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Three different proportions of TA15 and Ti2AlNb alloy powde were premixed and thin-walls with proportions of 40%TA15+60%Ti2AlNb, 50%TA15 +50% Ti2AlNb and 60%TA15+40%Ti2AlNb (mass fraction) were prepared by using laser melting deposition process. The composition, microstructure and mechanical properties of the three thin-walls were analyzed. The results indicate that the compositions of all the three kinds of alloys are uniform. The alloy appears as basketweave microstructure with acicular α phase and α2 phase distributing within primary β/B2 grain. Tensile strength of the three kinds of alloys are 1108 MPa and 1071 MPa, 1105 MPa, and elongation are 3.0%, 2.2% and 3.8% respectively; Tear ridge along α2 phases is visible on tensile fracture surface, and the fracture mode is subject to cleavage fracture.

In this paper, micron-sized TiB2/AlZnMgCu(Sc,Zr) composites were fabricated by selective laser melting (SLM) using directly mixed powder. Nearly fully dense (over 99.5%) and crack-free SLM-fabricated TiB2/AlZnMgCu(Sc,Zr) composite samples were obtained and its microstructure and mechanical properties were investigated. It is found that the laser absorption rate of powder is improved by introducing micron-sizedTiB2 particles, then the energy density required for SLM forming can be reduced, and the densification can finally be improved. Some crystalline TiB2 formed a coherent relationship with the matrix, while some broken TiB2 particles did not, however, MgZn2 and Al3(Sc,Zr) can perform as intermediate phases to connect these non-coherent surfaces to aluminum matrix. All these factors lead to an increase in strength of the composite. The SLM-fabricated micron-sized TiB2/AlZnMgCu(Sc,Zr) composite finally shows a very high ultimate tensile strength of ~646 MPa and yield strength of ~623 MPa, which are higher than many other aluminum composites fabricated by SLM, while maintaining a relatively good ductility of ~4.5%. The fracture of TiB2/AlZnMgCu(Sc,Zr) composite is occurred along the TiB2 particles and the bottom of the molten pool. This is due to the concentration of stress from the sharp tip of TiB2 particles and the coarse precipitated phase at the bottom of the molten pool. The results show that TiB2 plays a positive role in AlZnMgCu alloys fabricated by SLM, but finer TiB2 particles should be studied. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) offers obvious advantages in the production of complex parts. However, the traditional 7xxx series aluminum alloy has a serious cracking tendency in the SLM process. Therefore, in order to analyze the microstructure and cracking mechanism, and obtain crack-free aluminum alloy fabricated by SLM, this paper studied the microstructure characteristics of as-deposited Al-6.2Zn-2Mg-xSc-xZr alloy with different Sc, Zr content, as well as the influence mechanism of Sc, Zr on cracking. The results show that with the increase of Sc and Zr content, the crack tendency and grain size decrease. When Sc and Zr content reach 0.6% and 0.36% respectively, cracks can no longer be observed in the as deposited alloy. The microstructure of the as deposited Al-6.2Zn-2Mg-0.6Sc-0.36Zr alloy consists of fine equiaxed and columnar crystals, in which Sc and Zr mainly exist in the aluminum matrix as solid solutions, and some exist in the form of Al3(Sc, Zr). The immediate reason for the absence of cracks is that the microstructure changes from coarse columnar grains to fine equiaxed-columnar grains when the content of Sc and Zr increases. The refined grain size may have the following beneficial effects: It helps with reducing the thickness of the liquid films. This will increase the tear sensitivity of the liquid film and the cracking tendency and therefore lowers the hot cracking tendency; And a refined grain size improves fracture roughness, leading to an enhanced cracking resistance. At the same time, the refinement of the grains will make the feeding channel of the grain boundary shorter and easy to feed, and the fine equiaxed grains can coordinate stress-strain during solidification more effectively than coarse columnar grains, which will decrease the cracking tendency. [ABSTRACT FROM AUTHOR]

In this paper, the cracking of Al-Mn-Mg-Sc-Zr alloys prepared by selective laser melting (SLM) was comprehensively explored and the influence of process parameters on the generation and propagation of cracks was deeply studied. It was found that the higher laser power and volume energy density will lead to a decrease in the relative density of the material. The lower laser power or volume energy density will lead to cracking of the alloy. The microstructure analysis indicated that plenty of manganese-rich second phases precipitated at the bottom of the melt pool, which increased the tendency of cracking occurred at the bottom of the melt pool. Through the optimization of the process parameters, the SLM forming process parameters of the Al-5.22Mn-1.16Mg-0.81Sc-0.46Zr alloy are successfully obtained, and the crack-free tensile samples are prepared. The microstructure and mechanical properties of the as-deposited aluminum-manganese alloy is analyzed. The bottom and inside of the melt pool are equiaxed grains. The size of the equiaxial grains at the bottom of the melt pool is less than 2 μm, and the coarse equiaxial grains inside the melt pool are approximately 5 μm. As-deposited alloy has a room temperature tensile strength of 455.2 ± 0.7 MPa and elongation of 15.4 ± 0.3%. This study provides guidance for selective laser melting forming of high-strength aluminum-manganese alloy parts, and promotes the industrial production of high-strength aluminum alloy near net forming complex parts. [ABSTRACT FROM AUTHOR]

