Densification Level Research Articles

Influence of nozzle temperatures on the microstructures and physical properties of 316L stainless steel parts additively manufactured by material extrusion

PurposeMaterial extrusion (ME) is a low-cost additive manufacturing (AM) technique that is capable of producing metallic components using desktop 3D printers through a three-step printing, debinding and sintering process to obtain fully dense metallic parts. However, research on ME AM, specifically fused filament fabrication (FFF) of 316L SS, has mainly focused on improving densification and mechanical properties during the post-printing stage; sintering parameters. Therefore, this study aims to investigate the effect of varying processing parameters during the initial printing stage, specifically nozzle temperatures, Tn (190°C–300°C) on the relative density, porosity, microstructures and microhardness of FFF 3D printed 316L SS.Design/methodology/approachCube samples (25 x 25 x 25 mm) are printed via a low-cost Artillery Sidewinder X1 3D printer using a 316L SS filament comprising of metal-polymer binder mix by varying nozzle temperatures from 190 to 300°C. All samples are subjected to thermal debinding and sintering processes. The relative density of the sintered parts is determined based on the Archimedes Principle. Microscopy and analytical methods are conducted to evaluate the microstructures and phase compositions. Vickers microhardness (HV) measurements are used to assess the mechanical property. Finally, the correlation between relative density, microstructures and hardness is also reported.FindingsThe results from this study suggest a suitable temperature range of 195°C–205°C for the successful printing of 316L SS green parts with high dimensional accuracy. On the other hand, Tn = 200°C yields the highest relative density (97.6%) and highest hardness (292HV) in the sintered part, owing to the lowest porosity content (<3%) and the combination of the finest average grain size (∼47 µm) and the presence of Cr23C6 precipitates. However, increasing Tn = 205°C results in increased porosity percentage and grain coarsening, thereby reducing the HV values. Overall, these outcomes suggest that the microstructures and properties of sintered 316L SS parts fabricated by FFF AM could be significantly influenced even by adjusting the processing parameters during the initial printing stage only.Originality/valueThis paper addresses the gap by investigating the impact of initial FFF 3D printing parameters, particularly nozzle temperature, on the microstructures and physical characteristics of sintered FFF 316L SS parts. This study provides an understanding of the correlation between nozzle temperature and various factors such as dimensional integrity, densification level, microstructure and hardness of the fabricated parts.

The Effect of Different Densification Levels on the Mechanical Properties of Southern Yellow Pine

Plantations, typically involving the cultivation of fast-growing trees like southern yellow pine, offer avenues to enhance sustainability and manage limited resources more effectively. However, fast-growing trees suffer from low mechanical properties due to less dense wood. Densification and the development of engineered wood products represent approaches to developing high-performance products from fast-growing tree species. In this study, the correlation between the densification levels and mechanical properties of a fast-growing species, loblolly pine (Pinus taeda L.), was established to improve resource utilization. Wood specimens were densified at three compression ratios: 16.67%, 33.33%, and 50.00%. The impact of densification levels on bending strength, bending stiffness, shear strength, and hardness was studied. The findings highlighted the positive impact of densification on structural integrity, as bending stiffness consistently improved, eventually reaching a 42% enhancement at a compression ratio of 50.00%. However, bending strength showed an initial increasing trend but reached a plateau at higher densification levels. Densification levels showed minimal changes in shear strength parallel to the grain. Notably, densification significantly enhanced hardness properties, particularly on the tangential surface, where a fourfold increase was observed at a 50% compression ratio. Overall, these findings reveal the relation between the compression ratio and the mechanical properties of lumber and are beneficial for utilizing lower-quality wood species in construction and engineering applications.

