Temperature Sintering Behavior Research Articles

The effect of Y2O3 on the grain growth and densification of W matrix during low temperature sintering: Experiments and modelling

In this work, the effect of Y2O3 addition on the grain growth and densification of W matrix was explored from a kinetic perspective by comparing the low temperature sintering behavior of W-Y2O3 composite nanopowder system with that of pure W nanopowder system. By combining nonisothermal sintering experiment with the power law of grain growth, it was found that grain boundary diffusion is responsible for the mass transport mechanism in both systems. The inhibition of W grain growth after Y2O3 addition is closely related to the lower surface diffusivity of W skeleton. The densification rate of W skeleton in these two systems were modelled using a periodic 3D arrangement of identical particles and a much smaller grain boundary diffusivity of W skeleton was obtained for W-Y2O3 sample. Firstly, it is the decrease in dihedral angle of W matrix after Y2O3 addition that causes a decrease in thermodynamic driving force for densification. Secondly, from the view of atomic mobility, the inhibited W grain growth caused by limited surface diffusivity is one of the reasons impeding densification. Besides, Y2O3 grains distributed at W grain boundary coarsen through wetting W grain boundary, which also has an inhibition effect on the W skeleton densification.

Preliminary study of sintering zero‐rupture Fully Ceramic Microencapsulated (FCM) fuel

AbstractThe demonstration of industrially feasible zero‐rupture Fully Ceramic Microencapsulated (FCM) fuels has been achieved via layers of fuel particles vertically stacked and consolidated by Pulsed Electric Current Sintering. Uniaxial shrinkage, a key component of fuel arrangement, was analyzed via SEM, XRD and computational analyses, using cylindrical geometries from 0.25 to 1.5 “height‐to‐diameter” (h/d) aspect ratio. Bulk densities of ~3.1 g/cc were achieved on pellets at h/d ~0.25, using a ramp rate of 100°C per min to 1825°C and holding for 10 minutes with 10 MPa applied pressure. Using the same parameters, this value reduced to ~2.8 g/cc at h/d ~1.5. More extensive percolation of oxide sintering additives and earlier closure of interconnected pores in extreme ends of the pellet was attributed to higher temperatures in those regions. The top and bottom of the pellet densify before the center, also resulting reduced displacement between the fuel layers in these regions. Parametric studies of sintering with different temperature and time, with support of computational analyses, was used to map expected temperature distribution and sintering behavior. These tools will be used for further optimization of FCM fuel fabrication.

Computational modeling of heat transfer and sintering behavior during direct metal laser sintering of AlSi10Mg alloy powder

Direct Metal Laser Sintering (DMLS) is one of the leading additive manufacturing processes, which produces complex metallic parts directly from the powder. One of the major problems of this rapid manufacturing process is an inhomogeneous temperature distribution, which leads to residual stress in the build part. Thus, temperature analyses must be performed, to better understand the temperature distribution and sintering behavior of the powder bed with a different laser recipe. In this study, a comprehensive three-dimensional numerical model was developed to understand the temperature distribution during direct metal laser sintering of AlSi10Mg alloy powder. The computer simulation was carried out in ANSYS 17.0 platform. Further, the effect of process parameters such as laser power and scan speed on the temperature distribution and sintering behavior were studied. From the simulation results, it was found that, when the laser power increased from 70 W to 190 W, the maximum temperature of the molten pool increased from 731 °C to 2672 °C, and the molten pool length changed from 0.286 mm to 2.167 mm. A reverse phenomenon was observed with an increase in scan speed. The sintering depth of the powder layer increases significantly from 0.061 mm to 0.872 mm with increasing the applied laser power, but decreased from 0.973 mm to 0.209 mm as a higher scan speed was applied. The developed model helps to optimize the powder layer thickness and minimize the wastage of excess powders during the sintering process.

