Alumina Preforms Research Articles

Fabrication and tunable reinforcement of net-shaped aluminum matrix composite parts via 3D printing

Advanced materials, such as metal matrix composites (MMCs), are important for innovation, national security, and addressing climate change. MMCs are used in military, aerospace, and automotive applications because of their exceptional mechanical and thermal properties, however adoption has been slow due to costly and onerous manufacturing processes. A new process using fused filament fabrication 3D printing has been developed to make net shape MMCs without tooling or machining. The process involves printing an alumina preform and then using pressure-less infiltration with a molten aluminum alloy to form the composite. Arbitrary shapes can be formed in this process—a brake lever and a flange are demonstrated—and the properties can be tuned by varying the ceramic infill geometric pattern and ceramic loading. By using 35 vol% continuous fiber reinforcement over 800 MPa strength and 140 GPa modulus are achieved for the aluminum composite, 3.4 × and 2 × the matrix aluminum properties.

Experimental and numerical investigation of the thermal properties and related microstructural influences of an interpenetrating metal ceramic composite at elevated temperatures

An interpenetrating metal-ceramic composite (IMCC), consisting of an open-porous alumina preform (26vol%), infiltrated with an AlSi10Mg alloy is investigated for its thermal properties and the microstructural impact on the thermal cycling behavior. Specific heat capacity, thermal conductivity and the coefficient of thermal expansion are investigated experimentally. Next to dilatometry experiments, an in-situ SEM setup with digital image correlation of the natural microstructure of the composite is used as a recognizable pattern on the sample surface to evaluate strain and microstructural changes during heating and cooling. The interpenetrating phase composite is also modelled based on reconstructed and generated microstructures. Extensive numerical studies are conducted with varying boundary conditions, interface properties, initial cooling temperatures, temperature dependent material properties and inclusion of pores. Microstructural investigations show phenomena of plasticity, creep, crack formation and interface detachment which is supported by numerical findings. Microstructural changes during heating and cooling in form of crack formation occur in the metallic phase and metallic precipitation. The influence of the microstructural processes on the thermal expansion behavior are discussed in comparison to existing hypotheses from literature.

Dense and strong ceramic composites via binder jetting and spontaneous infiltration

The objective of this study is to test the feasibility to produce fully ceramic composites (i.e., without containing any metal phases) by binder jetting of alumina preforms and spontaneous infiltration by copper in air. Alumina powders of different particle sizes (submicron and micron) were used as the feedstock for binder jetting. Afterward, standard post-processing steps were first applied, including curing, depowdering, debinding, and sintering. The sintered specimens were then spontaneously infiltrated with copper in air. The sintered specimens made with both powders had high porosity and poor mechanical properties. The infiltrated specimens made with both powders approached full density, and their mechanical properties were significantly improved. The compressive strength of 826.0 MPa and the flexural strength of 317.5 MPa achieved in this study are greater than those of any alumina-based specimens made via binder jetting followed by sintering and/or infiltration in the literature.

Mechanical behaviour and pore morphology of functionally graded alumina preforms and their composites

Functionally-graded ceramic composites were produced using a hot pour-and-set method via freeze casting of alumina slurries with solid loading between 40% and 20%, with gelatine as a binder. The slurry and additives were tailored for controlling the microstructure and mechanical properties, such as pore morphology, preform density and compressive strength. Varying the gelatine concentration between 2.5% and 9%, transformed the pore morphology from lamelllar to honeycomb and into closed cell. At 3% concentration, increasing the solid loading from 10% to 30% yielded higher compressive strength from 48 MPa to 317 MPa. The resultant compressive behaviour closely matched to Gibson-Ashby closed cell predictive model. Alumina/epoxy composite mechanical performance plateau as the solid loading increased; the 20% solid loading composite produced the best performance. The compressive strengths of the alumina/epoxy and alumina/aluminium composites were on average 300% and 1110% higher than their respective preform counterparts, across a solid loading range of 10–20%.

