Sintering Of Compacts Research Articles

Control morphology and properties in additive manufacturing of functional gradient cemented carbides for polycrystalline diamond substrates

Cemented carbide substrates contribute mainly to the strength and impact toughness of polycrystalline diamond composites (PDC). By using a PW-MW-HDPE-EVA-SA mixed polymeric binder and combining Powder Extrusion Printing (PEP) with densification sintering processes, the YG10/YG15 functionally gradient cemented carbides (FGCCs) with different powder loadings were prepared. This study focuses on exploring process feasibility and the integrated regulatory mechanisms for FGCCs morphology and performance. The results showed that the configured cemented carbide feedstocks with different powder loadings exhibited uniform composition and good shear-thinning characteristics, making them suitable for extrusion printing. The FGCC green parts formed by PEP have macro-structurally intact, dense surfaces and uniformly stacked extrusion filaments with a roughness of 12.25 μm. After degreasing and sintering, FGCCs with densities exceeding 99.43% were obtained. The shrinkage and Co gradient distribution of the inner and outer layers were regulated by powder loading design, achieving integrated control of FGCCs morphology and properties. With powder loading increase in YG15, the density of FGCCs remained stable between 14.01 and 14.03 g/cm3, the gradient dimensions difference decreased from 14.34% to 7.9%, and the maximum hardness difference increased from 78 to 121 HV1/15.

Synthesis and characterization of Al-AlN composite

In the present work, Al-AlN metal matrix composite is synthesized by liquid metallurgy route. AlN particles are difficult to wet by molten Al because of their sinking tendency due to higher specific gravity. To retain them in a matrix for more time, it is attempted to add sintered powder compacts of Al and AlN into the Al melt at 1173 K using the vortex method. For the conceptual interfacial study of matrix and reinforcement, separate batches of Al-AlN composites with and without Mg are synthesized. The angle formed by particulate with matrix was studied to understand the bonding between them. Interfacial angle measurement indicates the improvement in the bonding of AlN particulates in Al matrix. Hardness is improved by 52% and specific wear rate reduced by 37% for Mg-modified Al-AlN composite than unmodified Al-AlN.

Sintering, microstructure, and mechanical properties of ZrO2-doped Al2O3

ABSTRACT In the present work, the effect of Zr-doping on the sintering, microstructure development, and mechanical properties of polycrystalline Al2O3 was studied. Dopant concentrations of 830 and 2070ppm cationic ratio of Zr in Al2O3 corresponding to 2000 and 5000 wt. ppm of ZrO2 in Al2O3, respectively, were used. The sintering schedule of undoped as well as Zr-doped Al2O3 samples was optimised following a series of precoarsening experiments. The Zr-doped Al2O3 ceramics exhibited controlled grain size and improved density. Upon increasing the Zr-dopant concentration from 830 cat. ppm to 2070 cat. ppm. Zr-doped Al2O3 ceramics having a refined microstructure with a homogeneous distribution of controllably grown ZrO2 in Al2O3 matrix was obtained. Microhardness of the Zr-doped samples showed negligible dependence with Zr-doping, whereas mechanical strength was found to improve with it. The improvement in strength was attributed to the combined effect of improved sinter density, microstructural refinement, and grain-boundary strengthening.

Studies towards activation of cobalt in W-Mo-Cu alloy sintered via large current electric field

W-Mo-Cu alloy is a novel, potential pseudo-alloy but demand efficient and reliable manufacturing approaches. In this study, W-Mo-Cu alloys with (1–5 wt%) Co additives were fabricated using large current electric field sintering at a pressure of 25 MPa and a low temperature of 950 °C. The effects of Co on the microstructure and properties of the W-Mo-Cu alloys were investigated. The results revealed an activation effect of Co on W-Mo-Cu alloys. Increasing the Co content from 0 to 5 wt%, resulted in a substantial reduction of the calculated sintering activation energy by 69.6%, thereby enhancing the sinterability of W-Mo-Cu mixed powder and increasing the sintering densification degree of W-Mo-Cu alloy. During the sintering process, a large quantity of Co was enriched around the matrix particles and partially dissolved in the W, Cu, whereas a small number of matrix atoms dissolved into Co, which followed the classical activated sintering model. Moreover, an appropriate increase in the Co content was conducive to an optimal microstructure with increased sintering densification accompanied by increased hardness. However, the addition of Co adversely affected the electrical conductivity of W-Mo-Cu alloys.

