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1.
    
The nature of amorphous ices has been debated for more than 35 years. In essence, the question is whether they are related to ice polymorphs or to liquids. The fact that amorphous ices are traditionally prepared from crystalline ice via pressure-induced amorphization has made a clear distinction tricky. In this work, we vitrify liquid droplets through cooling at ≥106 K ⋅ s−1 and pressurize the glassy deposit. We observe a first order–like densification upon pressurization and recover a high-density glass. The two glasses resemble low- and high-density amorphous ice in terms of both structure and thermal properties. Vitrified water shows all features that have been reported for amorphous ices made from crystalline ice. The only difference is that the hyperquenched and pressurized deposit shows slightly different crystallization kinetics to ice I upon heating at ambient pressure. This implies a thermodynamically continuous connection of amorphous ices with liquids, not crystals.  相似文献   

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3.
    
The paper presents a CNC component manufacturing process using the WAAM process. The study depicts all the execution steps of a component from the CAD drawing, deposition procedure (technological parameters, times, layers, etc.), examination, and economic calculation. The manufacturing of this component using WAAM is more advantageous given the fact that the execution time and delivery are significantly shorter, mainly when a single piece is required and also when discussing the raw material used, usually expensive titanium alloys. For example, for Ti-6AI-V used in the aircraft industry, for which the material price is about 90 Euro/kg, the costs for obtaining a given component using the WAAM process will be about 497 Euro/piece compared to 1657 Euro/piece when using another manufacturing process, as it is shown in this paper. In conclusion, additive manufacturing can easily become a feasible solution for several industrial applications when it replaces a classic manufacturing process of a single component or replacement products, even simple-shaped.  相似文献   

4.
    
Atomic Diffusion Additive Manufacturing (ADAM) is an innovative Additive Manufacturing process that allows the manufacture of complex parts in metallic material, such as copper among others, which provides new opportunities in Rapid Tooling. This work presents the development of a copper electrode manufactured with ADAM technology for Electrical Discharge Machining (EDM) and its performance compared to a conventional electrolytic copper. Density, electrical conductivity and energy-dispersive X-ray spectroscopy were performed for an initial analysis of both ADAM and electrolytic electrodes. Previously designed EDM experiments and optimizations using genetic algorithms were carried out to establish a comparative framework for both electrodes. Subsequently, the final EDM tests were carried out to evaluate the electrode wear rate, the roughness of the workpiece and the rate of material removal for both electrodes. The EDM results show that ADAM technology enables the manufacturing of functional EDM electrodes with similar material removal rates and rough workpiece finishes to conventional electrodes, but with greater electrode wear, mainly due to internal porosity, voids and other defects observed with field emission scanning electron microscopy.  相似文献   

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6.
    
Screen-additive manufacturing (SAM) is a potential method for producing small intricate parts without waste generation, offering minimal production cost. A wide range of materials, including gels, can be shaped using this method. A gel material is composed of a three-dimensional cross-linked polymer or colloidal network immersed in a fluid, known as hydrogel when its main constituent fluid is water. Hydrogels are capable of absorbing and retaining large amounts of water. Cellulose gel is among the materials that can form hydrogels and, as shown in this work, has the required properties to be directly SAM, including shear thinning and formation of post-shearing gel structure. In this study, we present the developed method of SAM for the fabrication of complex-shaped cellulose gel and examine whether successive printing layers can be completed without delamination. In addition, we evaluated cellulose SAM without the need for support material. Design of Experiments (DoE) was applied to optimize the SAM settings for printing the novel cellulose-based gel structure. The optimum print settings were then used to print a periodic structure with micro features and without the need for support material.  相似文献   

7.
    
Direct energy deposition is gaining much visibility in research as one of the most adaptable additive manufacturing technologies for industry due to its ease of application and high deposition rates. The possibility of combining these materials to obtain parts with variable mechanical properties is an important task to be studied. The combination of two types of steel, mild steel ER70-6 and stainless steel SS 316L, for the fabrication of a wall by direct energy deposition was studied for this paper. The separate fabrication of these two materials was studied for the microstructurally flawless fabrication of bimetallic walls. As a result of the application of superimposed and overlapped strategies, two walls were fabricated and the microstructure, mechanical properties and hardness of the resulting walls are analyzed. The walls obtained with both strategies present dissimilar regions; the hardness where the most present material is ER70-6 is around 380 HV, and for SS 316L, it is around 180 HV. The average values of ultimate tensile strength (UTS) are 869 and 628 MPa, yield strength (YS) are 584 and 389 MPa and elongation at break are 20% and 36%, respectively, in the cases where we have more ER70-6 in the sample than SS 316L. This indicates an important relationship between the distribution of the materials and their mechanical behavior.  相似文献   

8.
    
Additive manufacturing (AM) has the advantages of reducing material usage and geometrical complexity compared to subtractive manufacturing. Wire arc additive manufacturing (WAAM) is an additive manufacturing process that can be used to rapidly manufacture medium-and large-sized products. This study deals with the path-planning strategy in WAAM, which can affect the quality of deposited components. It aims at suggesting effective path planning to reduce the height error of intersection parts. A comparative analysis of the bead width and height at the intersection parts was performed to verify the effectiveness of the proposed path. The initial parameters were determined through single-layer deposition experiments, and multi-layer deposition experiments were performed. The resultant height error in the intersection part was 0.8%, while that in the non-intersection part was absent at the maximum height. Path planning is considered to be an effective method.  相似文献   

9.
    