Low energy repair of co-continuous metal-ceramic composites using electrodeposition

The concept of self-healing materials, mainly inspired from biological systems, in the last several decades has been pursued toward fully autonomous materials and structures. Self-healing of polymers (extensively) and metals (to much less extent) have been demonstrated, however, there are no such reports for metal-ceramic composites. Metal-ceramic composites are technologically significant as structural and functional materials and are among the most expensive materials to manufacture and repair. Hence, technologies for self-healing metal-ceramic composites are of paramount importance. Here, we demonstrate a concept to fabricate and heal co-continuous metal-ceramic composites at room temperature. The composites are fabricated by infiltration of metal (here copper) into a porous alumina preform (fabricated by freeze-casting) through electroplating; a low-temperature and low-cost (by ∼60-times lower cost compared to traditional molten metal infiltration) process for fabrication of such composites. Additionally, the same electroplating process is demonstrated for healing damages such as grooves and cracks in the original composite, such that the healed composite recovers its strength by more than 80%. Such technology may be expanded toward fully autonomous self-healing structures.

Bioinspired Alumina Preform with Aligned Micro-Platelets Printed by Vat Photopolymerization

Bioinspired Alumina Preform with Aligned Micro-Platelets Printed by Vat Photopolymerization

The Influence of the Microstructure of Ceramic-Elastomer Composites on Their Energy Absorption Capability.

The paper presents the experimental results of static and dynamic compressive tests conducted on ceramic-elastomer composites. The alumina ceramic preforms were fabricated by the four-step method: ceramic mixture preparation, consolidation under pressure, presintering, and sintering under pressure, respectively. To obtain ceramic preforms with a similar volume fraction of open pores, but with different pore sizes, alumina powder with different particle size and a ceramic binder were used, as well as pore-forming agents that were evenly distributed throughout the volume of the molding mass. The composites were obtained using vacuum pressure infiltration of porous alumina ceramic by urea-urethane elastomer in liquid form. As a result, the obtained composites were characterized by two phases that interpenetrated three-dimensionally and topologically throughout the microstructure. The microstructure of the ceramic preforms was revealed by X-ray tomography, which indicated that the alumina preforms had similar porosity of approximately 40% vol. but different pore diameter in the range of 6 to 34 µm. After composite fabrication, image analysis was carried out. Due to the microstructure of the ceramic preforms, the composites differed in the specific surface fraction of the interphase boundaries (Sv). The highest value of the Sv parameter was achieved for composite fabricated by infiltration method of using ceramic preform with the smallest pore size. Static and dynamic tests were carried out using different strain rate: 1.4·10−3, 7·10−2, 1.4·10−1, and 3·103 s−1. Compressive strength, stress at plateau zone, and absorbed energy were determined. It was found that the ceramic-elastomer composites’ ability to absorb energy depended on the specific surface fraction of the interphase boundaries and achieved a value between 15.3 MJ/m3 in static test and 51.1 MJ/m3 for dynamic strain rate.

Surface energy contributions to the work of infiltration in metal matrix composite processing

The work needed to mechanically drive molten metal into a porous solid preform when producing a composite material by infiltration can significantly exceed the energy change required for thermodynamically reversible infiltration. We measure, by quantitative metallographic analysis of partially infiltrated, particle- or fiber-based non-metallic preforms, the evolution with saturation of the three interfaces present during the process. Results show that irreversible energy losses in the infiltration of alumina preforms by molten copper, aluminium or aluminium-tin alloy cannot be ascribed to the creation of liquid meniscus surface area at intermediate metal saturation. This result agrees with similar observations in soil science and gives experimental confirmation of predictions from a recent simulation of capillarity-dominated metal infiltration [Acta Mater., vol. 210, 2021, 116831].

Effect of ceramic preform freeze-casting temperature and melt infiltration technique on the mechanical properties of a lamellar metal/ceramic composite

Elastic properties, compressive stress–strain behaviour and progressive damage evolution of poly-domain metal/ceramic composite samples fabricated by infiltration of Al12Si melt in freeze-cast alumina preforms are studied. Two different preform freezing temperatures were employed to vary the lamellae size while infiltration was carried out using two different techniques – squeeze-casting and die-casting. Due to the faster cooling kinetics at the lower freezing temperature, the lamellae size in the composites based on these preforms are finer and this results into higher compressive strength and stiffness of this composite along the freezing direction. Among the two techniques employed for melt infiltration, the very fast rate of pressure application in die-casting distorts the lamellar structure of the ceramic along the freezing direction. As a result, in die-cast composite samples, the strength and stiffness along the freezing direction are reduced significantly in comparison to the samples infiltrated by squeeze-casting. In-situ scanning electron microscopy under external compression was used to study the progressive damage mechanism in one poly-domain composite sample infiltrated by squeeze-casting. Transverse cracking of the high-angle ceramic lamellae is identified as the predominant damage mechanism.