In order to obtain high-performance aluminum alloy parts fabricated by selective laser melting, this paper investigates the relationship between the process parameters and microstructure properties of AlSi10Mg. The appropriate process parameters are obtained: the layer thickness is 0.03 mm, the laser power is 370 W, the scanning speed is 1454 mm/s, and the hatch spacing is 0.16 mm. With these process parameters, the ultimate tensile strength of the as-printed status is 500.7 ± 0.8 MPa, the yield strength is 311.5 ± 5.9 MPa, the elongation is 7.7 ± 0.5%, and the relative density is 99.94%. After annealing treatment at 275 °C for 2 h, the ultimate tensile strength is 310.8 ± 1.3 MPa, the yield strength is 198.0 ± 2.0 MPa, and the elongation is 13.7 ± 0.6%. The mechanical properties are mainly due to the high relative density, supersaturate solid solution, and fine dispersed Si. The supersaturate solid solution and nano-sized Si formed by the high cooling rate of SLM. After annealing treatment, the Si have been granulated and grown significantly. The ultimate tensile strength and yield strength are reduced, and the elongation is significantly improved. [ABSTRACT FROM AUTHOR]

Microstructural evolution, tensile and creep behavior of Ti-22Al-25Nb (at.%) orthorhombic alloy with three typical microstructures were investigated. The three typical microstructures were obtained by different solution and age treatment temperatures and analyzed by the BSE technique. The tensile strengths of the alloy at room temperature and 650 °C were investigated. The creep behaviors of the three typical microstructures were also studied at 650 °C/150 MPa for 100 h in air. The phase transformation mechanisms in creep deformation were also found. The experimental results showed that the formations of the three typical microstructures were decided by the isothermal forging and heat treatment. It was supposed that the high-temperature solution treatment might be dominant for the volume fraction and diameter of the equiaxed particles. While the double age treatment would lead to lamellar O phases. Due to grain refinement strengthening, the equiaxed microstructure presented the best tensile strength and ductility. The fully lamellar microstructure had the best creep resistance than that of other microstructures. In this paper, the phenomenon of creep-induced α phase decomposition was occurred during creep deformation of the equiaxed microstructure. [ABSTRACT FROM AUTHOR]

The Cu–9Al–4Ni-3.5Fe-0.5Mn Nickel-aluminum bronze (NAB) thin wall sample was prepared by laser melting deposition (LMD). The solidification characteristics, microstructure and mechanical properties were investigated. The LMD-NAB alloy consists of α, β′ and κ(κ II , κ III , κ IV) phase. The α phase shows directional growth trend along the deposition direction. Lamellar κ III phase distributed in α, and spherical shell κ III phase distributed on the surface of κ IV phase were found. Spherical and parallelogram κ IV phase was distributed in α phase. A core structure based on FeAl 3 phase was located in the spherical and parallelogram κ IV phase. The LMD-NAB alloy presents tensile properties with average ultimate tensile strength (UTS) of 645 ± 5.7 MPa and elongation of 21.2 ± 1.5% along the scanning direction, and tensile properties with average UTS of 637 ± 9.9 MPa and elongation of 26.0 ± 0% along the deposition direction. The fracture surfaces exhibit a mixture of brittle cleavage model and microvoid coalescence. This work shows great potential for fabricating NBA alloy by LMD technology. [ABSTRACT FROM AUTHOR]

The TA15-Ti 2 AlNb bimetallic samples with no defects were prepared by laser additive manufacturing. The evolution of the composition and microstructure in transition zone, and the mechanical properties were investigated. Composition in the transition region shows a step-and-platform distribution due to the rapid solidification and diffusion during the depositing process. The phase transformation from TA15 alloy side to Ti 2 AlNb-based alloy side is α (lath) +β→α (coarse acicular) +β→β+α 2 →α 2 +O + B2. The TA15-Ti 2 AlNb bimetallic structures present tensile properties with average tensile strength of 1025 MPa and elongation of 7.3%. The fracture position of samples is located in diffusion zone, and the fracture mode is quasi-cleavage fracture. The TA15-Ti 2 AlNb bimetallic circular structure with bell mouth was fabricated and this work shows great potential for fabricating bimetallic structures by laser additive manufacturing technology. • The composition transition zone of TA15/Ti 2 AlNb structures prepared by LAM show a step-and-platform distribution. • Phase transformation from TA15 alloy side to Ti 2 AlNb-based alloy side is α (lath) +β→α (coarse acicular) +β→β+α 2 →α 2 +O+B2. • The TA15/Ti 2 AlNb structures present tensile properties with average tensile strength of 1025 MPa and elongation of 7.3%. • A TA15-Ti 2 AlNb bimetallic circular structure with bell mouth was designed and fabricated. [ABSTRACT FROM AUTHOR]

• Eutectic high-entropy alloy is prepared by LMD method, and its formability problem is solved. • Significant improvement of both the strength and plasticity of the deposited alloy. • Comparison of deformation behavior of as-cast and as-deposited alloys. • The characteristic herringbone structure of the as-deposited alloy. In this study, laser melting deposition (LMD) was used to form AlCoCrFeNi 2.1 eutectic high-entropy alloys (EHEAs) to solve the formability problems. EHEAs were prepared with laser power of 600 W, scanning rate of 4 mm/s, powder feeding rate of 8 g/min. The microstructure and mechanical properties of the as-deposited alloy and the as-cast alloy were evaluated. The eutectic structure containing L1 2 and B2 phases is retained and grows along the deposition direction to form a characteristic herringbone structure. This characteristic structure makes the mechanical properties of the as-deposited alloy (σ b = 1097 ± 9 MPa, δ = 22 ± 2% in vertical; σ b = 996 ± 6 MPa, δ = 14 ± 2% in horizontal) are significantly improved compared to the as-cast alloy (σ b = 980 ± 6 MPa, δ = 14 ± 2%). [ABSTRACT FROM AUTHOR]