Relative Density Of Material Research Articles

The importance of adjusting the processing parameters for the resulting material density of PBF-LB AISI 316L lattice structures

Lattice structures are becoming more commonly used in the design of components for additive manufacturing. This is due to their ability to reduce the weight of manufactured parts, minimize material consumption, and achieve specific properties by modifying their geometry. As the applications of lattice structures continue to evolve, it is essential to determine whether the process parameters used in the PBF-LB (Laser Beam Powder Bed Fusion) process for manufacturing these structures should be the same as or different from those used for larger cross-sectional components. An analysis of the existing literature revealed insufficient data on this subject, which inspired this study. Experiments conducted using AISI 316L stainless steel showed that lattice structures can be produced with significantly lower volumetric energy density, while maintaining a high relative material density. In the experiment on lattice structures made of BCCZ and gyroid unit cells, a relative material density of over 99.5% was achieved with a volumetric energy density of approximately 33 J/mm3. These findings are significant for the fabrication of lattice structures. The lower volumetric energy density typically allows for greater geometric accuracy and reduced internal stresses. Furthermore, it has been proven that the nodes of the structure are critical places exposed to porosity formation.

Influence of Process Energy on the Formation of Imperfections in Body-Centered Cubic Cells with Struts in the Vertical Orientation Produced by Laser Powder Bed Fusion from the Magnesium Alloy WE43.

The low specific density and good strength-to-weight ratio make magnesium alloys a promising material for lightweight applications. The combination of the properties of magnesium alloys and Additive Manufacturing by the Laser Powder Bed Fusion (LPBF) process enables the production of complex geometries such as lattice or bionic structures. Magnesium structures are intended to drastically reduce the weight of components and enable a reduction in fuel consumption, particularly in the aerospace and automotive industries. However, the LPBF processing of magnesium structures is a challenge. In order to produce high-quality structures, the process parameters must be developed in such a way that imperfections such as porosity, high surface roughness and dimensional inaccuracy are suppressed. In this study, the contour scanning strategy is used to produce vertical and inclined struts with diameters ranging from 0.5 to 3 mm. The combination of process parameters such as laser power, laser speed and overlap depend on the inclination and diameter of the strut. The process parameters with an area energy of 1.15-1.46 J/mm2 for struts with a diameter of 0.5 mm and an area energy of 1.62-3.69 J/mm2 for diameters of 1, 2 and 3 mm achieve a relative material density of 99.2 to 99.6%, measured on the metallographic sections. The results are verified by CT analyses of BCCZ cells, which achieve a relative material density of over 99.3%. The influence of the process parameters on the quality of struts is described and discussed.

High‐temperature ablation of hot‐pressed HfC–SiC ceramics

AbstractEffective thermal insulation materials rely on the fabrication of dense, ultra‐high‐temperature ceramics that can withstand harsh environments. Hafnium carbide‐based ceramics are one of the leading materials that have the potential to perform relatively well in high‐temperature oxidizing environments under mechanical loading due to their thermal and mechanical stability. In this study, we explore the effects of processing conditions to create dense, ablation‐resistant HfC–SiC composites with a fixed composition of HfC–20 wt.% SiC using a hot‐pressing method. Sintering pressure, temperature, and time were varied and the material's relative density, phase composition, morphology, microstructure, and hardness were investigated. Composite ceramics with 99% relative density relative to a theoretical value were created by hot pressing at 2100°C for 1 h at 50 MPa and displayed a fine microstructure with an average grain size of ∼5 µm and a Vickers hardness of 22.9 ± .8 GPa. The mass loss was determined using an oxyacetylene torch with cross‐section investigations of oxide surface formations and subsurface microstructural changes. These HfC–SiC samples developed a 410 nm hafnium oxide layer on the surface upon torch exposure and had an average calculated recession rate of .028 µm/s.