Internal load transfer in an interpenetrating metal/ceramic composite material studied using energy dispersive synchrotron X-ray diffraction

The mechanism of internal load transfer in a newly developed interpenetrating metal/ceramic composite is studied for the first time in this work using energy dispersive synchrotron X-ray diffraction. The composite was fabricated by infiltration of Al12Si melt in an open porous alumina preform, fabricated using a mixture of two different polymer waxes as pore formers, by gas pressure infiltration. Several diffraction planes of all three crystalline phases of the composite – alumina, silicon and aluminum solid solution are investigated. Lattice strains, both along and transverse to the loading direction, in each phase are calculated from the shifts in the measured diffraction peak positions. Results show that until about 100 MPa applied compressive stress, all three phases undergo elastic deformation. At higher applied stresses aluminum undergoes plastic deformation and correspondingly load is transferred to alumina. The load carrying capability of alumina is however limited by incipient damage in this phase. At applied compressive stresses higher than 187 MPa, load carried by the alumina phase continuously decreases and correspondingly more load is again carried by the aluminum solid solution. Throughout, the fraction of load carried by silicon remains almost constant, suggesting no significant load transfer within the metallic alloy itself.

Bioinspired nacre-like alumina with a bulk-metallic glass-forming alloy as a compliant phase

Bioinspired ceramics with micron-scale ceramic “bricks” bonded by a metallic “mortar” are projected to result in higher strength and toughness ceramics, but their processing is challenging as metals do not typically wet ceramics. To resolve this issue, we made alumina structures using rapid pressureless infiltration of a zirconium-based bulk-metallic glass mortar that reactively wets the surface of freeze-cast alumina preforms. The mechanical properties of the resulting Al2O3 with a glass-forming compliant-phase change with infiltration temperature and ceramic content, leading to a trade-off between flexural strength (varying from 89 to 800 MPa) and fracture toughness (varying from 4 to more than 9 MPa·m½). The high toughness levels are attributed to brick pull-out and crack deflection along the ceramic/metal interfaces. Since these mechanisms are enabled by interfacial failure rather than failure within the metallic mortar, the potential for optimizing these bioinspired materials for damage tolerance has still not been fully realized.

Al2O3/Cu-O composites fabricated by pressureless infiltration of paper-derived Al2O3 porous preforms

Al2O3/Cu-O composites were fabricated from the paper-derived alumina matrix infiltrated with a Cu-3.2 wt% O alloy. Paper-derived alumina preforms with an open porosity ranging from ∼ 14 to ∼ 25 vol% were prepared by sintering of alumina-loaded preceramic papers at 1600 °C for 4 h. Pressureless infiltration at 1320 °C for 4 h of the preforms with Cu–O alloy resulted in the nearly dense materials with good mechanical and electrical properties, e.g. fracture toughness up to 6 MPa m0.5, four-point-bending strength up to 342 MPa, Young's modulus up to 281 GPa and electrical conductivity up to 2 MS/m depending on the volume fraction of copper alloy in the composites. The technological capability of this approach was demonstrated using prototypes in various engineering fields fabricated by lamination, corrugating and Laminated Object Manufacturing (LOM) methods.

MoSi2- and WSi2-based embedded ceramic composite thermocouples for high-temperature and harsh-environment sensing

MoSi2- and WSi2-based ceramic composite thick-film thermocouples were deposited on alumina substrates by a screen printing technique, and subsequently thermally processed and embedded within an alumina preform. The one leg of the thermocouple was formed with a MoSi2-Al2O3 composite, while the other leg was composed of a WSi2-Al2O3 composite. Four compositions were prepared by adjusting the volume percentages of MoSi2 and WSi2 from 50 to 90 vol%. The phase formation and microstructure of the sintered thermocouples were studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The thermoelectric response of the thermocouples was measured by a typical hot-cold junction temperature measurements using secondary thermocouples. The thermoelectric voltage and Seebeck coefficients of thermocouples generally increased with increasing metal silicide content, as well as, temperature difference. The highest thermoelectric performance was achieved with [90–10] vol% MoSi2-Al2O3//[90–10] vol% WSi2-Al2O3 composite thermocouples, which may be related to the increased amount of the 5–3 metal silicide phases (Mo5Si3, W5Si3) that were present in the composite systems after sintering. The 5–3 metal silicide content was shown to increase with metal silicide content after sintering. The measured effective Seebeck coefficients of the MoSi2-Al2O3//WSi2-Al2O3 composite thermocouples were higher than their estimated Seebeck coefficients. A long thermocouple (22.9 cm length, 0.6 cm width) with the legs composed of [90–10] vol% MoSi2-Al2O3 and [90–10] vol% WSi2-Al2O3 displayed stable thermoelectric performance at 1350 °C with a peak thermoelectric voltage of 19.3 mV.

