Additive manufacturing letters最新文献

We have assessed the structural evolution and dispersoid coarsening behaviors of the oxide dispersion-strengthened superalloy MA754 during two different melt-based additive manufacturing techniques – metal laser powder bed fusion (PBF-LB/M) and directed energy deposition (DED). The mechanically alloyed MA754 powder posed challenges for both processes due to its irregular flaky morphology and large particle size. Successful consolidation with PBF-LB/M required increasing the layer height, decreasing the scanning speed, and increasing the laser power relative to typical Ni superalloy printing parameters. The resulting materials contained residual porosity and large Y-Al-oxide slag inclusions which formed in situ. The more prolonged thermal excursion during DED resulted in even larger, mm-scale slag inclusions, which spanned several build layers. In both PBF-LB/M and DED, these inclusions grew at the expense of nanoscale dispersoids, depleting the material of this strengthening phase. These observations motivate alternative approaches for preparing dispersion-strengthened powder feedstocks besides mechanical alloying and highlight the deleterious effects of Al microalloying on dispersoid stability and structure.

Vat photopolymerization (VPP) is one of the most widely used additive manufacturing methods. The VPP process temperature and material curing reaction interplay with each other to critically determine the final product quality. Insights about the time-varying process temperature and degree of conversion (DoC) is desired for VPP process control but difficult to attain due to lacking effective operando characterization technologies. This work reports a new method to create a thermal-chemical model of the VPP process by solving an inverse heat conduction problem (IHCP) based on in-situ observable temperature measurement to estimate the chemistry reaction-induced heat source that is a function of DoC. Ex-situ photo differential scanning calorimetry (Photo-DSC) characterization is used to initialize the chemistry reaction model parameters so that DoC can be calculated. Specifically, vat substrate temperature is measured using an in-situ infrared thermal camera and used as input to solve an IHCP for estimating exothermic heat generation rate for the internal heat generation component at the curing part. Overall, the newly developed VPP modeling framework combines an IHCP that is optimized by in-situ thermal monitoring with a chemical reaction heat generation and conduction model that is educated by Photo-DSC characterization. The model predictions of temperature and DoC are experimentally validated by comparing against in-situ temperature measurement and ex-situ spectroscopy measurement of prints at different exposure times.

Laser-beam powder bed fusion (PBF-LB) technique was used to produce an Al–2.5 %Fe–2 %Cu ternary alloy, featuring a two-phase eutectic composition of α-Al/Al₂₃CuFe₄ in non-equilibrium solidification, as determined by thermodynamic calculations. The specimen manufactured by PBF-LB exhibited a high tensile strength exceeding 350 MPa and a low thermal conductivity of approximately 140 W m⁻¹ K⁻¹. Subsequent annealing at 300 °C improved the thermal conductivity to 175 W m⁻¹ K⁻¹ without compromising the strength. This improvement was attributable to forming numerous Al₂₃CuFe₄ nanoprecipitates, which consumed solute elements. By appropriately managing the factors contributing to strengthening, a superior strength–conductivity balance can be achieved by implementing post-heat treatments.

Additive manufacturing build parameters are used to engineer structural metamaterials lattices with controllable mechanical performance, achieved through microstructural grading of 17-4PH steel without compositional or geometric modification. The high solidification rates of laser powder-bed fusion suppress the thermal martensitic transformation and lead to elevated levels of retained austenite. Diamond cubic lattices built at low energy density (low thermal strain) retain a low martensite phase fraction (3 wt%) and exhibit a bend-dominated compression response. Lattices built at high energy density experience increased thermal strain during the build, causing in-situ deformation-driven transformation, yielding 44 wt% martensite; these exhibit a stretch-dominated compression response. Metamaterial lattices, with high and low energy density parameters in different configurations, exhibit mixed compression responses. Controllable mechanical response was achieved through control of microstructure, using build parameters to adjust thermal strain and selectively suppress or trigger the martensitic phase transformation in-situ.

A wide range of additive manufacturing (AM) processing conditions can be rapidly realized within a single specimen via high-speed direct energy deposition laser based (DED-LB), due to a variety of cooling conditions and in-situ powder mixing. Since existing approaches are inefficient in exploring the vast material and process design space in AM, high-speed DED-LB can be employed as a novel technology for high-throughput alloy design tool. However, an evaluation of the process transferability of the high-speed DED-LB process with respect to the currently dominating metal AM technologies, namely laser powder bed fusion (PBF LB/M) and conventional DED-LB, is required. In this study, high-speed DED-LB is applied for the high-throughput sample production, using the nickel alloy IN718 as reference material as well as the AM processes PBF LB/M and DED-LB as reference processes. The resulting microstructures are characterized and compared using optical microscopy and large-area scanning electron microscopy (SEM) analysis combined with energy-dispersive X-ray spectroscopy (EDS). Furthermore, a model for calculation of the volumetric energy density is developed to compare the applied AM processes. The significant influence of the processing conditions on the solidification behavior of the investigated material allows for efficient exploration of the microstructure and phase composition. Specific high-speed DED-LB-process conditions achieved the average solidification cell size and laves phase content as observed in the PBF LB/M- and DED-LB -produced counterparts. The applicability of the high-speed DED-LB process for rapid alloy and process development, i.e., process transferability, is critically evaluated. The results show that high-speed DED-LB can be used to emulate cooling conditions of PBF-LB/M and DED-LB and, therefore, be used as tool for rapid alloy development.

