Sintering Cycle Research Articles

Sintering process optimization of the additively manufactured pure copper parts through the metal paste deposited process

The fabrication process, sintering cycles through two sintering methods, microstructural and texture characterization, mechanical properties, and electrical conductivity of metal paste-deposited copper parts were investigated in this study. In the first condition, samples were air-debinded for carbon content removal followed by a sintering cycle. A sintering profile with the maximum sintering temperature and time of 1080 °C and 1 hr. was implemented after performing the air-debinding cycle at 250 °C for 2 hrs. In the second condition, samples were sintered in the environment of copper oxide for carbon removal in the early stages of the sintering cycle, i.e., 1070 °C for 1 hr and 1080 °C for 1, 2, and 3 hrs. The microstructural observations revealed coarser grains in the air-debinded samples, perhaps due to additional generated heat during carbon oxide formation, which may produce destructive effects on the boundary (HAGBs, twins, and CSL) volume and densification behavior of copper parts. However, through the second method, much finer grains and higher densities of boundaries were detected in the microstructure. Despite the significant effect of sintering conditions on the microstructure, texture interpretations revealed minor changes in the pole figures for different situations. Using the second sintering method and owing to the less carbon content and based on the density of the boundaries and their configurations, higher electrical conductivity (98.4±1.3 % IACS) was recorded by sintering the green parts. The comparison between the data from this study with other parts printed through other additive manufacturing techniques demonstrated a superior electrical conductivity level and acceptable balance between strain and strain notably with the sample sintered for 3 hrs.

Flash sintering of UO2 pellets for nuclear fuel and wasteform applications

Flash sintering (FS) has been shown to enhance the sintering kinetics in UO2. Using a bespoke AC-FS furnace, high density UO2 pellets, >95% theoretical density (TD) have been produced followed by scale up and Gd2O3 doping trials. Increasing furnace temperature during FS increases pellet density to a plateau, however, increasing hold time and maximum current both increased the density of UO2 samples to >95% TD and grain size to ~4µm, close to conventional sintering (CS). The optimised FS program reduced sintering temperature and cycle time by ~50% compared to CS. Scale up trials showed >96%TD pellets could be achieved for 11.3 and 14.125mm diameter green bodies, demonstrating typical fuel pellet diameters are feasible with FS. Gd doping experiments showed with 1wt.% Gd2O3 addition, a ~92%TD pellet with ~2µm grain size was obtainable, highlighting further optimisation is required for mixed oxide (MOx) materials.

Biomass erosion and its effect on heat carrying performance of alumina heat carrier during multiple cycle sintering in solar photothermal coupled with biomass gasification

Biomass coupled with solar photothermal gasification technology is an efficient technology using solar to provide energy by heat carrier for biomass gasification. However, the heat carrier that transferred heat to the biomass feedstock can be eroded by the effects of biomass ash, with the erosion problem worsening as the number of cycles increased. The erosion and adhesion caused by multiple sintering of corn stalk ash (CSA) to heat carrier particles (Al2O3) were investigated. K and Si elements in CSA are the main elements that erode Al2O3 particles, and their erosion depth increases with the number of sintering cycles. The erosion process of CSA on heat carriers deepens with multi-sintering, but the infiltration behavior of CSA can be fairly prevented due to the generation of high fusion minerals during erosion. The infiltration characteristics of CSA change abruptly upon contact, influencing the erosion behavior during the cyclic sintering process.

Effect of sintering cycle on the strength and translucency of multilayered zirconia.