Excess Li compensation powder for production of Li-garnet solid electrolytes

Powder covering is a typical Li compensation strategy in Li-garnet solid electrolyte pressureless sintering. The covering powders (CPs) usually have the same composition as the mother powders (MPs), thereby increasing the cost and complexity of electrolyte manufacturing. Herein, a covering powder is proposed; specifically, an excess Li compensation powder (ECP; Li6.4La3Zr1.4Ta0.6O12) replenished with 25 wt% excess Li2CO3. ECP is suitable for electrolytes doped with multiple elements and those with sintering additives; further, it can optimise the microstructure of electrolytes, significantly increasing the relative density and ionic conductivity. The advantageous properties of the ECP can be attributed to the Li2O(g) concentration gradient from the CPs to the electrolyte green body that is produced, which assists electrolyte sintering. Furthermore, the preferential allocation of the sintering system energy to the electrolyte green body originates from the lower surface energy of the ECP, which favours the sintering densification of the green body. The application of ECP has important implications for the low-cost synthesis and performance improvement of Li-garnet solid electrolytes.

Crystal structures, chemical bond features, and Raman vibrations of Li2Co2Mo3O12 microwave dielectric ceramics with low sintering temperature

AbstractLi2Co2Mo3O12 (LCMO) ceramics were synthesized using the solid‐state reaction method. X‐ray diffraction analysis results indicated that the sole crystalline phase present in the ceramics was LCMO, which belongs to the orthorhombic structure of the Pnma space group. The sample, which was sintered at 850°C, demonstrated outstanding microwave dielectric properties, with an εr value of 8.95, a Q × f value of 43 200 GHz, and a τf value of –71.3 ppm/°C. It was found that while the main factor influencing εr was ionic polarizability, sintering density had a lesser effect on it. Furthermore, Q × f was primarily affected by relative density, and there was no significant relationship between packing fraction and this property. The higher the degree of distortion of the [Li/CoO6] octahedron is, the poorer the τf value of LCMO ceramics. Additionally, the microwave dielectric properties of LCMO ceramics were intrinsically linked to ionicity, lattice energy, bond energy, and thermal expansion coefficient of chemical bonds, with Mo–O bonds being the primary factor affecting these properties, as supported by analysis using chemical bonding theories. Mo–O bond vibration dominated the Raman spectra. Good chemical compatibility between silver and LCMO ceramics was demonstrated through our co‐firing experiment.

Improved densification in cold sintering of gadolinia‐doped ceria with reactive sintering aids

AbstractThis study explores a novel reactive cold sintering method for improving the density of gadolinia‐doped ceria (GDC) ceramics while reducing the annealing temperature. Instead of using deionized water as an aid in conventional cold sintering, stoichiometrically mixed Ce(NO3)3·6H2O and Gd(NO3)3·6H2O precursors were added as additives during the CSP in this study. The effects of processing parameters such as sintering temperature and additive content on the relative density of the compacts were investigated using synthesized GDC and commercial GDC powders as raw materials. The results showed that with the aid of precursors, GDC ceramics were sintered up to 90% of their theoretical densities at 850°C and up to 94% at 950°C when the synthesized nanopowder GDC was used. Additionally, the sintering mechanism was investigated, and it was found that the GDC generated by the precursor reaction effectively filled the gaps between the original particles, promoting densification of the sample after cold‐pressing.

Evaluation of internal stress distribution during sintering of compacts using a computational framework

Computational modeling for manufacturing is a promising candidate for accelerating the development of devices consisting of compressed sintered powders. Understanding the internal stress formed in compacts during sintering is important for improving sintering conditions and optimizing the design of electronic devices consisting of powders with different sintering characteristics. This study presents a framework for evaluating the internal stress between particles in a compact using a discrete element model (DEM) and a finite element model (FEM). The results obtained by the DEM calculations, such as the position of the particles and the amount of shrinkage between individual pairs of particles during sintering, were set as the input data for the FEM. The developed method was adapted to virtually generated two-layer compacts, and microstructural factors affecting the internal stress of the compacts were evaluated. The velocities of the small particles in the two-layer compact in the direction parallel to the interface are larger than those of the large particles. The restriction due to the large particle layer reaches a position that is remote from the interface. The direction of stress at the interface in a two-layer compact indicates the formation of the tensile and compressive stresses above and beneath the interface.

