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Novel TiC-reinforced titanium matrix composites (TMCs) were in situ synthesized by laser powder bed fusion (L-PBF) of unique carbon nanotube (CNT)-decorated Ti-6Al-4V powders. Acid-treated CNTs were coated on the surface of Ti-6Al-4V particles by electrostatic self-assembly without varying the powder sphericity, leading to improved printability, as proved by laser-absorption and single-track experiments. During L-PBF, the CNTs were completely transformed into monocrystalline TiC dispersed in the α'-Ti matrix via a dissolution/precipitation mechanism. As illustrated by high-resolution transmission electron microscopy, the in situ-synthesized TiC crystals were closely bonded to the matrix, exhibiting typical TiC [001]//Ti [00−1] and TiC (220)//Ti (−100) orientation relationships. Significantly, the morphology of TiC underwent an interesting evolution from nanorods to micro-spheres, and to dendrites with an increase in the CNT content, causing a gradual increase in hardness of TMCs. This study may provide insights into the design of high-performance TMCs with unique microstructures, excellent properties, and tailored architectures. Unlabelled Image • CNTs were coated on the surface of Ti-6Al-4V powders by electrostatic self-assembly. • Effect of CNT addition on the powder characteristics and 3D-printability of Ti-6Al-4V particles was investigated. • Novel TiC nanorods were first synthesized by L-PBF. • Microstructure evolution and formation mechanism of in situ TiC was clarified. [ABSTRACT FROM AUTHOR]

Abstract The MoSiBTiC alloy is one promising candidate for ultrahigh–temperature materials. However, it faces severe challenges in the machining of complex shapes because of its significant brittleness, high melting point, and stiffness. To overcome this challenge, we have successfully fabricated MoSiBTiC alloy parts via laser powder bed fusion (L-PBF). A combination of arc-melting and controllable high-energy ball milling (HEBM) was employed to prepare suitable MoSiBTiC powders for L-PBF. The evolution of powder morphology, constituent phases, and laser absorptivity, as well as particle size and distribution during HEBM, was investigated. Moreover, the effects of L-PBF parameters on the densification, microstructure, and mechanical performance of MoSiBTiC alloy builds were studied. A dense MoSiBTiC alloy, mainly consisting of a Mo solid-solution, Mo 5 SiB 2 , Mo 2 C, and TiC phases, was obtained at an energy density of 156 J mm−3 using the laser power of 70 W. Compared to the as-cast alloy, the L-PBF-processed MoSiBTiC alloy possessed more uniform and finer grain structures, while exhibiting a lower Vickers hardness due to the existence of internal microcracks. It was also proved that the small quantity of ZrO 2 particles from HEBM processing was uniformly imbedded in L-PBF builds. This work may offer significant guidance for designing and producing complexly shaped refractory intermetallics with unique microstructures in ultrahigh–temperature applications. Graphical abstract Image 1 Highlights • Additive manufacturing of MoSiBTiC alloy for ultrahigh–temperature material was firstly attempted. • An effective approach was developed and optimized for large-scale production of starting MoSiBTiC powders. • High-density MoSiBTiC alloy (∼99.8%) was produced via optimizing laser processing conditions. • Additive-manufactured MoSiBTiC alloy had more uniform and finer grain structures than as-cast one. [ABSTRACT FROM AUTHOR]

A strategy utilizing carbon nanotubes (CNTs) was put forward to synthesize in situ TiC/Mo-based composites via laser powder bed fusion (laser PBF). The functionalized CNTs were dispersed with MoTiAl powders under electrostatic attraction by heteroagglomeration. During laser PBF, individual CNTs reacted with Ti elements and were completely transformed into monocrystalline TiC. Those TiC reinforcements were homogeneously dispersed and intimately contacted the matrix, giving rise to the morphological evolution of a MoTiAl matrix from the nearly columnar to fine equiaxed grains as well as improved mechanical performance. Our finding offers significant guidance for designing and producing advanced Mo-based composites in the application of heat-resistant materials. [ABSTRACT FROM AUTHOR]