Material extrusion additive manufacturing of thermoplastics is so advanced due to the tunable rheological properties and hence a suitable printability, which is deficient for metals. Even though semi-solid modification and binder indirect modification are used to realize metal extrusion printing, the uncontrollable flow behavior and the metallurgical defects make it challenging to bridge this gap. In this study, mixed powder remelting and printability assessment were first proposed for producing metallic slurry with pre-designed microstructure and suitable printability without adding fillers or polymer carriers. Specifically, the hypoeutectic Sn-Bi metallic slurry was obtained by remelting the mixed powder composed of SnBi58 powder and pure Sn powder. The microstructural characteristics at different temperatures were investigated, demonstrating the ability of microstructure predesign. Furthermore, the printability, including stability, extrudability, and buildability, was evaluated by an advanced rheometer. The combined slurry preparation and printability assessment provides a reliable method for parameters improvement to obtain the structural fidelity.

In this work, a novel Metal Additive Manufacturing using Powder sheets (MAPS) method for printing multi-material composites in one process is proposed. MAPS employs powder sheets (i.e. metal powder-polymer matrix flexible films) as the feedstock material. Its key advantages include a relatively rapid change from one material to another and a minimum wastage of materials due to the elimination of the powder bed. The powder sheets were fabricated using a ‘solvent casting’ method. They were then employed in a commercialised metal printer for printing metal multi-material composites. To prove the disruptive concept of MAPS, a 60-layer trimetallic multi-material composite (304 L stainless steel, In718 and CoCrFeMnNi high entropy alloy) was additively manufactured using three different types of powder sheet material in the same manufacturing system for the first time. Experimental results indicate a high density (99.80 %) multi-material composites was printed by MAPS. EDX and SEM observations of the multi-material composites revealed variations of chemical composition and microstructure along the build direction. The newly proposed MAPS manufacturing method and results of this study provide insights into a new avenue for multi-material metallic parts.

Transition to circular economy requires the production of sustainable and eco-designed materials that help to reduce environmental impacts of metallic components. The development of sensing layers providing luminescent tracking functionalities is a potential method for extending the service life of metallic parts. In this study, incorporation of luminescent Ce³⁺ doped yttrium aluminum garnet (YAG:Ce) within a stainless steel 316L (SS316L) matrix has been achieved for the first time by laser powder bed fusion (L-PBF). Embedding of phosphor particles was successfully carried out on a selected area of the 3D printed sample. Despite harsh processing conditions of L-PBF, luminescent emission was detected by optical spectroscopy. Microstructure and chemical composition of the incorporation zone were investigated in order to better understand optical properties. The precipitated particles exhibit new optical features, arising from the modification of the luminescent host lattice and the intricate interactions with the metal matrix.

Drop-on-Demand additive manufacturing could offer a facile solution for scalable on-site manufacturing. With an increasing number of functional materials available for this technology, there are growing opportunities for applications, such as electronics. Here we report on a novel printing strategy, Off-the-Grid (OtG), which enables refined positioning of individual droplets and enhanced resolution compared to the traditional printing strategy. We demonstrate successful printing of structures with feature position control smaller than a single droplet size, and hence enhanced shape fidelity for intricate designs. This strategy is extended to filled patterns, enabling improved layer coverage and customisable inter-layer droplet positioning to control surface morphology. The OtG strategy is applied to produce functional designs, such as conformable circuitry and miniaturized antennae, and is transferable to different materials, from metal nanoparticle and polymeric inks on inkjet platforms, to molten metals on a MetalJet printer. These results could advance exploitation of AM in electronics, wearable electronics, medical devices, and metamaterials.

Solid-state additive manufacturing (AM) via friction stir based processes is gaining increased attention as these techniques are feasible for several similar and dissimilar material combinations and induce significantly lower energy input to the subjacent structure than fusion-based approaches as material melting is avoided. Available research concentrates on linear depositions; however, further development of these techniques towards application necessitates more complex deposition paths, e.g. curves and the crossing of edges of previously deposited layers. In this study, the solid-state layer deposition process of friction surfacing (FS) is investigated in terms of process behavior and appearance of the resulting deposit when curved deposition paths are applied. With advancing side on the curve's inner edge, material build-up occurs predominantly on this side of the layer, which results in a deposit of inhomogeneous thickness. This phenomenon is related to the FS process characteristic due to the superposition of rotational and travel movement on a curvature, and is more pronounced for curves with small radii. A further challenge exists for closed structures, where the deposition has to cross previously deposited layers. This can be successfully achieved by reducing the travel speed prior to passing the edge to provide sufficient plasticized material thickness below the stud tip. Overall, the study provides an understanding of the FS process behavior and process parameters for curved paths. Furthermore, recommendations for process control and path planning, e.g. for building closed cylindrical shell structures, are deduced.