Nickel-based superalloys show severe cracking tendency during laser powder bed fusion (LPBF), which hinders their widespread applications in aerospace. A two-step heat treatment, including hot isostatic pressing (HIP) and solid solution heat treatment (SSHT), was proposed to obtain crack-free LPBF nickel-based superalloy components with a supersaturated solid solution of alloying elements for desirable mechanical performance. The HIP process aimed to annihilate microcracks, and the subsequent SSHT focused on modifying the microstructure and improving the solid solution extent of alloying elements. The pore-and-microcrack-containing defects with a volume fraction of 0.96% in the LPBF samples were transformed to pore-dominated defects with a volume fraction of 0.08% after the HIP process. After the SSHT, it was not observed the reappearance of the previously coalesced microcracks, but the porosity volume fraction showed a slight rebound to 0.11% due to the coarsening or regrowth of the pores. The tensile strength and elongation at break of HIP + SSHT samples printed along the horizontal plane at room temperature were 3.6% and 113.5% higher than those of as-fabricated ones. An 11.9% and 410.0% improvement in tensile strength and ductility at 900 degrees C was achieved after the two-step treatment. The development of the microstructure after the HIP and SSHT, involving sub-grains, dislocation networks, carbide precipitates, and grains, was revealed systematically. The correlation between the microstructure and tensile properties was unveiled in depth. This work is anticipated to provide an efficient route with excellent industrial applicability for LPBF superalloy components to mitigate microcracks and acquire attractive mechanical properties.

激光增材制造可实现高性能金属复杂构件整体化成形，在航空航天、汽车、医疗等领域具有广阔应用前景。但是，高斯激光作用产生不均匀温度场、极高的温度梯度以及不稳定的流场，导致飞溅、球化、匙孔、残余应力和裂纹等缺陷及各向异性的微宏观性能，影响了该技术更广泛的应用。光束整形和场辅助原位调控激光增材制造过程是控制缺陷产生的有效方法。本文综述了国内外在光束整形、热、磁和超声多场调控金属激光增材制造的研究进展，重点揭示外场-激光-材料-组织-性能间的作用机理，并对多场调控金属激光增材制造未来发展进行了展望，可为金属激光增材制造的高性能调控提供有益参考。

基于吸热墨水喷射3D打印原理设计开发了实验平台，主要包括机械运动系统、喷头与供墨系统、粉床加热系统以及控制与软件系统，共四个子系统。实验平台能够对粉末床预热温度、移动加热灯功率与速度、喷墨密度等工艺过程参数进行控制，并借助红外热像仪能够实时监测粉床温度分布。在此基础之上，用商业水性黑色染料墨水与自制炭黑墨水进行了单层打印实验，发现在移动加热灯照射功率1 500 W、累计照射时间为25 s时，使用自制墨水用于打印可使成形区与非成形温度差达到46℃，而使用商业墨水的温度差为7.1℃，说明自制炭黑墨水能够显著增强高分子粉末吸收红外辐射能量的能力。该吸热墨水喷射3D打印实验平台可为新材料开发和新工艺探索提供开放式平台，并为其他类型3D打印实验平台的自主开发提供有益借鉴。

In this work,in-situ experimental tests are first performed to investigate the powder spreading process of additive manufacturing,where different kinds of scrapers and spreading speeds are employed.Detailed kinetic be

The Sn macro-segregation is easy to produce in the traditional casting process for Cu-15Ni-8Sn alloy with high Sn content, which reduces the mechanical properties. In order to reduce the segregation, the alloy was fabricated by selective laser melting (SLM). The microstructure, tensile and tribological properties were investigated by X-ray diffractometer (XRD), optical microscope (OM), scanning electron microscope (SEM), electron probe micro-analyzer (EPMA), electron backscatter diffraction (EBSD), field emission transmission electron microscope (TEM) and laser confocal microscope. The results indicate that Sn segregation is inhibited at the micron level due to the rapid solidification, and a large amount of Sn atoms are dissolved into the matrix. The grains are also refined to about 2.13 μm. The microstructure is composed of Sn-depleted α-Cu(Ni, Sn) matrix and Sn-rich γ - (CuxNi1−x)3Sn precipitates. The diameter of γ particles is about 0.2 μm. The samples have excellent strength and toughness, with the ultimate tensile strength of (572.99±11.07) MPa and the elongation at break of (12.36±1.66)% . The high strength of SLM-fabricated Cu-15Ni-8Sn alloy is due to the contribution of the grain boundary strengthening, solid solution strengthening, precipitation strengthening and dislocation strengthening. The coefficient of friction is 0.5032, and abrasive wear is the dominant wear mechanism, leading to excellent wear resistance. © 2023 Central South University of Technology. All rights reserved.

利用激光选区熔化（Selective laser melting,SLM）技术制备了GH3536镍基高温合金，研究了不同热等静压（Hot isostatic pressing,HIP）温度对SLM成形GH3536合金裂纹和组织性能的影响。利用X射线衍射仪（X-ray diffraction,XRD）、扫描电镜（Scanning electron microscope,SEM）、电子背散射衍射（Electron backscatter diffraction,EBSD）、电子探针显微分析仪（Electron probe microanalyzer,EPMA）等方式表征了GH3536相组成和组织演变，利用高温持久性能试验机测试合金室温和高温拉伸性能。结果表明：经HIP后，SLM成形GH3536合金相组成保持不变，均为γ相，但晶格常数降低，且随着HIP温度的升高而降低。SLM态合金中存在10～100μm的微裂纹和气孔缺陷，微裂纹主要存在于熔池边界。经HIP后，合金中微裂纹完全消除，但仍存在少量孔洞。GH3536合金经高温高压处理后，晶粒尺寸增大，抗拉强度有所降低。其中SLM态试样室温抗拉强度和伸长率分别为871 MPa和26.2%,HIP处理后伸长率最高提升13.7%，强度降低13.0%。900℃下SLM态试样抗拉强度和伸长率分别为247 MPa和5.7%,HIP处理后伸长率最高提升13.4%，强度降低10.1%。

