Advanced Ceramic Components Research Articles

Manufacturing of a gear wheel made from reaction bonded alumina—numerical simulation of the sinterforming process

Sinter forming is a recently developed process for the production of advanced ceramic components. It combines pressure-supported sintering and superplastic deformation, and allows RBAO (Reaction Bonded Alumina) to be sintered without grain coarsening due to the reduction of process time and dwell temperature. Thus, sinterforming can achieve near net shaping and defect free components for highly stressed applications. As many phenomena interact during sinter forming, the process parameters for producing complex shaped parts are difficult to identify without numerical tools. Therefore, a micromechanical model for solid state sintering has been used to investigate the process. The model was extended to consider source controlled diffusion in order to describe the non-linear stress/strain dependence. Several experiments were made in order to determine the material parameters of the model. The model has been implemented as a user subroutine in ABAQUS/Explicit® and is validated by numerical simulations of the accomplished experiments. To show the possibilities of the finite element simulation, the sinter forming process is numerically carried out for a RBAO gear wheel.

Modeling of liquid desiccant drying method for gelcast ceramic parts

Gelcasting is a promising new technology for manufacturing of advanced structural ceramic components. The process involves drying of the “green” gelcast part before densification. Conventional methods in drying green gelcast part, using dry air or gas with a specific condition of humidity and temperature usually are confronted with many difficulties. Non uniform and differential drying in various regions due to the solvent gradient induces structural and residual stresses, that cause defects such as cracking, warping, bending and the other malformations, which make the part useless. Liquid desiccant drying method, as a novel method, has been used for drying green gelcast ceramic parts in the purpose of increasing the drying rate and removing the defects due to the release of residual stresses. In this study, the kinetics of one-dimensional drying of green gelcast ceramic parts through this method is described by a Fickian model, which accounts for the movement of the gel surface. For a constant mutual diffusion coefficient, D m, the fractional approach to equilibrium, F, is only a function of dimensionless time τ 0 ∗ , and the equilibrium volume ratio, Φ. By using simple method experimental values of D m which account for the movement of the gel boundary are obtained. Experimental data for alumina gelcast cylinders having diameters of 7 and 9 mm are well fitted by the model, and the amount of ceramic loading was 5, 10, 20, 30 and 35% by volume, respectively. Various concentrations of aqueous solution of PEG1000 were used as liquid desiccants.

Manufacturing of Advanced Ceramic Components via Electrophoretic Deposition

By means of electrophoretic deposition (EPD) ceramic or glass components and composites can be shaped fast with low energy input (electric field strengths in the range of 0.5 to 20 V/cm). High green densities up to 83% of the theoretical value could be achieved using suspensions with comparably low solid matter content (less than 75 wt.%) with optimised particle size distribution. The low viscosity of these suspension ({approx} 4 to 500 mPa.s) enables to deagglomerate effectively the suspended powders. Furthermore, the deposition rate is independent of the particle size. This enables the fast manufacture of ceramic of advanced glass and ceramic components from nanosized powders. Via electrophoretic deposition of nanosized particles within the pores of a green body a homogeneous densification can be achieved. Furthermore, components with functionally graded density, pore size or/and graded chemical composition were manufactured by means of electrophoretic impregnation (EPI). Another possible application of the EPI is the incorporation of secondary phases, that are difficult to incorporated from the fluid phase, into ceramic and glass-matrices. (orig.)

Plastic clay-like flow stress of saturated advanced ceramic powder compacts

The flow stresses of saturated, consolidated alumina powder compacts and a commercial throwing clay were measured and compared. The flow stresses of certain saturated alumina powder compacts formed by consolidating salt coagulated slurries were found to be almost identical to the flow stress of the commercial throwing clay. The effect of volume fraction of particles, particle size, interparticle attraction, and consolidation pressure on the flow stress were systematically investigated. Plastic behavior and flow stresses, controlled by changing the forces between the particles, may be useful in developing low cost plastic forming processes for the production of advanced ceramic components.

Processing of advanced electroceramic components by fused deposition technique

Abstract A variety of advanced ceramic components were fabricated using the fused deposition of ceramics (FDC) process. In FDC, ceramic loaded polymer filaments are used to build parts in a layer-by-layer fashion. A process map, based on the compressive strength and modulus of the FDC feedstock, was developed to predict the feasibility of deposition with a variety of FDC filaments. Alumina structures with photonic bandgap properties were deposited for high frequency (GHz) applications. Net shape bismuth titanate components with oriented grains were fabricated by pre-alignment of small volume of seeds in green FDC parts, followed by grain growth treatment. Piezoelectric actuators with novel structures such as spiral and bellows were manufactured and studied.