Pulse current enhanced densification and mechanical property of Inconel 718 superalloy fabricated by spark plasma sintering

The Inconel 718 superalloy was fabricated using spark plasma sintering (SPS) technology with varying sintering temperatures and heating rates. The densification and mechanical property of the sintered superalloys were characterized through tensile and compression tests at room temperature, as well as microscopic analyses. The evidence suggests that the plasma generated between the particles results in evaporative melting on the particle surface and plastic deformation of the particle boundaries, accelerating the densification process is by 3∼4 times. Besides, the grain size refinement coefficient affected by pulse current in the holding stage is 0.7–0.8, leading to a significant grain boundary strengthening during SPS process. The dislocation dominated by ball milling and SPS parameters also helps improve the strength and plasticity of the sintered superalloy. The superalloy sintered at 1050 °C with a heating rate of 100 °C/min demonstrated the highest tensile and compressive fracture strengths, measuring 1410 MPa and 1983 MPa, respectively, with the tensile and compressive yield strength of 712 MPa and 1557 MPa, respectively. Lower sintering temperatures or higher heating rates results in lower levels of densification and decreased strength. In addition, plasticity is reduced at higher sintering temperatures or lower heating rates due to excessive precipitation of brittle phases.

A new investigation on graphene-reinforced 304L nanocomposite made by additive manufacturing process: Microstructure and tribology study

In this study, selective laser melting (SLM), as an additive manufacturing method, was applied to produce graphene/304L nanocomposites with various graphene particle sizes and contents. The effect of the graphene particle size (1 μm and 50 nm) and volume fraction on the microstructure behaviors, constitutional phases, mechanical performance, and wear characteristics of the SLM-processed nanocomposite specimens was studied. It was concluded that the reinforcing particle content and size play a remarkable impact on the densification features and the densification level improvs when the fine starting reinforcing particles are used, due to the development of the reinforcement–matrix wettability. In addition, the microstructure refinement and increased hardness values occurred in the SLM-processed nanocomposite system with the addition of reinforcing particles (both sizes). The wear examination indicated that the coefficient of friction (COF), wear rate, and mass loss decreased due to the reinforcement prominent effect, namely grain refinement and grain-boundary strengthening. According to surface topography analysis, the depth of the groove in the processed sample made by fine graphene reinforcement is lower than the other sample.

Effect of dispersion behavior of silica fume on the rheological properties and early hydration characteristics of ultra-high strength mortar

Silica fume plays a crucial role in ultra-high performance cementitious materials, but its dispersion, influenced by varying densification levels, leads to different degrees of agglomeration. However, the precise impact of this on rheological properties and early hydration characteristics of ultra-high performance cementitious materials remains unclear. This study assesses the impact of highly densified silica fume (HDSF), moderately densified silica fume (MDSF), and raw silica fume (RSF) on the rheological prperties of ultra-high strength mortar (UHSM). Additionally, the early hydration characteristics of UHSM influenced by these silica fumes are investigated through both heat of hydration and penetration resistance methods. The results showed that HDSF contained numerous large agglomerates, contrasting with MDSF and RSF, where the agglomerate sizes were comparable to those of cement particles. As the content of HDSF increased, the yield stress, viscosity, and thixotropy of UHSM gradually rose, accompanied by a notable decrease in hydration rate. Conversely, increasing MDSF and RSF content initially decreased and then increased these rheological properties, while the hydration rate remained relatively unchanged. The distribution behavior of the silica fumes influences the rheological properties of UHSM through water film thickness (particle spacing). Large agglomerates in HDSF reduce the activity of the entire cementitious system, significantly decreasing the hydration rate. In contrast, MDSF and RSF primarily influence the particle spacing within the cementitious system, subsequently impacting the hydration rate. This study provides theoretical insights and practical guidance for construction professionals in selecting appropriate silica fume for designing and regulating ultra-high performance cementitious materials performance.

