Thermal Shock Resistance Of Ceramics Research Articles

A review of thermal shock behavior of ceramics: Fundamental theory, experimental methods, and outlooks

AbstractThe thermal shock resistance of ceramics is a key factor for determining the durability of ceramic components under transient thermal conditions and is also one of the key factors for evaluating the stability of ceramics under extreme thermal conditions. After rapid heating or cooling, the surface and internal thermal stress mismatches of ceramics can cause severe thermal damage. Two main types of ceramic thermal shock exist: rapid cooling and rapid heating thermal shock. This article presents a broad understanding and insight into fundamental theory and experimental methods for ceramic thermal shock testing. The experimental equipment and procedures, test result evaluation, and material characterization of ceramic thermal shock are summarized. Moreover, outlooks and perspectives are discussed for testing and characterizing ceramic thermal shock resistance. This review will be helpful to researchers performing studies in the relevant fields of ceramics.

The thermal shock resistance of in-situ synthesized mullite absorption and storage integrated ceramics for solar thermal power generation

Solar high-temperature thermal power generation systems require thermal storage materials with excellent thermal shock resistance due to the large temperature difference during operation (in the range of 20–800 °C). In this study, mullite-based absorption and storage integrated ceramics were prepared using low-cost bauxite and kaolin as raw materials and Fe2O3 as additive. The effect of Fe2O3 on the thermal shock resistance of mullite-based ceramics was investigated. The results showed that the absorption and bending strength of sample BK4 (bauxite: 50 wt%, kaolin: 50 wt%, Fe2O3: additional 11 wt%) increased by 2.98% (89.8%) and 8.00% (147.10 MPa), with a storage thermal density of 1185.75 kJ kg−1 after 30 thermal shock cycles. The mechanism for the excellent thermal shock resistance of the ceramics is revealed from the aspect of the changes in phase and microstructure of the samples induced by the changes in the mass transfer rate during the thermal shock process. It was calculated that a unit volume of BK4 (with a raw material cost of about 154.22 USD) could generate 974.95 kW h of electricity (saving 119.92 kg of coal) when used in a solar thermal storage system.

Cyclic thermal shock behaviors of carbon fibers reinforced SiCN ceramics with bio-inspired Bouligand-like architectures

Ceramic matrix composites (CMCs) are commonly used for high temperature components in aircrafts. However, thermal shock, as a typical loading case, will cause high thermal stresses in CMCs resulting in brittle fracture failure, and material cracking caused by thermal shock can further reduce the effectiveness of thermal protection function. In the present paper, we propose a bionic hierarchical fiber preform design method to improve the thermal shock resistance of ceramics. The effect of architectures of fiber preforms of continuous carbon fiber-reinforced CMCs on the thermal shock resistance was investigated to understand its importance and the related mechanical mechanisms. Thermal shock (cycling) tests were performed with continuous carbon fibers reinforced SiCN ceramic matrix composites (Cf/SiCN) prepared by PIP. 3D micro-CT scan and three-point bending tests were also conducted to evaluated the resultant damage. The results showed that smaller internal damage and higher thermal shock resistance can be obtained in comparison to pure SiCN ceramics, and the underlying mechanism can be explained by the fact that smaller pitch angle can resist the through-thickness crack propagation via promoting diffused in-plane damage. The present study offers a possibility in developing biomimetic Cf/SiCN ceramics with excellent thermal shock behavior.

Characterization of Ceramic Thermal Shock Cracks Based on the Multifractal Spectrum

Ceramics are commonly used as high-temperature structural materials which are easy to fracture because of the propagation of thermal shock cracks. Characterizing and controlling crack propagation are significant for the improvement of the thermal shock resistance of ceramics. However, observing crack morphology, based on macro and SEM images, costs much time and potentially includes subjective factors. In addition, complex cracks cannot be counted and will be simplified or omitted. Fractals are suitable to describe complex and inhomogeneous structures, and the multifractal spectrum describes this complexity and heterogeneity in more detail. This paper proposes a crack characterization method based on the multifractal spectrum. After thermal shocks, the multifractal spectrum of alumina ceramics was obtained, and the crack fractal features were extracted. Then, a deep learning method was employed to extract features and automatically classify ceramic crack materials with different strengths, with a recognition accuracy of 87.5%.

