Search Results (36)

Residual stresses and anisotropic structures characterize laser powder bed fusion (L-PBF) products due to rapid thermal changes during fabrication, potentially leading to microcracking and lower strength. Post-heat treatments are crucial for enhancing mechanical properties. Numerous dental technology laboratories worldwide are adopting the new technologies but must invest considerable time and resources to refine them for specific requirements. Our research can assist researchers in identifying thermal processes that enhance the mechanical properties of dental Co-Cr alloys. In this study, high cooling rates (quenching) and annealing after quenching were evaluated for L-PBF Co-Cr dental alloys. Cast samples (standard manufacturing method) were tested as a second reference material. Tensile strength, Vickers hardness, microstructure characterization, and phase identification were performed. Significant differences were found among the L-PBF groups and the cast samples. The lowest tensile strength (707 MPa) and hardness (345 HV) were observed for cast Starbond COS. The highest mechanical properties (1389 MPa, 535 HV) were observed for the samples subjected to the water quenching and reheating methods. XRD analysis revealed that the face-centered cubic (FCC) and hexagonal close-packed (HCP) phases are influenced by the composition and heat treatment. Annealing after quenching improved the microstructure homogeneity and increased the HCP content. L-PBF techniques yielded superior mechanical properties compared to traditional casting methods, offering efficiency and precision. Future research should focus on fatigue properties. Full article

The powder spreading process is a fundamental element within the laser powder bed fusion (PBF-LP) framework given its pivotal role in configuring the powder bed. This configuration significantly influences subsequent processing steps and ultimately determines the quality of the final manufactured part. This research paper presents a comprehensive analysis of the impacts of varying spreading speeds, which are enabled by different roller configurations, on powder distribution in PBF-LP. By utilizing extensive Discrete Element Method (DEM) modelling, we systematically examine how spreading speed affects vital parameters within the spreading process, including packing density, mass fraction, and actual layer thickness. Our exploration of various roller configurations has revealed that increasing spreading speed generally decreases packing density and layer thickness for non-rotating, counter-rotating, and forward-rotating rollers with low clockwise rotational speeds (sub-rolling) due to powder dragging. However, a forward-rotating roller with a high clockwise rotational speed (super-rolling) balances momentum transfer, enhancing packing density and layer thickness while increasing surface roughness. This configuration significantly improves the uniformity and density of the powder bed, providing a technique to accelerate the spreading process while maintaining and not reducing packing density. Furthermore, this configuration offers crucial insights into optimizing additive manufacturing processes by considering the complex relationships between spreading speed, roller configuration, and powder spreading quality. Full article

The following investigation focused on examining the kinetics of Fe₂B coating formation on the surface of ASTM A681 steel during the powder-pack boronizing process. The study measured Fe₂B coating thicknesses at various temperatures and exposure times to confirm the diffusion-controlled growth mechanism during boronizing. Five distinct mathematical models were devised to determine the boron diffusion coefficients in Fe₂B coatings. Understanding the growth kinetics of boronize coatings is imperative as it facilitates the optimization and automation of industrial processes. This ensures the efficient and consistent production of boronize coatings on cutting tools, such as drills and milling cutters, due to their high hardness and wear resistance. The value of the activation energy estimated with five mathematical diffusion models for the Fe₂B coating was 209.8 kJ∙mol⁻¹. The X-ray diffraction technique was used to identify the presence of the iron boronize phase. Tribological studies were also performed to evaluate the coefficient of friction (COF) of the boronized (0.256) and untreated (0.781) samples, having a 300% positive effect of the boronize coating on wear resistance. Finally, the models were empirically validated for two supplementary treatment conditions for 1223 K for 3 h and 1273 K for 1.5 h, where the percentage error for both conditions was estimated to be approximately 2.5%. Full article

This review, complemented by empirical investigations, delves into the intricate world of industrial powders, examining their elastic properties through diverse methodologies. The study critically assesses Young’s modulus (E) across eight different powder samples from various industries, including joint filler, wheat flour, wheat starch, gluten, glass beads, and sericite. Employing a multidisciplinary approach, integrating uniaxial compression methodologies—both single and cyclic—with vibration techniques, has revealed surprising insights. Particularly notable is the relationship between porosity and Young’s modulus, linking loose powders to the compacts generated under compression methods. Depending on the porosity of the powder bed, Young’s modulus can vary from a few MPa (loose powder) to several GPa (tablet), following an exponential trend. The discussion emphasizes the necessity of integrating various techniques, with a specific focus on the consolidation state of the powder bed, to achieve a comprehensive understanding of bulk elasticity. This underscores the need for low-consolidation methodologies that align more closely with powder technologies and unit operations such as conveying, transport, storage, and feeding. In conclusion, the study suggests avenues for further research, highlighting the importance of exploring bulk elastic properties in loose packing conditions, their relation with flowability, alongside the significance of powder conditioning. Full article