Elaboration of Parameters of Large-Size Rings Production Process Taking into Account the Evolution of Material Relative Density

The paper presents the selected problems in production chain of large-size rings for the offshore industry. There are two goals of the technology: 1) to obtain the correct shape of the rings, 2) to achieve required properties. A significant problem in the processes of large size forgings production is a proper prediction of the as-cast structure defects and their behaviour during deformation (forging). This study examines a method of prediction of relative density changes of the material during forging. Experimental procedure includes a forging test at the laboratory scale and numerical modelling. These results as well as boundary conditions were used as input data for the computer simulations of the large rings production processes. The presented procedure allows for a comprehensive analysis of the production process of large-size rings, taking into account areas with insufficient material compaction. The analysis allows for changes in the production chain at the design stage, which significantly reduces the costs associated with pre-implementation tests.

Effects of different configurations and gradients on compression responses of gradient honeycombs via selective laser melting

The structural design of gradient is universally considered to be an effective approach to improve the performance of cellular materials. In this study, the selective laser melting (SLM) was used to fabricate honeycomb components with different gradient configurations and gradient values. The influences of configurations and gradients on the manufacturability, microstructure evolution, and compression behavior were comprehensively investigated. The numerical simulation was conducted to study the deformation mechanism of honeycombs with different configurations. Results revealed that the small wall-thickness caused pore defect and reduced the relative material density of honeycomb components. The variation of the cooling rate of different building parts led to different size of grains. Different configurations and gradients greatly affected the compression behavior of gradient honeycombs. The symmetric positive gradient (SP) configuration exhibited the most excellent compression performance with the highest mean crushing strength, densification strain and CEF. With the increase of gradient values, the compression strength of gradient honeycombs greatly decreased, while the densification strain enhanced visibly. The elevation of gradient values also obviously increased the energy absorption capacity of honeycomb structures, up to 20.41%. The effect of the structure relative density on the compression properties was studied by the numerical simulation. With the increase of the structure relative density, the specific compression strength and the specific energy absorption apparently rose.

Smoothed-strain approach to topology optimization – a numerical study for optimal control parameters

Abstract In this study, three variants of strain smoothing technique, viz. the cell-based, edge-based, and node-based smoothed finite element method, are employed for structural topology optimization. The salient features of the strain smoothing technique are: (i) does not require an explicit form of shape functions and (ii) less sensitive to mesh distortion. Within the proposed framework, the structural materials are modelled as the relative material density powered by the power-law approach. An optimum structural topology is estimated from the condition that minimizes the total strain energy of the structures of interest. The efficacy and the robustness of the strain smoothing technique, when applied to topology optimization, are demonstrated with a few standard benchmark problems. A systematic parametric study is done to find suitable and optimal control parameters for the topology optimization, viz. filter size, tuning parameter, and move limit. The relative performance of different strain smoothing techniques for structural topology optimization is also presented.

3D-Printed Hermetic Alumina Housings.

Ceramics are repeatedly investigated as packaging materials because of their gas tightness, e.g., as hermetic implantable housing. Recent advances also make it possible to print the established aluminum oxide in a Fused Filament Fabrication process, creating new possibilities for manufacturing personalized devices with complex shapes. This study was able to achieve integration of channels with a diameter of 500 µm (pre-sintered) with a nozzle size of 250 µm (layer thickness 100 µm) and even closed hemispheres were printed without support structures. During sintering, the weight-bearing feedstock shrinks by 16.7%, resulting in a relative material density of 96.6%. The well-known challenges of the technology such as surface roughness (Ra = 15–20 µm) and integrated cavities remain. However, it could be shown that the hollow structures in bulk do not represent a mechanical weak point and that the material can be gas-tight (<10−12 mbar s−1). For verification, a volume-free helium leak test device was developed and validated. Finally, platinum coatings with high adhesion examined the functionalization of the ceramic. All the prerequisites for hermetic housings with integrated metal structures are given, with a new level of complexity of ceramic shapes available.