Additive manufacturing, especially material extrusion (MEX), has received a lot of attention recently. The reasons for this are the numerous advantages compared to conventional manufacturing processes, which result in various new possibilities for product development and -design. By applying material layer by layer, parts with complex, load-path optimized geometries can be manufactured at neutral costs. To expand the application fields of MEX, high-strength and simultaneously lightweight materials are required which fulfill the requirements of highly resilient technical parts. For instance, the embedding of continuous carbon and flax fibers in a polymer matrix offers great potential for this. To achieve the highest possible variability with regard to the material combinations while ensuring simple and economical production, the fiber–matrix bonding should be carried out in one process step together with the actual parts manufacture. This paper deals with the adaptation and improvement of the 3D printer on the one hand and the characterization of 3D printed test specimens based on carbon and flax fibers on the other hand. For this purpose, the print head development for in-situ processing of contin uous fiber-reinforced parts with improved mechanical properties is described. It was determined that compared to neat polylactic acid (PLA), the continuous fiber-reinforced test specimens achieve up to 430% higher tensile strength and 890% higher tensile modulus for the carbon fiber reinforcement and an increase of up to 325% in tensile strength and 570% in tensile modulus for the flax fibers. Similar improvements in performance were achieved in the bending tests.  相似文献   

10.
Knowledge of pressure-induced structural changes in glasses is important in various scientific fields as well as in engineering and industry. However, polyamorphism in glasses under high pressure remains poorly understood because of experimental challenges. Here we report new experimental findings of ultrahigh-pressure polyamorphism in GeO2 glass, investigated using a newly developed double-stage large-volume cell. The Ge–O coordination number (CN) is found to remain constant at ∼6 between 22.6 and 37.9 GPa. At higher pressures, CN begins to increase rapidly and reaches 7.4 at 91.7 GPa. This transformation begins when the oxygen-packing fraction in GeO2 glass is close to the maximal dense-packing state (the Kepler conjecture = ∼0.74), which provides new insights into structural changes in network-forming glasses and liquids with CN higher than 6 at ultrahigh-pressure conditions.Understanding the structural response of network-forming glasses to pressure is of great interest not only in condensed matter physics, geoscience, and materials science, but also in engineering and industry. As prototype network-forming glasses, silica (SiO2) and germania (GeO2) have been the most extensively studied (1–5). These two glasses have similar structural change pathways at high pressures. At ambient pressure, both glasses are composed of corner-linked AO4 tetrahedra, with atom A (Si or Ge) in fourfold coordination (6). Under compression, the coordination gradually changes from 4 to 6 over a wide pressure range [∼15–40 GPa for SiO2 glass (2, 4) and ∼5–15 GPa for GeO2 glass (1, 3, 5)].A recent study (7) found that evolution of network-forming structural motifs in glasses and liquids at high pressures can be rationalized in terms of oxygen-packing fraction (OPF). Fourfold-coordinated structural motifs in SiO2 and GeO2 glasses are stable over a wide range of OPF between 0.40 and ∼0.59. The fourfold-coordinated structural motifs become unstable when the OPF approaches the limit of random loose packing of hard spheres (0.55–0.60) (8, 9). When OPF >∼0.60, coordination number (CN) gradually increases with OPF to the limit of random close packing (0.64) (8, 9), where CN increases sharply to 6 with almost-constant OPF ∼0.64. Higher-pressure data for SiO2 glass suggest the existence of another stability plateau for sixfold-coordinated structural motifs, with OPF of up to ∼0.72 (7).The highest coordination that has been experimentally determined so far in SiO2 and GeO2 glasses is 6. X-ray diffraction measurement for SiO2 glass confirmed that sixfold-coordination structural motifs are stable up to 100 GPa (4). For GeO2 glass, X-ray and neutron diffraction data are limited to 18 GPa (1, 3, 5). X-ray absorption spectroscopic measurements were conducted to 64 GPa (10, 11). Ref. 11 showed no major change in X-ray absorption fine structure up to 64 GPa, although a slight discontinuous change in density is observed around 40–45 GPa.Some simulation studies predicted the existence of structural motifs with CN >6 above ∼100 GPa for SiO2 liquid (12) and glass (13) and above ∼60 GPa for GeO2 glass (13), with no experimental confirmation so far. A study (14) of SiO2 glass using Brillouin scattering in a diamond anvil cell (DAC) showed a kink in