Influence of adding Ti powder in preform on microstructure and mechanical properties of Al2O3p/steel composites by squeeze casting

To improve the mechanical properties of alumina particulates reinforced steel matrix composite, Ti powder was added into the alumina preform, a 5140 steel matrix composite was fabricated by squeeze casting, and the influences of Ti powder on the microstructure, hardness and bending strength of the composite were investigated, compared with the composite without adding Ti powder. Applied Ti powder and alumina particulates were 10-25 μm and 100-180 μm in size, respectively. Both composites were successfully fabricated, however Ti powder addition increased the infiltration thickness of the composite. In the Ti contained composite, a TiC film in micron scale is formed on the surface of alumina particles, many TiC aggregates are dispersed in the steel matrix without obvious remaining Ti powder. The hardness and the three-point bending strength of the composite reach 49.5 HRC and 1 018 MPa, respectively, which are 17.9% and 52.4% higher than those of the composite in the absence of Ti addition. Fracture morphology shows that the debonding of alumina particulates is eliminated for the composite in the presence of Ti addition. Sessile drop test shows the average wetting angle between 5140 steel and that of Ti coated Al2O3 is about 82.15°, much lower than the wetting angle 150° between steel and pure Al2O3. Therefore, the increase in the mechanical properties of the composite is attributed to the improvement of Al2O3p/steel interface wetting and bonding by adding Ti powder in the preform.

Effect of microstructure on mechanical properties and residual stresses in interpenetrating aluminum-alumina composites fabricated by squeeze casting

Aluminum-alumina composites with interpenetrating network structure are interesting structural materials due to their high resistance to elevated temperature and frictional wear, good heat conductivity, enhanced mechanical strength and fracture toughness. In this paper aluminum-alumina bulk composites and FGMs are manufactured by pressure infiltration of porous alumina preforms with molten aluminum alloy (EN AC-44200). Influence of the interpenetrating microstructure on the macroscopic bending strength, fracture toughness, hardness and heat conduction is examined. Special focus is on processing-induced thermal residual stresses in aluminum-alumina composites due to their potentially detrimental effects on material performance in structural elements under in-service conditions. The residual stresses are measured experimentally in the ceramic phase by neutron diffraction and simulated numerically using a micro-CT based Finite Element model, which takes into account the actual interpenetrating microstructure of the composite. The model predictions for two different volume fractions of alumina agree fairly well with the neutron diffraction measurements.

Processing Induced Flaws in Aluminum–Alumina Interpenetrating Phase Composites

This review paper deals with flaws in aluminum–alumina composites and FGMs induced by their manufacturing processes. Aluminum–alumina composites have been studied for many years as potentially interesting materials for applications, for example, in the automotive sector due to their enhanced mechanical strength, wear resistance, good heat conductivity and low specific weight. The focus here is on the interpenetrating phase composites (IPCs) manufactured by infiltration of porous alumina preforms with molten aluminum alloys. The primary objective is to provide an updated overview of research findings on a variety of flaws occurring at different stages of the manufacturing processes. Some precautions on how to avoid processing induced flaws in aluminum–alumina bulk composites and FGMs are mentioned.