Simulation of the thermal shock cracking behaviors of ceramics under water quenching for 3-dimension conditions

To overcome the limitations of widely used criteria, maximum principal stress and maximum tension stress, in simulating and evaluating thermal shock resistance of ceramics for 3-dimension (3D) problems, a temperature-dependent critical fracture energy density criterion was proposed based on the force-heat equivalence energy density principle for the 3D thermal shock fracture problems of ceramic materials in this paper. Taking advantage of the criterion and finite element method, the thermal shock behavior of water quenching of cuboid Al2O3 specimens with different temperature differences were simulated. The crack patterns of the simulation results were shown to be approximated in the experiments. Especially the essential features, the longitudinal main crack and crack branches, are embodied well in the simulation results. However, the thermal shock cracks obtained by using the criteria, maximum principal stress and maximum tension stress, failed to meet the experiments. The effects of water entry posture on thermal shock crack features revealed in the results confirm the efficiency of the criterion in 3D conditions of thermal shock fracture in this paper. Finally, the maximum temperature gradient, not maximum temperature difference, was found to be the main controlling factor which caused the fracture energy density to reach a critical value to produce thermal shock crack.

Thermal Shock Resistance of Porous Silicon Carbide Ceramics Prepared Using Clay and Alumina as Additives

ABSTRACTPorous silicon carbide ceramics were prepared by an in situ reaction bonding process using clay and alumina as additives. The effects of alumina additive, pore former on phase composition, microstructure, flexural strength and thermal shock resistance of the ceramics were studied. Thermal shock resistance of porous SiC ceramics due to cooling was evaluated as a function of quenching temperatures and quenching cycles using water- and air-quenching technique. It was observed that residual strength of the quenched samples in water decreased with increase in the quenching temperature but was almost independent of quenching cycles. In water quenching, the surface of the sample cooled almost instantly but the inside remained hot which created an uneven thermal profile and generated microcracks in the sample; as a result sudden reduction of flexural strength was observed. The results showed that flexural strength and thermal shock resistance properties of the ceramics prepared with alumina are better than those of the ceramics prepared without alumina and the material was found suitable for hot gas filtration application.

An ascending thermal shock study of ceramics: Size effects and the characterization method

The ascending thermal shock resistance of ceramics is studied using a new, simple and efficient test method. The results show that our testing succeeds in developing internal cracks in the shocked specimen that are cause by tensile stresses, while there is no visible change in the surface morphology. This coincides with the failure mechanism of ascending thermal shock, and this has not been reported before. Considering there is no proper experimental characterization parameter for evaluating the ascending thermal shock resistance, we propose an experimental evaluation index called the critical temperature difference of rupture, which is defined as the temperature difference after which a sharp decrease of retained strength appears until fracture. The value of the critical temperature difference of rupture is determined by the microstructures and material properties. A method for modelling the critical temperature difference of rupture of a rectangular specimen is proposed.

Effect of Al2O3 + 4SiO2 Additives on Sintering Behavior and Thermal Shock Resistance of MgO-Based Ceramics

In order to improve the sinterability and thermal shock resistance of ceramic based on MgO magnesium oxide of micron grain size composition is used as the main starting raw material with additions of nano-Al2O3 and nano-SiO2. Ceramic based on MgO is prepared by adding different amounts of Al2O3 and SiO2 to MgO in a molar ratio 1:4. The mixture is molded and sintered in an air atmosphere. Ceramic phase composition and microstructure are studied in an x-ray diffractometer and a scanning electron microscope. The effect of adding different amounts of Al2O3 + 4SiO2 on sinterability and thermal shock resistance of MgO base ceramic is studied. Addition of Al2O3 + 4SiO2 has a favorable effect on test ceramic sinterability and thermal shock resistance. During reaction of solid substances there is formation of magnesia-alumina-spinel and forsterite that leads to retardation of periclase phase grain migration. The degree of specimen compaction is improved and this has a favorable effect on sinterability of ceramic based on MgO. The degree of compaction increases as there is an increase in sintering temperature in the range 1400 to 1500°C. In addition, specimen thermal shock resistance is improved due to connection between microcracks. As a result of adding Al2O3 in an amount up to 30 wt.% + SiO2 in an amount up to 45 wt.% MgO sinterability and thermal shock resistance are improved.

Influence of thermal shock damage on the flexure strength of alumina ceramic at different temperatures

Alumina ceramic specimens that suffered a specific water quench thermal shock were used for three-point bending test at different temperatures to investigate the effect of thermal shock damage on flexure strength for the first time. Results indicate that the sensitivity of the alumina flexure strength to thermal shock damage decreased with increasing temperature. When evaluating the thermal shock resistance of alumina by using critical thermal shock temperature difference, which determined by thermal shock residual strength at room temperature, will result in one-sided conclusion for the thermal shock resistance of ceramics. The mechanism of sensitivity of alumina ceramic strength to the thermal shock damage at elevated temperature was analyzed by the microstructure of the facture surface with SEM images. Therefore, this study can provide references for engineering application of alumina materials and improve the understanding of thermal shock resistance for ceramic materials.