the pressure dependence of shear-wave velocity at ∼140 GPa and was interpreted as evidence of ultrahigh-pressure polyamorphism in SiO2. However, no structural information is available under such high pressures. In this study, we developed a new double-stage cell, which enables us to study structure of GeO2 glass at in situ high-pressure conditions up to 91.7 GPa.Large-volume samples are vital for accurate measurements on the structure of glasses at high pressures using X-ray diffraction because of the weak X-ray scattering from amorphous materials. In such measurements, a large diffraction angle is essential for accurately determining the structure factor with sufficiently large coverage of momentum transfer Q (Q = 4πEsinθ/12.398, where E is X-ray energy in keV and θ is the diffraction angle), and for high resolution in the reduced pair distribution function in real space. Recently, generation of pressure up to 94 GPa has been achieved in a DAC with 1-mm culet size anvils (15). However, this large-volume DAC is designed for neutron diffraction measurement; it is difficult to apply this apparatus for X-ray diffraction measurement because of limited solid-angle access. Similarly, there have been attempts to generate high pressures by inserting diamond anvils inside multianvil large-volume presses (16, 17). However, multianvil presses generally have even more limited solid-angle access for X-ray diffraction signals.We have developed a new double-stage Paris–Edinburgh (PE)-type large-volume press to generate high pressures with large sample volume (Fig. 1A). A pair of second-stage diamond anvils is introduced into the first-stage PE anvils. This combination of opposed anvils (both first- and second stage) provides a large opening in the horizontal plane for X-ray diffraction measurement. To reduce absorption of the gasket surrounding the sample, we used a cubic boron nitride + epoxy (10:1 in weight ratio) inner gasket with an aluminum alloy (7075) outer gasket, both of which are low X-ray absorbing, light-element materials. The diamond anvils had a culet diameter of 0.8 mm. The large culet size allowed us to use large samples 0.3 mm in diameter and 0.15 mm in height. In our study on structure of GeO2 glass, this new double-stage cell has reached pressures up to 91.7 GPa (Fig. 1B), where sample size was ∼0.24 mm in diameter and ∼0.06 mm in height, as determined by in situ X-ray radiography imaging (Fig. 1C).Open in a separate windowFig. 1.Newly developed double-stage large-volume cell. (A) Illustration of double-stage large-volume cell design. We use cup-shaped PE-type anvil as the first-stage anvil, and the second-stage diamond anvil is introduced inside the large-volume cell assembly. (B) Pressure generation as a function of oil load of the PE press. Solid symbols represent pressure conditions of structure measurement of GeO2 glass measured before and after structural measurement. Oil pressure was found to decrease slightly after each measurement, whereas sample pressure increased slightly. Error of pressure is smaller than the size of the symbol. (C) X-ray radiography image of the GeO2 glass sample and Au pressure standard through gasket at 91.7 GPa.Structure of GeO2 glass was investigated using the newly designed double-stage PE press with multiangle energy dispersive X-ray diffraction technique at Beamline 16-BM-B, High Pressure Collaborative Access Team (HPCAT) of the Advanced Photon Source (18). Structure factors, S(Q), were obtained up to 13 Å−1 (Fig. 2). The position of the first sharp diffraction peak (FSDP) in S(Q) shows essentially no pressure dependence between 22.6 and 37.9 GPa. Previous studies (3, 19) show that below ∼10 GPa, FSDP moves rapidly with increasing pressure toward higher Q values; above 10 GPa, the position becomes virtually pressure independent. This is consistent with our observation that the FSDP shifts rapidly from 0 to 22.6 GPa, and then remains almost constant between 22.6 and 37.9 GPa (Fig. 2). Interestingly, with further increase of pressure to 72.5 GPa, the FSDP begins shifting again toward higher Q and then becomes virtually constant once more between 72.5 and 91.7 GPa. Furthermore, a new peak at Q ∼ 7.1–7.3 Å-1 begins to emerge at a pressure between 22.6 and 37.9 GPa, with increasing intensity at higher pressures.Open in a separate windowFig. 