Although high-speed powder spreading can efficiently enhance the productivity of laser powder bed fusion (LPBF) additive manufacturing, it is rarely used because it is generally believed to be unfavourable for the part quality. However, there is no systematic investigation to confirm this "common sense ". In this work, a series of powder spreading and melting experiments are carried out to investigate the role of the spreading speed in LPBF. In the single-layer experiments, the high-speed powder spreading indeed reduces the packing density of the powder layer and seems unfavourable as expected. However, the multilayer LPBF processes of cubic samples with various high powder-spreading speeds are successful, and the samples possess even fewer defects and thus better mechanical properties particularly fatigue life, which is counterintuitive and has never been reported before. To understand the physical mechanisms, we fabricate staircase samples under different powder spreading speeds, revealing the layer-by-layer evolution of the powder bed and deposited dense region. It is found that regardless of the powder spreading speed, the actual powder layer thickness gradually increases due to the shrinkage during powder melting, but always reaches the steady state in ~10 layers, where the deposited dense layer thickness is equal to the nominal powder layer thickness, thereby achieving similar melting condition and quality. Furthermore, LPBF experiments with intended operational delays in the powder spreading procedure are conducted and prove our speculation that the slightly reduced pores and cracks in the samples fabricated with high-speed powder spreading are mainly attribute to the reduced cooling time between layers and consequently the higher temperature before next-layer melting as well as lower temperature gradients. The major drawback with the higher powder spreading speed is also discussed, which is the reduction of the dimensional accuracy of the fabricated sample along the building direction. This study provides unprecedented insight into the role of powder spreading speed in LPBF and corrects the inaccurate intuition that high-speed powder spreading is always unfavourable, which provides more potential solutions to enhance the productivity and part quality of LPBF. (C) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Objective: Guided bone regeneration (GBR) techniques use barrier membranes to augment the alveolar ridge for the site-specific growth of bone defects. However, current approaches using cast metal substructures exhibit poor adaptation to the surgical site and increased risk of infection. This study aimed to fabricate multi-functional coatings with 3D-printed porous titanium-niobium (Ti-Nb) alloy meshes to maintain space, prevent the ingrowth of fibroblasts and inhibit the colonization of bacteria for GBR.Methods: Ti-Nb alloy meshes were prepared by selective laser melting (SLM) and used as substrates for novel surface coatings. Porous chitosan (CS)/ gelatin (G)/ doxycycline (Dox) coatings were formed on the meshes using electrophoretic deposition (EPD) and freeze-drying. The process of EPD was characterized through Fourier transform infrared spectroscopy (FT-IR), zeta potential, and particle size analysis. The cytotoxicity of the coatings was evaluated through the culture of osteoblasts and immunostaining. The antibacterial activity of the coatings was tested using inhibition zone tests against Staphylococcus aureus (S. aureus) and scanning electron microscope (SEM). The inhibition of fibroblasts infiltration and nutrients transfer properties were analyzed using immunostaining and permeability tests.Results: High yield strength (567.5 +/- 3.5 MPa) and low elastic modulus (65.5 +/- 0.2 GPa) were achieved in Ti-Nb alloy bulk samples. The data of zeta potential, FT-IR and SEM indicated that porous spongy coatings were chemically bonded following EPD. In vitro analysis of CSGDox1 (containing Dox at 1 mg.mL(-1)) coating revealed its antibacterial effect and biocompatibility. Moreover, the CSGDox1 coating was proved to be effective for preventing the ingrowth of fibroblasts, whilst allowing the infiltration of nutrients.Significance: This study verified that the EPD of CSGDox coatings on the 3D-printed Ti-Nb meshes can maintain space, provide antibiotic release whilst maintaining a barrier against soft-tissue growth, which is essential for the success of GBR treatment. (C) 2021 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.

Cu-15Ni-8Sn alloy with layer-by-layer periodic heterogeneous microstructures composed of ultrafine equiaxed (similar to 2.6 mu m) and coarse columnar (similar to 12.8 mu m) grains was successfully fabricated by laser powder bed fusion (LPBF) additive manufacturing. The microstructures were composed of Sn-depleted alpha-Cu (Ni, Sn) matrix and Snenriched gamma-(CuxNi1-x)3Sn nano-precipitates. The gamma nano-precipitates were found to be mainly uniformly distributed at the melt pool boundaries due to Sn reverse segregation, as though the densely distributed seeds on the surface of a strawberry. The interesting periodic bi-modal microstructure exhibited a simultaneous positive effect on the enhancement of strength and ductility. The yield strength, ultimate tensile strength and elongation at break were (474.04 +/- 2.88) MPa, (584.36 +/- 4.74) MPa and (14.29 +/- 1.78)%, respectively. Remarkable improvements of 12% and 286% in the yield strength and elongation at break were achieved compared with those cast counterparts reported in the published literature. The high dislocations density (similar to 6.78 x10(14) m-2) were the dominant source of high strength and contributed-49% to the yield strength according to the theoretical calculation. Massive dislocation cells were generated around the gamma nano-precipitates during tensile deformation, improving the dislocation storage capacity and the work hardening ability. These findings validated the LPBF printability and the property enhancement of Cu-15Ni-8Sn and provided a promising strategy for the design of high strength and ductility copper alloys through layered precipitation microstructures.