Ceramic Core Research Articles

Inter-layer structures regulated by metallic Si powders in 3D printing of silica-based ceramic cores

3D printing is an excellent choice for manufacture of ceramic cores; however, the inter-layer structures in 3D printed sample leads to anisotropy in microstructure and properties. In this paper, silica-based ceramic cores were prepared by digital light processing, and metallic Si powder was employed as mineralizer to relieve the anisotropy. The metallic Si powder converts into SiO2 in oxidation reaction with significant volume expansion, which inhibits the shrinkage rate and partly fills the interlayer gaps of the ceramic core. Meanwhile, the metal Si powder leads to lower curing thickness in 3D printing, and thicken the interlayer gaps. Due to the cooperation of the oxidation reaction and decreased curing thickness by the metallic Si powder, the 0.4 wt.% of metallic Si powder reduced the anisotropy in structure and mechanical property due to the alleviated inter-layer structure and the interlayer and intralayer strengths show optimal values of 11.4 MPa and 17.2 MPa at room temperature, respectively. This work inspires new guidance to 3D printing of ceramic cores with uniform microstructure and excellent mechanical properties.

Effect of constraint removal on single-crystal blade dimensions during investment casting

Single-crystal turbine blades, manufactured via investment casting, are key components of high-performance aero engines and gas turbines. The final dimensions of the blades depend on the cumulative effect of heat shrinkage at different stages, including the superalloy, mold shell, and ceramic core, etc. To clarify the effect of these stages on the blade dimensions, we first use the heat transfer coefficient calculated from inverse heat-conduction analysis to simulate the directional solidification. By extracting and mapping the final physical field from the previous stage to the next stage, four successive constraint removal processes are performed at different time points. Subsequently, we establish a time-varying model for the entire process of directional solidification and constraint removal. The errors of the extraction/mapping are consistently less than 0.002 mm in all three directions, thus confirming the feasibility of data transfer. Secondly, we analyze the dimensional deviation patterns of the casting after sequentially removing the mold shell, process rib, grain selector, and ceramic core constraints, with emphasis on the dimensional accuracy of the airfoil while disregarding the dovetail generated from machining. The final average deviations of Section 1, Section 2, and Section 3 of the airfoil are 0.1896 mm, 0.1723 mm, and 0.1909 mm, and the maximum deviations occur consistently at the trailing edge near the tip. Finally, three section deviations are validated via measurements performed using a vacuum furnace and industrial computed tomography. The results show that the proposed method improves the dimensional accuracy of hollow turbine blades.

A Four-Variable Shear Deformation Theory for the Static Analysis of FG Sandwich Plates with Different Porosity Models

This study is centered on examining the static bending behavior of sandwich plates featuring functionally graded materials, specifically addressing distinct representations of porosity distribution across their thickness. The composition of the sandwich plate involves a ceramic core and two face sheets with functionally graded properties. Mechanical loads with a sinusoidal distribution are applied to the sandwich plate, and a four-variable shear deformation theory is employed to establish the displacement field. Notably, this theory involves only four unknowns, distinguishing it from alternative shear deformation theories. Equilibrium equations are derived using the virtual work concept, and Navier’s method is applied to obtain the solution. The study addresses the impact of varying porosities, inhomogeneity parameters, aspect ratios, and side-to-thickness ratios on the static bending behavior of the sandwich plates. The influence of various porosities, inhomogeneity parameter, aspect ratio, and side-to-thickness ratio of the sandwich plates are explored and compared in the context of static bending behavior. The three porosity distributions are compared in terms of their influence on the bending behavior of the sandwich plate. The findings indicate that a higher porosity causes larger deflections and Model A has the highest central deflection. Adopting the four-variable shear deformation theory demonstrated its validity since the results were similar to those obtained in the literature. Several important findings have been found, which could be useful in the construction and application of FG sandwich structures. Examples of comparison will be discussed to support the existing theory’s accuracy. Further findings are presented to serve as benchmarks for comparison.