2.Structure factor, S(Q), of GeO2 glass up to 91.7 GPa. S(Q) was determined at the Q range up to 13 Å-1. S(Q) at high pressure is displayed by a vertical offset of 0.4, with varying pressure, and S(Q) at ambient pressure is displayed by a vertical offset of −2. The dotted line is plotted at the first peak position at 22.6 GPa to guide the eyes. The first peak position is almost the same at 22.6 and 37.9 GPa, whereas it shifts to high Q at 49.4–72.5 GPa.Fourier transformation of S(Q) yields real-space pair distribution function (20), G(r) (Fig. 3). The first and second peak of G(r) in GeO2 glass is generally considered to represent Ge–O and Ge–Ge distance, respectively. Significant changes in peak shape and positions in G(r), particularly in the second peak, are evident. G(r) obtained at 22.6 and 37.9 GPa show a distinct shoulder at the lower “r” side of the second peak. This shoulder has been observed in previous studies (1, 3, 5) at pressures higher than ∼15 GPa. This double-peak feature is considered to represent two Ge–Ge distances in the sixfold-coordinated GeO2 structure. In contrast, we find that the second peak starts to become a single peak above 49.4 GPa. The second peak width markedly decreases between 37.9 and 49.4 GPa, although the second peak in G(r) at 49.4 and 61.4 GPa still shows a weak shoulder at the low-r side. The second peak becomes a single peak above 72.5 GPa.Open in a separate windowFig. 3.Pair distribution function, G(r), of GeO2 glass up to 91.7 GPa. G(r) at high pressures are displayed by additional vertical offset of 0.4, with varying pressure, and that at ambient pressure is displayed by an offset of −2.3. G(r) at 22.6 and 37.9 GPa show distinct two shoulders in the second peak, which is considered as an evidence of sixfold-coordinated GeO2 glass structure (1, 3, 5), whereas it gradually becomes a single peak above 49.4 GPa.Fig. 4 shows the pressure dependence of the first and second peak positions in G(r), with the numerical results summarized in Open in a separate windowFig. 4.The first and second peak position of G(r). (A) The first peak position of G(r) of GeO2 glass obtained in this study (solid red squares), compared with Ge–O bond distance of crystalline GeO2 with CaCl2-type structure (21) (open and solid blue diamonds) and pyrite-type structure (24) (open and solid blue squares). Blue cross symbols represent the median value of the two Ge–O bond distances in CaCl2-type GeO2. Error is smaller than the size of the symbol. (B) The second peak position of G(r) of GeO2 glass obtained in this study (red squares), compared with Ge–Ge bond distance of crystalline GeO2 with CaCl2-type structure (21) (open and solid blue diamonds) and pyrite-type structure (24) (solid blue square). Solid red squares represent the main second peak (r2) and open red squares represent shoulder peaks in the second peak at ∼2.7–2.8 Å (r2s) (
Pressure (GPa)r1, År2s, År2, ÅCN
0.01.738 ± 0.0013.177 ± 0.014.0 ± 0.2
22.6 ± 0.41.846 ± 0.0032.823 ± 0.023.209 ± 0.015.8 ± 0.2
37.9 ± 1.01.820 ± 0.0012.795 ± 0.023.245 ± 0.025.9 ± 0.2
49.4 ± 1.31.824 ± 0.0012.728 ± 0.023.149 ± 0.036.4 ± 0.2
61.4 ± 0.91.833 ± 0.0012.734 ± 0.033.130 ± 0.037.0 ± 0.2
72.5 ± 1.11.814 ± 0.0013.033 ± 0.127.0 ± 0.2
80.4 ± 0.31.813 ± 0.0013.011 ± 0.017.1 ± 0.2
91.7 ± 0.61.810 ± 0.0012.937 ± 0.067.4 ± 0.2
Open in a separate windowThe second peaks at 22.6–61.4 GPa are fitted by two peaks for shoulder peak at ∼2.7–2.8 Å (r2s) and main peak (r2).Our results reveal that a distinct change in the structure of GeO2 glass begins at a pressure between 37.9 and 49.4 GPa. Below 37.9 GPa, our structural data are similar to those obtained around 15–18 GPa in previous studies (1, 3, 5). Because the first and second peak positions of G(r) in GeO2 glass are considered to represent Ge–O and Ge–Ge distances, respectively, we compare the first and second peak positions of G(r) obtained in this study with Ge–O and Ge–Ge bond distances of crystalline GeO2 with sixfold-coordinated CaCl2-type structure (21) (Fig. 4). Previous studies argue that two distinct peaks in G(r) between 2.5 and 3.5 Å above ∼15 GPa are an indication of formation of sixfold-coordinated structural motifs (1, 3, 5). Our comparison also shows that the double-peak positions at 22.6 and 37.9 GPa are consistent with two Ge–Ge bond distances in CaCl2-type structured crystalline GeO2 (21) (Fig. 4B). In addition, the first peak position is similar to the median value of the two Ge–O distances of CaCl2-structured GeO2 (Fig. 4A). These observations strongly suggest that structure of GeO2 glass between 22.6 and 37.9 GPa is sixfold coordinated similar to CaCl2-type structured GeO2.At higher pressures, the double peak in G(r) merges into a single one above 49.4 GPa (Fig. 3). Crystalline GeO2 is known to transform to α-PbO2-type structure at 44 GPa (22) and to pyrite-type structure at pressures between 60 and 85.8 GPa (23). At 40 GPa, α-PbO2-type crystalline GeO2 is composed of three Ge–O bonds (1.772, 1.814, and 1.860 Å) and three Ge–Ge distances (2.817, 3.202, and 3.2658 Å) (24). The pyrite-type GeO2 is composed of rhombohedral polyhedra with a six-coordination structure plus two additional oxygens. At 70 GPa, the six Ge–O bonds are 1.800 Å in length, but two additional oxygen atoms are at much longer Ge–O distance of 2.622 Å (24, 25). The Ge–Ge distance is a single value (3.115 Å) (25), which is similar to the obtained second peak position in G(r) of GeO2 glass at 72.5 GPa (Fig. 4B). However, we found no peak in G(r) corresponding to the longer Ge–O distance at ∼2.6 