Slurry Infiltration Research Articles

Processing and characterization of 2D woven ZrB2‐based ultrahigh‐temperature ceramic matrix composites

AbstractCf‐ZrB2 and Cf‐ZrB2–SiC ultrahigh‐temperature ceramic matrix composites were produced using slurry infiltration in the 2D woven carbon fabric and hot pressing at 2000°C. The mixing time and amount of solid loading of the ZrB2–SiC slurry were found to have a significant effect on both microstructure and mechanical properties and were optimized to obtain an agglomerate‐free composite. The ZrB2–SiC slurry with a solid loading of 20%–30% was found to be effective for infiltration within the intra‐pore in carbon tows. The composites have a nearly completely dense matrix layer with a porous matrix within the fiber layers. The fabricated 2D woven Cf‐ZrB2 and Cf‐ZrB2–SiC composites were non‐brittle.

Y/YbB4-modified SiCf/SiC composites with enhanced water-oxygen corrosion resistance

Silicon carbide fibers-reinforced silicon carbide matrix (SiCf/SiC) composites, which are commonly used as thermal structural materials in different components, e.g., combustion chamber liners, are susceptible to water-oxygen corrosion, resulting in rapid performance degradation and structural collapse. To enhance their resistance to water-oxygen corrosion, the incorporation of rare-earth silicates (RE silicates) has been explored. In this study, novel Y/YbB4-modified SiCf/SiC composites, with superior resistance to water-oxygen corrosion, are fabricated using a combination of slurry infiltration (SI) and reactive melt infiltration (RMI) process. Results demonstrate that Y/YbB4-modified SiCf/SiC composites exhibit open porosity of 3.2 ± 0.4%, corresponding to remarkable reduction of 69.8% compared to CVI-SiCf/SiC composites. Furthermore, after being exposed to water-oxygen environment at 1200 °C for 100 h, the surface of Y/YbB4-modified SiCf/SiC composites displays various yttrium silicates and ytterbium silicates. The material exhibits strength retention of 76.84%, indicating a notable improvement of 15.71% over the CVI-SiCf/SiC composites.

Efficient fabrication and properties of 2D Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC high-entropy ceramic matrix composites via slurry infiltration lamination combined with precursor infiltration and pyrolysis

In this work, an efficient processing route was developed to fabricate Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites via slurry infiltration lamination (SIL) combined with precursor infiltration and pyrolysis (PIP). The (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C powder was initially synthesized at 1900 °C. Then the 2D Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites were obtained via SIL and PIP at temperatures no higher than 1100 °C. The as-fabricated composites show a density of 2.52 g/cm3 and an open porosity of 15.2 vol%, with a bending strength of 255 ± 15 MPa. The 2D Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites also present excellent ablation resistance, with the linear and mass recession rates of 0.33 µm/s and 0.60 mg/s after ablation at 2000 °C/300 s. This work provides a route for the efficient fabrication of Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC composites, and also inspires new strategies to develop high-entropy ceramic matrix composites with high performance.

Infiltration of silica slurry into silica-based ceramic cores prepared by selective laser sintering based on pre-sintering

The silica-based ceramic core is an important mold for manufacturing hollow blades. The preparation of silica-based ceramic cores by combining selective laser sintering (SLS) and vacuum infiltration (VI) technologies is a promising approach. To enhance infiltration effect, pre-sintering was introduced to obtain the bodies with high porosity and hydrophilicity. The infiltrated silica content increased from 29.58 wt% for samples infiltrated once to 68.91 wt% for samples infiltrated three times. The increase of silica content in the matrix reduced the porosity of final ceramics, thus improving the room-temperature flexural strength. The infiltrated silica gradually transformed into cristobalite during the high-temperature test, which improved the high-temperature flexural strength and creep resistance. When the final-sintering temperature was 1225 °C, room-temperature and high-temperature flexural strength reached 21.17 MPa and 21.21 MPa, respectively, due to the enhanced sintering necks and low porosity. These results indicate that our work provides a promising route to fabricate silica-based ceramic cores by SLS technology.

