Continuous carbon fiber reinforced poly‐ether–ether–ketone (CCF/PEEK) shows great potential in engineering applications attributed to superior mechanical properties together with excellent thermal ...and chemical resistance. In this study, a laser‐assisted additive manufacturing device was established to accurately collect and control the preheating temperature based on a coaxial infrared temperature measurement system. The influence on laser power consumption, interlaminar shear performance, and failure mechanism was investigated in condition of different preheating temperatures and printing speeds. Results indicated that the laser‐preheated specimens showed much higher ILSS with maximum values and increasing percentage reached 33.48 MPa and 157.0% compared to unpretreated specimens. With the increase of preheating temperature and printing speed, more laser power was consumed, while the ILSS and increasing percentage increased firstly and then decreased. The strengthening effect on the interlayer bonding was ascribed to promoting the penetration of PEEK molecular chain ends between adjacent layers, increasing the fluidity and enhancing the bonding effect between adjacent filament together with improving the impregnation behavior of the inner fibers. The proposed interlaminar strengthening method based on laser‐assisted preheating provides potential application prospects in aerospace and automotive industries.
•A novel additive manufacturing technique using wire-arc thermal spray was used to fabricate a heat sink with complex internal geometry.•Density-based topology optimization was implemented to ...minimize temperature non-uniformity on a uniformly applied heat load.•A 21% reduction in maximum temperature and 59% reduction in temperature non-uniformity was observed compared to a parallel channel layout.•Thermal spray additive manufacturing and topology optimization are a promising approach to the fabrication of liquid-cooled heat sinks with complex internal geometries.
Water-cooled mini-channel heat sinks are widely used for thermal management of electronic devices, but their flow paths are usually limited to simple designs, such as parallel channels, due to manufacturing limitations. Such designs do not distribute flow uniformly, resulting in non-uniform heat transfer across the heat sink and significant temperature gradients. A liquid-cooled heat sink with a millimeter high flow channel was designed and fabricated to cool an 86 mm x 63 mm uniformly distributed heat load. A density-based topology optimization model was implemented in COMSOL to generate a non-traditional internal geometry that minimizes temperature non-uniformity. The topologically optimized heat sink was made using a novel thermal spray additive manufacturing method in which molten aluminum was sprayed into a cavity machined in an aluminum plate through a polymer mask made in the shape of the desired flow channels by 3D printing. The cavity was closed with an aluminum plate to create a sealed heat sink. The thermal performance of the topologically optimized heat sink was compared experimentally to that of a heat sink with parallel channels. Each heat sink was placed on a uniformly heated copper block dissipating 180 – 630 W (corresponding to heat fluxes of 3.3 – 11.6 W/cm2) and its temperature measured by an array of 9 thermocouples embedded in the heated heat sink face while water flowed through it at rates of 100–1500 mL/min. The optimized heat sink maintained lower surface temperatures and reduced temperature non-uniformity on its surface at all flow rates tested. Numerical simulations demonstrated that this was due to better flow distribution by the topologically optimized flow channels.
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•Implementation and exploitation of a novel anisotropic Voronoi algorithm.•Generation of microstructures with spatially varying grain growth directions.•An ellipsoidal growth field ...closely mimics underlying solidification proces.•Extraction of grains in a grain-conforming and non-grain-conforming manner.•Two demonstration cases show a pronounced correspondence to input data.
In this paper, a novel anisotropic Voronoi algorithm is presented, along with its implementation and two application cases. In contrast to standard Voronoi tessellations, the proposed algorithm takes into account preferred growth directions, aspect ratios and areas of individual grains. Therefore, an elliptical growth field, which is defined on a per grain basis, is adopted which specifies the time a single grain seed point needs to grow to a specific point in the domain of interest. Grains can be extracted in a grain-conforming or non-grain-conforming manner. The latter case is applicable to simulations in which a predetermined mesh is used, e.g. voxel-mesh based simulations. The extraction can then be done in a straightforward manner. For the former case, a more elaborate extraction algorithm is presented. Finally, the characteristics of the resulting microstructural geometries of two application cases (wire + arc additively manufactured and cast metal microstructure) are studied. A pronounced correspondence with the experimental grain morphology is obtained. This algorithm is highly versatile for generating polycrystalline (metal) microstructures, especially since it closely mimics the underlying solidification process. However, it is more generally applicable to generate an anisotropic tessellation with spatially varying preferential growth directions.