Å in the pyrite-type GeO2 (Figs. 3 and ​and4).4). These data suggest that GeO2 glass above 49.4 GPa has a structure which differs from the known crystalline structures under similar pressure conditions.Ge–O coordination number can be quantitatively estimated by integrating the first peak of the radial distribution function:CN=2∫r0rmax4πr2ρG(r)dr,where r0 and rmax are the left edge position and the peak position of the first peak, respectively, and ρ is number density. To estimate the density of GeO2 glass at high pressure, we used the third-order Birch–Murnaghan equation of state of the GeO2 glass (ρ0 = 4.5 g/cm3, K0 = 35.8 GPa, K0′ = 4), which was determined at pressures between 15 and 56 GPa (11, 26). The obtained CN results are summarized in Fig. 5. Previous studies report that CN of GeO2 glass gradually increases from 4 to 6 with increasing pressure (1, 3, 5, 27), and reaches a value of 6 above ∼15 GPa (1, 5). Similarly, our data show CN of ∼6 between 22.6 and 37.9 GPa (Fig. 5). Remarkably, at higher pressures CN increases to 6.4 at 49.4 GPa, and continues to increase with pressure, reaching the highest CN of 7.4 at 91.7 GPa.Open in a separate windowFig. 5.Coordination number of Ge in GeO2 glass as a function of pressure. Red squares represent results of this study, and black symbols are results of previous studies [open diamonds (1), open circles (3), solid triangles (27), solid circles (5)]. Coordination number at 22.6 and 37.9 GPa is almost constant at around 6, whereas it increases markedly to 6.4 at 49.4 GPa. Coordination number continues to increase with pressure, and the highest coordination number of 7.4 is observed at 91.7 GPa. Vertical bars represent errors of coordination number. Error of pressure is represented by the size of the symbols.Because the density data of GeO2 glass were measured up to 56 GPa, extrapolation of the equation of state to higher pressures may result in uncertainties in the determination of CN. We note that our extrapolation of the equation of state of GeO2 glass yields densities of GeO2 glass higher than those of crystalline GeO2 with pyrite-type structure above 70 GPa. To assess the influence of density on the determination of CN, we calculated CN by using the density of pyrite-type crystalline GeO2 (24, 25) at pressures higher than 70 GPa. This yields ∼5% lower density at 91.7 GPa than the extrapolated GeO2 glass density values. If we adopt the density value of pyrite-type structure crystalline GeO2 at 72.5–91.7 GPa, CN becomes almost constant around 7. To precisely determine CN of GeO2 glass and to discuss the change of CN with increasing pressure, precise density data particularly above 70 GPa are required. Nevertheless, our structural results provide strong evidence of GeO2 glass possessing an ultrahigh-pressure polyamorphic structure with CN >6 above 49.4 GPa.A recent study (7) shows that the CN of network-forming structural motifs in oxide glasses and liquids can be rationalized in terms of the OPF. Because of the lack of experimental data with CN >6, the reported data (7) are limited to 3 < CN < 6. We can now extend the relationship between CN and OPF to ultradense glasses and liquids. We calculate OPF (ηO) by using the same method as given by ref. 7 [ηO=VOρcO,VO=(4/3)πrO3, where rO is the oxygen radius, and cO is the atomic fraction of oxygen] (i.e., assuming oxygen atoms are perfect spheres). rO of GeO2 glass at 22.6 and 37.9 GPa and crystalline GeO2 with CN = 6 are calculated by assuming an octahedral geometry (rO=rGeO/2) in the same way as ref. 7. For GeO2 glass with CN >6, similar to the linear dependence of rO between four- and sixfold-coordinated structures assumed in ref. 7, OPF is calculated by assuming a linear change of rO between sixfold-coordinated structure and the ninefold-coordinated cotunnite-type structure, which is the next higher-pressure form in crystalline GeO2 having a uniform CN >6, predicted by first-principles calculations (28). To estimate the oxygen radius for the possible CN = 9 structure motif of GeO2 glass, we first calculate the average O–O distance (‹O–O›) of the crystalline cotunnite-type GeO2, which consists of 21 O–O bonds at 1.929 (×2), 1.940 (×4), 1.948 (×4), 1.991 (×2), 2.055 (×2), 2.161 (×2), 2.243 (×2), and 2.540 (×3) Å, respectively (28). The oxygen radius rO for cotunnite-type GeO2 is then simply rO=‹O–O›/2. Uncertainty of this rO is assumed to be 1σ SD of ‹O–O›/2. Uncertainty in OPF is estimated based on error propagation. For estimating rO of GeO2 glass with CN >6, we calculated the rO/rGeO ratio (0.603) of crystalline cotunnite-type structure using its average Ge–O distance (1.735 Å) (28), and then, rO of GeO2 glass with CN = 9 structure motif is estimated from the measured Ge–O distances of GeO2 glass at 49.4–91.7 GPa (Fig. 4A) by using rO/rGeO = 0.603. Uncertainties in the rO/rGeO ratio due to 1σ SD in rO of the cotunnite-type GeO2 are adopted as errors in rO and the resultant