Exploration of the potential of polymer 4D printing: Experiments on the printing quality and the impact of temperature and geometry on the shape-changing effect

4D printing is a term for the additive manufacturing (AM) processes, in which shape-memory materials are used. A 4D printed component is capable of changing its shape to another, which implies that the transformation over time is regarded as the fourth dimension in addition to x, y, and z dimensions in AM. A common material type for 4D printing is the shape memory polymer (SMP) which has the advantages such as low cost and high shape recovery. Under this background, this research focuses on thermoplastic polyurethane (TPU)-based SMP and systematically investigates its performance using three experiments. In the first experiment, the printing quality of the SMP with different process parameters is analyzed and evaluated by its relative material density. In the second and third experiments, the impacts of, respectively, the ambient temperature and the geometry of SMP parts on the shape-changing process are analyzed and evaluated by different time-related parameters during the process. To implement the findings from the experiments, three use cases are described.

Intensive processing optimization for achieving strong and ductile Al-Mn-Mg-Sc-Zr alloy produced by selective laser melting

The Sc-containing AlMn alloy system produced by additive manufacturing (AM) has recently presented exciting new opportunities to achieve a step-change in mechanical properties, but its processability remains unclear. In this work, the optimum processing window for the Al-Mn-Mg-Sc-Zr alloy fabricated by selective laser melting (SLM) has been established for the first time. The window covers the range of processing parameters that can lead to a good combination of part density, strength, ductility, and processability. The alloys fabricated within this optimized processing window of SLM have the material relative density more than 99.8% with less porosity. Moreover, all these alloys have the yield strength exceeding 430 MPa and the ductility of over 17%. Further microstructural examinations suggest that such excellent mechanical properties are associated with a bimodal grain architecture. Also, a high number density of intermetallic particles has been detected in these two-grain regions. They are confirmed to be Al3Sc and Mn(Fe)-rich quasicrystal. Most of these particles distributing along grain boundaries are expected to pin the grain boundaries and contribute to the high strength of this alloy. The findings will provide an essential basis for achieving exceptional mechanical performance and intricate geometry designs of the alloy using AM.

Laser powder bed fusion of bio-inspired honeycomb structures: Effect of twist angle on compressive behaviors

In this study, novel honeycomb structures with twisted feature were designed and manufactured by laser powder bed fusion (LPBF). The manufacturability, microstructure evolution of LPBFed honeycomb components with twisted feature were studied. The influence of twist angle on the compressive behavior of components was experimentally investigated and the underlying mechanism was revealed using FE simulation. Results revealed that the material relative density of LPBFed components was reduced with the increase of twist angle, caused by the enlarging overhanging area. Different cooling rate of melt pool at different parts along the building direction resulted in different microstructures. The twist angle significantly affected the compressive behaviors of honeycomb structures. When the cell number along each side was 3, the honeycomb structure with 30° twist angle exhibited the most uniform stress distribution under compression, leading to the highest specific compressive strength and energy absorption ability. The influence of cell number and wall thickness on compressive properties of honeycomb structures with 30° twist angle were investigated through finite element simulation, and results revealed that the structure with 0.75 mm wall thickness and 3 unit cells along each side showed the highest specific energy absorption ability.

Arc erosion behavior and mechanism of Ag/Ti3SiC2 cathodes in different atmospheres