Microstructure and mechanical properties of Al2O3/Al2O3 composite densified through a slurry infiltration and sintering process

High fracture strength and fracture toughness are vital requirements for the Al2O3/Al2O3 composites. This advanced structural material is composed of two-dimensional alumina fiber fabrics with porous alumina matrices. However, the Al2O3/Al2O3 composites exhibit low delamination resistance under shear stress. In this study, an as-fabricated Al2O3/Al2O3 composite was densified through a slurry infiltration and sintering (SIS) process. The SIS-cycle-dependent mechanical properties of the Al2O3/Al2O3 composites were investigated. The results showed that the matrix was strengthened, and the fibers were unaffected after SIS process. With increasing SIS cycles, the flexural and interlaminar shear strengths increased, whereas the fracture toughness decreased. The best performance was reached after six SIS cycles, which had a flexural strength of 414.7 ± 41.6 MPa, an interlaminar shear strength of 25.6 ± 3.1 MPa, and a fracture toughness of 11.0 ± 0.3 MPa m1/2. The different changes in fracture strength and fracture toughness with the SIS cycles were attributed to matrix densification and enhanced interfacial bonding. The SIS process has the potential to improve the strength without sacrificing the damage tolerance.

Ceramic Foams with Controlled Geometries Through 3D‐Printed Sacrificial Templates

Powder‐based 3D printing was combined with sacrificial templating to realize highly porous yttria‐stabilized ZrO2 (YSZ) ceramic foam objects with well‐defined geometries. The porous sacrificial template is 3D printed using poly(methyl methacrylate) powder. Various methods are evaluated to optimize ceramic slurry infiltration into the 3D‐printed template and subsequent burn‐out. The optimized method yields ceramic foam objects with an open porosity of >66% and replicates the geometry of the 3D‐printed template with high fidelity.

Tunnel Face Stability Considering the Influence of Excess Slurry Pressure

With excess slurry pressures exerted on the tunnel face, slurry particles tend to infiltrate into the soil in front of the tunnel. There will be excess pore pressure ahead of the tunnel in the case of infiltration, leading to an impairment in the supporting effect contributed by the excess slurry pressure. Corresponding to three slurry infiltration scenarios distinguished by the forms of the filter cake, different pressure transfer models are employed to describe the pore pressure distribution. Using the kinematic approach of limit analysis and the numerically simulated seepage field, the study of tunnel face stability under different slurry infiltration cases is extended by employing a 3D discretization-based failure mechanism. In addition, two simple empirical formulas describing the pore pressure distributions above the tunnel and in advance of the tunnel are established and verified. Combined with the dichotomy method and strength reduction method, the safety factors yielding rigorous upper-bound solutions are obtained by optimization. The proposed method is validated by a comparative analysis. The developed framework allows considering the influence of excess pore pressure on the whole failure mechanism and the three-dimensional characteristics of seepage. A parameter analysis is performed to study the effect of the excess slurry pressure, hydraulic conditions, soil strength properties, and pressure drop coefficient. The results show that the steady-state flow model leads to much more conservative results than the full-membrane model. The safety factor increases with the increasing excess slurry pressure and the decreasing pressure drop coefficient. The present work provides an effective framework to quickly assess the face stability of tunnels under excess slurry pressure considering different filter cake scenarios.

Preparation of SiC/SiC composites with high toughness by reaction of the SiCP+C double-cladding layer with liquid silicon

SiC/SiC composites prepared by liquid silicon infiltration (LSI) have the advantages of high densification, matrix cracking stress and ultimate tensile strength, but the toughness is usually insufficient. Relieving the residual microstress in fiber and interphase, dissipating crack propagation energy, and improving the crystallization degree of interphase can effectively increase the toughness of the composites. In this work, a special SiC particles and C (SiCP +C) double-cladding layer is designed and prepared via the infiltration of SiCP slurry and chemical vapor infiltration (CVI) of C in the porous SiC/SiC composites prepared by CVI. After LSI, the SiC generated by the reaction of C with molten Si combines with the SiCP to form a layered structure matrix, which can effectually relieve residual microstress in fiber and interphase and dissipate crack propagation energy. The crystallization degree of BN interphase is increased under the effects of C-Si reaction exotherm. The as-received SiC/SiC composites possess a density of 2.64 g/cm3 and a porosity of 6.1%. The flexural strength of the SiC/SiC composites with layered structure matrix and highly crystalline BN interphase is 577 MPa, and the fracture toughness reaches up to 37 MPa·m1/2. The microstructure and properties of four groups of SiC/SiC composites prepared by different processes are also investigated and compared to demonstrate the effectiveness of the SiCP +C double-cladding layer design, which offers a strategy for developing the SiC/SiC composites with high performance.