Improving the thermal shock resistance of ceramics by crack arrest blocks

Ceramics used in the high temperature environment are inevitably subjected to sudden temperature change, which may lead to catastrophic thermal shock failure due to the intrinsic brittleness of ceramics. In this paper, an experimental platform is designed to realize the in-situ observation during the thermal shock experiments. Experimental results show that all the cracks initiate from one of the edge midpoints and propagate to another one for square specimens. Such experimental observation is consistent with the maximum tensile stress zone with the maximum temperature gradient given by the finite element method (FEM). The different crack modes resulting from different heating rates after thermal shock experiments are observed and analyzed. Comparison between different clamping methods is conducted to study the effects of boundary conditions on the thermal shock experiments. Furthermore, in order to improve the thermal shock performance of alumina ceramics, crack arrest blocks are added near the edge midpoint. The thickness, shape and arrangement of the blocks are systematically investigated to understand the mechanism of improvement of thermal shock resistance.

Study on Thermal Shock Resistance of Alumina Composite Ceramics by Indention Quenching Method

Alumina ceramics are the most widely used structural ceramics, especially in aviation, spaceflight and war industry area. However, alumina is of covalent bond, with low fracture toughness and poor thermal shock resistance, which baffle the application of the alumina ceramics in engineering. In this paper, mullite fiber was used to improve its toughness and thermal shock resistance. Alumina-mullite composite ceramics were prepared by hot press sintering. The effect of mullite fiber on thermal shock resistance of ceramics was investigated through indention quenching method. Meanwhile, the mechanism of its reinforcing and toughening and the relationship between mechanical properties and addition of mullite fiber were also discussed.

Effects of In-Plane Geometric Shapes on Thermal Shock Resistance of Ultra-High Temperature Ceramic Components

In thermal structural engineering, ceramic components can have various shapes and be constrained. It is traditionally known that the thermal shock resistance (TSR) of ceramic components (with conduction occurring in the thickness direction), such as disk, oval plate and rectangular plate, is independent of the in-plane geometric shapes. The present study shows that this is valid for ceramic components that are free, but when the components are constrained, the in-plane geometric shapes can have significant effects on the TSR of ceramics. Three types of components, with the edges of the lower surfaces clamped are studied. Under the second or third type thermal boundary conditions, the TSR of the disk is the best; that of the oval plate decreases as the ellipticity increases; and that of the rectangular plate is approximately equal to that of the oval plate with ellipticity of 1.2. This is because that the asymmetry of the in-plane geometric shapes, as well as the asymmetry of the mechanical boundary conditions, can worsen the TSR of the ceramics when the components are constrained. This is very important for the design and application of ceramics in the thermal structural engineering.

Effect of the cooling medium temperature on the thermal shock resistance of ceramic materials

The thermal shock behavior of ceramics with the cooling medium temperatures in the range 5°C to 100°C has been studied in detail by measuring the retained flexural strength after water quenching. The test materials is ZrO2(3Y). Results show that the thermal shock resistance of ceramics is very sensitive to the cooling medium temperature, even which is very low. When characterizing the thermal shock resistance of ceramics the effect of cooling medium temperature should be taken into account. A higher water-bath temperature may not correspond to a greater thermal shock resistance of ceramic materials owing to the effect of thermal shock initial temperature on the material properties. When the temperature difference in thermal shock is close to the critical temperature difference of rupture, a little change of which can cause a great change in the retained strength of materials. As the retained strength of materials is too sensitive to the temperature difference close to the critical temperature difference of rupture, it is unsuitable to use the critical temperature difference of rupture to characterize the thermal shock resistance of ceramic materials. This study shows some innegligible problems in the evaluation system for the thermal shock resistance of ceramic materials.

Effect of porosity on the crack pattern and residual strength of ceramics after quenching

The effect of porosity on the crack characteristics of ceramics after water-quenching is studied by measuring the cracks in ceramic sheets. The result reveals that the pore volume fraction has a slight effect on the enhancement of thermal shock resistance of ceramics when the porosity ranges from 0 to 20 %, because the length and density of the long crack in porous alumina are always slightly less than that in dense alumina. This result is in agreement with the prediction based on the minimum potential energy principle using experimentally measured data. Moreover, the proportion of the strength reduction in the third regime decreases significantly with increasing porosity, because the strength of unquenched specimens decreases more rapidly than that of quenched specimens with increasing porosity. The results of this study may help to further understand the thermal shock behavior of ceramics.

Theoretical Research on Thermal Shock Resistance of Ultra-High Temperature Ceramics Focusing on the Adjustment of Stress Reduction Factor.