Design and formation mechanism of in-situ synthesis YAG sintered necks in stereolithography 3D printed Al2O3-based ceramic cores

The intricate structure of ceramic cores is crucial in producing high-temperature-resistant hollow blades. Traditional techniques for ceramic cores preparation, such as hot injection, rely heavily on moulds, thus limiting the production of complex structures in ceramic cores. Stereolithography 3D printing technology provides a novel approach to creating these cores, leveraging its precision and model customization capabilities. However, issues like the challenge of effectively controlling both porosity and strength hinder its widespread adoption. In this study, high-performance ceramic cores reinforced with in-situ YAG were successfully prepared by adding Y2O3 using stereolithography 3D printing technology. Thorough thermodynamic calculations for Y2O3 incorporation into Al2O3-based ceramic cores were systematically analysed, revealing the formation of Y3Al5O12 (YAG) at elevated temperatures due to Y2O3 and Al2O3 interaction. Subsequently, the variations in microstructure and properties were investigated across different temperatures. Due to diffusion, YAG sintered necks and cohesive framework were formed on the surface of Y2O3, resulting from the reaction between Y2O3 and Al2O3. YAG sintered necks and Y2O3 effectively inhibited crack deflection. The high degree of densification of the in-situ generated YAG and cohesive framework improved the mechanical properties; meanwhile, the presence of porosity between YAG and Al2O3 contributed to the enhancement of porosity. The cores exhibited exceptional mechanical properties at 1823.15 K. The open porosity was 30.08%. The flexural strengths were 41.2 MPa (298.15 K) and 32.0 MPa (1773.15 K). The design of YAG sintered necks by adjusting the sintering temperature introduced a new idea for synergistically adjusting porosity and strength. The advancement is anticipated to improve the production of intricately structured ceramic cores with superior performance.

Additive manufacturing and performance research of aluminum-based ceramic cores

As a ceramic core for forming the cooling structure of the intrinsic cavern of turbine blades, the quality of tubular turbine blades is directly affected by their accuracy and performance. In this paper, based on the DLP photocuring technology, the 50% by volume alumina porcelain suspensions with low viscosity were successfully prepared. Secondly, the effects of printing parameters on the curing characteristics were explored to obtain the best printing parameters. The alumina porcelain properties were analyzed for the heating treatment process effect. As the temperature increases, its mechanical properties increase. In addition, the porosity of the patulous orifice reached 48%. The flexural strength of the alumina porcelain component was 26 MPa, which met the requirements of a high-temperature compound metal blade for the porcelain core.

Doping engineering for high-temperature broadband high emissivity and low thermal conductivity of ytterbium chromate-based ceramics

Developing highly reliable infrared radiation materials with broadband high emissivity at high temperatures, low thermal conductivity, and excellent thermal stability is highly desirable for aerospace thermal protection applications. However, it remains a huge challenge to take into account infrared radiation heat dissipation and blocking heat transfer through low thermal conduction simultaneously. In this work, we reported a broadband high emissivity Ca2+-doped YbCrO3 ceramic with emissivity above 0.89 at room temperature across the entire range of wavelength (1–14 μm). This doping strategy leads to the introduction of impurity energy levels into the band gap of YbCrO3, which increases the possibility of light absorption to promote electron transition, improving the emissivity of the near-infrared band (1–3 μm). Simultaneously, un-equivalent doping induces electron exchange between chromate ceramic ions, which complicates the electronic structure (producing lattice distortion and extra multi-mode vibrations) and reduces the band gap width, thus boosting the emissivity in the mid-infrared band (3–14 μm). More importantly, (Yb0.8Ca0.2)CrO3 presents a high emissivity (0.76) at an elevated temperature of 1200 °C, together with low thermal conductivity (2.5 W m−1 K−1 at 1000 °C) due to strong phonon scattering. Moreover, the doping-dominating phase stabilization effect contributes to impressive thermal stability (stable at 1300 °C for 50 h) and a high coefficient of thermal expansion (9.0–9.5 × 10−6 K−1), which makes it suitable for long-term high-temperature thermal protection application. All these merits render the development of thermally stable high-temperature infrared radiation ceramic materials core competitive.

Electromagnetic wave absorption mechanism and wear corrosion characteristics of Ti3SiC2 MAX phase-doped Ni/AlN composite coating with core-shell structure based on laser cladding-induced pitaya-like multi-level heterogeneous interface

To satisfy the service requirements of wave-absorbing materials in harsh environments, it is important to design and manufacture corrosion-resistant composite-absorbing materials. According to the strategy of impedance matching and the dissipation behavior of nickel-based alloys, AlN ceramics, and MAX-phase Ti3SiC2 multicomponent composite-regulated materials were studied. As an additive manufacturing technology, multilevel heterointerface composites with core–shell structures were obtained by laser cladding. The construction of a unique core–shell structure of a metal–ceramic and ceramic (core)–ceramic (shell) multi-level heterogeneous interface increased the interfacial relaxation and multiple dissipation and improved the impedance matching. The results enabled the N20M3 cladding coating to exhibit excellent microwave absorption characteristics, with a reflection loss of −32.84 dB at the ultra-thin thickness of 1.8 mm. Additionally, the composites exhibited excellent corrosion resistance, high hardness, and relatively good resistance to erosion wear. This work promotes the durability of wave-absorbing materials under severe conditions, as well as the integration of the efficient manufacturing of wave-absorbing materials.

