Infiltration Of Preforms Research Articles

Vacuum infiltration of copper aluminate by liquid aluminium

This paper studies attained microstructures and reactive mechanisms involved in vacuum infiltration of copper aluminate preforms with liquid aluminium. At high temperatures, under vacuum, the inherent alumina film enveloping the metal is overcome, and aluminium is expected to reduce copper aluminate, rendering alumina and copper. Under this approach, copper aluminate toils as a controlled infiltration path for aluminium, resulting in reactive wetting and infiltration of the preforms. Ceramic preforms containing a mixture of Al 2O 3 and CuAl 2O 4 were infiltrated with aluminium under distinct vacuum levels and temperatures, and the resulting reaction and infiltration behaviour is discussed. Copper aluminates stability ranges depend on vacuum level and oxygen partial pressure, which determine both CuAl 2O 4 and CuAlO 2 ability for liquid aluminium infiltration. At 1100 °C and 0.76 atm vacuum level CuAl 2O 4 is stable, indicating pO 2 above 0.11 atm. Reactive infiltration is achieved via reaction between aluminium and CuAl 2O 4; however, fast formation of an alumina film blocking liquid aluminium wicking results in incipient infiltration. At 1000 °C and 3.8 × 10 −7 atm vacuum level, CuAlO 2 decomposes to Cu and Al 2O 3 indicating a pO 2 below 6.0 × 10 −7 atm; infiltration of the ceramic is hindered by the non-wetting behaviour of the resulting metal alloy. At 1000 °C and 1.9 × 10 −6 atm vacuum level CuAlO 2 is stable, indicating pO 2 above 6.0 × 10 −7 atm. Extensive infiltration is achieved via redox reaction between aluminium and CuAlO 2, rendering a microstructure characterised by uniform distribution of alumina particles amid an aluminium matrix. This work evidences that liquid aluminium infiltration upon copper aluminate-rich preforms is a feasible route to produce Al–matrix alumina-reinforced composites. The associated reduction reaction renders alumina, as fine particulate composite reinforcements, and copper, which dissolves in liquid aluminium contributing as a matrix strengthener.

Minimal compliance design for metal–ceramic composites with lamellar microstructures

Metal–ceramic composites produced by melt infiltration of ceramic preforms are studied in an optimal design context. The ceramic preforms are manufactured through a process of freeze-casting of Al 2O 3 particle suspension. The microstructure of these composites can be presented as distributions of lamellar domains. With local ceramic volume fraction and lamella orientation chosen as the design variables, a minimum compliance optimization problem is solved based on topology optimization and finite element methods for metal–ceramic samples with different geometries and boundary conditions. Micromechanical models are applied for the calculation of the effective elastic properties of the composites. Optimized local lamella orientations and ceramic contents are calculated, and the difference between the initial (specimen with constant ceramic content and orientation) and the optimized designs is analyzed. Significant reductions in absolute values of the maximum, minimum and mean values of strain fields in the optimized structures are observed.

Fabrication of Complex-Shaped SiC Parts Based on Polymerization -Induced Phase Separation and Pyrolysis Technique

A route based on a technique of polymerization - induced phase separation and pyrolysis (PIPSP) has been developed to fabricate complex-shaped SiC parts. The capability of this process to produce complex component shapes has been demonstrated, and corresponding reactive mechanisms have been also discussed. Three types of porous carbon preforms, i.e. mesoporous carbon monoliths (MCMs), hierarchical porous carbon monoliths (HCMs) and porous carbon foam (PCFs) were obtained, which has different pore size distributions. The pore structures of the preforms can be controlled through changing starting mixture composition and polymerizing conditions. The apparent porosity of the preform was changed from 19.9 to 60%, which was a key parameter to obtain dense SiC parts. After reactive infiltration of the preform with Si, the SiC parts were obtained. Geometry of SiC parts were controlled by molds. The dimension shrinkage of SiC parts was less than 3% before/after siliconization and no distortion occurred. Compared with other molds assistance route, the wax mold assistance route was a most potential technique to fabricate SiC parts industrially because of its suitable forming precision, recycled mold materials and low-cost. The mechanism of the reactive infiltration of MCMs was different from that of the reactive infiltration of preforms with bigger pore size, i.e. the pore channels of MCMs were restructured at transitional stage of reaction.

