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GH3536 and GH4169 nickel-based superalloys are widely used in aerospace engines and other hot-end components. In this paper，GH3536 and GH4169 alloy samples were fabricated by optimizing the process parameters using selective laser melting（SLM），the defect characteristics and microstructure of two alloys，as well as the effects of different homogenization temperatures and holding times on microstructure evolution，average grain size，and properties of two alloys were studied. The defect characteristics and microstructure were investigated by OM，SEM，and EDS, et al. The Vickers hardness meter was used to test the alloy’s microhardness. The results indicate that the as-built GH3536 alloy exhibits more defects，including pores，cracks，and lack of fusion， while only pores are present in as-built GH4169 alloy. The melt pool of alloy is eliminated by homogenization treatment，and the grains grow into equiaxed grains. M23C6 are found to distribute within grain boundaries and grain interiors of GH3536 alloy，while NbC are found to distribute within grain boundaries and grain interiors of GH4169 alloy，and the amount of precipitates is significantly reduced with the increase of homogenization temperature. The average grain size of GH3536 alloy is increased by 106.8% from 48.5 μm at 1130 ℃/1 h to 100.9 μm at 1250 ℃/4 h . The grain size of GH4169 alloy is increased by 53.3% from 57 μm at 1080 ℃/1 h to 87.4 μm at 1200 ℃/4 h.The homogenization treatment of GH3536 alloy and GH4169 alloy results in a significant decrease in microhardness of the former，from 262HV to 180-190HV，while the latter shows a significant increase，from 313HV to 430-450HV.

Due to its lightweight, high strength, good machinability, and low cost, aluminum alloy has been widely used in fields such as aerospace, automotive, electronics, and construction. Traditional manufacturing processes for aluminum alloys often suffer from low material utilization, complex procedures, and long manufacturing cycles. Therefore, more and more scholars are turning their attention to the laser powder bed fusion (LPBF) process for aluminum alloys, which has the advantages of high material utilization, good formability for complex structures, and short manufacturing cycles. However, the widespread promotion and application of LPBF aluminum alloys still face challenges. The excellent printable ability, favorable mechanical performance, and low manufacturing cost are the main factors affecting the applicability of the LPBF process for aluminum alloys. This paper reviews the research status of traditional aluminum alloy processing and LPBF aluminum alloy and makes a comparison from various aspects such as microstructures, mechanical properties, application scenarios, and manufacturing costs. At present, the LPBF manufacturing cost for aluminum alloys is 2–120 times higher than that of traditional manufacturing methods, with the discrepancy depending on the complexity of the part. Therefore, it is necessary to promote the further development and application of aluminum alloy 3D printing technology from three aspects: the development of aluminum matrix composite materials reinforced with nanoceramic particles, the development of micro-alloyed aluminum alloy powders specially designed for LPBF, and the development of new technologies and equipment to reduce the manufacturing cost of LPBF aluminum alloy. [ABSTRACT FROM AUTHOR]

The paper comparatively investigates the microstructures and mechanical properties of Inconel 718 superalloy manufactured by selective laser melting (SLM) and casting. The finite element analysis (FEA) method is used to simulate the temperature fields during SLM and casting processes. Driven by ultra-high temperature gradient and ultra-fast cooling rate during SLM process, the fine grains (average grain size of 48 µm) and dispersed fine precipitation in SLM-ed sample even after HSA (homogenization + solution + aging) and HA (homogenization + aging) heat treatment significantly enhance its mechanical properties, which far exceeds that of casting with average grain size of 1300 µm, and is comparable to that of forging. The microstructure of casting with coarse irregular Laves phases, acicular δ precipitates and globular carbides in the interdendritic zones after HSA heat treatment and some defects existed possibly result in premature failure of tensile samples. The microstructure without δ phases but only some globular carbides in the grain boundary of SLM-ed sample after HA heat treatment possesses higher mechanical properties than that after HSA heat treatment, in which there is only some finer needle-like δ phase and few carbides are precipitated in the grain boundaries. The analysis shows the large amounts of δ phase precipitated in the matrix will deteriorate the plasticity of SLM-ed IN718 superalloy, the appropriate reduction of the δ phase will improve the strength and plasticity of material simultaneously. [ABSTRACT FROM AUTHOR]

In this paper, in order to effectively utilize salt lake magnesium resources, we focused on a functional material containing magnesium, i.e. magnesium oxide, MgO, which is a type of antibacterial material. Through a first-principles study from the atomic level, the microstructure of MgO containing doped point defects of different elements was studied. The relationship between the microscopic structure of the material and its special antibacterial function was explored. The results are as following: the interstitial impurities in MgO are more helpful than substituted impurities for the improvement of the electronic structure. The analysis of the influence of different doping elements on the microstructure confirmed theoretically that Ag and Cu have the same highly active antimicrobial properties with the same change of microstructure, thereby confirming the relationship between microstructure and antimicrobial activity. The results of the simulations match the experimental results, thereby theoretically demonstrating the relationship between defects and antibacterial activities and providing further insight into the nature of the antibacterial mechanism. [ABSTRACT FROM AUTHOR]

