456 research outputs found

    Microstructural, texture, plastic anisotropy and superplasticity development of ZK60 alloy during equal channel angular extrusion processing

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    In this study, equal channel angular pressing (ECAP) was exploited to refine the grain size of a ZK60 magnesium alloy in multi-processing steps, namely at temperatures of 250˚C, 200˚C and 150˚C, producing an ultrafine-grained (UFG) structure. The microstructural development and texture evolution during ECAP were systemically investigated by electron backscattered diffraction (EBSD) analysis. The microstructure of the ECAP processed alloy was remarkably refined to an average grain size of 600 nm. During ECAP process the original fiber texture of the as-extruded alloy was gradually weakened and eventually replaced by a stronger texture component coinciding with ECAP shear plane. The ECAP processed material showed a proper balance of tensile as well as compression strength and tensile ductility at room temperature. Yield strength of 273 and 253 MPa in tension and compression, respectively, ultimate tensile strength of 298 MPa and fracture elongation of about 30% were obtained in the UFG alloy. A transition from ductile–brittle to ductile fracture consisting of very fine and equiaxed dimples was also found in the ECAP processed material. Compared to the as-received alloy, a combination of grain refinement and texture development in the UFG alloy gave rise to a notable reduction in mechanical asymmetric behavior at room temperature. The superplastic behavior of the as-extruded and ECAP processed alloy was also investigated at 200˚C with strain rate of 1.0×10-3 s-1. The concurrent effect of grain boundary sliding and favorable basal texture in the UFG alloy led to an achievement of elongation value of about 300% while, under similar testing conditions, the elongation of about 140% was obtained in the as-extruded alloy

    Hydrogen Embrittlement Behavior of 18Ni 300 Maraging Steel Produced by Selective Laser Melting

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    A study was performed to investigate the hydrogen embrittlement behavior of 18-Ni 300 maraging steel produced by selective laser melting and subjected to different heat treatment strategies. Hydrogen was pre-charged into the tensile samples by an electro-chemical method at the constant current density of 1 A m(-2) and 50 A m(-2) for 48 h at room temperature. Charged and uncharged specimens were subjected to tensile tests and the hydrogen concentration was eventually analysed using quadrupole mass spectroscopy. After tensile tests, uncharged maraging samples showed fracture surfaces with dimples. Conversely, in H-charged alloys, quasi-cleavage mode fractures occurred. A lower concentration of trapped hydrogen atoms and higher elongation at fracture were measured in the H-charged samples that were subjected to solution treatment prior to hydrogen charging, compared to the as-built counterparts. Isothermal aging treatment performed at 460 degrees C for 8 h before hydrogen charging increased the concentration of trapped hydrogen, giving rise to higher hydrogen embrittlement susceptibility.11Ysciescopu

    Design of additively manufactured moulds for expanded polymers

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    The traditional tools used in steam-chest moulding technologies for the shaping of expanded polymers can be replaced today by lighter moulds, accurately designed and produced exploiting the additive manufacturing technology. New paradigms have to be considered for mould design, assuming that additive manufacturing enables the definition of different architectures that are able to improve the performance of the moulding process. This work describes the strategies adopted for the design and manufacturing by Laser powder bed fusion of the moulds, taking into specific consideration their functional surfaces, which rule the heat transfer to the moulded material, hence the quality of the products and the overall performance of the steamchest process. The description of a case study and the comparison between the performance of the traditional solution and the new moulds are also presented to demonstrate the effectiveness of the new approach. This study demonstrates that the redesign and optimization of the mould shape can lead to a significant reduction of the energy demand of the process, thanks to a homogeneous delivery of the heating steam throughout the part volume, which also results in a remarkable cutting of the cycle time

    Binder jetting additive manufacturing of biodegradable Zn

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    Biodegradable materials avoid second surgeries and long-term associated risks of conventional inert implants. Zn arose as a potential candidate for bioresorbable implants due to its proper degradation behaviour and biocompatibility [1]. However, its low melting point induces uncontrolled porosity in LPBF, promoting the future cracking of the implant. Therefore, new fabrication techniques need to be explored. In this work, binder jetting 3d printing (BJ3P) was studied for Zn powders. The samples were printed and sintered under different conditions. It is concluded that, the increase the temperature almost up to melting point leads to higher densification, at the same time, the rise of temperature provokes the formation and growth of oxidized layer on the surface of the powders