To better understand and control the crystallization of different polymorphs, a comprehensive crystal structure analysis was conducted by using fluralaner as a model compound, and the thermodynamic stability, phase transformation, and selective nucleation mechanisms were studied. Various analytical techniques such as powder X-ray diffraction, thermal analysis, and FT-IR spectra were used to comprehensively characterize Form I, Form Ⅱ, and Form III of fluralaner, and it was found that there is structural similarity between Form I and Form III, which was further confirmed by single crystal X-ray diffraction. However, it was found that Form Ⅱ had unique molecular conformation and packing pattern. The lattice energy was calculated by Materials Studio 7.0 and the thermodynamic stability of three forms was explored by phase transformation experiments, which suggested that the order of thermodynamic stability was Form Ⅱ > Form I > Form III. The selective nucleation of Form I and Form III with similar structure was studied through FT-IR spectra and molecular dynamics simulations. The results indicated that the addition of n-hexane may hinder the solute–solute interaction in the solution, thus resulting in the nucleation of different polymorphs. Full article

Powder-bed-based additive manufacturing processes (PBAM) are sensitive to variations in powder feedstock characteristics, and yet the link between the powder properties and process performance is still not well established, which complicates the powder selection, quality control, and process improvement processes. An accurate assessment of the powder characteristics and behavior during recoating is important and must include the flow and packing properties of the powders, which are dependent on the application conditions. To fulfill the need for suitable powder testing techniques, a novel apparatus is developed to reproduce the generic PBAM powder spreading procedure and allow the measurements of the powder bed density, surface uniformity, and spreading forces as functions of the powder characteristics and spreading conditions, including the spreading speed and the type of spreading mechanism. This equipment could be used for research and development purposes as well as for the quality control of the PBAM powder feedstock, as showcased in this paper using a gas-atomized Ti-6Al-4V powder (D10 = 25.3 µm, D50 = 35.8 µm and D90 = 46.4 µm) spread using a rigid blade by varying the recoating speed from 100 to 500 mm/s and the layer thickness from 30 to 100 µm. Full article

The mix design of UHPC has always been based on a large number of experiments; in order to reduce the number of repeated experiments, in this study, silica fume (SF), fly ash (FA), and limestone powder (LP) were used as the raw materials to conduct 15 groups of experiments to determine the particle size distribution (PSD) properties of UHPC. A model of multi-component hydration based on the SF, FA, and LP pozzolanic reactions was devised to quantify the rate and total heat release during the hydration process. Additionally, a microscopic pore development model, which was based on the accumulation of hydration products, was established to measure the effect of these products on the particle-packing properties. Utilizing this model, a UHPC strength prediction technique was formulated to precisely forecast the compressive strength based on a restricted experimental data set. The applicability of this prediction method was verified using 15 sets of existing experimental data along with the data collected from 4 research articles. The results show that the prediction method can predict the strength values of different mix proportions with an accuracy rate of over 80%. Full article

This research focuses on the fabrication and characterization of TAZ532-xNb composites, employing high-purity, micron-sized powders of Mg, Sn, Al, Zn, Mn, and Nb as the raw materials. These powders were subjected to a paraffin coating process aimed at mitigating oxidation. The formation of composites was achieved via hot pressing and was followed by surface preparation and analysis using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). An X-ray diffraction (XRD) study was conducted to identify the microstructural phases. Quantitative assessments including the theoretical density, actual density, and relative density were computed, and their fluctuations in relation to the increasing Nb reinforcement ratio were scrutinized. Furthermore, the mechanical attributes of the composites, such as hardness and tensile strength, were assessed via experimental procedures. The absence of oxygen-related peaks in the XRD patterns endorsed the successful execution of the paraffin coating technique and protective gas atmosphere during sintering. The detection of α-Mg, Mg₂Sn, MgZn, Mg₁₇Al₁₂, and Nb phases within the Nb-reinforced composite patterns authenticated the formation of the intended phases. Notably, the relative density values of the composites surpassed 95%, indicating efficient sintering. SEM results disclosed a densely packed microstructure, with Nb reinforcement particles evenly distributed along the grain boundaries, devoid of particle clustering or significant grain growth. These composites manifested exceptional wetting characteristics, which can be attributed to the employment of Mg alloy as the matrix material. EDS data confirmed the proportions of Nb within the composites, aligning with the quantities incorporated during fabrication. The composites showcased an increase in microhardness values with the escalating Nb reinforcement ratio, credited to the harder constitution of Nb particles in comparison to the matrix alloy. Concurrently, tensile strength showed a significant improvement with the increment in Nb reinforcement, while elongation values peaked at a specific Nb reinforcement level. The positive evolution of tensile strength properties was ascribed to the escalated Nb reinforcement ratio, grain size, and consequent higher sample densities. Full article