Effects of glass chemistry on the optical properties of highly translucent alumina-glass biocomposites for dental restorations

Abstract Glass-infiltrated ceramic biocomposites have shown high strength and toughness, which results in long lifetime, but their translucency is relatively low, limiting the aesthetic quality of dental restorations. This study evaluated the effects of glass compositions based on the system SiO 2 -B 2 O 3 -Al 2 O 3 -La 2 O 3 -TiO 2 -CaO-CeO 2 , designed using SciGlass software, on the optical properties of alumina-based biocomposites. For (45-x)SiO 2 -xB 2 O 3 -25Al 2 O 3 -15La 2 O 3 -15TiO 2 glasses, the increase in B 2 O 3 content enhanced the infiltration of glass in the alumina preform because of the decrease in glass viscosity. The addition of CaO enhanced the infiltration depth and increased light transmittance of the biocomposite in the visible region (wavelength between 360 and 740 nm); however, the addition of CeO 2 significantly decreased the transmittance, particularly at the low wavelength range, because of the coloring effect (yellowish color due to the formation of cerium-titanium complexes). The highest transmittance was measured for biocomposites infiltrated with glass of composition 25% SiO 2 -20% B 2 O 3 -20% Al 2 O 3 -15% La 2 O 3 -15% TiO 2 -5% CaO (mol%).

Germania and Alumina Dopant Diffusion and Viscous Flow Effects at Preparation of Doped Optical Fibers

We report on germania and alumina dopant profile shift effects at preparation of compact optical fibers using packaging methods (Stack-and-Draw method, Rod-in-Tube (RiT) technique). The sintering of package hollow volume by viscous flow results in a shift of the core-pitch ratio in all-solid microstructured fibers. The ratio is increased by about 5% in the case of a hexagonal package. The shift by diffusion effects of both dopants is simulated for typical slow speed drawing parameters. Thermodynamic approximations of surface dissociation of germania doped silica suggest the need of an adequate undoped silica barrier layer to prevent an undesired bubble formation at fiber drawing. In contrast, alumina doping does not estimate critical dissociation effects with vaporous aluminium oxide components. We report guide values of diffusion length of germania and alumina for the drawing process by kinetic approximation. The germania diffusion involves a small core enlargement, typically in the sub-micrometer scale. Though, the alumina diffusion enlarges it by a few micrometers. A drawn pure alumina preform core rod transforms to an amorphous aluminosilicate core with a molar alumina concentration of only about 50% and a non-gaussian concentration profile.

Devitrification in SiO<sub>2</sub>-B<sub>2</sub>O<sub>3</sub>-Al<sub>2</sub>O<sub>3</sub>-La<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub> Glass during the Infiltration of Ceramic Composite

Dental prostheses made of ceramic composites infiltrated with glasses have been used due to their biocompatibility and possibility to mimic the natural teeth. In this study, the devitrification behavior of 20SiO2-25B2O3-25Al2O3-15La2O3-15TiO2 glass during the infiltration process in a porous alumina preform was investigated. Glass frits were prepared by melting the raw materials at 1500 °C for 60 min. The glass was infiltrated into the alumina preform at 1,150 or 1,200 °C for 60 min. The specimens were characterized by X-ray diffraction analysis and scanning electron microscopy. After the infiltration, it was possible to note that the devitrification process occurred in the remaining glass (excess glass that did not infiltrate in the preform), forming mostly aluminum borate and mullite crystalline phases. However, within the infiltrated composite no devitrification was noticed in the infiltrated glass. Possible explanations for this behavior are discussed.

Systematic approach to preparing ceramic–glass composites with high translucency for dental restorations

ObjectiveCeramic composites are promising materials for dental restorations. However, it is difficult to prepare highly translucent composites due to the light scattering that occurs in multiphase ceramics. The objective of this work was to verify the effectiveness of a systematic approach in designing specific glass compositions with target properties in order to prepare glass infiltrated ceramic composites with high translucency. MethodsFirst it was necessary to calculate from literature data the viscosity of glass at the infiltration temperature using the SciGlass software. Then, a glass composition was designed for targeted viscosity and refractive index. The glass of the system SiO2–B2O3–Al2O3–La2O3–TiO2 prepared by melting the oxide raw materials was spontaneously infiltrated into porous alumina preforms at 1200°C. The optical properties were evaluated using a refractometer and a spectrophotometer. The absorption and scattering coefficients were calculated using the Kubelka–Munk model. ResultsThe light transmittance of prepared composite was significantly higher than a commercial ceramic–glass composite, due to the matching of glass and preform refractive indexes which decreased the scattering, and also to the decrease in absorption coefficient. SignificanceThe proposed systematic approach was efficient for development of glass infiltrated ceramic composites with high translucency, which benefits include the better aesthetic performance of the final prosthesis.