Preparation of dense ThO2-based ceramics by Sc doping and simple sintering method

The Th1-xScxO2-x/2 (0 ≤ x ≤ 0.1) ceramic system with high density was originally prepared via a co-precipitation route and simple sintering method. XRD analysis indicates that the Th1-xScxO2-x/2 ceramics exhibited a single cubic fluorite structure and a slight increase of cell parameters. SEM images show that Sc doping contributed a decreasing pores and more uniform grain distribution. The calculated relative densities could reach up to a value higher than 99.0% for x = 0.01 during the isothermal process while the maximum actual relative density was only about 77.4% during the non-isothermal sintering process. And the analysis of grain growth kinetics demonstrates that Th1-xScxO2-x/2 was a solid solution with a high solubility of Sc for x = 0.01 and a low solubility of Sc for both x = 0.05 and x = 0.1, which resulted in a strongly slow grain growth for x = 0.1 due to the solute drag effect. The sintering mechanism investigation also illustrates that low amount (x = 0.01) of Sc doping could significantly enhance the densification sintering of ThO2-based ceramics and reduce the sintering temperature by nearly 150 °C. Such strategy has issued the bottleneck problem existed in the densification sintering of ThO2-based ceramics at a lower temperature without any other special sintering atmosphere, which even could be applicable for other ceramics difficult to sinter.

Influence of a powder-forming additive on the physical-mechanical properties and structure of a ceramic material

The purpose of the study was to explore the effect of various pore-forming additives on the porosity and permeability of alumina ceramic material. Analysis of mineralogical, particle size distribution and chemical composition of raw materials and ceramics samples was performed using standard research methods, JCM-6000 (JEOL) and field emission scanning electron microscopy (FESEM) microscopes, LW600LT, x-ray diffractometer Rigaku D/max-RA, Hitachi SU-70 and Pore Master. The microstructure of the composite ceramic material in all experiments demonstrated the presence of numerous cross-sectionally elongated pores, which proves the dependence of the pore-forming structure on the shape of the pore-forming agent. The high permeability of samples with lignin is due to the improved plastic properties of the clays. By increasing the clay content from 5 to 10 wt.% it was possible to increase the sintering density of the samples and reduce their overall porosity. The permeability porosity increases with the introduction of more urea, and the strength of the samples is then at its maximum. Samples with the addition of lignin demonstrated resistance to mechanical stress and high permeability. The study identifies the prospects of using crystallised urea and lignin from manufacturing waste as a pore former, which will allow the establishment of environmentally friendly ceramic materials with high permeability and durability and solve the problem of atmospheric pollution.

Utilizing multi-solid waste to prepare and characterize foam glass ceramics

Incorporating multi-solid wastes to prepare foam glass ceramics could effectively improve the utilization rate of solid wastes, beneficial to promoting the crystallization and bloating of samples. In this study, foam glass ceramics were prepared by a one-step sintering method using waste glass (WG), granite tailings (GT), and high titanium blast furnace slag (HTBFS). At the same time, the phase transformation, sintering, and physical properties of the samples were studied. The results showed that the sintering of foam glass ceramics consisted of three stages: sintering densification, bloating, and bubble coalescence. The low-temperature melting of WG created a favorable liquid phase environment to precipitate microcrystalline phases, such as wollastonite, diopside, and titanite. Adding HTBFS helped crystallize the sample, but increased the viscosity of the system, not favorable for bloating. When the HTBFS content was <15%, the physical properties of the samples were as follows: a bloating temperature of 980–1100 °C, crystallinity of 0%–38.9%, porosity of 48.5%–60.2%, water absorption of 0.6%–1.2%, compressive strength of 9.3–22.6 MPa, and thermal conductivity of 0.31–0.43 W/(m·K). Consequently, the foam glass ceramics prepared in this study can be used in the field of structural insulation of buildings and has significant economic and social benefits.