A multi-field model for growth and dissipation of excess pore water pressure induced by slurry shield tunneling in semi-confined aquifer

This study focuses on the mechanism of slurry infiltration in front of the tunnel face during the construction of a slurry shield machine. A multi-field transient model is proposed to describe the growth and dissipation of the excess pore water pressure and the deposition of bentonite particles for slurry shield tunneling in the saturated semi-confined aquifer. Based on the conservation principle, the governing equations for the mass continuity of bentonite particles and volume continuity of slurry are derived with consideration of particle deposition and the elastic storage of the aquifer. The proposed model is validated by field measurements. The results indicate that the excess pore water pressure drops steeply close to the tunnel face and then gradually decreases to a stable value over several tunnel diameters due to the retardation of the infiltration zone. The retardation effect is positively correlated with the permeability coefficient of the soil and the filtration coefficient, while it is negatively correlated with the specific storage coefficient. The penetration distance of bentonite particles decreases with smaller soil pores and a higher slurry concentration. Besides, a quantitative equation is proposed to evaluate the influence of slurry concentration, filtration coefficient, and storability of the soil on slurry support efficiency.

Numerical study on the hydrodynamic properties of bentonite slurries with Herschel-Bulkley-Papanastasiou rheology model

During the construction of slurry shield tunnels, bentonite slurries play a significant part in maintaining excavation face stability where suitable slurries infiltrate into the stratum to form an impermeable filter cake. To enhance filter cake quality, accurate prediction of the hydrodynamic properties of bentonite slurries is always required during slurry parameters design. The main purpose of this study is to investigate the flow characteristics of bentonite slurries with different polymer contents using computational fluid dynamics (CFD) simulation. Mixtures of sodium bentonite powder, carboxymethyl cellulose (CMC), and water in different ratios were prepared, and a series of indoor rheological tests were conducted. Then an optimized numerical method for slurry flow simulation was developed by incorporating the Herschel- Bulkley-Papanastasiou (HBP) rheology model with the finite volume method (FVM). The proposed model was implanted in OpenFOAM, and then applied to theoretical cases of non-Newtonian plane-Poiseuille flow for model verification. Results show the theoretical and simulation results were in good accordance, with a successful description of the shear thinning characteristics of fluids and no divergency during the numerical solution procedure. Based on it, CFD simulations were implemented to investigate pipe flow characteristics of bentonite slurries with different CMC contents. Results indicate when the inlet velocity is constant, the decrease of pipe diameter can cause a more inhomogeneous flow and the growth of pressure drop; rises in rheological parameters can all increase the energy consumption and reduce the infiltration distance. When the yield stress is 25 Pa, the pressure drop reaches a maximum value of 5.47 kPa, compared with 2.69 kPa for slurries with a yield stress of 5 Pa. Furthermore, the infiltration law of bentonite slurries in pipes essentially conforms to a non-Darcy infiltration with an initial hydraulic gradient i0, which has a positive relationship with yield stress of fluids. i0 increases from 0.082 to 0.414 after adding 0.3% CMC into bentonite slurries. This research can provide significant guidance for the establishment of slurry infiltration theories and relevant numerical simulations.