Novel Ag matrix electrical contacts, which are environment-friendly, are required to operate under complex service conditions and harsh environments. Therefore, it becomes necessary to urgently study their arc erosion properties in different atmospheres. Herein, Ag/Ti3SiC2 composite samples were fabricated by hot-pressing sintering, and the material's relative density, electrical resistivity, thermal conductivity, Brinell hardness, and flexural strength were measured. Moreover, the arc erosion behaviors of Ag/Ti3SiC2 cathodes in sulfur hexafluoride, nitrogen, and oxygen environments were investigated at 3 kV and 6 kV, and the mass loss, arc current, and discharge duration of the Ag/Ti3SiC2 cathodes in the 3 atm were recorded. The surface morphology and composition of the Ag/Ti3SiC2 cathodes were examined after arc erosion. In this study, the arc energy and mass loss had the highest values in oxygen, followed by nitrogen and sulfur hexafluoride. Following the same trend of operating atmospheres, the erosion-region shape gradually changed from circular to irregular. By means of the Raman spectra, there was no composition change can be detected on the cathode in sulfur hexafluoride, TiNx was detected on the cathode in nitrogen, Ag2O, TiO2 and SiO2 were found on the cathode in oxygen. The resistance of the cathode material to arc erosion deteriorated gradually in the sulfur hexafluoride, nitrogen, and oxygen environments. Importantly, the arc erosion mechanism of the Ag/Ti3SiC2 cathodes in different atmospheres is also proposed in this study. This research can provide a reference for the applications of environmentally friendly Ag matrix electrical contact materials in different atmospheres.

Reducing MRI susceptibility artefacts in implants using additively manufactured porous Ti-6Al-4V structures

Magnetic Resonance Imaging (MRI) is critical in diagnosing post-operative complications following implant surgery and imaging anatomy adjacent to implants. Increasing field strengths and use of gradient-echo sequences have highlighted difficulties from susceptibility artefacts in scan data. Artefacts manifest around metal implants, including those made from titanium alloys, making detection of complications (e.g. bleeding, infection) difficult and hindering imaging of surrounding structures such as the brain or inner ear.Existing research focusses on post-processing and unorthodox scan sequences to better capture data around these devices. This study proposes a complementary up-stream design approach using lightweight structures produced via additive manufacturing (AM). Strategic implant mass reduction presents a potential tool in managing artefacts.Uniform specimens of Ti-6Al-4V structures, including lattices, were produced using the AM process, selective laser melting, with various unit cell designs and relative densities (3.1%–96.7%). Samples, submerged in water, were imaged in a 3T MRI system using clinically relevant sequences. Artefacts were quantified by image analysis revealing a strong linear relationship (RR2 = 0.99) between severity and relative sample density. Likewise, distortion due to slice selection errors showed a squared relationship (RR2 = 0.92) with sample density. Unique artefact features were identified surrounding honeycomb samples suggesting a complex relationship exists for larger unit cells.To demonstrate clinical utility, a honeycomb design was applied to a representative cranioplasty. Analysis revealed 10% artefact reduction compared to traditional solid material illustrating the feasibility of this approach.This study provides a basis to strategically design implants to reduce MRI artefacts and improve post-operative diagnosis capability. Statement of SignificanceMRI susceptibility artefacts surrounding metal implants present a clinical challenge for the diagnosis of post-operative complications relating to the implant itself or underlying anatomy. In this study for the first time we demonstrate that additive manufacturing may be exploited to create lattice structures that predictably reduce MRI image artefact severity surrounding titanium alloy implants. Specifically, a direct correlation of artefact severity, both total signal loss and distortion, with the relative material density of these functionalised materials has been demonstrated within clinically relevant MRI sequences. This approach opens the door for strategic implant design, utilising this structurally functionalised material, that may improve post-operative patient outcomes and compliments existing efforts in this area which focus on data acquisition and post-processing methods.

High Performance Dense Proton Ceramic Electrolyte Material Obtained by Cold Sintering Process

The cold sintering process (CSP) was applied for the first time to the high temperature proton conductor BaCe0.8Zr0.1Y0.1O3-δ. The CSP parameters were optimized in order to obtain the best relative density: the amount of water 0-20 wt.%, the pressing temperature 120-180°C and the pressure ranges between 125 to 500 MPa (for 30 minutes). We demonstrate the ability of CSP to achieve a relative density of 83% at only 180°C and 375 MPa using 5 wt.% water. It has been found that a post CSP annealing at 100°C improves the material relative density which reaches 93%. Ceramic materials were investigated for their microstructure-electrochemical properties relations. The ionic conductivity was measured between 150 and 800°C on dense and well defined microstructure materials. When the annealing temperature increases from 1000, 1100, 1200°C a large increase of the conductivity is observed reaching 2.3x10-2 S·cm-1 at 700°C for pellet sintered 10 h at 1200°C.