OPF of GeO2 glass with CN >6.Fig. 6 shows CN as a function of OPF extended to CN >6, combined with the data of GeO2 glass for 4 < CN < 6 (7). Ref. 7 showed that fourfold-coordinated GeO2 glass is stable in a wide range of OPF up to ∼0.60 (Fig. 6). CN begins increasing when OPF approaches ∼0.60. The positive correlation between CN and OPF continues until OPF reaches ∼0.64. Then CN sharply increases to 6, with OPF remaining essentially constant at ∼0.64. At pressures of 22.6 and 37.9 GPa, OPF of GeO2 glass increases, with CN remaining almost constant at 6 (Fig. 6). This is a stable plateau for sixfold-coordinated structure, similar to the plateau for CN = 4. The sixfold-coordinated GeO2 glass is structurally stable in a wide range of OPF between ∼0.64 and ∼0.71, similar to the behavior of sixfold-coordinated SiO2 glass (7). Then, the CN of GeO2 glass increases to 6.4 at OPF = 0.72. At higher pressures, CN increases further to CN = 7.4 at 94 GPa, while OPF remains essentially constant at ∼0.72 (Fig. 6).Open in a separate windowFig. 6.Relationship between the OPF and the coordination number of Ge. GeO2 glass data from this study (solid red squares) and from ref. 7 (open black circles) are compared with those of GeO2 crystals with coordination numbers of 4 (cristobalite and alpha quartz, ref. 7) (blue triangles), 6 (rutile and CaCl2 structures, ref. 21) (blue diamonds), and 9 (cotunnite-type structure, ref. 28) (blue square). OPF was calculated by using the method of ref. 7. Vertical broken line represents the maximal dense-packing state (KC = ∼0.74, ref. 31).Ref. 7 has shown that the CN and OPF relationship is “universal” in many network-forming glasses and liquids such as SiO2, GeO2, silicate, aluminate, and germanate systems at high pressures in the CN range between 3 and 6. For example, for SiO2 glass, the fourfold-coordinated structure is stable at OPF up to ∼0.55–0.60 (7). At OPF >∼0.60, CN of SiO2 glass increases to 6, and the sixfold-coordinated structure is stable at the OPF up to ∼0.72 (7). The CN–OPF relation for SiO2 coincides with that of GeO2 as illustrated by the gray band in Fig. 6. Although experimentally determined highest CN in SiO2 glass is 6 at 101.5 GPa (4), similar to crystalline GeO2, a cotunnite-type structure is also known as the next high-pressure form for crystalline SiO2 having a uniform CN of 9 (29, 30). OPF of the cotunnite-type SiO2 (30), calculated using the same method as GeO2, is 0.71, similar to that of cotunnite-type GeO2. Thus, similar to GeO2 glass, SiO2 glass may also change structure toward CN = 9 at higher pressure conditions. In addition to SiO2 glass, the relation between CN and OPF in basalt melt also follows the same curve with CN between 4 and 6 (7), further confirming that the CN–OPF relationship describes a master curve for predicting structural changes in glasses and liquids at high pressure.Our data on GeO2 show that structural changes in glasses and liquids are closely associated with hard-sphere packing even to higher coordination numbers. Fourfold-coordinated structures are stable with OPF up to 0.55–0.60, corresponding to random loose packing of hard spheres (8, 9). Further compression increases CN sharply to 6 at OPF of ∼0.64, which is the most-disordered random closed-packing limit of hard spheres (8, 9), known as the maximally random jammed (MRJ) state (29) (Fig. 6). Our data show that there is a stable plateau for the sixfold-coordinated structure at OPF between ∼0.64 and ∼0.72. OPF of ∼0.72 is close to the maximal dense-packing state [the Kepler conjecture(KC) = ∼0.74, ref. 31], where a certain degree of local ordering, relative to the MRJ state, must be involved (32). Structure evolves to higher CN with OPF remaining essentially constant just below the KC state packing limit (∼0.74).This extended CN versus OPF relation provides new insights into structural changes in other glasses and liquids under extreme compression. For SiO2 glass, experimentally determined highest CN is 6 at 101.5 GPa (4). The number density (0.154/Å-3) and Si–O distance (1.67 Å) at 101.5 GPa (4) yield OPF = 0.71, which is still lower than that of the KC packing state. OPF of SiO2 glass with CN = 6, calculated based on the results of ref. 4, increases from ∼0.68 at 35.2 GPa to ∼0.71 at 101.5 GPa (Fig. S1). If we linearly extrapolate the OPF–pressure trend, OPF of SiO2 glass reaches 0.74 around 108 GPa, where structural change to CN higher than 6 is expected. We expect that further compression of silica (and likely other silicate glasses and liquids) should follow the dashed gray band shown in Fig. 6 toward higher CN.Open in a separate windowFig. S1.OPF of SiO2 glass with increasing pressure, calculated based on the results of Si–O distance and number density (4). Error of the OPF is calculated based on uncertainty in the Si–O distance. Linear extrapolation of the OPF–pressure trend shows that OPF of SiO2 glass reaches 0.74 around 108 GPa.  相似文献   