Raw powders are processed in water during the freeze-dry pulsated orifice ejection method (FD-POEM), leading to the inclusion of oxygen impurities. This study proposes a strategy for removing the oxygen content and enhancing the mechanical performance of laser powder bed fusion (L-PBF) builds from powders using carbon nanotubes (CNTs) and H2 reduction. Spherical 1.5 wt.% CNT/Mo composite powders with uniform dispersion were fabricated via FD-POEM. The quantity of MoO2 decreased significantly, and a hexagonally structured Mo2C phase was simultaneously formed in the L-PBF build. The Mo2C with network structure was distributed along the boundaries of equiaxed Mo grains, leading to an increased Vickers hardness of the matrix. This study demonstrates the feasibility of fabricating oxygen-free and high-strength refractory parts during L-PBF for ultrahigh-temperature applications. [ABSTRACT FROM AUTHOR]

The low laser absorptivity and high thermal conductivity of Al are the foremost concerns when developing Al matrix composites (AMCs) through laser powder bed fusion (L-PBF) process. In this study, we demonstrated an example of improving the 3D-printability of AMCs by means of powder surface modification. Flexible graphene oxide (GO) sheets were carefully coated onto the surface of AlSi10Mg powders under electrostatic self-assembly via a hetero-agglomeration process. In addition to maintaining a shape and particle size similar to the initial metallic powders, the GO-coated AlSi10Mg powders exhibited enhanced laser absorptivity and decreased thermal conductivity, beneficial to their fusion. Under high-energy irradiation, the GO sheets were partially transformed to Al 4 C 3 nanorods individually distributed in the matrix, while the un-reacted parts floated within molten pools under buoyancy, forming an in-situ carbon layer tightly deposited on the surface of the composite build. This work may provide significant guidance for the design and production of high-performance AMCs with advanced architectures for practical applications. • Graphene oxide (GO) sheets were uniformly coated onto the surface of AlSi10Mg powders via electrostatic self-assembly. • The mixed powders exhibited enhanced laser absorptivity and lower thermal conductivity, beneficial to the 3D-printability. • The microstructure evolution of GO was investigated systematically during laser additive manufacturing. • A carbon layer was in-situ deposited on the surface of composite builds. [ABSTRACT FROM AUTHOR]

MoSiB-based alloys are extremely promising ultrahigh–temperature materials, owing to their high melting points, good thermal stability, and excellent elevated-temperature mechanical properties. However, their fabrication is limited to conventional manufacturing techniques. In this work, a MoSiBTiC multiphase alloy, mainly consisting of Mo solid solution (Mo ss), Mo 5 SiB 2 (T 2), and TiC phases, was fabricated by laser powder bed fusion (L-PBF) using ball-milled alloy powders; subsequently, the effect of hot isostatic pressing (HIP) on its microstructure and fracture toughness was investigated. Due to the non-equilibrium metallurgical characteristics of L-PBF, the as-built alloy included uniform and fine-grained structures, as well as internal microcracks. The length of microcracks was effectively reduced with the assistance of the TiC bridging effect during HIP. As revealed by a high-resolution transmission electron microscope, the TiC was uniformly dispersed and was in close contact with the Mo ss or T 2 phase. Consequently, the MoSiBTiC multiphase alloy exhibited a high fracture toughness of 9.0 MPa(m)1/2 after HIP at 1973 K. This work could be an important step towards the fabrication of high-performance refractory components with advanced properties in ultrahigh–temperature use. Unlabelled Image • A high-performance MoSiBTiC alloy was designed by laser powder bed fusion (L-PBF) and hot isostatic pressing (HIP). • L-PBF process was optimized to fabricate a MoSiBTiC alloy using ball-milled powders. • Microstructural evolution during HIP was observed via high-resolution TEM. • TiC phase acted as a healing agent for repairing internal microcracks. [ABSTRACT FROM AUTHOR]