Microstructure and mechanical properties of tungsten fiber reinforced tungsten composites prepared by Fe activated sintering

Tungsten fiber reinforced tungsten composites were fabricated by Fe activated sintering. The effect of Fe content (0.5% ∼ 1.0%(wt%)) and original fiber volume fraction (10% ∼ 50%(vol%)) on relative density, microstructure and mechanical properties were studied. The interaction between the Fe and tungsten fiber was analyzed. The fracture behavior as well as the strengthening and toughening mechanisms were revealed. The results indicated that the Fe not only promoted the sintering densification of the tungsten matrix, but also caused the recrystallization of tungsten fiber from the surface to the center due to the element diffusion. The (i) relative density, (ii) residual fiber diameter (or residual fiber volume fraction) and (iii) flexural strength were (i) increased, (ii) decreased and (iii) increased with Fe content increased, respectively, while were (i) decreased, and (ii, iii) first increased and then decreased with the original fiber volume fraction increased, respectively. As for the composites containing 1.0%Fe, the fracture toughness was monotonically increased with the increase of the original fiber volume fraction. The fracture mode of the matrix was intergranular. The strength and toughness of the composites were enhanced as a result of fiber fracture, crack deflection, interface debonding, and fiber pull-out.

Influence of bismuth oxide as a sintering aid on the densification of cold sintering of zirconia

In the past decades, Zirconia (ZrO2) has emerged as a promising technical ceramic, both as high temperature structural material and electrolyte for fuel cells, etc. The traditional synthesis of ZrO2 with spark plasma sintering (SPS) usually requires a sintering temperature as high as 1200 °C. General interest in lowering the sintering temperature to reduce energy consumption and thermal stresses has led to research on two promising routes – cold sintering via temperature-dependent chemical reactivity and sintering aids, which facilitates mass transport and improves densification. Here we combine both by developing a single-step sintering process benefitting from both water vapor through the in-situ conversion of Zr(OH)4 to ZrO2 and liquid phase Bi2O3 as a sintering aid. The resultant ZrO2 has a relative density above 80% with a sintering temperature as low as 900 °C, significantly higher than that of ZrO2 without sintering aids, which had a relative density of 54%, both sintered at 50 MPa. The dependence of porosity of sintered samples as a function of sintering pressure (range: 50 MPa–300 MPa) and temperature (range 400 °C–1200 °C) is mapped out as guidance for further material property design. A linear relationship between hardness and relative density was found, with a maximal hardness of 6.6 GPa achieved in samples with 30% porosity. In addition to sintered density, phase stabilization of tetragonal ZrO2 is enhanced at sintering temperature of 900 °C with water vapor and Bi2O3, respectively.

Microstructure, mechanical property and cutting performance of (Ti,W)C/Mo/Co/Ni cermet tool material prepared by spark plasma sintering and high frequency induction heating

The (Ti,W)C/Mo/Co/Ni cermet tool material is produced using a combination of spark plasma sintering and high frequency induction heating (HFIH-SPS) mixed sintering technology. This study investigates the influence of various sintering parameters on the microstructure and mechanical properties of (Ti,W)C/Mo/Co/Ni cermet tool material. The findings indicate that the rapid sintering densification of (Ti,W)C/Mo/Co/Ni cermet tool material can be achieved by the mixed sintering technology at a lower sintering temperature. The rapid sintering process observed in this study can be mainly attributed to the plasma activation effect generated by pulse current and the Joule heat effect produced by the metal particles under high frequency induction. The optimized relative density of the (Ti,W)C/Mo/Co/Ni cermet tool material reaches 99.10%, with the hardness of 20.28 ± 0.58 GPa, the fracture toughness of 7.74 ± 0.14 MPa·m1/2 and the flexural strength of 796.12 ± 36.55 MPa. The indentation of (Ti,W)C cermet exhibits a regular cross shape, and the indentation edge is smooth, which indicates a good fracture toughness. The high mechanical properties of (Ti,W)C/Mo/Co/Ni cermet tool material are mainly attributed to the interaction between crystal grain boundary solute strengthening and dislocation movement. The tool has shown good cutting performance during the subsequent dry cutting of 40Cr steel, with the lowest surface roughness Ra value of 1.097 µm.