A novel hydro‐mechanical coupled multiphysics model for slurry penetration in sand with application to face stability analysis of shield tunnel

AbstractThe slurry penetration in tunnels driven by the slurry TBM in the highly permeable water‐bearing ground is a complicated multiphysics process, which significantly affects the stability of the excavation face but has not been fully modelled. This study establishes a novel hydro‐mechanical coupled multiphysics modelling approach for face stability analysis. Different from existing methods, the proposed one is able to quantify simultaneously the spatial and temporal variation of slurry concentration, viscosity, stagnation gradient, soil porosity and pore pressure, as well as the soil skeleton deformation induced by the transferred slurry pressure in two or three‐dimension. The spatial and temporal pressure transfer from slurry suspension to soil skeleton during slurry penetration can be obtained. The coupled formulations are implemented into a finite element package for initial and boundary value problems at the engineering scale and enhanced by the Petrov‐Galerkin weighted residual stabilisation technique. After being validated through the experimental slurry infiltration tests, it is applied to a field case analysis to predict the excess pore pressure in front of the tunnel face, which shows good agreement with the field measurement. The efficiency of the applied slurry pressure and the pressure transfer mechanism are thus verified. Comparative calculations about the influence of the pressure transfer model are presented to further improve the understanding of the pressure transfer mechanism. The proposed approach is also verified applicable to estimate the optimum slurry pressure.

Progress in preparation and ablation resistance of ultra-high-temperature ceramics modified C/C composites for extreme environment

Abstract Carbon/carbon (C/C) composites have received considerable attention for one of the most promising materials in thermal-structural applications owing to their low density, excellent mechanical strength at high temperature, and superior thermal shock resistance. However, C/C composites are susceptible to destructive oxidation in atmospheric environment at high temperature. Matrix modification by adding ultra-high-temperature ceramics (UHTCs) into carbon substrate has been proved to be a favorable route to achieve the improved ablation resistance of C/C composites. In this work, the main fabrication approaches of UHTCs-modified C/C composites were summarized, including chemical vapor infiltration/deposition, precursor infiltration and pyrolysis, reactive melt infiltration, and slurry infiltration, and the advantages and drawbacks of each process were also briefly analyzed. In addition, anti-ablation properties of UHTCs-modified C/C composites under different ablation tests with different shape specimens were introduced. Finally, some likely future challenges and research directions in the development and application of these materials were presented.

Microstructure and properties of C/C–ZrC composites with matrix modification by slurry infiltration

C/C–ZrC composites are promising thermal structural materials for aerospace applications. However, until now, the reported C/C–ZrC composites exhibited a porous matrix and weaker mechanical properties. In this study, the matrices of C/C–ZrC composites were modified by slurry infiltration in order to improve density and properties. Different slurry powders such as SiC, ZrC, and ZrB2 were used to densify the C/C–ZrC composites. After slurry infiltration, the loose C–ZrC matrix was connected to a dense matrix, and some ceramic powders settled on the surface of the composites. The density of the composites increased from 1.94 to 2.42 ± 0.06 g cm-3, while the porosity decreased from 39.4 ± 4.4% to 10.3 ± 1.9% after infiltration with various slurries. The ablation and mechanical properties of the C/C–ZrC composites improved significantly by matrix modification. The flexural strength of the composites increased from 116 to 269 ± 21 MPa after slurry infiltration. Furthermore, the ablation properties of C/C–ZrC composites infiltrated with the ZrB2 slurry showed the lowest linear rate (24.7 μm s-1) and mass recession rate (7.5 mg s-1).

Low-temperature thermally modified fir-derived biomorphic C–SiC composites prepared by sol-gel infiltration

In order to solve the problems (i.e. low infiltration efficiency, cracks, interface separation and poor mechanical properties) in the process of wood-derived C–SiC composites, the thermal modification of fir at low temperatures (300 °C ∼ 350 °C) combined with sol-gel infiltration was used to successfully produce biomorphic ceramics. The prepared materials were comprehensively characterized and exhibited improved interfacial bonding between C and SiC and mechanical properties. The weight gain per unit volume (0.123 g/cm3) of SiO2 gel in the fir thermally modified at 300 °C is 167.4%, higher than that (0.046 g/cm3) of the unmodified fir. A well-bonded interface was formed between the SiO2 gel and the pore wall of the fir thermally modified at 300 °C. With the increase of modification temperature from 300 °C to 350 °C, the distance between SiO2 gel and the pore wall increases, and a gap (1–3 μm) is observed between SiO2 gel and the pore wall of the fir carbonized at 600 °C. The C–SiC composites sintered at 1400 °C exhibited the highest compressive strength and bending strength of 40.8 ± 5.8 MPa and 11.7 ± 2.1 MPa, respectively, owing to the well-bonded interface between C of fir thermally modified at 300 °C and SiC. However, the composites sintered at 1600 °C for 120 min exhibited the lowest compressive strength and bending strength of 28.1 ± 13.4 MPa and 5.7 ± 1.6 MPa, respectively, which are 31.1% and 51.3% lower than those sintered at 1400 °C for 120 min, respectively. This might result from the porous structure formed by the excessive consumption of fir-derived carbon during the reaction between C and SiO2 at 1600 °C for 120 min. Therefore, thermal modification in the preparation of biomorphic C–SiC composites can promote slurry infiltration and the formation of a well-bonded interface between C and SiC, thus improving the mechanical properties of the composites.