11.
    
Grzegorz Socha 《Materials》2021,14(13)
A new version of failure criterion for additively manufactured materials, together with simple and accurate calibration procedures, is proposed and experimentally verified in this paper. The proposition is based on void growth-based ductile failure models. The failure criterion for ductile materials proposed by Hancock–Mackenzie was calibrated using simple methods and accessories. The calibration procedure allows the determination of failure strain under pure shear. The method is accurate and simple due to the fact that it prevents strain localization disturbing stress distribution at the failure zone. The original criterion was modified to better suit the deformation behavior of additively manufactured materials. Examples of calibration of the original and modified failure criteria for additively manufactured 316L alloy steel is also given in this paper, along with analyses of the obtained results.  相似文献   

12.
    
Xinyi Xiao  Hanbin Xiao 《Materials》2022,15(1)
Robotic additive manufacturing (AM) has gained much attention for its continuous material deposition capability with continuously changeable building orientations, reducing support structure volume and post-processing complexity. However, the current robotic additive process heavily relies on manual geometric reasoning that identifies additive features, related building orientations, tool approach direction, trajectory generation, and sequencing all features in a non-collision manner. In addition, multi-directional material accumulation cannot ensure the nozzle always stays above the building geometry. Thus, the collision between these two becomes a significant issue that needs to be solved. Hence, the common use of a robotic additive is hindered by the lack of fully autonomous tools based on the abovementioned issues. We present a systematic approach to the robotic AM process that can automate the abovementioned planning procedures in the aspect of collision-free. Typically, input models to robotic AM have diverse information contents and data formats, hindering the feature recognition, extraction, and relations to the robotic motion. Our proposed method integrates the collision-avoidance condition to the model decomposition step. Therefore, the decomposed volumes can be associated with additional constraints, such as accessibility, connectivity, and trajectory planning. This generates an entire workspace for the robotic additive building platform, rotatability, and additive features to determine the entire sequence and avoid potential collisions. This approach classifies the uniqueness of autonomous manufacturing on the robotic AM system to build large and complex metal components that are non-achievable through traditional one-directional AM in a computationally effective manner. This approach also paves the path in constructing an in situ monitoring and closed-loop control on robotic AM to control and enhance the build quality of the robotic metal AM process.  相似文献   

13.
    
Jingjunjiao Long  Ashveen Nand  Sudip Ray 《Materials》2021,14(1)
Additive manufacturing (AM) is a rapidly expanding material production technique that brings new opportunities in various fields as it enables fast and low-cost prototyping as well as easy customisation. However, it is still hindered by raw material selection, processing defects and final product assessment/adjustment in pre-, in- and post-processing stages. Spectroscopic techniques offer suitable inspection, diagnosis and product trouble-shooting at each stage of AM processing. This review outlines the limitations in AM processes and the prospective role of spectroscopy in addressing these challenges. An overview on the principles and applications of AM techniques is presented, followed by the principles of spectroscopic techniques involved in AM and their applications in assessing additively manufactured parts.  相似文献   

14.
    
Xavier Fernndez-Francos  Osman Konuray  Xavier Ramis   ngels Serra  Silvia De la Flor 《Materials》2021,14(1)
Dual-curing thermosetting systems are recently being developed as an alternative to conventional curing systems due to their processing flexibility and the possibility of enhancing the properties of cured parts in single- or multi-stage processing scenarios. Most dual-curing systems currently employed in three-dimensional (3D) printing technologies are aimed at improving the quality and properties of the printed parts. However, further benefit can be obtained from control in the curing sequence, making it possible to obtain partially reacted 3D-printed parts with tailored structure and properties, and to complete the reaction by activation of a second polymerization reaction in a subsequent processing stage. This paves the way for a range of novel applications based on the controlled reactivity and functionality of this intermediate material and the final consolidation of the 3D-printed part after this second processing stage. In this review, different strategies and the latest developments based on the concept of dual-curing are analyzed, with a focus on the enhanced functionality and emerging applications of the processed materials.  相似文献   

15.
    
Vladimir V. Popov  Maria Luisa Grilli  Andrey Koptyug  Lucyna Jaworska  Alexander Katz-Demyanetz  Damjan Klob ar  Sebastian Balos  Bogdan O. Postolnyi  Saurav Goel 《Materials》2021,14(4)
The term “critical raw materials” (CRMs) refers to various metals and nonmetals that are crucial to Europe’s economic progress. Modern technologies enabling effective use and recyclability of CRMs are in critical demand for the EU industries. The use of CRMs, especially in the fields of biomedicine, aerospace, electric vehicles, and energy applications, is almost irreplaceable. Additive manufacturing (also referred to as 3D printing) is one of the key enabling technologies in the field of manufacturing which underpins the Fourth Industrial Revolution. 3D printing not only suppresses waste but also provides an efficient buy-to-fly ratio and possesses the potential to entirely change supply and distribution chains, significantly reducing costs and revolutionizing all logistics. This review provides comprehensive new insights into CRM-containing materials processed by modern additive manufacturing techniques and outlines the potential for increasing the efficiency of CRMs utilization and reducing the dependence on CRMs through wider industrial incorporation of AM and specifics of powder bed AM methods making them prime candidates for such developments.  相似文献   

16.
    
Tomer Ron  Ohad Dolev  Avi Leon  Amnon Shirizly  Eli Aghion 《Materials》2021,14(1)
The present study aims to evaluate the stress corrosion behavior of additively manufactured austenitic stainless steel produced by the wire arc additive manufacturing (WAAM) process. This was examined in comparison with its counterpart, wrought alloy, by electrochemical analysis in terms of potentiodynamic polarization and impedance spectroscopy and by slow strain rate testing (SSRT) in a corrosive environment. The microstructure assessment was performed using optical and scanning electron microscopy along with X-ray diffraction analysis. The obtained results indicated that in spite of the inherent differences in microstructure and mechanical properties between the additively manufactured austenitic stainless steel and its counterpart wrought alloy, their electrochemical performance and stress corrosion susceptibility were similar. The corrosion attack in the additively manufactured alloy was mainly concentrated at the interface between the austenitic matrix and the secondary ferritic phase. In the case of the counterpart wrought alloy with a single austenitic phase, the corrosion attack was manifested by uniform pitting evenly scattered at the external surface. Both alloys showed ductile failure in the form of “cap and cone” fractures in post-SSRT experiments in corrosive environment.  相似文献   

17.
    