This study used underwater friction stir additive manufacturing (FSAM) to fabricate a multilayered Al–Zn–Mg–Cu aluminum alloy build. The relationship between the local microstructures and mechanical ...properties for the water-cooled build was established. Consequently, the underwater FSAM effectively reduced the thermal cycle effect on the former FSAM pass during the FSAM process. The common phenomenon of microhardness decrease from top to bottom in the air-cooled build was suppressed. However, after aging treatment, a low-hardness zone (LHZ) was observed in the bottom of the pin-driven zone + pin-driven zone (PDZ + PDZ). A high-hardness zone (HHZ) was located in the shoulder-driven zone + pin-driven zone (SDZ + PDZ). Furthermore, the tensile properties in the bottom of the PDZ + PDZ were inferior to those in the SDZ + PDZ. The microstructural results show that, compared to the SDZ + PDZ, the higher density of the T (AlZnMgCu) and η (MgZn2) phases precipitated in the bottom of the PDZ + PDZ, which was attributed to the finer grains and the higher density of subgrains and dislocations in this region. In addition, the peak temperature in the bottom of the PDZ + PDZ was in the range of the η-phase precipitation temperature, which also resulted in the increasing in the number of η phases. The high-density T- and η-phase precipitation in the bottom of the PDZ + PDZ implied a low-degree supersaturation, directly leading to the decrease of the aging-strengthening ability. In conclusion, low hardness and strength were observed in the bottom of the PDZ + PDZ after the aging treatment, whereas high hardness and strength were observed in the SDZ + PDZ because of the more efficient dissolution in this region.
Nickel-aluminum bronze (NAB) alloys are commonly used for marine applications such as propellers by the U.S. Navy. These NAB components are conventionally manufactured using casting techniques, but ...recent interest has shifted to the possibility of additive manufacturing (AM) processes. The following literature review discusses the microstructural evolution of (nominally) Cu-9Al-5Ni-5Fe-1Mn NAB alloys in the cast, wrought, friction stir processed, arc-welded, electron beam welded and laser-welded conditions. NAB alloys exhibit a complex microstructure, consisting of a mixture of five κ precipitates distributed in an α or β’ martensitic matrix. The size, morphology, and distribution of these phases are sensitive to changes in cooling rate and thermal history such as those imposed by AM and welding. Although the microstructure is well documented under casting conditions, no continuous cooling diagrams have been developed to describe phase transformations under arc and laser processing conditions for NAB. As such, this review investigates recent reports related to arc, electron beam and laser-based additive manufacturing processes and the associated microstructures and properties. Studies have reported additively manufactured NAB alloys with improved properties compared to cast material, associated with differences in microstructure. At moderate cooling rates, such as those associated with arc-based processing, the microstructure consists of Widmanstätten α and various κ phases, which become more refined with increasing cooling rate. This leads to an improvement in the tensile properties of wire-arc direct energy deposited NAB, with > 17% increase in yield strength and > 90% increase in ductility when compared to cast material. At rapid cooling rates representative of laser-based and electron beam processing, the microstructure consists primarily of a twin-related β’ martensite with nanoscale κ phases. This leads to a significant increase in yield strength (>60–100%) at the expense of ductility (<−30%) when compared to cast material. Additionally, previous studies have reported that the refined microstructure from these high cooling rate processes leads to an improvement in the corrosion resistance of as deposited NAB. There is also evidence that the conventional heat treatments for cast NAB alloys need to be optimized for additively manufactured materials. The report includes the methods and challenges associated with characterizing NAB alloys under these processing conditions and provides recommendations for future research.
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Additive manufacturing (AM), also known as additive manufacturing, permits the fabrication of fully customized objects with a high level of geometrical complexity at reduced ...fabrication time and cost. Besides metals and ceramics, polymers have become a widely researched class of materials for applications in AM. The synthetic versatility and adaptability, as well as the wide range of properties that can be achieved using polymer materials, have rendered polymers the most widely employed class of materials for AM methodologies. In this review, the basic principles, considering the printing mechanism as well as the advantages and disadvantages, of the most relevant polymer AM technologies are described. The particular features, properties and limitations of currently employed polymer systems in the various AM technology areas are presented and analyzed. Subsequently, 4D printing, that is the fabrication of 3D printed structures that are cabable to change with time, is discussed. A brief description of the polymeric materials and technologies under development for 4D printed structures as well as the different shape changes explored are presented. Finally, based on the characteristics of the polymers employed for each technology illustrative examples of the principal applications are discussed.