Local Stability in the Process of Excavation Located in High Permeability Saturated Sand of Diaphragm Wall Construction

The stability of the slurry trench is very important in the construction of the underground diaphragm wall. In the current research, the local instability of the slurry trench is mainly investigated after the excavation of a unit slot is completely completed. However, the local stability in the process of excavation has received little attention. In this paper, the local stability in the process of excavation located in high permeability strata of diaphragm wall construction is investigated. A slurry infiltration experiment was carried out to investigate the distribution of the excess pore pressure in the high permeability strata, which can determine the effective support pressure. Then, the local stability of the slurry trench in the process of excavation located in high permeability saturated sand is calculated. The results show that the same types of sand according to the design code cannot be simply treated to have the same permeability and similar distribution of the excess pore pressure, since whether the filter cake can be formed and the quality of the filter cake are the key factors to determine the distribution of the excess pore pressure. This is also crucial for the local stability in the process of excavation located in high permeability saturated sand. It is suggested that attention should be paid to the local stability in the process of excavation located in high permeability strata when the slurry infiltration mode is the pure permeable zone.

Improving the delamination resistance of oxide/oxide composites using three-dimension fiber preform

In this work, a new Slurry Infiltration and Sintering (SIS) process was proposed to fabricate three-dimensional (3D) oxide fiber perform reinforced oxide (oxide/oxide) composites. The aim of this study was to investigate the effect of slurry concentration (20–45 vol%) on mechanical properties of the 3D oxide/oxide composites. Results indicated that the SIS process had high infiltration efficient, leading to the porous matrix distributed evenly in the composite. With the increase of slurry concentration, the interlaminar shear strength increased, while the fracture toughness and work of fracture decreased. A good balance between delamination resistance and damage tolerance was achieved on the 40 vol% slurry fabricated 3D oxide/oxide composite, which had a high flexural strength of ∼332.4 MPa, a high interlaminar shear strength of ∼25.2 MPa, and a high fracture toughness of ∼11.5 MPa m1/2.

A Mesoscopic Viewpoint on Slurry Penetration and Pressure Transfer Mechanisms for Slurry Shield Tunneling

The penetration characteristics of the slurry and the support pressure transfer mechanisms are critical to the tunnel face stability control during a mechanized excavation. In this paper, numerical calculations coupling computational fluid dynamics (CFD) with the discrete element method (DEM) are carried out to simulate sand column penetration tests considering different particle size ratios. The reasonableness of the numerical model is verified by comparing the variation patterns of the soil permeability coefficients monitored in the numerical tests with the results of existing laboratory tests. The mesoscopic transport characteristics of the slurry particles in the sand soil pores are considered based on numerical tests, while the slurry support effects corresponding to different penetration types are evaluated. Three main basic types of slurry infiltration are observed due to the different ratios of slurry particle size over soil pore size. For the first penetration type, the slurry particles are accumulated and able to form a supporting filter cake. The slurry support is effective because of the significant pressure drop generated on both sides of the filter cake. For the second penetration type, both a filter cake and an infiltration zone are present. A dense filling network is formed between the filter cake and the penetration zone. The third type corresponds to a purely penetration zone. An effective impermeable filling network cannot be formed, and the slurry support effect is not obvious. The development of slurry penetration distance shows an obvious time effect; the farther the penetration distance, the larger the slurry filtration loss, and the worse the transformation effect of slurry support pressure.