Microstructural and mechanical evaluation of porous biomorphic silicon carbide for high temperature filtering applications

Biomorphic SiC (bioSiC) is a low cost SiC/Si composite obtained by melt infiltration of carbon preforms obtained from the pyrolysis of cellulose precursors. The porosity and pore size distribution of bioSiC can be tailored for specific applications by adequate selection of the wood precursor. Natural and artificial industrial woods were explored as possible bioSiC precursors. Silicon was removed by chemical etching. Relevant microstructural parameters such as pore size distribution, total porosity, and permeability were characterized. Since the filtration process involves large pressure gradients along the material at high temperatures, mechanical properties of porous bioSiC from the different precursors were evaluated at room temperature and 800 °C. The feasibility of porous bioSiC as a filtration material for high temperature gasification processes is discussed in terms of these properties. MDF-bioSiC is shown to be a promising material for such applications because of its good mechanical properties, interconnected porosity, pore sizes, and permeability.

Fabrication of aluminium composites reinforced with carbon fibres by a centrifugal infiltration process

Centrifugal-force infiltration was used for obtaining aluminium alloy composites reinforced with carbon fibre by the infiltration of preforms. The lost-wax-casting technique was used during the manufacturing process. Preforms fabricated with different percentages of reinforcement were heated to facilitate their filling with aluminium. Some samples were coated with nickel to favor the reinforcement wetting by the molten aluminium alloy. Composites with volume fraction of reinforcements above 7 vol.% and porosity values lower than 0.5 vol.% were obtained with this technique. The hardness of the composites increased with the volume fraction of reinforcement and the solution and the later precipitation of nickel coating caused an additional hardening effect.

Pressureless Infiltration and Resulting Mechanical Properties of Al-AlN Preforms Fabricated by Selective Laser Sintering and Partial Nitridation

A novel manufacturing process has recently been developed for the fabrication of intricate Al-AlN composite parts. The process involves green shape formation by selective laser sintering, preform development by nitridation, and net shape forming by pressureless infiltration. The infiltration atmosphere has an important influence on the final fabrication and mechanical properties. This work presents a detailed investigation on the infiltration of Al-AlN preforms with AA 6061 at various temperatures above its liquidus under nitrogen, vacuum, and argon. The green shapes are formed by selective laser sintering of a premix of AA 6061-2Mg-1Sn-3Nylon (wt pct) powders. They are then partially nitrided to create a rigid, 2- to 3-μm-thick AlN skeleton for subsequent infiltration. Nitrogen infiltration results in the highest density (2.4 gcm−3) and best tensile properties (UTS: 214 MPa; elongation: 2.5 pct), while argon infiltration gives the lowest density. Fractographs confirmed the difference in density arising from the use of different atmospheres where small pores are evident on the fracture surfaces of both argon and vacuum-infiltrated samples. The molten AA 6061 infiltrant reacts with nitrogen during infiltration leading to a 5-μm-thick AlN skeleton compared to the original 2- to 3-μm-thick skeleton in both argon and vacuum-infiltrated samples. Transmission electron microscope (TEM) examination revealed inclusions of Mg2Si and Mg2SixSn1−x in both nitrogen- and argon-infiltrated samples but not in vacuum-infiltrated samples. Vacuum infiltration is slower than nitrogen and argon infiltration. The mechanisms that affect each infiltration process are discussed. Infiltration under nitrogen is preferred.

Manufacture of Biomorphic SiC Components with Homogeneous Properties from Sawdust by Reactive Infiltration with Liquid Silicon

Biomorphic SiC components with homogeneous properties were manufactured from sawdust using a novel method to produce preforms, without addition of any extra binder, but with enough mechanical strength to be carbonized up to 1400°C without deformation. Reactive infiltration of carbon preforms of an adequate open porosity with liquid silicon has been successfully used to prepare biomorphic components. Moreover, the modification of bioSiC properties induced by the structural rearrangement of carbon preforms when they are further heat treated at 2500°C was additionally studied. BioSiC components showed a maximum in bending strength when the material is processed from carbon preforms exhibiting around 40% of open porosity, which seems to be the optimum value for carbon preforms treated at 1400° and 2500°C. However, the heat treatment of the carbon preforms at 2500°C produced bioSiC components with a finer and more homogeneous microstructure than those obtained from carbon preforms treated at 1400°C, improving their bending strength up to 22%.