Manufacturing process of water-soluble salt-based ceramic cores based on vat photopolymerization

Manufacturing process of water-soluble salt-based ceramic cores based on vat photopolymerization

Microstructure Evolution and Online Thermal Resistance of Ag Sintered SiC/DBA Power Module During Power Cycling

With the increasing power and miniaturization of power electronics, the power cycling reliability and thermal management of power modules have become increasingly crucial. To address this issue, our Lab. has developed a novel instrument that allows simultaneous power cycling and real-time thermal resistance measurement. Utilizing this specific instrument, we investigated the microstructural evolution of the die attachment layer during power cycling and monitored the real-time thermal resistance of the SiC-TEG (Silicon Carbide-Thermal Engineering Group) heater chip/sintered Ag/DBA (Directed Bonded Aluminum with ceramic core of Si3N4) structure. Additionally, strategies to improve the degradation of the microstructure were proposed. The results indicate that after 10000 power cycles, numerous cracks were observed in the sintered Ag layer. However, the addition of 5 wt. % A1 suppressed the generation of cracks significantly. The addition of A1 particles has little effect on the transient thermal resistance during power cycling.

New approach to preparing near zero shrinkage alumina ceramic cores with excellent properties by vat photopolymerization

Vat photopolymerization (VPP) 3D printing technology has broken through mold limitations and shown great potential to manufacture complex-structured ceramic cores for turbine blades. However, improving dimensional accuracy is difficult for the VPP 3D printed parts due to the high contraction deformation. Reducing shrinkage is a key challenge for developing 3D-printed ceramic cores. In this study, 3D-printed alumina ceramic cores with near-zero shrinkage in the X direction were achieved for the first time using a novel approach that was called atmosphere-controlled in-situ oxidation of aluminum powder. The in-situ oxidation reaction of the aluminum powder was creatively tuned by changing the atmosphere transition temperature from argon to air. Then, the microstructure and properties of the ceramic core could be controlled by the liquid-phase sintering with the participation of atmosphere-protected molten aluminum. As a result, the pore size of the ceramic cores was significantly increased by almost ten times, but the bonding strength of the grains was also increased. In addition, the powder consolidation generated by the action of molten aluminum was considered to be an important reason for reducing the linear shrinkage of ceramic cores. Under the optimized parameters, the linear shrinkage of the ceramic cores was as low as 0.3% in the X direction. The high apparent porosity (45.02%) and flexural strength (72.7 MPa) of the alumina ceramic cores were realized at the same time. The in-situ control of sintering by changing the atmosphere will be a creative method for regulating the properties of ceramic materials.

Wetting and interfacial phenomena between a Ni-based superalloy and silica-based ceramic cores with ZrSiO4 additions

Wetting behavior and interfacial reactions between a Ni-based superalloy and silica-based ceramic cores containing 10 wt.%, 30 wt.% and 50 wt.% ZrSiO4 were studied using a sessile drop method. The reaction products were characterized by SEM/EDS, EPMA and XPS analysis. SiO2 was the main component in the ceramic cores taking part in the interfacial reactions and the reaction products were composed mainly of Al2O3 layer with some ZrOx scattered. A Cr2O3 halo formed outside the wetted ceramic surface. The wetting angle increased in the initial stage to a peak value and then decreased to a constant value. The increase of the wetting angle may be attributed to the gas evaporation at the interface and the decrease of the wetting angle was due to the formation of the reaction layer at the interface.

Parameter Optimization and Surface Accuracy Control of Water Soluble Calcia Ceramic Core Prepared by Extrusion 3D Printing Technology

Parameter Optimization and Surface Accuracy Control of Water Soluble Calcia Ceramic Core Prepared by Extrusion 3D Printing Technology

The Influence of Alumina-Zircon Fibers on The Mechanical, and Chemical properties of Silica-Based Ceramic Cores

The Influence of Alumina-Zircon Fibers on The Mechanical, and Chemical properties of Silica-Based Ceramic Cores

Optimization and experimental characterization of the innovative thermo-brachytherapy seed for prostate cancer treatment.