Low temperature sintering behavior and microwave dielectric properties of LaNbO4 ceramics with BaCu(B2O5) additive

In this paper, LaNbO4 ceramics with BaCu(B2O5) additives were prepared via the conventional solid state reaction method. The effects of BaCu(B2O5) on sintering behavior, phase structure and microwave dielectric properties of LaNbO4 ceramics were investigated. The optimum sintering temperature of LaNbO4 ceramics could be lowered from 1325 °C to 925 °C with the addition of BaCu(B2O5) due to liquid phase sintering. X-ray diffraction patterns showed that single-phase LaNbO4 could be achieved when BaCu(B2O5) content is ≤ 1 wt%. However, with further increase in BaCu(B2O5) content, small amount of second phases such as BaNb3.6O10 and Ba6Nb2O11 would be found. The variation trends of εr and Q×f value were similar to that of bulk density, the temperature coefficient of resonant frequency (τf) could be affected by additives. Typically, LaNbO4 ceramics with 1 wt% BaCu(B2O5) sintered at 925 °C for 4 h possessed dense structure and exhibited enhanced microwave dielectric properties: εr = 21.2, Q×f = 22600 GHz and τf = 10.01 ppm/°C.

Low temperature sintering behavior of La-Co substituted M-type strontium hexaferrites for use in microwave LTCC technology

The La-Co substituted Sr1-xLaxFe12-xCoxO19 (x=0-0.5) ferrites with appropriate Bi2O3 additive were prepared by conventional sintering method and microwave sintering method at low sintering temperatures compatible with LTCC (low temperature co-fired ceramics) systems, and their sintering behavior was chiefly investigated, including the crystal structure, saturation magnetization Ms, magnetic anisotropy field Ha, intrinsic coercivity Hci, and Curie temperature TC. Experiment results clearly showed that the pure M-type crystal phase was successfully obtained when the La-Co substitution amount x did not exceed 0.3. However, the single M-type phase structure transformed to multiphase structure with further increased x, where the M-type phase coexisted with the non-magnetic phase such as α-Fe2O3 phase, La2O3 phase, and LaCoO3 phase. Appropriate La-Co substitution improved the Ms (>62 emu/g), Ha (>1400 kA/m), and Hci (>320 kA/m) for the ferrites with x varying from 0.1 to 0.3, but the TC decreased with increasing substitution amount. Moreover, the microwave sintered ferrites could provide larger Hci and similar Ms compared with the conventional sintered ferrites.

Ni–Ti equiatomic co-substitution of hexagonal M-type Ba(NiTi)xFe12−2xO19 ferrites

Ionic substitution is considered the most effective way to expand the operational frequency of barium hexaferrites. So far, little attention has been paid to high level substitutions and their impacts on low temperature sintering behavior. Here, co-substituted equiatomic Ni–Ti M-type barium ferrites of nominal compositions Ba(NiTi)xFe12−2xO19 (x = 0.30, 0.60, 0.90, 1.20) were prepared by a solid state reaction method and studied for their structural, and static and high frequency magnetic properties. It was found that the phase purity of M-type hexagonal barium ferrite does not depend upon the amount of Ni–Ti substitution investigated here. Concomitantly, Bi2O3 additives are shown effective in lowering the sintering temperature of hexaferrite materials. For low temperature processed samples, the addition of Bi2O3 enables improved densification from localized liquid phase formation and restricted grain growth from its colocation at grain boundaries. By comparing samples and process conditions, the effect of grain growth and sintering aid upon sample microstructure, bulk density (ρ), saturation magnetization (Ms), coercivity (Hc) and magnetic permeability (μ′ and μ″) is made clear.

High Temperature Sintering and Oxidation Behavior in Plasma Sprayed TBCs [Single Splat Studies] Paper 1—Role of Heat Treatment Variations

The TBC system is examined with regards to its response to thermal exposure at high temperature. It has been established before that the thermally grown oxide (TGO) layer that forms upon bond coat oxidation is the key factor determining the performance of the TBC system and/or its failure. However, characteristics of TGO growth, bond coat rumpling, principles governing failure of TBC systems and the various failure mechanisms have been studied extensively in case of just super alloy with bond coat or with thick top coating. In this study super alloy/bond coat system with single splats of YSZ instead of thick topcoat is analyzed in order to scrutinize the effect on the first layer of splats during thermal exposure. The splats with microcracks are the building blocks of the top coat. The most important aspect of this layer is the inherent inter-splat and intra-splat porosity which undergoes sintering during thermal exposure. The interactions between the YSZ splats and the evolving TGO is directly linked to the presence or absence of bond coat oxidation. Therefore the high temperature behavior of this system is analyzed with variations in heat treatment involving, temperature, duration and environment of thermal exposure.