Mg/B4C Composites with a High Volume Fraction of Fine Ceramic Reinforcement

The results of a study aimed at establishing an understanding of the role of particulate reinforcement on the hardness and tensile deformation of a magnesium-based matrix discontinuously-reinforced with a high volume fraction (approx. 50 vol%) of boron carbide (B4C) particulates are reported. Composites were fabricated by pressureless infiltration of porous boron carbide preforms with molten magnesium under a flowing nitrogen atmosphere. The capabilities of such a fabrication route for production of magnesium-based composites with a high volume fraction of a bimodal mixture of coarse (d 50 = 44 µm) and fine (d 50 = 0.8 µm) boron carbide particulates uniformly distributed in the matrix were also investigated. The successful initiation of spontaneous infiltration was found to be influenced by several processing parameters which were identified and investigated. Thus, the microstructure and mechanical properties of the fabricated composites were investigated in the light of the influence of the initial perform composition (boron carbide bimodal mixture composition and the wetting agents (Si and Ti powders) applied) and the infiltration parameters. The high volume fraction of particulate reinforcement content successfully achieved by pressureless infiltration was found to improve the hardness and tensile properties of the composites significantly compared to unreinforced counterparts. On the contrary, the reinforcement had a detrimental influence on ductility. Moreover, the experimental findings clearly confirmed that the influence of the reinforcing boron carbide phase on the mechanical response of Mg/B4C composites is predominantly through the volume fraction of ceramic particulate in the matrix, and much less through the average particle size of the ceramic filler applied.

Microstructural evolution during silicon carbide (SiC) formation by liquid silicon infiltration using optical microscopy

Abstract Optical microscopy and quantitative digital image analysis were used to examine the formation of fully dense, net shape silicon carbide by liquid silicon infiltration (LSI) of porous carbon preforms. By examining the phase distribution and structural changes during the reaction, we identified six reaction stages (I–VI) that describe reaction mechanisms and their time scales. The initial stages (0–15 min) of the LSI reaction include (I) liquid silicon infiltration of the carbon preform, (II) dissolution of carbon, and (III) formation of silicon carbide at the liquid–solid interfacial regions. These initial stages occur simultaneously and very rapidly, and culminate in (IV) the completion of a continuous silicon carbide layer of about 10 μm at every liquid–solid interface. Further reaction can only be achieved by (V) carbon diffusion through this layer. The reaction is essentially complete after ∼120 min. Longer reaction times should be avoided because over-reacting causes (VI) long, thin silicon-filled cracks to develop within the continuous silicon carbide matrix.

Numerical Simulation of Segregation Phenomena Coupled with Phase Change and Fluid Flow: Application to Metal Matrix Composites Processing

The injection of a liquid metal through a fibrous preform, located in an initially preheated mold, is one of the techniques used to manufacture metal matrix composites (MMCs). In order to reduce the chemical reactions between the fibers and the metal matrix, the fibrous reinforcement and the mold are commonly preheated up to initial temperatures much lower than the metal solidification temperature. Therefore, local metal solidification instantaneously occurs on fiber during liquid metal infiltration. When infiltrating metal alloy, unlike what happens when infiltrating a pure metal, both temperature and composition may vary within the matrix; this heterogeneity induces segregation within composites. A fiber scale numerical simulation was developed taking into account coupled physical phenomena which occur during the processing: flow of the liquid metal around the fibers, phase change phenomena, solute redistribution at the liquid/solid interface during alloy solidification, and species diffusion. This model predicts the segregation phenomena associated with fibrous preform infiltration by a binary alloy.

Fabrication, chemical etching, and compressive strength of porous biomimetic SiC for medical implants

BioSiC is a biomimetic SiC-based ceramic material fabricated by Si melt infiltration of carbon preforms obtained from wood. The microstructure of bioSiC mimics that of the wood precursor, which can be chosen for tailored properties. When the remaining, unreacted Si is removed, a SiC material with interconnected porosity is obtained. This porous bioSiC is under study for its use as a medical implant material. We have successfully fabricated bioSiC from Sipo wood and studied the kinetics of Si removal by wet etching. The results suggest that the reaction is diffusion-limited, and the etch rate follows a t−0.5 law. The etching rate is found to be anisotropic, which can be explained attending to the anisotropy of the pore distribution. The compressive strength was studied as a function of etching time, and the results show a quadratic dependence with density. In the attainable range of densities, the strength is similar or better than that of human bone.

Formation of dense silicon carbide by liquid silicon infiltration of carbon with engineered structure