A newly introduced sintering protocol promises to offer higher translucency while not significantly compromising the flexural strength of the material. However, the effect of the novel sintering protocol has not been thoroughly validated. The purpose of this study was to measure and compare the effect of two sintering protocols on the translucency and flexural strength of two multilayered zirconia materials. Two types of multilayered zirconia materials (ZirCAD Prime and Prime esthetic) were selected. Presintered disk specimens were obtained from Translucent, Gradient, and Dentin layers (n = 20). The disks were allocated to 2 groups: standard sintering protocol (peak temperature 1500°C) and high translucency sintering protocol (peak temperature 1600°C). After the sintering process, 10 specimens from each group were randomly selected. The optical values (L*, a*, b*) were measured and used to assess translucency using the relative translucency parameter (RTP00) and translucency differences (ΔRTP00). Then, all 20 specimens were tested for biaxial flexural strength. The outcomes were analyzed. The analysis of variance is used to analyze any significant effects on translucency and flexural strength. Then, any significant difference in the translucency and flexural strength between all pairs of materials was analyzed using Bonferroni-corrected Student's t-test (α = 0.05). The high translucency sintering protocol significantly decreased biaxial strength in the Prime translucent and dentine layer, Prime esthetic translucent, and gradient layer. RTP00 was significantly reduced in the Prime gradient and Prime esthetic gradient layer when sintered with a high translucency protocol. The lowest ΔRTP00 was observed in the Prime dentine layer, while the highest ΔRTP00 was observed in the Prime esthetic dentin layer. High translucency protocol significantly lowers the biaxial flexural strength of both multilayered materials, but the alteration in translucency is within clinically acceptable thresholds (TAT00 = 2.62).

Effect of different sintering cycles on the flexural strength and translucency of CAD-CAM milled monolithic zirconia with different thicknesses

Effect of different sintering cycles on the flexural strength and translucency of CAD-CAM milled monolithic zirconia with different thicknesses

Experimental investigation and modeling of densification during sintering of binder jetted Ti–6Al–4V

Binder-jetted parts require a subsequent sintering process to achieve the desired density and mechanical properties, resulting in anisotropic shrinkage and creep distortion. To compensate for this, accurate prediction of densification behavior is required. Although there has been research on optimizing the printing and sintering process to increase the reproducibility of Ti–6Al–4V parts, there is no accessible literature on modeling the densification behavior. In this study, the densification of binder-jetted Ti–6Al–4V samples is investigated experimentally through experiments with interrupted sintering cycles and dilatometry. Through these experiments, it is possible to determine the density changes throughout the entire sintering cycle as well as the anisotropic shrinkage of the printed samples. The results are used to calibrate phenomenological diffusion models for intermediate stage and final stage sintering capable of mapping the densification behavior throughout the entire sintering process. Due to experimental limitations, material parameters for grain growth are determined from experimental densification data.

Effect of the cycle number of multistep sintering on the properties of FeSe0.4Te0.6 superconductors

AbstractFeSe0.4Te0.6 polycrystal bulks were synthesized using the solid‐state sintering method. We developed a novel multistep sintering process and studied the impact of the sintering cycle number. Different cycles of multistep sintering, ranging from one to four cycles were systematically arranged. It was found that the superconducting properties of the FeSe0.4Te0.6 polycrystal bulk using three cycles of sintering surpassed those of other samples, reaching a maximum of = 13.4 K, = 14.7 K, and a minimum of ∆ = 1.3 K. And the superconducting current density at 4 K reached 1.77 × 104 A/cm2, exhibiting a weak fishtail effect. At 9 K, a composite pinning effect emerged, consisting of normal point pinning and ∆κ surface pinning. The enhancement in superconductivity is attributed to improve uniformity in grain arrangement and more effective element diffusion. After multiple sintering cycles, the stacked grains exhibited increased thickness and the grain arrangement became dense.

Modeling and simulation of ceramic tiles linear shrinkage variation during the sintering process

Linear shrinkage (SL) is utilized as a criterion to modify the size of the sintered ceramic tiles, and the sintering cycle affects the shrinkage variation. The exact sintering cycle associated with the SL of ceramic tiles is difficult to verify experimentally, and it affects the quality of the final ceramic tiles. Production costs also increased due to the large amount of experimental work. This study investigated a powerful numeric model of the sintering process within ceramic tile, using computational fluid dynamics (CFD) to evaluate the variation of the SL in ceramic tiles during the sintering process. The sintering process was simultaneous and integrated with energy and mass transport phenomena. Numerical formulas were developed for the sintering operation, and the SL behavior of ceramic tiles during sintering was examined using a kinetic model. An unsteady 3D model was established, and simulation was performed using the CFD tool by varying the temperature profile. The results of CFD simulation can ascertain the temporal and spatial changes in the SL of ceramic tiles through sintering. To validate the model, the green body mixture of ceramic tile was prepared and analyzed. Ceramic tiles were shaped by a powder pressing technique on a laboratory scale. Dried tiles were sintered in a laboratory furnace by adjusting the maximum sintering temperatures. The structure of sintered ceramic tiles was analyzed. The SL variation of each sintered tile was determined and compared with the results of CFD simulations. The results of the CFD simulation were validated and concurred with experimental outcomes, and the R2 value of the results was 0.9. The developed CFD model is capable of predicting the temporal and spatial changes in SL of ceramic tiles through sintering, and it is a great help to find the exact sintering cycle associated with SL. Finally, the quality of the tile is increased, and production costs are also reduced.

