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The change of layer thickness can effectively influence the solidification condition and thermal history of the Al-5Si-1Cu-Mg aluminum alloy fabricated by laser additive manufacturing, and thus affect the microstructures and mechanical properties. Samples with ultrafine grain structures and excellent mechanical properties were successfully fabricated, and the microstructure and mechanical property differences related to the variations of layer thickness were systematically investigated. Results indicate that when higher layer thickness is employed, columnar grain structure is established with {100} Al texture due to high temperature gradient, while decreasing the layer thickness promotes the formation of equiaxed grains. Lower layer thickness sample with finer near-equiaxed grain structure has improved elongations. However, the strength is unexpectedly poorer than the higher layer thickness sample with near-columnar grain structure. The comparably better plasticity but poorer strength is attributed to the relatively coarser microstructure within grains, i.e. larger primary dendrite arm spacing with Si phases distributing more dispersed, introduced by more heat effect of subsequent deposition when applying lower layer thickness. For near-columnar sample, the cracked Si phases with different spacings perpendicular to loading direction would result in different microcrack coalescence behaviors and thus cause plasticity anisotropy. Whereas for near-equiaxed sample, due to the tailored distribution of Si phases, the direction-dependent elongation discrepancy is reduced. • High-property Al-5Si-1Cu-Mg samples were produced by laser additive manufacture. • The microstructure and tensile property related to layer thickness are examined. • Near-columnar and near-equiaxed grain structures are formed for different samples. • Near-equiaxed sample exhibits better plasticity but slightly lower strengths. • Plasticity anisotropy is lessen in near-equiaxed one and the mechanism is studied. [ABSTRACT FROM AUTHOR]

Abstract Under high strain rate loadings, many engineering materials exhibit quite different deformation behavior from those under quasi-static loadings, and adiabatic shear band (ASB) is normally generated with degradation of material property. In this study, the deformation response of LAMed Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy (TC11) under high strain rates (2800s−1 and 2900s−1) is investigated for both as-deposited state and heat-treated state (annealed at 1263 K for 1 h followed by annealed at 803 K for 6 h) by using the split Hopkinson pressure bar (SHPB). Results indicate that the as-deposited alloy has a unique mixed grain morphology (coarse columnar grains and fine equiaxed grains) with ultrafine basket-weave microstructure. Under high strain rate loadings, the as-deposited alloy possesses excellent yield strength but with poor plasticity and high adiabatic shear susceptibility. After heat treatment, the yield strength of alloy is sacrificed due to the reduced contents of ultrafine α lamellas, but the partially globularization of continuous grain boundary α phases greatly improves the plasticity of alloy that the adiabatic shear susceptibility is efficiently suppressed. Highlights • TC11 titanium alloy plate was fabricated by laser additive manufacture technology. • High strain rate response of the prepared alloy was investigated. • Dynamic mechanical properties corresponding to different microstructures are given. • Heat treatment efficiently suppress the adiabatic shear susceptibility of alloy. [ABSTRACT FROM AUTHOR]

The near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) was treated by laser surface remelting (LSR) with a series of holding times at 500 °C in order to study the growth behavior of ω-assisted α phase and its effect on mechanical properties. Transmission electron microscope and hardness test was used to characterize different phases and surface property of different samples. Results show that only a small quantity of athermal ω phases precipitate from β matrix at the remelted zone and there are incomplete collapsed {111} β lattice planes at the β/ω boundaries because Ti-55511 has low electron/atom ratio and high Al contents. So the athermal ω phase precipitated during LSR process has little effect on increasing surface hardness of Ti-55511. ω-Assisted nano-scaled α lamellas can be formed by the connection of some initial α phases at the early stage of low temperature isothermal heat treatment. And all the ω phase dissolved after 500°C/10min. Further increasing of holding times will cause volume fractions increase of the nano-scaled α lamellas, resulting in gradually improving hardness of the alloy at the remelted zone. [ABSTRACT FROM AUTHOR]

Experimental process optimization is essential to obtain reliable processing conditions prior to performing actual laser additive manufacturing (LAM) of single-crystal (SX) nickel-base superalloys. The influence of processing parameters on deposited productivity and epitaxial SX growth in powder-feeding LAM process was systematically investigated by the orthogonal experiment (OE) method, a statistical experiment design method. This method can rapidly and economically estimate the effect of each processing parameter by a small number of experiments. Resulting relationship between the processing variables and each of deposited productivity and microstructure formation contributes to the selection of detailed processing conditions to balance the factors crucial to successful SX LAM, which means that appropriate adjustment of the processing parameters during actual SX LAM is easy to be performed. On the basis of the analyses of the OE results, a combination of relatively high power, low scanning velocity and moderate powder feeding rate is beneficial to both deposited productivity and epitaxial SX growth during powder-feeding LAM, and allows the preparation of good multilayer SX deposits with fine dendrites. [ABSTRACT FROM AUTHOR]

Primary dendritic arm spacing (PDAS) is an important microstructure feature in the nickel-base single-crystal (SX) superalloys by laser rapid directional solidification (LRDS). A combined numerical model was developed in this paper to investigate the influence of laser processing parameters on the PDAS. This model consists of (1) the theoretical PDAS models which relate PDAS to the solidification conditions and (2) the heat-flux calculations of laser processing which provide the solidification conditions as a function of the processing parameters. It is therefore able to immediately relate the PDAS to the processing parameters and obtain corresponding processing–microstructure maps. To verify the predicted accuracy, the PDAS values calculated by different theoretical models were compared with those produced under different processing conditions. Results show that the PDAS firstly decreases and then increases at a lower laser power whereas it decreases with increasing scanning velocity at a higher laser power, leading to nose-shape contour lines. The predicted accuracy depends on appropriate selections of material thermo-physical properties. These processing–microstructure maps can accurately capture the trends of the PDAS variation with the processing parameters and contribute to the control and optimization of dendritic microstructure while determining relevant processing windows for controlled SX laser processing. [ABSTRACT FROM AUTHOR]