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Developing additive manufacturing (AM) aluminum alloys with high temperature strength remains a formidable scientific challenge, primarily due to the strengthening precipitates coarsening above 200°C. Conventional heat-resistant alloy design strategies aim to hinder the precipitate coarsening by incorporating low diffusive alloying elements. However, such approaches remain ineffective against thermally driven defect mobilization, especially for vacancy diffusion and dislocation climbing, which are dominant drivers of high temperature weakening. As a result, most AM Al alloys exhibit a rapid decline in strength within this critical temperature range. Through reverse-engineering of intrinsic atom-defect/atom attraction, we employ an intrinsic attraction (IA) strategy to trigger multi-dimensional defect confinement mechanisms. This approach achieves: divacancy clusters anchoring free vacancies; solute atmospheres capturing mobile dislocations and suppressing creep deformation; specific segregation forming nanostructures at precipitate interfaces and interiors to inhibit coarsening. The AM heat-resistant Al alloy demonstrates satisfactory high temperature performance, exhibiting yield strengths of ~305 MPa at 300°C, ~190 MPa at 400°C, coupled with creep resistance at 200-400°C ( ε °  < 10 -7 /s) and prominent processability for large-size bladed disk. This strategy transcends the conventional empirical paradigm by engineering elemental segregation tendencies at specific sites, provides a universal design approach for the development of aluminum alloys or other high temperature structural materials. This study introduces an intrinsic attraction strategy to enhance the high-temperature performance of additively manufactured aluminum alloys. By confining atomic defects and stabilizing precipitates, the alloy retains 305 MPa at 300 °C with creep resistance up to 400 °C.

Additive manufacturing of an equimolar CoCrNi medium entropy alloy (MEA) by selective laser melting (SLM) was investigated, emphasizing its microstructure, properties, and metallurgical defects. It was found that SLM sample density exhibited a non-monotonic relation with their volume energy density (VED); the density first increased but then decreased while the input VED was gradually increasing. A maximal relative density of 98.9 pct was accessible at a VED of 83.3 J/mm3. X-ray diffraction indicated that the printed CoCrNi MEA exhibited an FCC single-crystal structure where the lattice constant decreased with the increasing VED owing to the evaporation of the Cr element in the SLM process. The average grain size gradually increased with increasing VED, irrespective of whether viewed from the top or the side of the printed part. Similarly, the residual stress increased with increasing VED, which produced more microcracks and deteriorated the tensile preformation of the printed samples, although the yield strength (630 MPa) showed no apparent difference at different VEDs. Owing to the ultrafine cell structure, the mechanical property of the SLM printed sample was twice that of cast or wrought CoCrNi MEA.

Ni 51 Ti 49 at.% bulk was additively manufactured by laser-directed energy deposition (DED) to reveal the microstructure evolution, phase distribution, and mechanical properties. It is found that the localized remelting, reheating, and heat accumulation during DED leads to the spatial heterogeneous distribution of columnar crystal and equiaxed crystal, a gradient distribution of Ni 4 Ti 3 precipitates along the building direction, and preferential formation of Ni 4 Ti 3 precipitates in the columnar zone. The austenite transformation finish temperature ( A f ) varies from −12.65 °C ( Z = 33 mm) to 60.35 °C ( Z = 10 mm), corresponding to tensile yield strength ( σ 0.2 ) changed from 120 ± 30 MPa to 570 ± 20 MPa, and functional properties changed from shape memory effect to superelasticity at room temperature. The sample in the Z = 20.4 mm height has the best plasticity of 9.6% and the best recoverable strain of 4.2%. This work provided insights and guidelines for the spatial characterization of DEDed NiTi. 1. The study revealed the internal physical mechanism responsible for the spatial heterogeneity of microstructure and properties observed in large-volume, Ni-rich NiTi alloy blocks produced using laser-directed energy deposition (L-DED). 2. L-DED was used to fabricate even larger Ni-rich NiTi blocks that were three times the size of the largest one previously studied. 3. DEDed NiTi with mechanical anisotropy and gradient mechanical performance was prepared and discovered that the heat generated during the process can control the properties of the alloy. 4. This paper proposed a simple new preparation method for shape memory alloy functionally graded materials.