[Display omitted] • Combining the FD-POEM and PS processes enables elemental fabrication of high quality spherical MoSiBTiC powders for 3D-printing. • The morphology, chemical composition, and microstructure evolution of FD-POEM MoSiBTiC powders during PS treatment were exhaustively investigated. • An innovative approach for reducing the oxygen content in refractory powders to be used for additive manufacturing was provided. • This work is expected to provide a valuable reference for the development of advanced refractory alloys. The freeze–dry pulsated orifice ejection method (FD-POEM) can be coupled with plasma spheroidization (PS) as an advanced approach for fabricating spherical refractory powders used in laser additive manufacturing. However, the microstructure evolution of FD-POEM powders, which include components of various melting points, during ultrahigh-temperature PS treatment remains unclear. In this work, the morphology, chemical composition, and microstructure of MoSiBTiC alloy powders, as representative PS powders, were systematically investigated. The mesh-structured FD-POEM powders underwent complete densification, resulting in a 52 % reduction in particle size. The PS powders were composed of coarse solid solution Mo (Mo ss) and fine eutectic Mo 5 SiB 2 /TiC phases, consistent with the composition of additively manufactured MoSiBTiC alloys. With an increase in Si content, the volume fraction of fine Mo 5 SiB 2 phases increased, resulting in increased Vickers hardness. Notably, the oxygen content of FD-POEM powders decreased by > 99 %, owing to the effective elimination of surface oxides on the initial elemental powders during ultrahigh-temperature PS treatment. This research provides an innovative approach for reducing the oxygen content in refractory powders to be used for additive manufacturing. Enhanced understanding of the microstructure evolution of PS powders can facilitate the composition optimization of refractory powders and development of a microstructure–property database for additively manufactured materials. [ABSTRACT FROM AUTHOR]

In this work, we demonstrated an example of leveraging the intrinsic morphology features of one-dimensional SiC nanofiber (SiC nf) to design high-performance Ag-metal matrix composites (MMCs) using powder metallurgy techniques. To break up the SiC nf agglomerates and increase surface functionality while maintaining its integrity, the raw SiC nf underwent a specially developed surface modification process. Following a combination of hetero-agglomeration, spark plasma sintering and hot extrusion, the SiC nf was homogeneously dispersed and singly aligned throughout the Ag matrix. Microstructure observations revealed close contact between the SiC nf and the Ag matrix, resulting in a sawtooth-like SiC nf -Ag interface induced by the plastic flow of Ag. Thanks to the presence of strong mechanical anchors at SiC nf protrusions, the load transfer efficiency of the SiC nf -Ag interface reached 72 %. Consequently, the SiC nf /Ag composite exhibited a high tensile strength of 219 MPa and a substantial failure elongation of 39.2 %. This work underscores the importance of optimizing interfacial microstructures and offers the new insights of designing novel Ag-MMCs for applications in conductive devices. [ABSTRACT FROM AUTHOR]

To maintain the high thermal conductivity (TC) and reduce the coefficient of thermal expansion (CTE) of conventional copper (Cu)/graphite composites, novel Cu/graphite/carbon fibers (CFs) hybrid composites were designed by replacing part of graphite with Cu-coated CFs and prepared by spark plasma sintering (SPS) process. The incorporation of CFs resulted in increased interface density, reduced twin boundaries, and significant grain refinement of the Cu matrix. TEM observations revealed that the Cu-coating on surfaces of CFs enhanced the interfacial bonding between CFs and Cu matrix. The Cu-coated CFs can act as connecting channels between graphite particles, which partially compensate the negative effect on TC. Furthermore, strong interfacial bonding and large Cu/CFs contact areas contribute to the reduction in CTE. As a result, the Cu/30%graphite/10%CFs composite showed TC and CTE of 453.5 Wm−1 K−1 and 10.9 × 10−6 K−1, respectively. Compared to the Cu/40%graphite composite, the CTE of Cu/30%graphite/10%CFs composite was reduced by ∼20 % with only 4.4 % sacrifice in TC. Consequently, the Cu/graphite/CFs hybrid composites showed an excellent balance between TC and CTE, which are superior to the conventional Cu/graphite and Cu/CFs composites. The findings of this work provide new insights for designing and preparing new thermal management materials. [Display omitted] • Novel Cu/graphite/CFs hybrid composites were designed. • Microstructure and thermal properties of the hybrid composites were first reported. • The CFs can act as connecting channels between graphite particles. • Strong and large Cu/Cu-coated CFs contact areas can cause lower CTE. • The hybrid composites showed an excellent balance between TC and CTE. [ABSTRACT FROM AUTHOR]