A constitutive law to predict the compression of gas diffusion layers

The mechanical behavior of gas diffusion layers (GDLs) is predicted via existing models developed for fibrous materials. For this purpose, a new representation of the behavior is required, function of the material relative density rather than the classical mechanical strain. This allows to shed light on the evolution of the GDLs mechanical properties according to the different levels of mechanical stresses encountered during its lifetime. Compression tests are performed in order to differentiate the experimental mechanical properties of two types of GDLs. Different levels of mechanical stress are applied on the samples to simulate a mechanical history similar to the one encountered in real use. Two different behaviors are observed; the compression is at first governed by the mechanical history of the samples before recovering the GDL original behavior. Accordingly, two sets of parameters are required to fit these different behaviors. The GDLs mechanical properties can be then predicted regardless of the samples state, i.e. pristine or used. Excellent correlations are found between predicted and experimental data. This model brings a better understanding of the mechanisms implied during the GDL compression which plays a major role in the performance of proton exchange membrane fuel cells.

On the die compaction of powders used in pharmaceutics

Die compaction is widely used in the compaction of pharmaceutical powders (tableting). It is well known that the powder densification is a result of particle rearrangement and particle deformation. The former is considered to be the governing mechanism of densification in an initial stage of compaction and the latter is regarded as the governing mechanism in the compaction at the higher pressure range. As a more realistic assumption, one can consider that a simultaneous performance of both the rearrangement and deformation mechanisms takes place from the beginning of compaction. To mathematically formulate this assumption, a piston equation is presented where the material relative density is given as a function of the applied pressure on the powder. From the equation, it is possible to obtain the contribution of each mechanism to the material densification at each value of the applied pressure. In the continuation, the piston equation is applied to the tabletting of some pharmaceutical powders. These are the powders of Ascorbic Acid, Avicel® PH 101, Avicel® PH 301, Emcompress®, Sodium Chloride, and Tablettose® whose tableting results have been previously published in the literature. The results show the piston equation as a suitable approach to describe the tabletting of pharmaceutical powders.

Effect of Plastic Deformation of the Initial Components and Particle Size Reduction on the Structure and Properties of the PN85YU15-Ni Composite Material Produced by Spark Plasma Sintering

Structure and mechanical properties of the PN85YU15 - Ni composite materials obtained by spark plasma sintering were investigated. Two types of powder mixtures, namely, nickel mixed with coarse-grained nickel aluminide and nickel mixed with fine-grained nickel aluminide were used to obtain the composites. Nickel aluminide and nickel powders were taken in the ratio 7:3 respectively. The effect of the initial nickel aluminide particle sizes and plastic deformation due to the ball milling on the structure and mechanical properties of materials sintered at 1100 °C and pressure of 40 MPa was determined. Plastic deformation and refining the initial intermetallic powder particle sizes leads to increasing the sintered material relative density to 95%. The tensile strength of the PN85YU15-Ni composite material obtained by sintering of the milled PN85YU15 powder and nickel in the ratio 7:3 was 1060 MPa. This value is almost twice as high as the tensile strength of the composite containing a no significant plastic deformed coarse-grained intermetallic compound powder (590 MPa), and three times higher than the tensile strength of the sintered nickel aluminide powder (380 MPa).