Lightweight aluminum (Al) alloys have been widely used in frontier fields like aerospace and automotive industries, which attracts great interest in additive manufacturing (AM) to process high-value Al parts. As a mainstream AM technique, laser-directed energy deposition (LDED) shows good scalability to meet the requirements for large-format component manufacturing and repair. However, LDED Al alloys are highly challenging due to their inherent poor printability (e.g. low laser absorption, high oxidation sensitivity and cracking tendency). To further promote the development of LDED high-performance Al alloys, this review offers a deep understanding of the challenges and strategies to improve printability in LDED Al alloys. The porosity, cracking, distortion, inclusions, element evaporation and resultant inferior mechanical properties (worse than laser powder bed fusion) are the key challenges in LDED Al alloys. Processing parameter optimizations, in-situ alloy design, reinforcing particle addition and field assistance are the efficient approaches to improving the printability and performance of LDED Al alloys. The underlying correlations between processes, alloy innovation, characteristic microstructures, and achievable performances in LDED Al alloys are discussed. The benchmark mechanical properties and primary strengthening mechanism of LDED Al alloys are summarized. This review aims to provide a critical and in-depth evaluation of current progress in LDED Al alloys. Future opportunities and perspectives in LDED high-performance Al alloys are also outlined. A rigorous review to understand the root causes of poor printability of Al alloys. Practical strategies to improve Al printability for better mechanical performance. Correlations among process-alloy innovation-microstructure-properties. Benchmark achievable mechanical properties in LDED Al alloys. Future opportunities and perspectives in LDED high-performance Al alloys.

Background Calcitonin gene-related peptide (CGRP) as a mediator of microglial activation at the transcriptional level may facilitate nociceptive signaling. Trimethylation of H3 lysine 27 (H3K27me3) by enhancer of zeste homolog 2 (EZH2) is an epigenetic mark that regulates inflammatory-related gene expression after peripheral nerve injury. In this study, we explored the relationship between CGRP and H3K27me3 in microglial activation after nerve injury, and elucidated the underlying mechanisms in the pathogenesis of chronic neuropathic pain. Methods Microglial cells (BV2) were treated with CGRP and differentially enrichments of H3K27me3 on gene promoters were examined using ChIP-seq. A chronic constriction injury (CCI) rat model was used to evaluate the role of CGRP on microglial activation and EZH2/H3K27me3 signaling in CCI-induced neuropathic pain. Results Overexpressions of EZH2 and H3K27me3 were confirmed in spinal microglia of CCI rats by immunofluorescence. CGRP treatment induced the increased of H3K27me3 expression in the spinal dorsal horn and cultured microglial cells (BV2) through EZH2. ChIP-seq data indicated that CGRP significantly altered H3K27me3 enrichments on gene promoters in microglia following CGRP treatment, including 173 gaining H3K27me3 and 75 losing this mark, which mostly enriched in regulation of cell growth, phagosome, and inflammation. qRT-PCR verified expressions of representative candidate genes (TRAF3IP2, BCL2L11, ITGAM, DAB2, NLRP12, WNT3, ADAM10) and real-time cell analysis (RTCA) verified microglial proliferation. Additionally, CGRP treatment and CCI increased expressions of ITGAM, ADAM10, MCP-1, and CX3CR1, key mediators of microglial activation in spinal dorsal horn and cultured microglial cells. Such increased effects induced by CCI were suppressed by CGRP antagonist and EZH2 inhibitor, which were concurrently associated with the attenuated mechanical and thermal hyperalgesia in CCI rats. Conclusion Our findings highly indicate that CGRP is implicated in the genesis of neuropathic pain through regulating microglial activation via EZH2-mediated H3K27me3 in the spinal dorsal horn.