To save rare-earth (RE) resource and develop creep-resistant Mg alloys in a low-cost way, RE-free Mg alloys are strongly recommended recently. However, serious creep anisotropy and poor creep resistance are still the main problems of safely using RE-free Mg alloys. In the present research, one binary Mg-2wt%Sn hot-rolled plate was employed for studying the compressive creep performance at 393 K. It was found that different activities of basal slip, twinning and pyramidal slip weakened the creep performance along the rolling direction and caused the inevitable creep anisotropy. To weaken the creep anisotropy between the rolling direction and normal direction, multi-directional forging (MDF) with three passes was performed at 393 K. Through inducing high-density twins before creep loading, detwinning was frequently activated during creep loading instead of inducing new twins. As a result, the creep anisotropy was successfully weakened in the MDF processed alloy. Moreover, the creep performance was synchronously enhanced along both loading directions rather than deteriorating the creep performance along the normal direction. It is thus expected that this RE-free way of preparing creep-resistant Mg alloys can be widely accepted in the relative application fields. • Serious compressive creep anisotropy exists along the RD and ND of Mg-2wt%Sn alloy. • Creep anisotropy is drastically weakened by multi-directional forging with 3 passes. • Creep resistance is strengthened along both directions without any deterioration. • Incomplete detwinning assisted by dislocation slip avoids long dislocation slip path. • Dislocations have short slip path and decelerate the creep rate of MDFed samples. [ABSTRACT FROM AUTHOR]

In order to depress the "susceptibility artifacts" in magnetic resonance imaging (MRI), improve the mechanical reliability for biomedical structural applications and realize tailor-made medical devices with complex shape, low magnetic Zr-1Mo(wt%) alloy builds with high relative density (c.a. 99.9%) fabricated by laser powder bed fusion process(L-PBF) were subjected to various heat treatment conditions followed by water quenching. After quenching process acicular α′ microsturcture in as-build Zr-1Mo(wt%) alloy builds changed to basket weave α + β structure, unique retained α + ultra fine (α′ + α″) martensite structure or retained α + acicular α′ microsturcture depending on quenching conditions. X-ray diffraction (XRD) and high resolution-transmission electron microscope(HR-TEM) revealed a unique retained α + ultra fine (α′ + α″) martensite microstructure in 1123 K specimens. The stress-induced competition between β to α′ transformation and β to α″ transformation contributed to this unique microstructure. This unique microstructure contributed to a good balance between strength (UTS:822 MPa) and ductility (Elongation:11.7%). The volume magnetic susceptibility of quenched Zr-1Mo(wt%) alloy builds maintained low(about 1.01 × 10−4) indicating good MRI compatibility. The magnetic susceptibility of each phase was modified to be χ α″ > χ β > χ α > χ α ′ > χ ω. Zr-1Mo(wt%) alloy quenched from 1123 K will be an promising candidates for tailor made devices under MRI environments. Unlabelled Image • L-PBF-processed Zr 1Mo alloy builds were subjected to various quenching process. • A unique retain α + ultra fine (α′α″) structure was confirmed in 1123 K specimens. • 1123 K specimens exhibited good balance between strength and ductility. • All the quenched Zr 1Mo alloy builds maintain low magnetic susceptibility. • Phase magnetic susceptibility in Zr was modified to be χ α ″ > χ β > χ α > χ α ′ > χ ω. [ABSTRACT FROM AUTHOR]