The thermal shock resistance of ceramics depends on not only the mechanical and thermal properties of materials, but also the external constraint and thermal condition. So, in order to study the actual situation in its service process, a temperature-dependent thermal shock resistance model for ultra-high temperature ceramics considering the effects of the thermal environment and external constraint was established based on the existing theory. The present work mainly focused on the adjustment of the stress reduction factor according to different thermal shock situations. The influences of external constraint on both critical rupture temperature difference and the second thermal shock resistance parameter in either case of rapid heating or cooling conditions had been studied based on this model. The results show the necessity of adjustment of the stress reduction factor in different thermal shock situations and the limitations of the applicable range of the second thermal shock resistance parameter. Furthermore, the model was validated by the finite element method.

Two Scale-Based Continuum Damage Model for Brittle Materials under Thermomechanical Loading

Ceramic refractory materials initially contain a multitude of defects such as voids, microcracks, grain boundaries etc. Particularly being exposed to high temperatures above 1000 °C the macroscopic properties such as effective compliance, strength and lifetime are essentially determined by microscopic features of the material. The deformation process and failure mechanisms are going along with the creation of new microdefects as well as the growth and coalescence of cracks. A brittle material damage model for dynamic thermomechanical loading conditions is presented in this paper. Representative volume elements (RVE) include microcrack initiation and growth. The material laws are formulated on the continuum level using appropriate homogenisation methods. To demonstrate the potential of the numerical tools, two examples are presented which are taken from applications. Based on experiments, cyclic thermal shock tests at refractory plates are simulated by FEM. To quantify the thermal shock resistance of ceramics, experiments suggested by Hasselman are simulated numerically supplying a critical temperature slope.

Properties and appropriate conditions of stress reduction factor and thermal shock resistance parameters for ceramics

Through introducing the analytical solution of the transient heat conduction problem of the plate with convection into the thermal stress field model of the elastic plate, the stress reduction factor is presented explicitly in its dimensionless form. A new stress reduction factor is introduced for the purpose of comparison. The properties and appropriate conditions of the stress reduction factor, the first and second thermal shock resistance (TSR) parameters for the high and low Biot numbers, respectively, and the approximation formulas for the intermediate Biot number-interval are discussed. To investigate the TSR of ceramics more accurately, it is recommended to combine the heat transfer theory with the theory of thermoelasticity or fracture mechanics or use a numerical method. The critical rupture temperature difference and the critical rupture dimensionless time can be used to characterize the TSR of ceramics intuitively and legibly.

Thermal shock resistance of ultra-high temperature ceramics including the effects of thermal environment and external constraints

The thermal shock resistance of ceramics depends on the materials mechanical and thermal properties, also is affected by component geometry and external factors and so on. Therefore, the thermal shock resistance of ceramic materials is the comprehensive performance of their mechanical and thermal properties corresponding to the various heat conditions and external constraints. In the present work, a thermal shock resistance model of the ultra-high temperature ceramics which considered the effects of thermal environment and constraints was established. With this model, the influence of constraints on the thermal shock resistance and critical fracture temperature difference had been studied and an effective idea to improve thermal shock resistance for ceramic material and structure was found. Furthermore, the model was validated by finite element method.

Thermal shock resistance of ceramics with temperature-dependent material properties at elevated temperature

This paper conducts thermal shock case studies for three typical thermal shock specimens that are important in thermal shock tests: a ceramic layer under a hot shock, a ceramic layer under a cold shock and a ceramic coating under a cold shock. All material properties are assumed to be functions of temperature. The temperature field without cracking is obtained by using the finite element/finite difference method. Time-varied thermal stress intensity factors are obtained by using the weight function method for various parameters of the problem. The thermal shock resistance curves are obtained and the critical size parameters, which control the applicability of the stress-based criterion and the fracture-mechanics-based criterion for the determination of the thermal shock resistance of ceramics, are explored. The studies demonstrate the significance of incorporating temperature-dependent material properties on the thermal shock resistance of ceramic materials for high-temperature applications. The dominant property change responsible for the improvement is the significant reduction in Young’s modulus with increasing temperature. As a result, the thermal stress level is reduced considerably and the thermal shock resistance of the ceramic material is improved greatly.

Enhanced Thermal Shock Resistance of Ceramics through Biomimetically Inspired Nanofins

We propose here a new method to make ceramics insensitive to thermal shock up to their melting temperature. In this method the surface of ceramics was biomimetically roughened into nanofinned surface that creates a thin air layer enveloping the surface of the ceramics during quenching. This air layer increases the heat transfer resistance of the surface of the ceramics by about 10,000 times so that the strong thermal gradient and stresses produced by the steep temperature difference in thermal shock did not occur both on the actual surface and in the interior of the ceramics. This method effectively extends the applications of existing ceramics in the extreme thermal environments.