Additive manufacturing of Hastelloy X superalloys remains challenges for practical aerospace applications due to the inadequate mechanical property at both ambient and high temperatures. To this end, this work proposes a novel Ta-modified strategy manipulating elemental segregation to stabilize cellular structures, thereby obtaining an outstanding combination between strength and ductility across a wide temperature regime. In particular, the tensile strength and elongation of Ta-modified superalloys can reach up to 1 214 MPa and 28.4%, respectively, highly increased by 47% and 10% compared to original Hastelloy X superalloys at 25 ℃. Meanwhile, the tensile strength and elongation at 650 ℃ significantly increase to 843 MPa and 26.8% respectively, 38% and 150% stronger than their counterparts of the original Ta-free Hastelloy X superalloys at identical conditions. Microstructural observations reveal that prominent local segregation of Ta/Mo elements and in situ MC precipitates along cellular boundaries synergistically enhanced the stability of cellular structures. The stabilized cellular structures serve as continuous and skeleton-like networks during deformation, synergistically contributing to outstanding ductility and enhanced mechanical strength, as well as sustained strain-hardening ability. The present work provides new insights into an efficient alloy design method for additively manufactured nickel-based superalloys with outstanding mechanical property within a wide temperature regime.

The effect of pulse current (PC) on the interdiffusion of Ti-Ni system was investigated under spark plasma sintering. The growth rate of Ni-Ti intermetallics under PC was 3.22 to 6.44 times higher than that with direct current (DC). The reaction activation energy of intermetallics at PC was 18.4 to 79.0 kJ/mol, which is lower than the activation energy of 275.1 to 313.9 kJ/mol at DC; thus, the increased growth rate at PC may have resulted from the decrease of activation energy.

Selective laser melting (SLM) and direct energy deposition (DED) are two widely used technologies in additive manufacturing (AM). However, there are few studies on the combination of the two technologies, which can synthetically combine the advantages of the two technologies for more flexible material design. This paper systematically studies the Al-Mg-Sc-Zr alloy by combination of SLM and DED with emphasis on its bonding properties, microstructure, and metallurgical defects. It is found that the aluminum alloy prepared by the two methods achieves a good metallurgical combination. The microstructure of aluminum alloy prepared by DED is composed of equiaxed crystals, and there are a large number of Al3(Sc, Zr) precipitated phase particles rich in Sc and Zr. The microstructure of SLM aluminum alloy is composed of equiaxed crystals and columnar crystals, and there is a fine-grained area at the boundary of the molten pool. With the decrease of laser volumetric energy density (VED), the width and depth of the molten pool at the interface junction gradually decrease. The porosity gradually increases with the decrease of VED, and the microhardness shows a downward trend. Tensile strength and elongation at fracture of the SLM printed sample at 133.3 J/mm3 are about 400 MPa and 9.4%, while the direct energy depositioned sample are about 280 MPa and 5.9%. Due to the excellent bonding performance, this research has certain guiding significance for SLM–DED composite aluminum alloy.

The interdiffusion behaviors of elements at the W/Co interface under the application of current during SPS were investigated. It is found that Co7W6 and Co3W are formed at the W/Co bonding interface. The growth of the Co3W layer is apparently improved by the high current during SPS. The growth rate constant of the Co3W layer undercurrent is 1.73–3.03 times faster than that without current. The research shows that the growth rate is increased with the current density. The growth activation energy of the Co3W layer is calculated to be 229.51 ± 27 kJ mol−1 undercurrent, which is smaller than that without current (279.38 ± 11 kJ mol−1). Moreover, the growth activation energy of the Co3W layer is decreased with the increase of the current density. The mechanism of current-improved growth of the Co3W layer is suggested to be the fact that the current lowers the nucleation barrier of intermetallic layer, which accordingly promotes chemical reactions.