•The TC25G/Ti2AlNb gradient material was fabricated by LDED.•The microstructure evolution for the material was systematically investigated.•The microstructure and composition transition is smooth in ...the transition zone.•The microhardness has no sudden change in the transition zone.
Laser directed energy deposition (LDED) is one of the most effective ways to manufacture structural gradient materials. The microstructure changes in transition zone (TZ) and heat-affected zone (HAZ) are often considered to be very important which could affect the mechanical property of the component. In this study, a titanium based gradient material, which is potentially used in high pressure compressor was fabricated by deposition of Ti2AlNb alloy on a forged TC25G alloy substrate. The thickness of the transition zone is around 2000 μm, and the phase transformation from TC25G alloy to Ti2AlNb alloy is followed as: α + β (TC25G alloy) → α + β (Heat affected zone) → α + α2 + B2/β + O (Transition zone) → α2 + B2/β + O (Ti2AlNb alloy). There is no any sudden change of microhardness in the gradient material with the lowest microhardness is found in Ti2AlNb alloy.
Functionally Graded Porous Scaffold (FGPS) becomes an attractive candidate for bone graft due to its combination of better mechanical and biological requirements with the scaffold gradient to better ...mimic host tissue. This paper focuses on the graded change requirements of bio-porous scaffolds in terms of physical and mechanical properties. Gradients in three patterns (density, heterostructure and cell-size gradients) with Gyroid and Diamond unit cells were proposed based on Triply Periodic Minimal Surfaces (TPMS), and fabricated by Selective Laser Melting (SLM) using Ti-6Al-4V. Among them, cell-size gradient was described for the first time, realizing a variation of graded pore size on a specific way. Morphological properties of porous samples were characterized by micro-CT and SEM, followed by compressive tests for determining their mechanical behaviors. It was found that the TPMS method is an effective way to achieve gradients in multiple patterns which are comparable to natural tissue with respect to both continuous topology and interconnectivity. The porous surface area and pore size, could be controlled by the cell-size gradient without relatively density alteration, stabilizing the modulus and strength within 11% and 20%, respectively. Both Gyroid and Diamond structures possess a superior strength (152.6 MPa, 145.7 MPa) and comparable elastic modulus (3.8GPa) with natural cortical bone.
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•Cell-size gradient porous scaffold was designed based on triply periodic minimal surfaces (TPMS).•Cell-size gradient can adjust surface area and pore size of scaffolds without relative density alteration.•TPMS is a feasible way to achieve gradient scaffolds in multiple patterns with continuous topology and interconnectivity.•The studied scaffolds of TC4 have a superior strength and comparable elastic modulus with cortical bone.
Mechanical and thermal processing of wire-arc additively deposited stainless steel is investigated with the purpose of improving its microstructure, surface morphology, formability, and stress ...response. Microscopy helps identifying the processing conditions that permit full recrystallization of the as-built columnar microstructure. Combination with strain loading paths, topography and fractography in tensile tests show that mechanical processing consisting of 20 % thickness reduction followed by annealing at 1100 °C under 4 h eliminates anisotropy and increases the fracture forming limits by 30 %. The work is a step forward to consolidate the hybridization of wire-arc additive manufacturing with metal forming as an alternative to conventional manufacturing.
Duplex stainless steels (DSS) are defined by their equal phase composition of ferrite and austenite. However, the in-situ formation of this duplex microstructure in laser-based additive manufacturing ...(AM) is still a challenging topic. Nanoparticle addition is a promising approach to tailor the microstructure of steels in AM. Therefore, DSS doped with 0.5 wt.-% NiO nanoparticles was fabricated by laser-based powder bed fusion (PBF-LB) and directed energy deposition (DED-LB). While having no impact on the phase composition in PBF-LB, the addition of NiO nanoparticles showed a significant increase in austenite content of 9% compared to the unmodified powder in DED-LB.
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