Fully dense and net-shaped silicon carbide monoliths were produced by liquid silicon infiltration of carbon preforms with engineered bulk density, median pore diameter, and chemical reactivity derived from carbonization of crystalline cellulose and phenolic resin blends. The ideal carbon bulk density and minimum median pore diameter for successful formation of fully dense silicon carbide by liquid silicon infiltration are 0.964 g cm−3and approximately 1 μm. By blending crystalline cellulose and phenolic resin in various mass ratios as carbon precursors, we were able to adjust the bulk density, median pore diameter, and overall chemical reactivity of the carbon preforms produced. The liquid silicon infiltration reactions were performed in a graphite element furnace at temperatures between 1414 and 1900 °C and under argon pressures of 1550, 760, and 0.5 Torr for periods of 10, 15, 30, 60, 120, and 300 min. Examination of the results indicated that the ideal carbon preform was produced from the crystalline cellulose and phenolic resin blend of 6:4 mass ratio. This carbon preform has a bulk density of 0.7910 g cm−3, an actual density of 2.1911 g cm−3, median pore diameter of 1.45 μm, and specific surface area of 644.75 m2g−1. The ideal liquid silicon infiltration reaction conditions were identified as 1800 °C, 0.5 Torr, and 120 min. The optimum reaction product has a bulk density of 2.9566 g cm−3, greater than 91% of that of pure β–SiC, with a β–SiC volume fraction of approximately 82.5%.

Degradation of Al/SiCp Composites Processed with Fly Ash via Reactive Infiltration

The degradation in ambient atmosphere of Al/SiCp composites prepared by the reactive infiltration of SiCp preforms containing fly ash has been investigated. SiCp/fly-ash preforms in the form of plates (3 cm x 4 cm x 0.5 cm) with 50 % porosity are infiltrated by an Al- 8 Si-15 Mg (wt. %) alloy under argon atmosphere at 1050, 1100 and 1150 °C, for 50, 60 and 70 min. Characterization by XRD, SEM and EDX of composite specimens shortly after processing do not reveal the presence of the unwanted Al4C3 phase. However, in addition to Al, Si and SiC, MgAl2O4 and Mg2Si phases are detected. One month after the infiltration trials, white and gray powders are present on the composite specimens, accompanied by pitting corrosion and cracks which propagate with time. Although analysis by XRD of the degradation products reveals only Al4C3 in addition to the above mentioned phases, results from SEM, IR absorption and ICP also suggest the presence of Al(OH)3 and Mg(OH)2, probably from the interaction of Al4C3 and Mg2Si with water. It is considered that Mg2Si in the powders acts as an anode in a galvanic couple with atmospheric moisture as the electrolyte. The crack pathway through SiC, intermetallic AlFeMnSi and Si rich zones implies that one or more of these phases worked as the cathode. In summary, degradation of the composites is explained by the combined effect of galvanic corrosion caused by second phases and the interaction of Al4C3 with atmospheric moisture.

The low-pressure infiltration of diamond by silicon to form diamond–silicon carbide composites

The infiltration of fine-grained diamond preforms by molten silicon is limited by the blocking of the pores as a result of the volume increase during the reaction of diamond with SiC. Therefore in the present paper the infiltration of preforms made with diamond powders with different grain sizes was investigated. The preforms were prepared using phenolic resin as a binder. With increasing resin content the pore size increases, but the pore volume decreases. As a result the infiltration depth increases strongly for medium resin content. For the fine-grained ∼1.5 μm diamond preforms, a maximum infiltration depth of 2.5 mm is obtained at 10% resin, whereas at 5% resin only 1.25 mm could be infiltrated.

Metal/ceramic composites from freeze-cast ceramic preforms: Domain structure and elastic properties

Innovative metal/ceramic composites produced by melt infiltration of ceramic preforms prepared by a freeze-casting technique are examined in this study. These composites exhibit a characteristic hierarchical structure: On a mesoscopic length scale, lamellar domains with sizes up to several millimetres are observed. The aim of the present study was to analyze the anisotropic elastic properties of such a composite on different length scales. Experimental studies were carried out on samples containing about 44% alumina ceramic and 56% aluminium-based alloy (Al–12Si). Ultrasonic wave velocity measurements were carried out on macroscopic poly-domain samples as well as on miniature single-domain samples. The elastic constants derived from these measurements are discussed in light of elasticity models established for lamellar and for fibrous composites.

Infiltration of graphite preforms with Al–Si eutectic alloy and mercury

Porous isotropic graphite preforms are infiltrated with Al–12 wt.%Si at 680 °C using an applied pressure of between 2 and 8 MPa. Densitometry after infiltration and solidification is then used to deduce the relevant drainage curve. For comparison, the same preforms are also characterized by mercury porosimetry. By comparing the curves obtained from those two measurements using the Brooks–Corey relation, a contact angle of the Al–Si eutectic on graphite of 139° is obtained, in relatively good agreement with literature data.