Effects of sand and slurry characteristics on pressure infiltration of bentonite slurry into sand

Two series of experiments were carried out to examine pressurised bentonite slurry infiltration into saturated sand columns. Three types of sand were examined, and water–bentonite and water–bentonite–sand slurries were used in series 1 and 2, respectively. Series 1 investigated the effect of sand particle size and series 2 examined the effect of the fine-sand particle content in the slurry. Scanning electron microscopy (SEM) imaging was used to observe the morphological features of the dry slurry-infiltrated sand samples. A solution for the infiltration distance during mud spurt for water–bentonite–sand slurry infiltration was verified using the data from series 2. The infiltration test results showed that the hydraulic conductivity of the slurry-infiltrated coarse sand for slurry in series 2 was lower than that in series 1. Visual observations and the SEM images showed that sand particles were bound to a bentonite film, indicating that, during infiltration, the channels for fluid flow among the sand particles are blocked by the bentonite particles adhered to the sand particles. The solution for the infiltration distance during mud spurt for water–bentonite–sand slurry infiltration showed good agreement with the experimental results.

Experimental study on rheological behaviors of Na-bentonite slurries under seawater intrusion

During the construction of submarine tunnels, the phenomenon that the seawater contaminates slurries is inevitably encountered. This will lead to obvious deterioration in rheological properties of the slurry, and even cause tunnel face instability. This study aimed to identify the constitutive relationship and rheological characteristics of slurries under seawater intrusion using laboratory experiments. Carboxymethyl cellulose (CMC) was selected as the effective additive to slurries in this paper. Mixtures of Na-bentonite slurries, CMC, and seawater in different ratios were prepared. The viscosity, flow curve, rheological model and physical stability of slurry samples were studied. Furthermore, the viscosity enhancement mechanisms of additives in freshwater and seawater slurries were also investigated. The results show that the increase of CMC and Na-bentonite contents can both greatly enhance the viscosity and make the shear-thinning behavior of slurries more obvious. The exponential equation and linear equation can be used to describe the growing relationships between the yield stress of slurries and the contents of Na-bentonite and CMC, respectively. In addition, the accuracy of the Bingham model predictions in the flow pattern of freshwater slurries was reduced when the viscosity was relatively high. At this time, the constitutive relationship can be better described by the Herschel-Bulkley model. Moreover, seawater intrusion significantly deteriorated the rheology and physical stability and changed the flow pattern of slurries. CMC played a more obvious role in altering the rheological model and increasing viscosities of slurries mixed with less seawater, which can effectively alleviate the deterioration in rheological behavior and maintain physical stability. Microscopically, CMC can make agglomerations more compact and continuous due to the formation of hydrogen bonds with bentonite particles, thus guaranteeing the swelling of bentonite particles and maintaining the excellent rheological properties of slurries contaminated by seawater. This research can provide significant guidance for the establishment of slurry infiltration theories and numerical models under seawater intrusion.

Microstructure and mechanical properties of three-dimensional oxide/oxide composite fabricated by a slurry infiltration and sintering process

Oxide/oxide composites reinforced by two-dimensional fiber fabrics are important structural materials at high temperatures but exhibit low delamination resistance. This study developed a simple slurry infiltration and sintering (SIS) process to fabricate three-dimensional oxide/oxide composites. The results showed that a homogeneous microstructure in three directions was obtained. This composite possessed a weak matrix, which had a porous structure and low elastic modulus. Typical mechanical properties of the composite were not lower than those of two-dimensional oxide/oxide composites since the flexural strength and fracture toughness were 332.4 MPa and 11.6 MPa·m1/2, respectively. Particularly, the composite had a good interlaminar shear strength of 25.4 MPa and a superior transthickness tensile strength of 5.6 MPa. X-ray computed tomography showed that fiber yarns in the through-thickness direction effectively impeded crack propagation and enhanced delamination resistance. Therefore, the reported SIS process is a very promising method for manufacturing three-dimensional oxide/oxide composites.