Periodic Reporting for period 4 - CeraText (Tailoring Microstructure and Architecture to Build Ceramic Components with Unprecedented Damage Tolerance)
Berichtszeitraum: 2023-11-01 bis 2024-10-31
Advanced ceramics incorporate multifunctional design and innovation to produce high-performance applications in the fields of biomedicine, automotive engineering, electronics, energy and mechanical engineering. The combination of ceramics with other materials (metals, polymers or other ceramics) has enabled the fabrication of hybrid systems with exceptional structural and functional properties. Examples are bio-implants for hip joint replacements, piezo-ceramic actuators in car injection devices, resistors and capacitors in microelectronics, batteries or solid oxide fuel cells for energy storage, among others. However, a critical issue affecting the functionality, lifetime and reliability of these systems is the initiation and uncontrolled propagation of cracks in the brittle ceramic parts, yielding in some cases very high rejection rates of component production.
In contrast to metals and polymers, crack propagation in ceramics is usually catastrophic due to their high stiffness and lack of plastic deformation upon loading. As a result, ceramics have low tolerance to damage. In this regard, the remarkable “damage tolerance” found in natural materials such as wood, bone or mollusc shells, has yet to be achieved in technical ceramics. You can replace a mobile phone, but we do not want a fracture of a hip-joint or a ceramic sensor that fails in an “autonomous car”. Novel “bio-inspired” ceramic designs combining microstructure and architecture could change this situation.
The overall objective of this project aimed to establish new scientific principles for the design and fabrication of innovative ceramics with unprecedented damage tolerance and high reliability. The main strategy has been based on tailoring microstructural features (e.g. texture degree, tailored internal stresses, second phases, interface bonding) in a hierarchical architecture, in order to provide outstanding lifetime and reliability in structural and functional ceramic devices.
In contrast to metals and polymers, crack propagation in ceramics is usually catastrophic due to their high stiffness and lack of plastic deformation upon loading. As a result, ceramics have low tolerance to damage. In this regard, the remarkable “damage tolerance” found in natural materials such as wood, bone or mollusc shells, has yet to be achieved in technical ceramics. You can replace a mobile phone, but we do not want a fracture of a hip-joint or a ceramic sensor that fails in an “autonomous car”. Novel “bio-inspired” ceramic designs combining microstructure and architecture could change this situation.
The overall objective of this project aimed to establish new scientific principles for the design and fabrication of innovative ceramics with unprecedented damage tolerance and high reliability. The main strategy has been based on tailoring microstructural features (e.g. texture degree, tailored internal stresses, second phases, interface bonding) in a hierarchical architecture, in order to provide outstanding lifetime and reliability in structural and functional ceramic devices.
The project was structured on 3 Work packages (WP) running in parallel. WP1 focussed on the design and processing of novel ceramic architectures (building blocks), WP2 on the modelling of crack initiation and fracture resistance of the materials and architectures investigated, and WP3 was dedicated to experimental validation and testing of the architectures under various loading conditions, which are relevant for the application of trchnical ceramics in sectors such as biomedicine, energy, communication and transport.
In the first stage of the action, we were able to set-up a state-of-the art “processing lab” (with help of the acquired equipment within the Grant), and succeeded in the fabrication of multilayer architectures (based on alumina-zirconia ceramic compositions), as planned in WP1. We could process stable slurries that combined sub-micron powders with “templates” (particles with high aspect ratio), which are crucial for achieving a nacre-like microstructure during sintering. Fabrication of ceramic parts have been carried out using both the Tape Casting method (as planned in WP1) and also 3D-printing technique base on “stereolithography” (to access more geometrical complexity).
In order to ensure the fabrication of “crack-free” multi-materials, a new computational model based on a “stress-energy” finite fracture mechanics approach was developed (as planned in WP2). This model has been also applied to predict crack formation in the ceramic architectures under different loading situations (e.g. cooling down from sintering in multimaterials, contact loading and/or thermal shock).
An important part of the project has been the development (or adaptation) of testing protocolls to evaluate the performance of the ceramic architectures under different loading scenarios (e.g. contact loading) and length scales (from micro to macro), as planned in WP3. For instance, micro-scaled testing of “single grains” in textured alumina has delivered important results that helps understanding the macroscopic behaviour of the layered-based ceramic materials fabricated in WP1. This methodology, based on testing of notched micro-cantilevers, may be now applied to other ceramic materials and/or composites. In addition, our hypothesis regarding the combined effect of residual stresses and (nacre-like) microstructural textured on the “damage tolerance” capability of the ceramic parts has been validated with bending experiments (performed at room temperature and up to 1200°C), showing the potential of these designs also for high temperature applications.This has been carried out also in WP3.