Material extrusion additive manufacturing of zirconia: from filament characterisation to Weibull statistics

PurposeThis study aims to investigate the performance of filament-based material extrusion additive manufacturing (MEX), combined with debinding and sintering, as a novel approach to manufacturing ceramic components.Design/methodology/approachA commercial ZrO2 filament was selected and analysed by infra-red (IR) spectroscopy, rheology and thermo-gravimetry. The influence of the print parameters (layer thickness, flow rate multiplier, printing speed) and sintering cycle were investigated to define a suitable printing and sintering strategy. Biaxial flexure tests were applied on sintered discs realised with optimised printing strategies, and the results were analysed via Weibull statistics to evaluate the mechanical properties of printed components. The hardness and thermal conductivity of sintered components were also tested.FindingsLayer thickness and flow rate multiplier of the printing process were proved to have significant effect on the density of as-printed parts. Optimised samples display a sintered density >99% of the theoretical density, 20% linear sintering shrinkage, a characteristic flexural strength of 871 MPa with a Weibull modulus of 4.9, a Vickers hardness of 12.90 ± 0.3 GPa and a thermal conductivity of 3.62 W/mK. Gyroids were printed for demonstration purposes.Originality/valueTo the best of the authors’ knowledge, this work is the first to apply biaxial flexure tests and Weibull statistics to additively manufactured MEX zirconia components, hence providing comparable results to other additive technologies. Moreover, fractography analysis builds the connection between printing defects and the fracture mechanism of bending. This study also provides guidelines for fabricating high-density zirconia components with MEX.

Facile synthesis of high entropy carbide-nickel based cermets by in-situ carbo-thermal reduction of transition metal oxides

Equimolar and non-equimolar high entropy carbide-nickel based cermets were successfully prepared by in-situ carbo-thermal reduction of constituent metal oxides in a single pressureless vacuum sintering cycle at 1420°C. The carbon content in quinary (Ti0.2V0.2Nb0.2Ta0.2W0.2)Cx-10wt.%Ni and senary (Ti0.2V0.2Nb0.2Ta0.2W0.1Mo0.1)Cx-10wt.% Ni high entropy carbide cermets was varied (x = 0.6–1.0). Two-phase HEC-Ni cermets were formed at x = 0.75–0.85, whereas M6C (η-phase) and graphite phase coexisted at lower and higher carbon contents (x = 0.6, 0.9 and 1.0) in both HEC 5 and HEC 6 systems. In HEC 5, submicrometric WC precipitates were observed, which were attributed to the limited solubility of hexagonal-WC within the in-situ formed HEC 5 phase, contrasting with HEC 6 where no such precipitations were formed across the entire carbon content range. The partial replacement of W with Mo in the (Ti0.2V0.2Nb0.2Ta0.2W0.1Mo0.1)Cx-10 wt% Ni cermets promoted solid solution formation at lower temperature, and the grain size and hardness decreased and the fracture toughness increased. Both HEC-Ni cermets showed a homogeneous distribution of elements within the carbide phase, resulting in (HV30) hardness around 16 GPa and a fracture toughness around 8 MPa.m1/2. The phase evolution was systematically investigated by interrupting the sintering cycle at 600–1400 °C, employing XRD analysis. Thermodynamic calculations were performed to predict the critical reaction temperatures for carbo-thermal reduction. To evaluate the intrinsic mechanical properties of each phase and establish the correlation with microstructural features, micromechanical mapping was performed utilizing the high-speed nano-indentation technique.