Wear and corrosion properties of Cu–AlN composite coatings deposited by cold spray

Copper and copper alloy are commonly used to fabricate ship propellers and sealing valves that encounter harsh corrosion and wear. To improve their service life, Cu coating and Cu–AlN composite coatings with different volume content of AlN (10%, 20%, 30%) were prepared by cold spraying. The investigation focused on analyzing the coatings’ microstructure, microhardness, resistance to wear, and corrosion. Results show that the composite coatings with AlN have fewer pores and denser microstructure than the Cu coating. The coating demonstrates a relatively low deposition efficiency, resulting in the attainment of only 3.8 vol% of AlN when the feedstock AlN powder content was 30 vol%. The microhardness of Cu-3.8AlN coating is 159.7 HV, about 53.1% higher than that of Cu coating. The specific wear rate of Cu-3.8AlN coating is reduced by about 73.5% compared to that of Cu coating, measuring at 1.69 × 10−3 mm3/(N·m). Compared with other coatings, Cu-3.8AlN has the highest corrosion resistance (Ecorr = −0.199 V, Icorr = 1.2 μA/cm2, Rct = 3200 Ω·cm2). The Cu-3.8AlN coating exhibits superior wear and corrosion resistance among the four coatings, attributed to its highest level of densification and the presence of AlN particles.

Assessment of carbon nanotube sheet densification level

Assessment of carbon nanotube sheet densification level

Laser additive manufacturing of Miura-origami tube inspired quasi-zero stiffness metamaterial with prominent longitudinal wave propagation

ABSTRACT Origami metamaterials have become frontiers of research in many disciplines due to their infinite design space, simple size variation, and topologically variable properties. In this study, a novel metamaterial inspired by Miura-origami tubes with a complex quasi-zero-stiffness (QZS) structure was fabricated via laser powder bed fusion (LPBF). The unit of the QZS metamaterial consists of a two-layer quadrilateral frame and two vertical springs attached to its diagonal points. The geometric accuracy, densification level and mechanical properties of the QZS parts fabricated at various processing conditions were investigated and the optimised processing parameters were determined. The displacement response of the QZS parts was analysed by experiments in conjunction with simulation analysis. The results show that the LPBF-fabricated QZS metamaterials form four extra-wide longitudinal wave band gaps under low frequencies from 660 Hz to 2500 Hz. The proposed LPBF-fabricated QZS metamaterial shows great potential in impeding the longitudinal vibration of engineering structures.

The Role of 5 G in Optical Fiber

Abstract: Connected society and people is a vision nursed and promoted by most business and social enterprises for several years. This is supported aptly by 5G networks. 5G is one of the most advanced wireless technologies that assure ultra-low latency and swift data delivery. Unlike 3G and 4G networks, the 5G uses a different set of frequencies to deliver services. It uses Sub-6- GHz worldwide for mobile connectivity and 24 GHz for high-bandwidth coverage. In 4G networks, small number of macro cells was employed to cover one square mile. However, in 5G, many microcells are used to cover a square mile. The deployment would vary on a case-to-case basis, but a 1:600 ratio assures a new level of densification. Optical fiber is the new choice for connecting this dense mesh of 5G microcells. Why is it so?

High Densification Level and Hardness Values of Additively Manufactured 316L Stainless Steel Fabricated by Fused Filament Fabrication

Laser powder bed fusion (L-PBF) has emerged as the most widely used additive manufacturing (AM) process, also known as 3D printing, to fabricate 316L stainless steel (316L SS) components for various applications. However, the initial setup, operation, and maintenance costs are too expensive due to the complex machinery, high energy-consuming laser beam, and proprietary software required. Therefore, in this paper, fused fiament fabrication (FFF) is proposed as a low-cost AM approach to fabricate 316L SS specimens via a 3-step printing-debinding-and sintering process. The specimens are initially printed on a desktop FFF AM 3D printer by varying nozzle temperatures from 195 – 220°C, followed by debinding up to 427°C for 4 hours, and finally sintering at 1260°C for 4 hours. The results show that nozzle temperature 200°C yielded the highest densification level of 97.6% and highest average hardness value of 292 HV, indicating that 3D printing parameters, particularly nozzle temperature plays an important role in influencing the properties of the sintered specimens. Overall, the results from this study prove that FFF is a viable and cost-effective AM process that has the potential to produce 316L SS parts that meet industrial requirements.

Basic Design Parameters Influencing on Axial Stiffness of the Spiral Wound Gasket.