Solid bacterial agents are required to accelerate stover degradation in low-temperature areas. However, the laboratory-to-practice translation of bioprocessing techniques is hindered by high cost, poor practicality, and short shelf life. Using corn stover powder, starch, and bran as additives, we screened Pseudomonas putida and Acinetobacter lwoffii, which effectively degrades corn stover at low temperatures, to develop a sustainable and low-cost bacterial agent formula that ensures bacterial viability in low-temperature soil and storage. The optimal formulation included precipitates and additives at a 1:4 ratio, including corn stover powder, starch, and bran at a 4:3:9 ratio. The viable bacterial count with this formulation reached 7.5 × 10¹⁰ colony-forming units/g, with high lignocellulase activities. The degradation effect of the optimal formulation on stover and its components, in both lab soil culture simulation and the field environment, was significantly higher than that without bacterial agent application. This formulation had an outstanding effect on lignin. The optimal storage conditions included vacuum packing under 10% water content at 4 °C; the survival rate of viable bacteria reached 85.33% after 180 d. Given the global value of stover-return agriculture, our results offer a valuable strategy for application in low-temperature soils where stover degradation rates are otherwise low. Full article

Thermal polymorphism in the alkali-metal salts incorporating the icosohedral monocarba-hydridoborate anion, CB₁₁H₁₂⁻, results in intriguing dynamical properties leading to superionic conductivity for the lightest alkali-metal analogues, LiCB₁₁H₁₂ and NaCB₁₁H₁₂. As such, these two have been the focus of most recent CB₁₁H₁₂⁻ related studies, with less attention paid to the heavier alkali-metal salts, such as CsCB₁₁H₁₂. Nonetheless, it is of fundamental importance to compare the nature of the structural arrangements and interactions across the entire alkali-metal series. Thermal polymorphism in CsCB₁₁H₁₂ was investigated using a combination of techniques: X-ray powder diffraction; differential scanning calorimetry; Raman, infrared, and neutron spectroscopies; and ab initio calculations. The unexpected temperature-dependent structural behavior of anhydrous CsCB₁₁H₁₂ can be potentially justified assuming the existence of two polymorphs with similar free energies at room temperature: (i) a previously reported, ordered R3 polymorph stabilized upon drying and transforming first to R3c symmetry near 313 K and then to a similarly packed but disordered I43d polymorph near 353 K and (ii) a disordered Fm3 polymorph that initially appears from the disordered I43d polymorph near 513 K along with another disordered high-temperature P6₃mc polymorph. Quasielastic neutron scattering results indicate that the CB₁₁H₁₂⁻ anions in the disordered phase at 560 K are undergoing isotropic rotational diffusion, with a jump correlation frequency [1.19(9) × 10¹¹ s⁻¹] in line with those for the lighter-metal analogues. Full article

The inherent properties of magnesium (Mg) make it one of the most challenging metals to process with additive manufacturing (AM), especially with fusion-based techniques. Binder jetting is a two-step AM method in which green Mg objects print near room temperature, then the as-printed green object sinters at a high temperature. Thus far, a limited number of studies have been reported on the binder jetting of Mg powder. This study aimed to push the knowledge base of binder jetting and sintering for AZ91D powder. To this end, the principle of capillary-mediated binderless printing was used to determine the ink saturation level (SL) required for the binder jetting of a green AZ91 object. The effects of various SLs on forming interparticle bridges between AZ91 powder particles and the dimensional accuracy of the resultant as-printed objects were investigated. Green AZ91 objects sintered at different temperatures ranging from 530 °C to 575 °C showed a marginal increment in density with an increase in sintering temperature (i.e., 1.5% to 5.1%). The root cause of such a low sintering densification rate in the presence of up to 54.5 vol. % liquid phase was discussed in the context of the powder packing density of as-printed objects and swelling occurring at sintering temperatures ≥ 45 °C. Overall, this work demonstrates the great potential of binderless printing for AM of Mg powder and the need for pushing sintering boundaries for further densification of as-printed Mg components. Full article