Toward the Improvement of the Short‐Loop Recycling of Dy‐Rich Nd–Fe–B Permanent Magnets: Experimental and Numerical Approaches

The method of short‐loop recycling of Nd–Fe–B magnets is implemented, with end‐of‐life (EoL) magnets used as a source of heavy rare earth (HRE). Partially recycled magnets are fabricated by co‐sintering HRE‐free powders obtained from strip casted alloys, blended with HRE‐rich powders obtained from EoL magnets. The impact of several process parameters (blending ratio, sintering cycle, and HRE‐rich recycled particle sizes) on the microstructure and magnetic properties is discussed. A coercivity gain up to 160 kA m−1 wt%−1 of Dy with respect to the HRE‐free magnets is reported, even though impurities are incorporated. Microstructural characterizations show a heterogeneous Dy localization in core–shell/anticore–shell structures, and thus a nonoptimal use of HRE. The experimental results are compared with finite element simulations of the Dy diffusion transport performed using existing data of bulk Dy diffusion coefficients. The simulation model consists of a network of square grains separated by a liquid phase, whose fraction is based on the ternary Nd–Fe–B phase diagram. Results show similarities with the observed microstructures, and point to the interest of reducing the Dy‐rich particle size with respect to the main powder. This study provides new insights into the Dy transport mechanisms at stake in an efficient short‐loop recycling of HRE.

Flexural strength, flexural modulus and microhardness of milled vs. fused deposition modeling printed Zirconia; effect of conventional vs. speed sintering

BackgroundVarious methods can be used for creating zirconia dental restorations, including 3-dimensional (3D) printing and computer-aided design/ computer-aided manufacturing (CAD/CAM) milling. The fused deposition modeling (FDM) printing method for zirconia presents numerous advantages, albeit research on the mechanical properties of these materials and resultant restorations remains scarce. Such developments are undeniably intriguing and warrant further investigation. The objective of the present study was to evaluate the impact of the sintering firing cycle (Conventional vs. Speed sintering) on the flexural strength, flexural modulus, and Vickers Microhardness of milled vs. FDM printed zirconia.MethodsA total of 60 bars (2 × 5 × 27 mm) were fabricated for flexural strength testing, along with 40 discs (12 × 1.5 mm) for Vickers microhardness testing. Half of the specimens underwent conventional sintering, while the other half underwent a speed sintering cycle. The flexural strength and modulus were determined by a three-point bending test in a universal testing machine. The microhardness of the specimens was evaluated using a Vickers microhardness tester. Statistical analysis was performed using a two-way ANOVA test with a post-hoc Tukey test (p < 0.05).ResultsCAD/CAM milled zirconia had significantly higher flexural strength and modulus than FDM-printed zirconia. The sintering process did not significantly affect the flexural strength or modulus of milled or FDM-printed zirconia. The milled speed sintering group had significantly higher values in the Vickers microhardness test compared to the other groups.ConclusionsThe mechanical properties of FDM-printed zirconia specimens were not found to be comparable to those of milled zirconia. Speed sintering cycle may produce milled zirconia restorations with similar flexural strength and modulus to conventional sintering, and even higher Vickers Microhardness values.

Rapid densification mechanism and properties of h-BN/ZrO2 composites with oxide additives by spark plasma sintering

Large size high density h-BN/ZrO2 composites (ø=110 mm, h=15 mm) were rapidly prepared by spark plasma sintering (SPS) with sintering cycle 20 min. The effects of additives on the mechanical properties, microstructure evolution, and corrosion resistance of the h-BN/ZrO2 composites were studied. The Al2O3, MgO, SiO2, La2O3 and ZrO2 rapidly formed heterogeneous eutectic crystals under the action of SPS. The low eutectic compounds significantly promoted the diffusion of h-BN or ZrO2, also increased the density. The flexural strength of h-BN/ZrO2 composites could reach 196.31 MPa, and the apparent porosity was only 0.42%. The additives are combined with zirconia to form a high viscosity eutectic, whose corrosion resistance to molten steel is obviously better than that of single ZrO2. The corrosion depth of h-BN/ZrO2 composites was only 114 μm after corroded in molten steel at 1550℃ for 80 min. The comprehensive properties of h-BN/ZrO2 composites were obviously improved by appropriate additives.