Adjuvant administration of hyperthermia (HT) with radiation therapy in the treatment of cancer has been extensively studied in the past five decades. Concurrent use of the two modalities leads to both complementary and synergetic enhancements in tumor management, but presents a practical challenge. Their simultaneous administration using the same implantable thermo-brachytherapy (TB) seed source has been established theoretically through magnetically mediated heat induction with ferromagnetic materials. Careful consideration, however, showed that regular ferromagnetic alloys lack the required conductivity to generate enough power through eddy current to overcome heat dissipation due to blood perfusion at clinically measuredrates. We characterized the TB implant that combines a sealed radioactive source with a ferrimagnetic ceramic (ferrite) core, serving as a self-regulating HT source when placed in an alternating electromagnetic field. To increase the heat production and uniformity of temperature distribution the empty spacers between radioisotope seeds were replaced by hyperthermia-only (HT-only)seeds. The heat generation due to eddy currents circulating in the seed's thin metal shell, surrounding the core, depends drastically on the core permeability. We identified a soft ferrite material ( ) as the best candidate for the core, owing to its high permeability, the HT-range Curie temperature, adjustable through material composition, and a sharp Curie transition, leading to heat self-regulation, with no invasive thermometry required. The core permeability as a function of temperature was calculated based on measured resistor-inductor (RL) circuit parameters and material B-H curves. The thickness of the shell was optimized separately for TB and HT-only seeds, having slightly different dimensions. Heat generation was calculated using the power versus temperature approximation. Finally, the temperature distribution for a realistic prostate LDR brachytherapy plan was modeled with COMSOL Multiphysics for a set of blood perfusion rates found in theliterature. The small size of the investigated ferrite core samples resulted in demagnetization significantly decreasing the relative permeability from its intrinsic value of ∼5000 to about 11 in the range of magnetic field amplitude and frequency values relevant to HT. The power generated by the seed dropped sharply as the shell thickness deviated from the optimal value. The optimized TB and HT-only seeds generated 45 and 267 mW power, respectively, providing a HT source sufficient for >90% volume coverage even for the highest blood perfusion rates. The toxicity of the surrounding normal tissues was minimal due to the rapid temperature fall off within a few millimeters distance from aseed. The investigated TB and HT-only seed prototypes were shown to provide sufficient power for the concurrent administration of radiation and HT. In addition to being used as a source for both radiation and heat at the onset of cancer therapy, these implanted seeds would be available for treatment intensification in the setting of salvage brachytherapy for locally radiorecurrent disease, possibly as a sensitizer to systemic therapies or as a modulator of the immune response, without another invasive procedure. Experimentally determined parameters of the ferrite material cores provided in this study establish a mechanistic foundation for future pre-clinical and clinical validationstudies.

Nonlocal dual-phase-lag thermoelastic damping analysis in functionally graded sandwich microbeam resonators utilizing the modified coupled stress theory

Functionally graded (FG) sandwich structures stand as one of the most representative composite structures owing to the thermal resistance and the energy absorption property in non-unfiorm thermal environment. Additionally, accurately estimating thermoelastic damping (TED) is of great importance for the design of high-performance micro/nano-resonators. Nevertheless, the classical TED models fail on the micro/nano-scale structures due to without considering the influences of the spatial size-dependent effects related to heat transfer and elastic deformation. The nonlocal heat conduction model and modified coupled stress theory are responsible for the size-dependent effects. To address this issue, present study aims to conduct the size-dependent TED model of FG sandwich microbeam resonators for TED analysis by incorporating the nonlocal dual-phase-lag (NDPL) heat conduction model and the modified coupled stress theory (MCST). It is assumed that the FG sandwich microbeam resonators consist of a ceramic core and FG surfaces. The energy equation and the transverse motion equation are formulated, and then, the analytical solution is solved by complex frequency method. Exact and closed-form expressions for TED can be obtained through the complex frequency method. The results are validated, and the parameter effects of the nonlocal thermal parameter, the material length-scale parameter, the power-law index and the vibration modes on the TED are analyzed. The results show that the energy dissipation can be reduced by the size-dependent effects resulting in improving the quality factor of microstructures. It is expected that these results may provide a theoretical basis for predicating TED in the design of FG sandwich micro/nano-resonators with high quality factor in extreme heat transfer environment.