A highly textured pure Sb 2 Te 3 is fabricated via a hydrothermal method combined with high-pressure spark plasma sintering. The nanoscale texture gives rise to an extremely low thermal conductivity in the out-of-plane direction, while shows weak influence on the carrier mobility which reaches the level of single crystal. Microstructure analysis reveals large amount of low-angle boundaries, whose discriminated effect on scattering phonons and carriers should account for the observed phenomenon. Consequently, the structurally nanocrystalline electrical monocrystalline behavior leads to a high average ZT with peak value above 1 at 525 K, which is the best TE performance for undoped Sb 2 Te 3. Unlabelled Image [ABSTRACT FROM AUTHOR]

Bi 2 Te 3 thin films were fabricated on the (00 l )-oriented MgO substrates by the magnetron co-sputtering method. The films microstructure of highly preferred orientation along the c-axis had been obtained through the inducing of single crystal MgO substrates. And some abundant Te was introduced into the Bi 2 Te 3 films through sputtering tellurium target, which affected the scattering process. The (00 l ) preferred orientation is beneficial to the carriers transport. In this case, the higher performance of Bi 2 Te 3 thin films can be obtained. And microstructure and thermoelectric properties of Bi 2 Te 3 thin films were investigated systematically. [ABSTRACT FROM AUTHOR]

Hot isostatic pressing and subsequent heat treatment were performed to achieve defect-free and high-mechanical-performance Zr-1Mo components manufactured by laser powder bed fusion. The strong but brittle acicular α' martensite phase was observed in the as-fabricated Zr-1Mo components, which transformed into a basketweave α + β microstructure after the HIP process and then transformed into a stress-relieved α phase after subsequent HT. Optical microscopy images and fracture observations revealed that the defects in the as-fabricated components were eliminated after the HIP process and did not regrow during subsequent HT. An ultimate tensile strength of 990 MPa, yield strength of 831 MPa, and elongation of 9.1% were achieved in the heat-treated Zr-1Mo components. The combination of HIP and subsequent HT could be a promising post-processing treatment for L-PBF-fabricated Zr-1Mo components. [ABSTRACT FROM AUTHOR]

In recent years, a low magnetic and fully dense Zr–1Mo (wt%) part was successfully manufactured via the laser powder bed fusion (L-PBF) process, which shows the great potential as metallic biomaterials under the magnetic resonance imaging (MRI) environment. However, due to the high cooling rate after laser incident during the L-PBF process, the as-fabricated Zr–1Mo part consists of a non-equilibrium α′ phase, which contributed to high strength (UTS: 1107 MPa) but insufficient ductility (elongation: 4.3%) for biomedical applications. In order to enhance the mechanical performance of as-fabricated Zr–1Mo parts, various annealing processes that have been recognized as an efficient post-treatment to adjust the mechanical performance of additive manufactured products were executed. After the annealing process, acicular martensite α' microstructure in as-fabricated Zr–1Mo parts changed to stress relieved/partial relieved acicular α microstructure, basketweave α + β microstructure, lamellar α + β microstructure or retain α+ lamellar α + β microstructure depending on different annealing conditions. In the meantime, elongation increased with increasing holding temperature and residence time, but the tensile strength exhibits a converse trend. The specimens annealed at 873 K, 803 K for 2 h and at 773 K for 8 h possessed UTS of 779 MPa, 964 MPa and 981 MPa as well as elongation of 14.3%, 11.0% and 9.6%, respectively. These annealing conditions could contributed to adequate strength and sufficient ductility, and should be the appropriate annealing conditions for Zr–1Mo parts produced by the L-PBF technology. By comparison with other conventional metallic biomaterials, annealed Zr–1Mo alloy could be applied for the medical devices under MRI environments. • Various annealing processes was executed for L-PBF-produced Zr–1Mo parts. • Correlation between microstructure and tensile properties of Zr–1Mo was understood. • Stress-relieved acicular structure contribute to high UTS and sufficient elongation. • 803 K-2 h shows comparable tensile properties to the several metallic biomaterials. • Excellent MRI compatibility was maintained after the annealing process. [ABSTRACT FROM AUTHOR]