It is of great importance to thoroughly explore the evolving temperature fields of direct laser metal deposition (abbreviated as LMD) in vertical thin wall manufacturing. It is helpful to control the temperature gradient, and even to adjust to forming microstructures and accumulation of residual stress. In this paper, a comprehensive three-dimensional transient model is developed for evolving temperature fields. The manufactured material is DS superalloy Rene80. The laser-powder interaction during the powder flowing process is simulated first, and its possible effect on the temperature field of the melting pool is analyzed. Then a 3D numerical simulation for the evolving temperature field is carried out based on considering transport phenomena during LMD such as the change in phase, powder injection and liquid flow. The applied deposition parameters are derived from experimental investigation with optimized vertical wall manufacturing. The simulated results explain why a balance between heat input and dissipation could form inside the vertical thin wall. These reconstruct the instability at an early phase of the building process without any temperature control unit and exhibit the influence of parameters such as laser power, deposition velocity and laser beam deposition pattern. The simulation results of temperature evolution are consistent with experimental investigation. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamics technique has been employed to investigate the relationship between the intrinsic structure and transport properties of lithium ions in LiFePO4 cathode materials. The results show that it is more favorable for Li ion diffusion when crystalline LiFePO4 grows along specific [100] directions, which may cause higher lithium diffusivity through a one dimensional [010] migration path. The change of Li ion diffusivity with temperature reveals that higher temperatures result in higher disorder of the atoms (or ions) and makes Li–O bonding relatively weaker, suggesting that Li diffusion is influenced by the microstructure of LiFePO4, particularly the bonding strength between Li and O atoms. [Copyright &y& Elsevier]

Abstract: LiFePO4 has become a highly promising cathode material for use in the next generation of lithium-ion batteries, in which metal-doping is typically employed to improve the electrochemical properties. However, it is always difficult to resolve the issue that how the doping element and its position cause the microstructural changes and eventually influence the material properties. In this work, the X-ray diffraction (XRD) patterns of a series of metal-doped LiFePO4 were simulated by software MS Reflex to investigate those factors since XRD is a typical technique for the study of crystal structures. The effect of simulation conditions, doping position, and types of doping elements were discussed. The results revealed that: (1) the suitable step size should be 0.02° or less, and the simulation position had little influence on the XRD pattern; (2) the peak intensity changed with doping position, and had been affected more evidently at the Li-site compare with the Fe-site; (3) there was a close relationship between the doping elements and peak intensities in XRD patterns, and the variation degree of the peak intensity increased linearly with the atomic number of doping elements. [ABSTRACT FROM AUTHOR]

• The microstructure of TA15 fabricated by laser powder bed fusion (LPBF) was studied and the formation mechanism of martensite classification was mainly explained. • The influence of different heat treatment temperatures on evolution of microstructure, mechanical properties and fracture mechanism were studied. • The sample after heat treatment at 940 °C obtains excellent comprehensive mechanical properties, because the quartic acicular α phases precipitate in the transformed β phase. TA15 titanium alloy has been widely used in the aerospace industry due to its moderate high-temperature performance. In this research, TA15 samples with excellent mechanical properties were successfully fabricated by laser powder bed fusion (LPBF). Results show that the microstructure of TA15 sample is composed of acicular α′ martensites within the columnar prior β grain. During manufacturing process of LPBF, the non-equilibrium heating and cooling of the thermal cycles experiencing different peak temperatures result in the hierarchical structure of martensite. After heat treatment at 750 °C, 840 °C, 900 °C, and 940 °C for two hours, the fine martensitic structure has transformed into a mixture of α and β. With the increase of temperature, the volume fraction of β increases from 10.3% to 49.9%, the width of primary α increases from 0.72 ± 0.16 µm to 2.96 ± 0.17 µm because of the simultaneous fragmentation of the primary α. So the ultimate and yield strengths decrease while the elongation increases. After heat treatment at 940 °C, the specimen shows the best comprehensive mechanical properties, the elongation increases to 11.5%, the tensile strength is 1061 MPa, and the yield strength is 961 MPa. The fracture surface shows the typically ductile fracture character. [ABSTRACT FROM AUTHOR]

[Display omitted] • Increasing Er content could reduce crack density in Al-Mg alloy fabricated by laser powder bed fusion. • Al 3 Zr particles with L1 2 structure promote the formation of equiaxed grains and refine the grain size. • Er-Zr synergistic effect promotes the precipitation of Al 3 (Er,Zr) and improves the tensile properties during aging treatment. • The Al-6Mg-0.7Mn-0.4Er-1.2Zr alloy has a strength of more than 500 MPa after heat treatment and has a cost advantage. This paper centers on high-strength Al-Mg-Mn-Er-Zr alloy, which was developed through the addition of Er, a cheap rare earth element, and suitable for additive manufacturing (3D printing). The microstructure and mechanical properties of Al-Mg-Mn-Er-Zr alloy of as-built and heat treated samples have been characterized, which shows: the precipitation of Al 3 Zr primary phase at the boundary of molten pool promotes heterogeneous nucleation and refines the grains, which suppresses the formation of solidification cracking in Al-Mg alloy. To bring the Er-Zr synergistic effect into play during the aging heat treatment, the nano-scale precipitation phase of Al 3 Er that diffuses nucleation at an earlier stage promotes the precipitation of Zr, leading to the formation of Al 3 (Er,Zr) core-shell structure and enhancing precipitation strengthening effect. Under the combined effects of multiple strengthening mechanisms, the yield strength could reach 440 ± 3 MPa; tensile strength, 520 ± 2 MPa and elongation 15.5 ± 1.0 %. [ABSTRACT FROM AUTHOR]

Abstract: A molecular dynamics simulation method was used to study the effects of the microstructure on the solidification process of different cooling rates in the MgO–Al2O3–SiO2 glass–ceramics with cordierite as the main crystalline phase. The reasons for changes in the microstructure during the solidification process were analysed by the radial distribution function curve, the bond angular distribution, the coordination number and the volume changes. The results showed that the cooling rate greatly affected the crystallisation process and the glass transition process. When the cooling rate was too fast, the atoms could not undergo a massive displacement before they were “frozen”, and the ability of atoms to achieve an equilibrium position was limited. Some amorphous phases were formed as a result of the disorder of the atomic arrangement, then some crystalline phase precipitated from the vitreous, and a glass–ceramic material was eventually formed. [Copyright &y& Elsevier]