Cellular porous SiC ceramics derived from Indian dicotyledonous woods and their application potential as hot gas filtration materials

Three dicotyledonous woods of local origin mango (Mangifera indica), jackfruit (Artocarpus integrifolia) and teak (Tectona grandis) were transformed by pyrolysis into carbonaceous preforms and subsequently converted into cellular porous SiC ceramics by liquid Si infiltration under vacuum. The pyrolysed mango, jackfruit and teak were characterised in terms of pyrolysis weight loss, shrinkages, bulk density and microstructures. The end ceramics were light weight and found to have porosities in the range of 35·5–54·5 vol.-% depending on the preform carbon density and infiltration temperatures. Scanning electron microscope (SEM) imaging confirmed the preservation of cellular tissue anatomy of the precursor wood structure in the morphologies of final ceramics. The cellular porous SiC ceramics from mango, jackfruit and teak exhibited excellent oxidation resistance during heating to 1350°C in flowing air. Porous SiC mango gives the highest porosity with more than 80% pores being in the range of 0·5–11·58 μm and an average pore diameter of 7·82 μm, while the lowest porosity is obtained in the case of porous SiC jackfruit which has a mean pore diameter of 7 μm with ∼89% of pores in the range of 0·51–11·56 μm, indicating that the cellular porous SiC ceramic possesses application potential in the hot gas filtration area.

Numerical simulation of the pressure infiltration of fibrous preforms during MMC processing

In the pressure infiltration process of metal-matrix composites, molten metal is injected under external pressure into a porous preform of the reinforcing phase and solidified, either during infiltration or after the mold is filled. To simplify the problem, the assumption of isothermally saturated fibrous preform with molten metal is adopted. The flow of molten metal is a moving boundary phenomenon which is similar to a fluid flowing through a porous medium. A numerical technique, body-fitted finite element method (FEM), is used to generate grids inside the physical domain and to calculate the distribution of pressure and other relative properties. Results show that the injection flow rate exponentially decreases with the infiltration time. Increasing injection pressure can effectively reduce the infiltration time. A simple and practical prediction of infiltration time under the various parameters is also provided in this study.

Carbon infiltration of carbon-fiber preforms by catalytic CVI

Experimental studies were conducted to assess catalytic chemical vapor infiltration processing for preparing carbon/carbon composites as a potential improvement to conventional one. The catalyst was introduced into the carbon fiber preforms by wet impregnation. Using C 3H 6/Ar/H 2 as the original gas, catalytic carbon was formed at 500–1000 °C for 1–3 h. It was found that carbon filaments were formed as the preparing temperatures were 500–700 °C, and carbon particles could be obtained at 800–1000 °C. The increasing rate of density was up to 0.916 g/ml/h when the sample was formed at 600 °C for 1 h with the catalytic of 0.7 wt.% Ni, and the carbon yield arrived to 90 wt.% . According to the micrographs of catalytic carbon, the forming mechanism of carbon filaments agreed with that of carbon filaments due to a metal catalyst. The weighted average interlayer spacing of C/C composites with catalytic carbon decreased to 0.341.

Metal matrix composite processing: numerical study of heat transfer between fibers and metal

PurposeTo study heat transfer kinetics at the fiber scale in order to describe injection of liquid metal through a fibrous perform initially situated in a preheated mould, which is one of the various methods used in order to produce metal matrix composite materials (MMCs).Design/methodology/approachThe first part presents a preliminary study in a static case to describe heat transfer kinetics between a fiber and the matrix in the case of a sudden contact of both components initially set up at different temperatures. This model enables to study the influence of the various parameters of the problem on heat transfer kinetics with phase change. In the second part, we present a modeling which takes into account the metal convection within the pores of the preform.FindingsThe numerical results of these two models justify the instantaneous thermal equilibrium assumption classically admitted to describe MMCs manufacturing methods. The results of this dynamic microscopic model are compared with the results issued from a single temperature macroscopic model to justify the methodological approach and the choice of the microscopic domain geometry representative of the MMCs manufacturing process.Research limitations/implicationsThis first numerical model at the microscopic scale deals with the study of heat transfer between fibers and a pure metal. Next step will be the extension of this study to the preform infiltration by a metal alloy. Injection of matrix alloy implies the appearance of phenomena generated by segregation during phase changes.Originality/valueThe results of simulation tests, making use of the usual conditions of MMCs processing, show pretty good agreement with those of macroscopic models describing the anisothermal flow of a pure metal through a porous medium. From this coherence and from the results of the microscopic models as well, the hypothesis of instantaneous thermal equilibrium between fibers and metal (widely used in the literature to study the production of MMCs by infiltration of the liquid metal through the fibrous reinforcement) is justified. Moreover, it will be possible to extend it to the study of infiltration by an alloy, taking then into account thermal and solutal coupled transfers inside the study domain defined in the present work.