    Effect of Dilution on Microstructure and Wear Resistance of a Fe-Based Hardfacing Alloy with a High Amount of Carbide-Forming Elements

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    Hardfacing is a widely diffused technique adopted to increase service life of parts for heavy-duty applications. Even though hardfacing alloys feature optimized chemistry and microstructure for specific service conditions, dilution with substrate modifies the resulting properties along a significant fraction of the deposit thickness. In particular, C and B diffusion to the substrate alters hypereutectic alloys reducing the carbide-forming ability andmodifying the solidification sequence. In the present paper, the effect of dilution on a hypereutectic Fe-C-B based alloy containing Cr and Mo was investigated. The effect of dilution on the reference alloy was studied by producing laboratory castings with an increased amount of Fe, up to 50 mass %. The obtained results were compared with the dilution of the hardfacing alloy cast on steel substrates. The microstructural evolution was analyzed by XRD (X-ray diffraction), differential scanning calorimetry (DSC), optical microscopy (OM), and scanning electron microscopy (SEM), whereas mechanical behaviour was evaluated by hardness measurements and wear resistance by pin-on-disc tests

    Tungsten Fabricated by Laser Powder Bed Fusion

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    AbstractAdditive Manufacturing (AM) is the process that allows the production of complex geometry and lightweight components. Thanks to the high density of refractory metals, AM could be a possible solution for their application in the aerospace field and for biomedical or future nuclear fusion devices. Yet, Laser Powder Bed Fusion (LPBF) of refractory metals as Ta, Mo, and W faces some challenges due to their main properties: high melting point, heat conductivity, and susceptibility to cracks.The purpose of this study is to optimize the process parameters in order to produce high-density Tungsten parts by LPBF on an EOS M100 (maximum power of 170 W). The characterization is performed through physical properties measurements and microstructural analysis. Single Scan Tracks (SSTs) are produced on the top surfaces of Tungsten blocks to evaluate the process parameters that give regular-shape and continuous melt-pools. Both analytical and experimental optimizations of process parameters were performed. Micro-hardness measurements were done for dense bulk specimens. Finally, a description of susceptibility to cracks of additively manufactured Tungsten was performed

    On the preparation and characterization of thin NiTi shape memory alloy wires for MEMS

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    Shape memory alloy (SMA) wires are employed as actuators in small devices for consumer electronics, valves and automotive applications. Because of the continued miniaturization of all the industrial products, nowadays the tendency is to produce MEMS (micro electromechanical systems). Among the most promising functional MEMS materials, the thin SMA wires that are offering a rapid actuating response with high power/weigh ratio of the material, are attracting a world wide interest. This paper is aimed at showing the production process and the characterizations of thin NiTi shape memory wires. The activity was focused on drawing procedure and on functional and TEM characterizations of the final products. In particular, it was evaluated the performance of the SMA wires for actuators in terms of functional fatigue and thermo-mechanical properties by means of an experimental apparatus design ad hoc for these specific test

    On the preparation and characterization of thin NiTi shape memory alloy wires for MEMS

    Get PDF
    Shape memory alloy (SMA) wires are employed as actuators in small devices for consumerelectronics, valves and automotive applications. Because of the continued miniaturization of all the industrialproducts, nowadays the tendency is to produce MEMS (micro electromechanical systems). Among the mostpromising functional MEMS materials, the thin SMA wires that are offering a rapid actuating response withhigh power/weigh ratio of the material, are attracting a world wide interest. This paper is aimed at showing theproduction process and the characterizations of thin NiTi shape memory wires. The activity was focused ondrawing procedure and on functional and TEM characterizations of the final products. In particular, it wasevaluated the performance of the SMA wires for actuators in terms of functional fatigue and thermo-mechanicalproperties by means of an experimental apparatus design ad hoc for these specific test
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