The Effect of Two Sintering Cycles and Aging on Biaxial Flexural Strength of Strength Gradient Multi-Layered Zirconia (In vitro Study)

The Effect of Two Sintering Cycles and Aging on Biaxial Flexural Strength of Strength Gradient Multi-Layered Zirconia (In vitro Study)

Hybrid microwave sintering of Zirconia Toughened Alumina in a multimode cavity – Influence of the content of 3 mol% yttria stabilized zirconia and sintering configurations

MW sintering is a sintering process in which samples directly heat by absorption of the electromagnetic field, leading to a fast volume heating. Thus, the materials are heated due to their own dielectric properties. Zirconia Toughened Alumina (ZTA) is of particular interest for MW sintering because of the difference of dielectric properties between alumina and zirconia. In this study, ZTA pellets with different volume fractions of zirconia were sintered in a MW multimode cavity with different sintering cells, i.e., with or without susceptor. These experiments show that all the samples were densified whatever the configuration. But the evolution of power and temperature vs time during the sintering cycle shows a better heating capability when the volume fraction of zirconia increases. The influence of the material to heat is more visible when sintering without susceptor. This was confirmed by other experiments, where the samples were heated by a constant incident power in a single-mode cavity.

Spark Plasma Sintering of Complex Metal and Ceramic Structures Produced by Material Extrusion.

Alternative approaches to laser fusion for the additive manufacturing (AM) of metals are often hampered by the need for long sintering cycles. Typical sintering cycles require heating at temperatures above 80% of the melting point for several hours. The process is time- and energy-consuming, particularly when high-melting materials are involved. Applying pressure can drastically reduce the time and temperature required for densification. Recently, a particular kind of pressure-assisted sintering process known as spark plasma sintering (SPS) or field-assisted sintering (FAST) received considerable attention in academia and industry due to its ability to enhance densification. However, conventional SPS/FAST techniques cannot be directly applied to the densification of objects presenting a complex geometry. This work shows how a modified SPS/FAST setup, operating in a pseudoisostatic mode, can be used for debinding and sinter objects produced by material extrusion. This approach can be applied to metals and metal-based and ceramic-based composites when their geometry does not include closed cavities. Depending on the characteristics of the pressure-transfer medium, some level of anisotropy in the volume reduction associated with the densification can be observed. Still, it can easily be corrected by appropriately compensating sintering deformation during printing. Using this approach, the time required for the debinding and sintering can be reduced considerably. It represents an alternative approach to the AM of a wide range of inorganic materials characterized by a relatively low-cost, high material flexibility, and low environmental impact.

Laser powder bed fusion of Alumina/Fe–Ni ceramic matrix particulate composites impregnated with a polymeric resin

Additive Manufacturing (AM) plays a key role in meeting the vital demands of Industry. The AM industry needs the range of applicable materials to be expanded by conducting research on novel ones. In the present investigation, alumina/Fe–Ni (steel) ceramic matrix particulate composite was fabricated employing laser powder bed fusion (LPBF) additive manufacturing (AM) technology. The quality of the printed samples was associated with the LPBF process parameters, which were optimized for this process. In general, the fabricated samples showed a microstructure of alumina matrix with uniform distribution of steel (Fe–Ni) particles. The as-printed samples exhibited pores. Thus, they were subjected to a sintering heat treatment cycle under an inert atmosphere. Although the sintering cycle considerably increased the average Vickers hardness, pores were not eliminated entirely. Therefore, polymer impregnation of the as-sintered samples was carried out to reduce porosities and microcracks. The mercury porosimeter showed that the porosity decreased sequentially after sintering and polymer impregnation. In addition, mechanical investigations revealed that the polymer impregnation improved the compressive strength of the sintered samples (from 56 to 120 MPa). Alumina-based materials find wide applications in various fields, including the manufacturing of electronic components, cutting tools, biomedical implants, and catalyst converters, owing to their low density, high hardness, wear and corrosion resistance, and biocompatibility. This study presents a viable approach for the fabrication of these materials, with developed samples exhibiting promising properties. The study emphasizes the potential of additive manufacturing as an approach for the fabrication of ceramic matrix composites reinforced with metallic particulates in future research.