Ulf Ziesing  Jonathan Lentz  Arne Rttger  Werner Theisen  Sebastian Weber 《Materials》2022,15(21)
This work investigates the processability of hot-work tool steels by wire-arc additive manufacturing (DED-Arc) from metal-cored wires. The investigations were carried out with the hot-work tool steel X36CrMoWVTi10-3-2. It is shown that a crack-free processing from metal-cored wire is possible, resulting from a low martensite start (Ms) temperature, high amounts of retained austenite (RA) in combination with increased interpass temperatures during deposition. Overall mechanical properties are similar over the built-up height of 110 mm. High alloying leads to pronounced segregation during processing by DED-Arc, achieving a shift of the secondary hardness maximum towards higher temperatures and higher hardness in as-built + tempered condition in contrast to hardened + tempered condition, which appears to be beneficial for applications of DED-Arc processed material at elevated temperatures.  相似文献   

18.
    
Miguel R. Silva  Antnio M. Pereira   lvaro M. Sampaio  Antnio J. Pontes 《Materials》2021,14(8)
Additive Manufacturing (AM) technology has been increasing its penetration not only for the production of prototypes and validation models, but also for final parts. This technology allows producing parts with almost no geometry restrictions, even on a micro-scale. However, the micro-Detail (mD) measurement of complex parts remains an open field of investigation. To be able to develop all the potential that this technology offers, it is necessary to quantify a process’s precision limitations, repeatability, and reproducibility. New design methodologies focus on optimization, designing microstructured parts with a complex material distribution. These methodologies are based on mathematical formulations, whose numerical models assume the model discretization through volumetric unitary elements (voxels) with explicit dimensions and geometries. The accuracy of these models in predicting the behavior of the pieces is influenced by the fidelity of the object’s physical reproduction. Despite that the Material Jetting (MJ) process makes it possible to produce complex parts, it is crucial to experimentally establish the minimum dimensional and geometric limits to produce parts with mDs. This work aims to support designers and engineers in selecting the most appropriate scale to produce parts discretized by hexahedral meshes (cubes). This study evaluated the dimensional and geometric precision of MJ equipment in the production of mDs (cubes) comparing the nominal design dimensions. A Sample Test (ST) with different sizes of mDs was modeled and produced. The dimensional and geometric precision of the mDs were quantified concerning the nominal value and the calculated deviations. From the tests performed, it was possible to conclude that: (i) more than 90% of all analyzed mDs exhibit three dimensions (xyz) higher than the nominal ones; (ii) for micro-details smaller than 423 μm, they show a distorted geometry, and below 212 μm, printing fails.  相似文献   

19.
    
Babette Goetzendorfer  Hannah Kirchgaessner  Ralf Hellmann 《Materials》2021,14(18)
In this study, we report on a novel approach to produce defined porous selectively laser molten structures with predictable anisotropic permeability. For this purpose, in an initial step, the smallest possible wall proximity distance for selectively laser molten structures is investigated by applying a single line scan strategy. The obtained parameters are adapted to a rectangular and, subsequently, to a more complex honeycomb structure. As variation of the hatch distance directly affects the pore size, and thus the resulting porosity and finally permeability, we, in addition, propose and verify a mathematical correlation between selective laser melting process parameters, porosity, and permeability. Moreover, a triangular based anisotropic single line selectively laser molten structure is introduced, which offers the possibility of controlling the three-dimensional flow ratio of passing fluids. Basically, one spatial direction exhibits unhindered flow, whereas the second nearly completely prohibits any passage of the fluid. The amount to which the remaining orientation accounts for is controlled by spreading the basic triangular structure by variation of the included angle. As acute angles yield low passage ratios of 0.25 relative to continuous flow, more obtuse angles show increased ratios up to equal bidirectional flow. Hence, this novel procedure permits (for the first time) fabrication of selective laser molten structures with adjustable permeable properties independent of the applied process parameters.  相似文献   

20.
    
Benedikt Kirchebner  Maximilian Ploetz  Christoph Rehekampff  Philipp Lechner  Wolfram Volk 《Materials》2021,14(15)
Like most additive manufacturing processes for metals, material jetting processes require support structures in order to attain full 3D capability. The support structures have to be removed in subsequent operations, which increases costs and slows down the manufacturing process. One approach to this issue is the use of water-soluble support structures made from salts that allow a fast and economic support removal. In this paper, we analyze the influence of salt support structures on material jetted aluminum parts. The salt is applied in its molten state, and because molten salts are typically corrosive substances, it is important to investigate the interaction between support and build material. Other characteristic properties of salts are high melting temperatures and low thermal conductivity, which could potentially lead to remelting of already printed structures and might influence the microstructure of aluminum that is printed on top of the salt due to low cooling rates. Three different sample geometries have been examined using optical microscopy, confocal laser scanning microscopy, energy-dispersive X-ray spectroscopy and micro-hardness testing. The results indicate that there is no distinct influence on the process with respect to remelting, micro-hardness and chemical reactions. However, a larger dendrite arm spacing is observed in aluminum that is printed on salt.  相似文献   

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