A Physical Model for the Drying of Gelcast Ceramics

Gelcasting is a promising new technology for manufactur‐ing advanced structural ceramic components. The process involves drying of the “green” gelcast part before densifi‐cation. The physical mechanisms that control this relatively long drying process are not well understood. In this study, several controlled experiments have been performed to elu‐cidate the key mechanisms. A one‐dimensional drying model has been formulated, based on evaporation and gas‐eous diffusion through the part. Experimental data have been used to obtain correlations for model parameters. This model predicts the instantaneous moisture content of a gelcast sample with an accuracy of better than 10% when the dryer humidity, dryer temperature, and sample thick‐ness are specified.

Direct-Write Fabrication of Integrated, Multilayer Ceramic Components

The need for advanced electronic ceramic components with smaller size, greater functionality and enhanced reliability requires the ability to integrate electronic ceramics in complex 3-D architectures. However, traditional tape casting and screen printing approaches are poorly suited to the requirements of rapid prototyping and small-lot manufacturing. To address this need, a direct-write approach for fabricating highly integrated, multilayer components using a Micropen to deposit slurries in precise patterns is being developed at Sandia. This approach provides the ability to fabricate multifunctional, multimaterial integrated ceramic components (MMICCs) in an agile and rapid way. Commercial ceramic thick-film pastes can be used directly in the system, as can polymer thick-film pastes (PTF). The quality of printed components depends on both the rheology and drying behavior of the pastes. Pastes with highly volatile solvents are inappropriate for the Micropen. This system has been used to make integrated passive devices such as RC filters, inductors, and voltage transformers.

Modern approaches for the production of ceramic components

New materials are vitally important in industrial development. They are mostly the start of a technology chain leading to the final product via a number of value-added stages. Application experience often produces feedback for improvement and optimization of the production process and the material itself. Machining ceramics makes high demands in terms of component quality and process economics. ‘Ceramic-adapted machining’ is therefore essential for production of advanced ceramic components. This includes both optimization of existing processes and development and testing of new machining technologies. This article presents material-adapted machining technologies and their potential for advanced ceramic components.

95/01719 Five years of industrial experience with the use of advanced ceramic components in burner systems

95/01719 Five years of industrial experience with the use of advanced ceramic components in burner systems

PRACTICAL ISSUES IN THE NDE OF ADVANCED CERAMICS

Abstract Practical issues raised by the necessity to NDE advanced-ceramic components are reviewed. Ultrasonic inspection is identified as the economically viable method and implications of ceramic inspection by transducers on the properties of the latter, are discussed. The high-frequency/high-power requirements have led to the synthesis of AIN piezoelectrics and these are discussed. Economics require array transducers and their development is outlined. The establishment of a database for the ultrasonic NDE of advanced-ceramic components is described. The probes developed were used to examine model spherical inclusions (voids (≥20μm), Zr02, MgO, and Pt inclusions (≥30μm)) in model matrices (glass, crystallized glass and partially stabilized zirconia). Surface breaking cracks were also analysed. Actual frequency spectra obtained from these defects as a function of defect size are compared with their calculated spectra and good agreement obtained.

AGT101/ATTAP Ceramic Technology Development

The Garrett Turbine Engine Company/Ford Advanced Gas Turbine Program, designated AGT101, came to an end in June 1987. During this ceramic technology program, ceramic components were exposed to over 250 h of engine test. The 85-h test of the all-ceramic hot section to 1204C (2200F) was a significant accomplishment. However, this AGT101 test program also identified ceramic technology challenges that require continued development. These technology challenges are the basis for the five-year Advanced Turbine Technology Applications Project (ATTAP), which began in Aug. 1987. The objectives of this program include: (1) further development of analytical tools for ceramic component design utilizing the evolving ceramic material properties data base; (2) establishment of improved processes for fabricating advanced ceramic components; (3) development of improved procedures for testing ceramic components and test verification of design methods; and (4) evaluation of ceramic component reliability and durability in an engine environment. These activities are necessary to demonstrate that structural ceramic technology has the potential for competitive automotive engine life cycle cost and life.