High Temperature Sintering and Oxidation Behavior in Plasma Sprayed TBCs [Single Splat Studies] Paper 2—Relevance of Variation in Materials Systems of TBC Components

The TBC system’s response to thermal exposure at high temperature is discussed here. The relevance of the microstructural aspects of each component of the TBC system is emphasized. The top coat is a YSZ ceramic coating consisting of a collection of splats on top of one another. The most important aspect of this layer is the inherent inter-splat and intra-splat porosity which undergoes sintering during thermal exposure. This study investigates the effect of thermal exposure on the microstructure and sintering behavior in single splats produced using different starting powders since this has been shown to influence the basic microstructure of YSZ topcoat. The bond coat is an MCrAlY metallic coating which serves as an Al reservoir and allows the formation of a protective alumina, Thermally Grown Oxide (TGO) layer between the bond coat (BC) and the top coat (TC) layers. This oxide scale formed upon thermal exposure prevents further oxidation of the underlying component (substrate) and thus provides protection. As such, the content of free Al in the bond coat layer is of significance and makes it crucial to understand the influence of bond coat microstructure evolution and oxidation involved during its formation. The interaction between the bond coat, the TGO and the top coat layers is examined in this study to understand the high temperature behavior of the TBC system with regards to variations in the top coat and bond coat material systems used.

Low Temperature Sintering Behavior and Giant Dielectric Properties of CuO Doped (Ba0.5Sr0.5)TiO3 Ceramics

The effects of CuO additions on the sintering temperature and dielectric properties of (Ba0.5Sr0.5)TiO3 ceramic have been investigated by employing X-ray diffraction analysis, and dielectric properties measurements. In this research, 1–5 wt% CuO was added to the (Ba0.5Sr0.5)TiO3 powders to reduce the sintering temperature. CuO-doped (Ba0.5Sr0.5)TiO3 ceramics were sintered from 750 to 1350°C to confirm the sintering temperature with various dopants, respectively. It was found that the addition of CuO to (Ba0.5Sr0.5)TiO3 could lower the sintering temperature from 1350 to 1150°C. Moreover giant dielectric permittivity was observed in the 5 wt% CuO doped (Ba0.5Sr0.5)TiO3 ceramics.

Synthesis of Cordierite Powders by Low Temperature Combustion Method

The cordierite powders have been synthesized by low temperature combustion technique using urea as fuel, nitrates as oxidizer and silicic acid as silica source. The sintering behavior and crystallization process were investigated. The results showed that the powders could be sintered at a temperature lower than 1000 °C. The μ-cordierite crystallized from glass at first, and then transformed into α-cordierite at higher temperature. The obtained cordierite based glass ceramics at different temperatures have low dielectric constant (4.16 ~ 5.02 at 1 MHz) and low dielectric dissipation factor (≈ 0.003 at 1 MHz) as well as low temperature sintering behavior, which is compatible for electronic packaging.

Low Temperature Sintering and Dielectric Properties of BiNbO4and ZnNb2O6Ceramics with Zinc Borosilicate Glass

Low temperature sintering behavior and microwave dielectric properties of the <TEX>$BiNbO_{4^-}$</TEX> and the <TEX>$ZnNb_2O_{6^-}zinc$</TEX> borosilicate glass(ZBS) systems were investigated with a view to applying the composition to LTCC technology. The addition of <TEX>$10{\sim}30$</TEX> wt% ZBS in both systems ensured successful sintering below <TEX>$900^{\circ}C$</TEX>. For the <TEX>$BiNbO_{4^-}ZBS$</TEX> system, the sintering was completed when 15 wt% ZBS was added whereas 25 wt% ZBS was necessary for the <TEX>$ZnNb_2O_{6^-}zinc$</TEX> system. Secondary phase was not observed in the <TEX>$BiNbO_{4^-}ZBS$</TEX> system but a small amount of <TEX>$ZnNb_2O_6$</TEX> with the willemite structure as the secondary phase was observed in the <TEX>$ZnNb_2O_{6^-}ZBS$</TEX> system. In terms of dielectric properties, the application of the <TEX>$BiNbO_{4^-}$</TEX> and the <TEX>$ZnNb_2O_{6^-}ZBS$</TEX> systems sintered at <TEX>$900^{\circ}C$</TEX> to LTCC were shown to be appropriate; <TEX>$BiNbO_{4^-}15$</TEX> wt% ZBS(<TEX>$\varepsilon_r=25,\;Q{\times}f\;value=3,700GHz,\;\tau_f=-32ppm/^{\circ}C$</TEX>) and <TEX>$ZnNb_2O_{6^-}25$</TEX> wt% ZBS(<TEX>$\varepsilon_r=15.8,\;Q{\times}f\;value=5,400GHz,\;\tau_f=-98ppm/^{\circ}C$</TEX>).