Microstructures and properties of silica-based ceramic cores reinforced by alumina sol-modified fused-silica fibers

In this study, silica-based ceramic cores with zircon as a mineralizer and fused-silica fibers modified with alumina sol as an additive were prepared via injection molding method, the effects and mechanisms of fused-silica fibers on the mechanical and high-temperature dimensional stability properties of silica-based ceramic cores were investigated. The results demonstrate that both modified and unmodified fused-silica fibers are advantageous for the mechanical properties of silica-based ceramic cores, and the improvement level depends on the bonding strength of the interface between the fibers and the matrix. However, the unmodified fused-silica fibers melted with the matrix and aggravated the viscous flow of the liquid glass phase at high temperatures, thereby severely increasing the creep deformation of the silica-based cores. The modified fused-silica fibers remain intact because the mullite shell on the surface obstructed the fusion flow of the fibers at high temperatures, which helped to retard crack propagation and also considerably reduce the creep deformation of the silica-based cores by significantly accelerating cristobalite crystallization. The core with 1 wt% alumina sol-modified fused-silica fibers exhibited excellent comprehensive performance with bending strengths of 21.48 and 23.65 MPa at room temperature and 1550 °C, respectively; creep deformation of 0.37 mm; and apparent porosity of 37.98 %, well fulfilling the requirements for single crystal hollow blade casting.

The influence of graphite on the physical, thermal, and mechanical properties of silica‐based ceramic cores

AbstractDue to their excellent thermal stability and chemical resistivity against molten metals, silica‐based ceramic cores have been prepared for use in nickel‐based superalloy investment casting via injection molding under 12 kPa pressure and 115°C temperature. This paper evaluated the effect of graphite as an additive on the thermal and mechanical properties of silica‐based ceramic cores. The results show that adding graphite increases the core's modulus of rupture (MOR) and hot MOR (at 1200°C) by 6% and 35% to 10.65 and 18 MPa, respectively. According to phase analysis by X‐ray diffraction, the presence of graphite reduced the crystallization behavior of fused silica and increased the open and closed porosity amounts by 2.5%–33.6%. Additionally, the formation of the in situ SiC phase due to reduction reactions decreases the shrinkage and enhances the strength of graphite‐containing bodies. No difference in the thermal expansion coefficient of samples in the presence of graphite has been detected.

Forming deviation coupling model and control method in the photopolymerization process of ceramic slurry

In the process of photocuring using ceramic slurry, the scattering of ceramic particles is widely acknowledged as the primary cause of deviations. However, when aiming to minimize scattering deviations for the production of intricate structures, it is crucial to also consider deviations resulting from resin shrinkage, an aspect that has been overlooked in previous research. This study successfully reduced scattering deviations by incorporating graphite as a light absorber. This approach enabled the evaluation and analysis of the impact of shrinkage deviations on forming deviations. Experimental results investigating deviations in size and shape across various feature structures demonstrated the substantial impact of shrinkage deviations on the final forming deviations. By combining theoretical analysis with empirical findings, this study proposes a coupled model that accounts for the combined effects of scattering deviations and shrinkage deviations. Additionally, a control method is introduced to enhance forming accuracy by compensating for scattering deviations using shrinkage deviations. Moreover, it elucidates the variation curve of forming deviations with the addition of graphite under different photocuring parameters. Ultimately, this model facilitated the enhancement of ceramic slurry formulation and photocuring process parameters, enabling the high-precision printing of intricate ceramic core molds with incorporated grids.

Core shift limitation in investment casting process of hollow turbine blade

The deviation in wall thickness caused by core shift during the investment casting process significantly impacts the strength and service life of hollow turbine blades. To address this issue, a core shift limitation method is developed in this study. Firstly, a shift model is established based on computational fluid dynamics and motion simulation to predict the movement of the ceramic core in investment casting process. Subsequently, utilizing this model, an optimization method for fixturing layout inside the refractory ceramic shell is devised for the ceramic core. The casting experiment demonstrates that by utilizing the optimized fixture layout, not only can core shift during the investment casting pouring process be effectively controlled, but also the maximum wall thickness error of the blade can be reduced by 42.02%. In addition, the core shift prediction is also validated, with a prediction error of less than 26.9%.

Optimisation and application of high solid loading stereolithography 3D printing ceramic cores slurry

The properties of ceramic slurry play a crucial role in the production of high-quality ceramic cores. In stereolithography 3D printing process, ceramic slurry should have high solid loading as far as possible. In this work, slurry with high solid loading and low viscosity was successfully prepared by changing the resin composition. When HDDA:TMPTA was 6:2, slurry exhibited low viscosity, high stability and excellent curing properties. Ceramic cores were successfully prepared by the optimized slurry with a solid loading of 60 vol%. The effects of sintering temperature on ceramic cores were studied. As the increase of sintering temperature, the bulk density gradually increased and the open porosity decreased. The ceramic cores exhibited excellent properties at 1250 °C. This work provided a theoretical basis for the optimisation and application of slurry on stereolithography 3D printing ceramic cores.