Direct configuration mode microwave sintering of natural uranium dioxide pellets

The direct microwave sintering of natural uranium dioxide (UO2) pellets at bulk scale is first time successfully demonstrated. The process of the microwave sintering is carried out at 1700 °C, 6h in reducing atmosphere with a sintering cycle spanning over 31h in an indigenously designed and developed sintering set-up deploying 2.45 GHz microwave radiation. The process is demonstrated for obtaining defect-free pellets (devoid of cracks and any plasma induced edge/surface melting or burnouts) in bulk quantity consisting of a batch size of 3 kg (500–550 pellets). The sinter density of pellets was found to be uniform and in the acceptable range of 92–96%TD for nuclear fuel. The comparison of optical microstructures prima facie indicates that the UO2 grain size is smaller in microwave sintered pellets (5–20 μm) as compared to conventionally sintered UO2 pellets (10–40 μm) under identical parameters. The axial and the diameteral shrinkages during densification were observed to be 18–20% which are comparable to the conventional sintering. The microwave sintered UO2 pellets has O/U mole ratio as 2.002. The process is consistent and easily up-scalable to sinter large size of batches so as to meet the industrial scale demands.

Effect of Different Sintering Cycles on the Flexural Strength of Full Contour Monolithic Zirconia – An In-Vitro Comparative Study

BACKGROUND&#x0D; Monolithic zirconia restorations are known to exhibit good mechanical properties and acceptable aesthetics. During the fabrication of zirconia prostheses, the sintering process is the most critical step which determines the performance of the final product. However, a lot of issues with zirconia restorations were related to sintering cycles which can affect the crystalline content and grain growth that can affect its mechanical properties. The purpose of this study was to evaluate and compare the effect of different sintering cycles on the flexural strength of full-contour monolithic zirconia.&#x0D; METHODS&#x0D; In this in-vitro study, a total of 44 bar-shaped zirconia samples (Amann Girrbach Ceramill® CAD/CAM Material – ZOLID HT+) of final dimensions 20 x 4 x 2 mm were fabricated using Amann Girrbach Ceramill mind – computer-aided designing software and Amann Girrbach Ceramill® motion2 – computer-aided milling unit. These samples were randomly allocated into four groups with 11 samples in each group namely, Group 1, 2, 3 and 4 (Group 1: Long sintering cycle, Group 2: Intermediate sintering cycle, Group 3: Short sintering cycle, Group 4: Ultra-short sintering cycle) and sintered under the respective sintering cycles. The Ceramill® therm (Amann Girrbach) sintering furnace provided 3 sintering cycles ranging from the longest group-1 (19 hours), to the short sintering cycle group-3 (8 hours), with an intermediate sintering cycle group-2 (15 hours). The zircon (KDS) sintering furnace provided an ultra-short sintering cycle group-4 (2 hours). The testing of flexural strength was performed using a three-point bend test on a universal testing machine. Statistical analysis of the collected data was performed by one-way ANOVA using SPSS software.&#x0D; RESULTS&#x0D; One-way ANOVA showed no statistically significant difference in the flexural strength of full-contour monolithic zirconia sintered under the four different sintering cycles. (P &gt; 0.05).&#x0D; CONCLUSIONS&#x0D; The flexural strength of full-contour monolithic zirconia was influenced to some extent by various sintering cycles. The longest sintering cycle (Group 1) showed the least flexural strength whereas the intermediate sintering cycle (Group 2) showed the highest flexural strength. Also, the ultra-short sintering cycle (Group 4) of 2 hours exhibited flexural strength comparable to the rest of the groups with longer sintering cycles, thus making the cycle a viable alternative to the conventional sintering cycles, thereby making the ‘tooth-in-a-day‘ possible for the patients.

Upscaling Ultrafast High-Temperature Sintering (UHS) to consolidate large-sized and complex-shaped ceramics

Despite the well-recognized advantages of Ultrafast High-temperature Sintering (UHS) based on the application of a graphite felt/paper heater, the technology, however, remains mostly suitable to consolidate thin-shaped samples. This work proposes a novel UHS configuration based on the graphite powder medium (P-UHS) to obtain much larger and complex-shaped products. As a proof-of-concept, nearly full dense and homogeneous macro-/microstructures bulk alumina ceramics with size of 10×10×25 mm3 were densified under a heating rate of 770 °C/min. In comparison with the conventional firing (5 °C/min) approach, the combination of ultrafast heating rate and high temperature (≥1772 °C) induced a very high densification rate mostly driven by lattice diffusion. The very rapid sintering cycle also prevented any detectable carbon contamination. Indeed, the proposed P-UHS approach combines together fine tuning of the microstructures and ultralow energy requirements.