The article presents the influence of important design parameters of a spiral gasket on axial stiffness and leakage level. These parameters were the angle of inclination of the central part of the spiral section, the length of the vertical part of the spiral section, and the degree of densification of the material filling the metal coils. The scope of work was divided into two stages. In the first, experimental tests were conducted to determine the stiffness and tightness of a standard spiral gasket at two extreme levels of densification of the filler material, and the elastic-plastic properties of expanded graphite, which is the filler material of the metal spirals, were determined. In the second stage, multivariate numerical calculations were carried out to determine the axial stiffness of the gasket and to evaluate the distribution of contact pressure on the sealing surface. A novel aspect of the work is the proposal of a mathematical model to estimate the averaged value of the modulus of elasticity of the filler material as a function of the degree of densification and the execution of an experimental plan that significantly allowed the adoption of a limited number of analysed model variants used in the numerical calculations.

Ultrafast crystallization and sintering of Li1.3Al0.3Ti1.7(PO4)3 glass through flash sinter‐crystallization

AbstractFlash sinter‐crystallization (FSC) is a new technique for concurrently crystallizing and sintering glasses, derived from flash sintering. In this study, we explore, for the first time, the use of FSC as a processing method for producing Li1.3Al0.3Ti1.7(PO4)3 (LATP) glass ceramics. Using FSC, LATP with NaSICON structure is produced at a furnace temperature as low as 460°C and a processing time of 5 min. The FSC‐processed samples with different current density limits were compared with those conventionally sinter‐crystallized (CSC) at 950°C for 1 h. We show that FSC can significantly improve the densification of LATP glass ceramics due to the volumetric high heating rate. Furthermore, the LATP samples processed by FSC exhibit superior total ionic conductivity than those processed by CSC, also surpassing the reported results for LATP with similar levels of densification. Therefore, our results suggest that FSC is a promising method for processing glass ceramics, particularly for materials with high crystallization kinetics like LATP, opening up new possibilities for the production of solid electrolytes.

Effect of laser energy density on surface morphology, microstructure and mechanical behaviour of direct metal laser melted 17-4 PH stainless steel

Abstract The surface and microstructural characteristics of 3D printed parts play a significant role under mechanical loading. The authors have explored the effect of laser energy densities on the surface morphology, microstructure and mechanical behaviour of 17-4 precipitation hardened stainless steel fabricated under the direct metal laser melting technique. The considered processing parameters were laser energy density and its technical parameters: laser power, layer thickness, hatch spacing and scanning speed. The mechanical and metallurgical properties of the as-printed samples appeared better than the wrought counterpart due to the higher densification level (99.74 %) induced by the rotating scanning strategy. X‐ray diffraction revealed the presence of both the martensitic α phase and austenitic γ phase in the as-printed sample. There is no significant anisotropy in the mechanical behaviour as the build direction has a random texture with a fine columnar grain structure. The high laser energy density with low layer thickness results in an excellent surface finish. The tensile strength (1180 MPa) and the elongation for the as-printed sample (45.0 %) were considerably more significant than that for the wrought sample (1160 MPa and 26.0 %), which is attributed to the combination of low and high-angle boundaries, as confirmed by the electron backscatter diffraction results.

Inconel 718 produced by hot pressing: optimization of temperature and pressure conditions

This paper aims to act as a useful engineering tool for researchers who are studying the production of well-densified IN718 parts by uniaxial vacuum hot pressing. To the best of the authors’ knowledge, there is no relevant information on literature about densification of IN718 parts by this technique. This work is focused on understanding the influence of uniaxial vacuum hot pressing sintering conditions (temperature and pressure) on Inconel 718 (IN718) powder densification, microstructural, fracture mode, and hardness properties. The optimization of temperature and pressure sintering conditions are presented as well as its influence on the densification, microstructural features, and hardness properties. The sintering conditions included temperatures of 1000, 1068, 1150, and 1200 °C; pressures of 50 and 60 MPa; and a dwell time of 60 min.The results showed an increase in the grain size (GS) of the compacts with the processing temperature and a change on the fracture mode from intergranular dominant fracture to fully dimple ductile fracture. Regarding the microstructural properties, the results showed that γ′(Ni3(Al, Ti)) intermetallic precipitate originated from IN718 powders was retained in the sintered specimens. The hardness results revealed that the sintering temperature of 1000 °C is not enough to promote accurate densification. The optimum hardness results were achieved at 1200 °C (327 HV) with high levels of densification and pure intragranular fracture mode. In future studies, shear and tensile strength test should be performed in order to properly evaluate the mechanical behavior of hot-pressed IN718 specimens.