Ni-doping effect on spark-plasma sintering of tungsten compacts: Synergy of grain boundary strengthening and secondary phase formation for mechanical behavior improvement

Pure tungsten is known to be a strong material but very brittle, due to its grain boundary structure. In a quest for improvement of the cold-work capacity of tungsten alloys, pure tungsten powder was doped with 1 wt% nickel. The mixture was consolidated by spark plasma sintering at temperature conditions below and above the Ni melting point. The addition of Ni tends to remove oxygen from W grain boundaries. Spherical particles of WO2 are then formed when the sintering temperature is below the melting point of nickel; while tangled sticks of W oxide encapsulated by a submicron rim of Ni-rich phase are observed when the sintering is carried out above this melting point. Quasi-static compression tests at room temperature have been operated to assess the cold-working capacity of the obtained materials. Ni-doped materials sintered at a temperature below the Ni melting point revealed an increase in the strain at rupture by a factor of six approximately (12 % and 23 % in Ni-doped materials, whereas their W counterparts presents 1.9 % and 3.9 %, respectively), accompanied by a moderate decrease in the compressive strength (1300 and 1250 MPa, in respect with 1615 and 1325 MPa, respectively). The substantially improved mechanical properties of the Ni-doped samples is caused by the combination of the oxygen cleaning at the grain boundaries of the W matrix and local accommodation of the deformation by the created Ni-rich phase. The material consolidated at a temperature higher than Ni melting point underlines the formation of submicron thick ductile Ni-rich phase, accompanied with an improvement of both the strain at rupture and the compression strength of 3.5 times and 25 %, respectively. This configuration is expected to enhance the load transfer between the hard W matrix and the soft Ni-rich phases, which promote the activation of slip activity of the W matrix, in line with the extensive ductile phenomena distinctly observed on the ruptured specimens.

Synthesis of BaZr0.1Ce0.7Y0.2O3‐δ nano‐powders by aqueous gel‐casting for proton‐conducting solid oxide fuel cells

AbstractFor the sake of enhance the sinter ability and electrical conductivity of BaZr0.1Ce0.7Y0.2O3‐δ (BZCY) electrolytes, a modified aqueous gel‐casting method was applied to synthesize high sintering active and high conductive BZCY nano‐powders. The new approach makes it easy to obtain pure perovskite. The highly sintering active purity‐phase of BZCY nano‐powder (particle size of 50∼100 nm) was obtained by calcining at 1100°C for 2 h. Nano‐powders effectively reduce the sintering densification temperature and successfully prepare BZCY electrolyte with relative density &gt; 96 % at 1450°C, and promote grain growth with an average grain size of 2.36 μm. Benefiting from this, improved electrical conductivities (e.g., 12.4×10−3 S cm−1 at 700°C, in wet air) are obtained. The NiO‐BZCY/BZCY/LSCF‐BZCY anode‐supporting single cell shows a peak power density of 0.75 W cm−2 at 700°C while taking ambient air as oxidants and wet H2 (∼3 vol.% H2O) as fuels.

Structural characteristics and microwave dielectric performances of ZnZrNb2-xVx/2O8-1.25x-based ceramics for LTCC applications

The ZnZrNb2-xVx/2O8-1.25x-based (0.2 ≤ x ≤ 0.6) ceramics with monoclinic wolframite structure were prepared by the solid-phase method at low temperature. The microscopic morphology, phase structure, low-temperature sintering mechanism, and microwave dielectric performances of ZnZrNb2-xVx/2O8-1.25x-based (0.2 ≤ x ≤ 0.6) ceramics were thoroughly analyzed. Low-temperature sintering densification of microwave dielectric ceramics was made achievable by substituting non-dense vanadium at the Nb location. The sintering temperature of ZnZrNb2-xVx/2O8-1.25x (x = 0.4) ceramics was reduced by 340 °C when compared to pure ZnZrNb2O8 ceramics due to the mechanism of liquid phase aided sintering. The self-generated low melting point phase forms a liquid phase during the sintering process reducing the sintering temperature. It is noteworthy that when sintered at 900 °C, the ZnZrNb2-xVx/2O8-1.25x (x = 0.4) ceramic exhibits extremely exceptional microwave dielectric performances: εr = 25.15, Q×f = 17,600 GHz (at 8.01 GHz), and τf = −53.25 ppm/°C. The proposed material configuration provides a candidate material with extremely broad application potential for LTCC applications and a practical and effective strategy for low-temperature sintering of Nb-based monoclinic wolframite structured microwave dielectric ceramics.