Avoiding loose powders and resins, material extrusion additive manufacturing is a powerful technique to produce near-net shape parts, being a cheap and safe alternative for developing complex industrial-grade products. Filaments embedded with a high packing density of metallic or ceramic granules are being increasingly used, resulting in almost fully dense parts, whereby geometries are shaped, debinded and sintered sequentially until the completion of the part. Traditionally, “brown” debinded geometries are transported to conventional furnaces to densify the powder compacts, requiring careful tailoring of the heating profiles and sintering environment. This approach is decoupled and often involves time-consuming post-processing, whereby after the completion of the shaping and debinding steps, the parts need to be transported to a sintering furnace. Here, it is shown that sintering via indirect induction heating of a highly filled commercially available filament embedded with stainless steel 316L powder can be an effective route to densify Fused Filament Fabricated (FFF) parts. The results show that densities of 99.8% can be reached with very short soaking times, representing a significant improvement compared to prior methods. A hybrid machine is proposed, whereby a custom-built machine is integrated with an induction heater to combine FFF with local indirect induction sintering. Sintering in situ, without the need for part transportation, simplifies the processing of metal parts produced through material extrusion additive manufacturing. Full article

Shell printing is an advantageous binder jetting technique that prints only a thin shell of the intended object to enclose the loose powder in the core. In this study, powder packing in the shell and core was investigated for the first time. By examining the density and microstructure of the printed samples, powder packing was found to be different between the shell and core. In addition, the powder particle size and layer thickness were found to affect the powder packing in the shell and core differently. At a 200 µm layer thickness, for the 10 µm and 20 µm powders, the core was less dense than the shell and had a layered microstructure. At a 200 µm layer thickness, for the 70 µm powder, the core was denser and had a homogeneous microstructure. For the 20 µm powder, by reducing the layer thickness from 200 µm to 70 µm, the core became denser than the shell, and the microstructure of the core became homogeneous. The different results could be attributed to the different scenarios of particle rearrangement between the shell and core for powders of different particle sizes and at different layer thicknesses. Considering that the core was denser and more homogeneous than the shell when the proper layer thickness and powder particle size were selected, shell printing could be a promising method to tailor density and reduce anisotropy. Full article

The powder-pack boriding technique with an open retort was used to form borided layers on X165CrV12 tool steel. The process was carried out at 1123, 1173, and 1223 K for 3, 6, and 9 h. As a result of boriding the high-chromium substrate, the produced layers consisted of three zones: an outer FeB layer, an inner Fe₂B layer, and a transition zone, below which the substrate material was present. Depending on the applied parameters of boriding, the total thickness of the borided layers ranged from 12.45 to 78.76 µm. The increased temperature, as well as longer duration, was accompanied by an increase in the thickness of the FeB zone and the total layer thickness. The integral diffusion model was utilized to kinetically describe the time evolution of the thickness of the FeB and (FeB + Fe₂B) layers grown on the surface of powder-pack borided X165CrV12 steel. The activation energy of boron for the FeB phase was lower than that for the Fe₂B phase. This suggested that the FeB phase could be formed before the Fe₂B phase appeared in the microstructure. The high chromium concentration in X165CrV12 steel led to the formation of chromium borides in the borided layer, which increased the hardness (21.88 ± 1.35 GPa for FeB zone, 17.45 ± 1.20 GPa for Fe₂B zone) and Young’s modulus (386.27 ± 27.04 GPa for FeB zone, 339.75 ± 17.44 GPa for Fe₂B zone). The presence of the transition zone resulted from the accumulation of chromium and carbon atoms at the interface between the tips of Fe₂B needles and the substrate material. The presence of hard iron and chromium borides provided significant improvement in the wear resistance of X165CrV12 steel. The powder-pack borided steel was characterized by a four times lower mass wear intensity factor and nine times lower ratio of mass loss to the length or wear path compared to the non-borided material. Full article

The development of convenient, non-complicated, and cost-efficient processing techniques for packing low-density MOF powders for industry implementation is essential nowadays. To increase MOFs’ availability in industrial settings, we propose the synthesis of a novel 3D Tb-MOF (1) and a simple and non-expensive method for its immobilization in the form of pellets and membranes in polymethacrylate (PMMA) and polysulphone (PSF). The photoluminescent properties of the processed materials were investigated. To simulate industrial conditions, stability towards temperature and humidity have been explored in the pelletized material. Water-adsorption studies have been carried out in bulk and processed materials, and because of the considerable capacity to adsorb water, proton-conduction studies have been investigated for 1. Full article