About the relationship of the processing conditions, mechanical properties, and microstructure of a co-precipitated Fe/Cu prealloyed powder

The sinterability of a commercial Fe–Cu pre-alloyed powder, designed to be used as a metallic bond in diamond impregnated tools, has been greatly analyzed by combining dilatometry, computational thermodynamic calculations, and microstructural analysis. The effect of sintering temperature and alloying elements such as graphite and iron phosphide have been taken into consideration in order to demonstrate the capability of tailoring final properties through different strategies, and dilatometry and microstructural analysis have been used to understand the densification process of the alloys. Solid phase sintering was the mechanism taking place during thermal cycle. In fact, a liquid phase appears but because of the high densification level at that time mechanisms associated with LPS do not contribute to densification. Discussion about mechanical properties has been related to key microstructural phenomena, i.e., grain growth, phase transformation, precipitation, and solid solution. Obtained hardness ranged from 83 HRB to 106 HRB with yield stresses between 450 MPa and 700 MPa and elongations above 3%, while final tensile properties similar to those obtained by cobalt-based powders processed by hot pressing were also obtained.

Microstructures and Hardening Mechanisms of a 316L Stainless Steel/Inconel 718 Interface Additively Manufactured by Multi-Material Selective Laser Melting

For the first time, the interfacial microstructures and hardening mechanisms of a multi-material (MM) 316L stainless steel/Inconel 718 (316L SS/IN 718) interface fabricated by a novel multi-material selective laser melting (MM SLM) additive manufacturing (AM) system have been investigated in this study. MM 316L SS/IN 718 parts were successfully built with high densification levels (&gt;99%) and low porosity content (average: ~0.81%). Microscopy analysis indicates that the interfacial microstructures are characterised by dense dislocation tangling networks, NbC and TiC, and very small amounts of Laves phase (&lt;2 wt. %). In addition, equiaxed grains (average: 45 ± 3 μm) are attained in the interfacial region, whereas both individual IN 718 and 316L SS regions exhibit show columnar grains with average sizes of 55 ± 5 μm and 85 ± 3 μm, respectively. Vickers microhardness (HV) and nanoindentation measurements exhibit that the hardness values of the interfacial region are between those of the individual material regions. A strengthening model is built to assess the contribution of intrinsic strength, solid solution, precipitations, dislocations, and grain boundaries to the overall interfacial hardness of the as-built MM alloy.

Chemical and microstructural characterisation of HfO2-Y2O3 ceramics with high amount of Y2O3 (33, 40 and 50 mol. %) manufactured using spark plasma sintering

Hafnia based ceramics are potential promising candidates to be used as thermal barrier coatings (TBC) for applications in the field of propulsion. In this study, Spark Plasma Sintering (SPS) of fully stabilised hafnia with yttrium oxide (yttria) was investigated to provide a better understanding of the effect of manufacturing parameters, on the crystallography, chemistry and microstructure of the material. Several hafnia powders, containing different amounts of yttria (33 mol. %, 40 mol. % or 50 mol. %), were sintered by SPS at different temperature levels ranging from 1600 °C to 1850 °C. On these materials, X-ray diffraction patterns associated with scanning electron micrographs have highlighted the influence of both the sintering temperature and the amount of yttria on the final composition, the lattice parameter and the microstructure of hafnia-based materials. In the end, it is established that, for all quantities of yttrium employed, the main phase is Y2Hf2O7 with very high densification levels.