Low temperature sintering behavior of B 2O 3 vapor in BaTiO 3-based PTCR thermistors

The effects of B 2O 3 vapor on the sintering and the PTCR effect of BaTiO 3-based ceramics are investigated in this study. It is revealed that B 2O 3 vapor can be doped into both pure and Y-doped BaTiO 3 ceramics during sintering. B 2O 3 vapor not only obviously influences the densification and the grain growth but also increases the grain lattice parameters. The PTCR effect is improved through the doping of B 2O 3 vapor as the room temperature resistivity is considerably decreased and the resistance jump is greatly increased. With the doping of 1 mol% B 2O 3 vapor, semiconducting Y-BaTiO 3 with the room temperature resistivity of 30 Ω cm is obtained when the ceramics are sintered at as low as 1150 °C; while when the ceramics are sintered at 1350 °C with the doping of 0.25 mol% B 2O 3 vapor, the PTCR effect is enhanced by nearly two orders of magnitude and the room temperature resistivity is decreased from 25 to 9 Ω cm.

Low temperature sintering behavior of B2O3 vapor in BaTiO3-based PTCR thermistors

The effects of B2O3 vapor on the sintering and the PTCR effect of BaTiO3-based ceramics are investigated in this study. It is revealed that B2O3 vapor can be doped into both pure and Y-doped BaTiO3 ceramics during sintering. B2O3 vapor not only obviously influences the densification and the grain growth but also increases the grain lattice parameters. The PTCR effect is improved through the doping of B2O3 vapor as the room temperature resistivity is considerably decreased and the resistance jump is greatly increased. With the doping of 1 mol% B2O3 vapor, semiconducting Y-BaTiO3 with the room temperature resistivity of 30 Ω cm is obtained when the ceramics are sintered at as low as 1150 °C; while when the ceramics are sintered at 1350 °C with the doping of 0.25 mol% B2O3 vapor, the PTCR effect is enhanced by nearly two orders of magnitude and the room temperature resistivity is decreased from 25 to 9 Ω cm.

Microstructure and electrical conductivity of LaNi 0.6Fe 0.4O 3 prepared by combustion synthesis routes

The continuing development of new materials suitable for solid oxide fuel cells operating at about 650–800 °C is of great interest in recent days. The present investigation deals with the development of a perovskite composition–LaNi 0.6Fe 0.4O 3 (LNF)–prepared following two combustion synthesis routes: citrate-gel (LNC) and urea (LNU). The powders were sintered over a wide temperature range (900–1400 °C) and sintering behavior for LNC and LNU was compared. The thermal expansion coefficient (TEC), electrical and microstructural characteristics of LNF was thoroughly investigated. Electrical conductivities were found to be one and a half times higher than that of most commonly used cathode material, La(Sr)MnO 3. Moreover, the TEC value of LNF was found to be ≈11.4×10 −6 K −1 at 800 °C. The study opens up a possibility of using LNF as a promising cell component for SOFC.

Densification, crystallization, and electrical properties of lead zirconate titanate glass-ceramics

Piezoelectric glass-ceramics in the lead zirconate titanato-lead silicate system were developed. SiO(2) was required for glass formability, and excess PbO allowed low temperature processing. The amounts of those constituents were limited by the optimization of the piezoelectric properties. Only a small region of compositions in this system yielded the desired combination of glass formability, crystallization and densification behavior, and resulting piezoelectric properties. Selected compositions were melted and roller quenched to form glass ribbon, then milled into glass powder. Pressed glass powder densified to closed porosity at 850 degrees C with piezoelectric d(33 ) and g(33) coefficients of 26 pC/N and 33x10(-3 ) Vm/N. The low temperature sintering behavior of these ferroelectric glass-ceramics provides the possibility of incorporating a piezoelectric material as a sensor or actuator in thick film circuits or low-fire multilayer packages.