also vary greatly when the height changes. • By characterizing the deformation behaviors under the indentations, it is concluded that the phase constitution is responsible for the variation of the mechanical properties. Additive manufactured metals sometimes exhibit extraordinary microstructures and mechanical properties due to the particular processes. In this paper, we focus on a novel gradient TiAl alloys fabricated by high-power direct laser deposition, whose chemical composition, microstructure, and mechanical property vary along the building direction. The results indicate that Al concentration dramatically decreases from 39.5 at.% to 30.1 at.% as the height increases from the bottom to the top. Meanwhile, microstructural characterization indicates that the specimen appears basket-weave microstructure at the bottom, then the α 2 and γ phase gradually decrease, and eventually it transforms into acicular martensite microstructure in the top region. The indentation analysis shows that the associated hardness increases as the height increases, while the plasticity reaches a minimum value in the middle region. The increasing amount of β o (ω) is considered to be responsible for the increasing hardness because of the strong precipitation strengthening effect. The high plasticity in the bottom and top regions results from the strong deformation behaviors of the γ and β o phases. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract This work aims to establish the effect of laser energy area density (EAD) as the laser incident energy on density, microstructures and mechanical properties of direct laser deposition (DLD) 12CrNi2Y alloy steel. The results show that the density of DLD 12CrNi2Y alloy steel increases at initial stage and then decreases with an increase of EAD, the highest density of alloy steel sample is 98.95%. The microstructures of DLD 12CrNi2Y alloy steel samples are composed of bainite, ferrite and carbide. With increase of EAD, the microstructures transform from polygonal ferrite (PF) to granular bainite (GB). The martensite-austenite constituent (M-A) in GB transforms from flake-like paralleling to the bainite ferrite laths to granular morphology. It is also found that the average width of laths in finer GB can be refined from 532 nm to 302 nm, which improves the comprehensive properties of DLD 12CrNi2Y alloy steel such as high hardness of 342 ± 9 HV 0.2 , yield strength of 702 ± 16 MPa, tensile strength of 901 ± 14 MPa and large elongation of 15.2%±0.6%. The DLD 12CrNi2Y material with good strength and toughness could meet the demand of alloy steel components manufacturing. [ABSTRACT FROM AUTHOR]