Crystal Structures and Microwave Dielectric Properties of Novel MgCu2Nb2O8 Ceramics Prepared by Two-Step Sintering Technique.

In this work, novel MgCu2Nb2O8 (MCN) ceramics were synthesized by the two-step sintering (TSS) technique, and the phase composition, crystal structures, and microwave dielectric properties were comprehensively studied. X-ray diffraction (XRD) and Raman analysis demonstrated that MCN ceramics are multi-phase ceramics consisting of MgNb2O6 and CuO phases. X-ray photoelectron spectroscopy (XPS) was utilized to investigate the chemical composition and element valence of MgCu2Nb2O8 ceramics. Scanning electron microscopy (SEM) analysis demonstrated dense microstructures in the MCN ceramics prepared at a sintering temperature of 925 °C. The microwave dielectric properties were largely affected by the lattice vibrational modes and densification level of the ceramics. The outstanding microwave dielectric properties of εr = 17.15, Q × f = 34.355 GHz, and τf = -22.5 ppm/°C were obtained for the MCN ceramics sintered at 925 °C, which are results that hold promise for low temperature co-fired ceramic (LTCC) applications.

Planning instruments enhance the acceptance of urban densification.

Dense and compact cities yield several benefits for both the population and the environment, including the containment of urban sprawl, reduced carbon emissions, and increased housing supply. Densification of the built environment is thus a key contemporary urban planning paradigm worldwide. However, local residents often oppose urban densification, motivating a need to understand their underlying concerns. In order to do so, we examined different factors driving public acceptance of housing densification projects through a combination of a conjoint survey experiment and different proximity frames among 12,402 participants across Berlin, Chicago, London, Los Angeles, New York, and Paris. Respondents compared housing densification projects with varying attributes, including their geographic proximity, project-related factors, and accompanying planning instruments. The results indicate that the acceptance of such projects decreases with project proximity and that project-related factors, such as the type of investor, usage, and climate goals, impact densification project acceptance. More specifically, we see a negative effect on acceptance levels for projects with for-profit investors and a positive effect when the suggested developments are mixed use or climate neutral. In addition, planning instruments, such as rent control, inclusionary zoning, and participatory planning, appear to positively influence acceptance. Interestingly, a cross-continental comparison shows overall higher acceptance levels of densification by US respondents. These multifaceted results allow us to better understand what drives people's acceptance of housing projects and how projects and planning processes can be designed to increase democratic acceptance of urban densification.

The Influence of Processing Parameters on the Al-Mn Enriched Nano-Precipitates Formation in a Novel Al-Mn-Cr-Zr Alloy Tailored for Power Bed Fusion-Laser Beam Process

Among the recently developed compositions tailored for the power bed fusion-laser beam process (PBF-LB), the novel Al-Mn-Cr-Zr alloy stands out. This composition exploits high solid solution strengthening, achieving a high hardness value in the as-built condition. The produced samples are inherently crack-free and have a good level of densification (~99.5%). The goal of this study is to investigate how this quaternary system is affected by the laser power while retaining a similar volumetric energy density. A comparison between the microstructural features and the mechanical performance was performed on a set of samples processed with power values ranging from 100 to 170 W. Microstructural features were investigated through optical microscopy, Electron Back Scattered Diffraction (EBSD) investigation and feature analysis using advanced microscopy to examine the amount, distribution, and shape of precipitates in the different process conditions. Although the quantitative feature analysis permitted analysis of more than 60 k precipitates for each power condition, all samples demonstrated a low level of precipitation (below 0.3%) with nanometric size (around 75 nm). The mechanical performances of this quaternary system as a function of the laser power value were evaluated with a microhardness test, recording very similar values for the different process conditions with a mean value of approximately 104 HV. The results suggested a very stable system over the tested range of process parameters. In addition, considering the low level of precipitation of nanometric phases enriched in Al-Mn, a supersaturated state could be established in each process condition.