Perceived object stability depends on shape and material properties

Humans can detect whether an unstable object will fall or right itself, suggesting that the visual system can extract an object’s center of mass (COM) and relate this to its base of support. While the COM can be approximated by its shape, this assumes uniform density. We created images of computer-generated goblets made of different materials to assess whether the visual system estimates an object’s COM from both shape and material properties. The images were either uniformly dense (e.g., glass, gold, etc.) or made of composite materials (e.g., glass and gold) and positioned upright or upside-down near a table ledge. We compared each goblet’s critical angle (CA), the angle at which each goblet is equally likely to fall or right itself, to the perceived CA in a two-alternative-forced-choice paradigm. Participants also rank-ordered 20 materials by density on a questionnaire. The results show that observers accurately estimate the CA for all goblets and are sensitive to subtle changes of an object’s COM with change in shape and composite material properties. Importantly, rated density – as measured from the questionnaire – and true material density were positively correlated, suggesting that humans might maintain a representation of relative material density with which to assess object stability. We conclude that the brain is able to assess an object’s behavior in a gravitational environment by forming a reliable assessment of an object’s COM from both its geometric shape and material properties.

Employing of the discrete Fourier transform for evaluation of crack-tip field in periodic materials

An approach for numerical evaluation of a self-similar crack-tip field for a long (semi-infinite) crack embedded in a material with periodic microstructure is suggested. The conditions at the boundaries of a rectangular domain around the tip are formulated by the use of K-field for the homogeneous material possessing effective elastic properties and then the finite discrete Fourier transform is applied. This allows to replace standard analysis of a large periodic domain with many cells by the analysis of a single repetitive cell in the transform space which can be carried out by any numerical method. Consequently, the volume of calculations in comparison with the standard approach is reduced and the problem of a macrocrack embedded in a material with fine microstructure can be addressed without simplifying assumptions. The accuracy of the proposed approach is verified by a comparison with the analytical solution for a crack embedded in a homogeneous plane.Application of the suggested method is given for a crack in a two-dimensional periodically voided material with triangular isotropic layout. The cell problem is resolved by the finite element method. The fracture toughness of the material in the framework of stress criterion for crack propagation is determined and its dependence upon the material relative density is investigated. A comparison of the fracture toughnesses of the solid and voided materials has shown for which parameter combinations voided ones will provide better crack resistance.

Healing Behavior of Micropores in Powder Metallurgy 316L Stainless Steel during Hot Forging and Heat Treatment

The healing behavior of micropores in powder metallurgy (P/M) 316L stainless steel during hot forging and subsequent heat treatment was studied. The results showed that hot forging can improve the homogeneity of the pore size and enhance the relative density of material in varying degree due to different forging temperatures. As a result of deformation and diffusion bonding at high temperature, the irregular pores were spheroidized and finally turned into stable inner grain pores. The comparison of compression behavior between P/M and wrought dense materials has shown that the pores can either be the obstacles of dislocation movement or be the nucleation sites accelerating the recrystallization according to the difference of deformation temperatures.

Perceived Stability of Composite Material Objects

An object's centre of mass (COM) is determined by its shape and density distribution. To assess whether the human visual system can detect an object's COM from both shape and material properties, we created computer-generated images of goblets made of different materials (e.g., glass, polystyrene) that were either uniform or made of composite materials (e.g., glass and gold) and positioned upright or upside down near a table ledge. Observers were instructed to indicate whether the goblet was more likely to fall off the table or right itself. The critical angle (CA), the angle at which the goblet is equally likely to fall or right itself, was used as a measure of perceived object stability. Participants rank-ordered materials by density on a questionnaire after completing the experiment. If object stability were judged in accordance with physical laws, then we would expect no change in the CA across uniform material objects, while we would expect differences in the CA depending on the relative position of materials for composite material objects. The results show that observers correctly recognize that change to a uniform object's material will not affect its stability. Importantly, perceived and true material density were positively correlated suggesting that observers have a good representation of relative material density. Results for composite material objects revealed that the perceived CA changes with the true CA, suggesting that observers use this accurate representation of relative material density to assess object stability. We conclude that the human visual system is able to form a reliable estimate of an object's COM from shape geometry and material properties that is used to assess an object's behaviour. Meeting abstract presented at VSS 2014