It is worth highlighting that the models to predict crack formation developed in this action (in WP2) have been successfully validated experimentally (in WP3).
In the first stage of the action, we were able to set-up a state-of-the art “processing lab” (with help of the acquired equipment within the Grant), and succeeded in the fabrication of multilayer architectures (based on alumina-zirconia ceramic compositions), as planned in WP1. We could process stable slurries that combined sub-micron powders with “templates” (particles with high aspect ratio), which are crucial for achieving a nacre-like microstructure during sintering. Fabrication of ceramic parts have been carried out using both the Tape Casting method (as planned in WP1) and also 3D-printing technique base on “stereolithography” (to access more geometrical complexity).
In order to ensure the fabrication of “crack-free” multi-materials, a new computational model based on a “stress-energy” finite fracture mechanics approach was developed (as planned in WP2). This model has been also applied to predict crack formation in the ceramic architectures under different loading situations (e.g. cooling down from sintering in multimaterials, contact loading and/or thermal shock).
An important part of the project has been the development (or adaptation) of testing protocolls to evaluate the performance of the ceramic architectures under different loading scenarios (e.g. contact loading) and length scales (from micro to macro), as planned in WP3. For instance, micro-scaled testing of “single grains” in textured alumina has delivered important results that helps understanding the macroscopic behaviour of the layered-based ceramic materials fabricated in WP1. This methodology, based on testing of notched micro-cantilevers, may be now applied to other ceramic materials and/or composites. In addition, our hypothesis regarding the combined effect of residual stresses and (nacre-like) microstructural textured on the “damage tolerance” capability of the ceramic parts has been validated with bending experiments (performed at room temperature and up to 1200°C), showing the potential of these designs also for high temperature applications.This has been carried out also in WP3.
It is worth highlighting that the models to predict crack formation developed in this action (in WP2) have been successfully validated experimentally (in WP3).
From the processing point of view, it has been feasible to obtain high-degree (up to 80%) of textured microstructures using both Tape Casting and 3D-printing. This is the first time that so-called “textured” (nacre-like) ceramic have been fabricated using a 3D printer, which opens new possibilities for the fabrication of complex geometries with reinforced mechanical properties (as hypothesized in the ERC proposal). The introduction of additive manufacturing into the project has enabled us to increase the complexity of the fabricated parts.
Concepts hypothesized such as “combination of layers with residual stresses to increase strength” has been proved in alumina-based 3D-pinted architectures, obtaining strength values higher than 1GPa (never reported in literature for alumina).
In addition, significant progress is being achieved in modelling crack formation in layered ceramics (so-called “tunnelling cracks”) associated with the combination of layers with different properties.
The introduction of “stress-energy” approaches for predicting crack formation in our ceramic samples can explain (not reported in literature so far) effects of ball-geometry on crack initiation forces, which can have implications for predictive models in other areas, such as coatings for tooling applications, dentistry, etc.
In the later stage of the action, we have explored additional sintering techniques, such as “rapid sintering”, which in combination with 3D-printing can give us a high degree of controlling the microstructure, reduction in production times and energy consumption, which would mean a breakthrough in the way of making advanced ceramics, and shall contribute to reduce resources and energy for production of ceramic parts.
The application of multi-material concepts into 3D-printed architectures has been pioneer during this action. The idea of desgining with multi-materials using the 3D-printing technology for ceramics is now being explored as a "proof-of-concept" on ceramic bio-implants for hip joint replacements. A "ERC-PoC" proposal has been submitted in the fall of 2024 is awaiting revision.
Concepts hypothesized such as “combination of layers with residual stresses to increase strength” has been proved in alumina-based 3D-pinted architectures, obtaining strength values higher than 1GPa (never reported in literature for alumina).
In addition, significant progress is being achieved in modelling crack formation in layered ceramics (so-called “tunnelling cracks”) associated with the combination of layers with different properties.
The introduction of “stress-energy” approaches for predicting crack formation in our ceramic samples can explain (not reported in literature so far) effects of ball-geometry on crack initiation forces, which can have implications for predictive models in other areas, such as coatings for tooling applications, dentistry, etc.
In the later stage of the action, we have explored additional sintering techniques, such as “rapid sintering”, which in combination with 3D-printing can give us a high degree of controlling the microstructure, reduction in production times and energy consumption, which would mean a breakthrough in the way of making advanced ceramics, and shall contribute to reduce resources and energy for production of ceramic parts.
The application of multi-material concepts into 3D-printed architectures has been pioneer during this action. The idea of desgining with multi-materials using the 3D-printing technology for ceramics is now being explored as a "proof-of-concept" on ceramic bio-implants for hip joint replacements. A "ERC-PoC" proposal has been submitted in the fall of 2024 is awaiting revision.