XRD analysis and surface roughness of AL2024 alloy produced through P/M route and machined by using CNC milling machine

The purpose of this analysis is to examine the surface roughness during machining of aluminum 2024 prepared through the powder metallurgical (P/M) route. Aluminium 2024 alloy is prepared with different compositions, such as pure Al, 1.5 W% of Mg, and 2–6% of Cu powders. Powders are blended with the ball milling machine according to the composition required, and green compacts are prepared in a square-shaped die (25*25mm) by applying a uniaxial load of 250 Mpa ±50. The sintering process was performed at a temperature of 594 °C for 60 minutes, and the heating profile consisted of a 10-minute isothermal keep at 594 °C followed by cooling in Furness. It presents and addresses compaction characteristics, green density, dimensional changes during sintering, sintering density, mechanical properties, and microstructures. Also determined were the surface roughness and MRR during machining with a CNC milling machine at different depths of cut.

3D printed plastic molds utilization for WC-15Co cemented carbide cold pressing

In this work, we propose the use of 3D printing to make molds for pressing cemented carbide compacts. The fused material extrusion technique was used to make solid molds from polylactide for pressing a rectangular standard sample and a square cutting insert. The densification of the WC-15Co powder mixture combined with rubber (2%) was studied at pressures ranging from 41 to 121 MPa in the obtained molds. A comparative analysis of the density of powder compacts and sintered products and their properties was performed against their analogs formed by pressing in a hardened steel mold at a pressure of 210 MPa. Increasing the pressure in the plastic molds from 41 to 121 MPa led to an increase in the relative density of powder compacts from 65% to 70%. The relative density of powder compacts (75%) obtained by the steel mold pressing at a pressure of 210 MPa was only 5% higher. The density of sintered samples increased from 99.22% to 99.5% when the molding pressure was increased, which was only 0.29% lower than the density obtained by steel mold pressing. The hardness (1130–1160 HV) and fracture toughness (23.1–24 MPa m1/2) of samples produced in the plastic molds differed slightly from those produced in the steel molds (1170 HV and 24.4 MPa m1/2). In terms of the hardness and fracture toughness combination, the samples obtained by this technique were superior to those obtained by the selective laser melting method and were comparable to the samples obtained by sintering of powder compacts produced by various 3D printing methods (binder jetting, 3D gel printing, material extrusion).

Effect of CaF2 on sintering behavior and thermal shock resistance of Y2O3 materials

Y2O3 materials have become a popular candidate for preparing refractory crucibles for ultra-pure high-temperature alloy melting in recent years. However, its difficulty in sintering and poor thermal shock resistance limited its industrial application. The effect of CaF2 on the densification microstructure, mechanical properties, and thermal shock resistance of Y2O3 materials was investigated in this paper. The main purpose of this study was to optimize the amount of CaF2 added in the preparation of Y2O3 materials to improve its thermal shock resistance and get better mechanical properties. The mechanism of the densification process of CaF2-doped Y2O3 materials was analyzed by phase analysis and microstructure. The results showed that successive doping of large Ca2+ ions caused more lattice distortion in the Y2O3 materials, and the diffusion rate of Y3+ was increased, thus enhanced grain boundary diffusion and promoted sintering densification in the Y2O3 materials. Meanwhile, the addition of CaF2 also significantly reduced the apparent porosity and enhanced the mechanical properties of the materials. The improvement of these properties was attributed to the increased relative density of CaF2-doped Y2O3 materials and the high sintering activity of CaF2. In addition, crack deflections effectively improved the thermal shock resistance of the materials. The residual flexural strength ratio of Y2O3 materials doped with 1 wt % CaF2 was increased by 21.2% after thermal shock test compared with undoped specimens.