Thermal Shock Damage Research Articles

Thermal shock behaviour of mullite–cordierite refractory materials

The characterisation of thermal shock damage in cordierite–mullite refractory plates used as substrates in fast firing of porcelain whiteware has been investigated. Two different refractory compositions (termed REFO and CONC), characterised by different silica to alumina ratios, were studied. Thermal shock damage was induced in as received samples by water quenching tests from 1250°C. Thermal and mechanical properties were measured at room temperature by means of standard techniques and then the thermal shock resistance parameter R was calculated. The fracture toughness of selected samples was measured before and after thermal shock by the chevron notched specimen technique. The reliability of this technique for evaluation of small differences in fracture toughness after a given number of thermal shock cycles was investigated. The suitability of KIc measurements by the chevron notched specimen technique to characterise the development of thermal shock damage in refractory materials was proved in this investigation.

Acoustic Emission Research on Thermal Shock Behaviors of Three-Dimensional C/SiC Composites in Different Environments

Three-dimensional (3D) carbon fiber reinforced silicon carbide matrix composites (C/SiC) were prepared by a low-pressure chemical vapor infiltration method. The thermal shock behaviors of the composites in different environments were researched using an advanced acoustic emission (AE) system. Damage initiation and propagation were easily detected and evaluated by AE. The thermal shock damage to C/SiC composites mainly occurred at the process of cooling and was limited at argon but unlimited at wet oxygen atmosphere. Also correlations have been established between the different damage mechanisms and the characteristics of acoustic emission signals obtained during thermal shock tests. In this way, the paper contributes to the development of the acoustic emission technique for monitoring of damage development in ceramic-matrix composites.

Thermal shock behaviour of mullite-bonded porous silicon carbide ceramics with yttria addition

Thermal shock resistance of mullite (3Al2O3 · 2SiO2)-bonded porous silicon carbide (SiC) ceramics with 3.0 wt% yttria (Y2O3) addition was evaluated by a water-quenching technique. The thermal shock damage was investigated as a function of the quenching temperature, quenching cycles and specimen thickness. The residual flexural strength of the quenched specimens decreases with increasing quenching temperature and specimen thickness due to the larger thermal stress caused by thermal shock. However, quenching cycles at the temperature difference of 1200 °C have no effect on the residual strength since the same thermal stress was produced in repeated thermal shock processes. The good thermal shock damage resistance of the specimens is contributed mainly by the low strength and moderate elastic modulus. Moreover, the pores prevent the continuous propagation of cracks and alleviate further damage.

Nondestructive Evaluation on Thermal Shock Damage of Ceramics

The objective of this paper is to investigate the applicability of ultrasonic wave technique to monitor the progress of the thermal shock damage on alumina ceramic. For this purpose, alumina ceramic specimen was heated in the furnace and then was quenched into the water tank. The initiation, growth behaviors of surface micro-cracks as a function of the number of thermal shock cycle have been discussed by taking into account the change of ultrasonic wave velocity and attenuation. The change of both velocity and attenuation of ultrasonic wave showed good relation with the surface crack density changing due to the number of thermal shock cycle. Measuring the change of attenuation gives more effective information to evaluate thermal shock damage than that of velocity nondestructively. The flexural strength was also measured for the thermal shocked specimen. The flexural strength was decreased rapidly at the point of time of observation of microcracks on the surface of specimen, and the flexural strength decline by the crack growth caused thermal shock cycles was slight.

Thermal shock behavior of a three-dimensional SiC/SiC composite

Thermal shock behavior of a three-dimensional (3-D) SiC/SiC composite was studied using the water-quenched method. Thermal shock damage of the composite was assessed by scanning electron microscopy characterization and residual three-point-bending strength. In the thermal shock process, the composite displayed the same bending mechanical behaviors as those of the original composite and retained 80 pct of the original strength in the longitudinal direction after being quenched from 1200°C to 25°C in water for 100 cycles. However, the composite displayed anisotropy in resistance to thermal shock damage. The observed microdamage processes were as follows: (1) formation of micropores and long crack, (2) transfer and growth of pores, (3) saturation of the dimension and the density of pores, and (4) accelerated growth of the long crack along the longitudinal direction. The critical thermal shock number for the composite was about 50. When thermal shock was less than 50 cycles, the residual flexural strength of the composite decreased with thermal shock cycles increasing. When the number was greater than 50, the strength of the composite did not decrease further.

Thermal shock residual strength of functionally graded ceramics

When subjected to severe thermal shocks functionally graded ceramics (FGCs) suffer strength degradation due to microcrack growth, coalescence and macrocrack propagation induced by the shocks. This paper presents a thermo-fracture mechanics model to study the residual strength behavior of thermally shocked FGCs. It is assumed that thermal shock damage mainly results from the extension of a pre-existing edge crack initially located at the thermally shocked surface of an FGC specimen. Thermal shock threshold, or the critical thermal shock that causes precipitous strength drop, is determined. The paper describes applications of the model to calculate the thermal shock residual strength of FGCs as a function of thermal shock severity. Two FGC systems, i.e., Al 2O 3/Si 3N 4 and TiC/SiC FGCs are considered in the numerical studies. The numerical results show that material gradation profile has a pronounced effect on the thermal shock threshold and the thermal shock residual strength of FGCs.

Determination of thermal shock resistance in refractory materials by ultrasonic pulse velocity measurement

Thermal shock resistance of refractory materials is one of the most important parameters in refractory material characterization since it determines their performance in many applications. Ultrasonic pulse velocity testing was used for non-destructive quantification of thermal shock damage in refractory plates used as support for the firing of porcelain articles. When refractory materials are subjected to the industrial thermal cycles crack nucleation and propagation occurs resulting in loss of strength and material degradation. The formation of cracks decreases the velocity of ultrasonic pulses travelling in the refractory because it depends on the density and elastic properties of the material. Therefore measuring either of these properties can directly monitor the development of thermal shock damage level. Young's modulus of representative samples was calculated using measured values of ultrasonic velocities obtained by ultrasonic pulse velocity technique. Results were compared with industrial statistical data of thermal shock behaviour of the investigated materials. The capability of the ultrasonic velocity technique for simple, sensitive, and reliable non-destructive characterisation of thermal shock damage was demonstrated in this investigation.

Thermal shock resistance of in situ reaction bonded porous silicon carbide ceramics

Porous silicon carbide (SiC) ceramics were prepared by an in situ reaction bonding process. Their thermal shock resistance to cooling was evaluated as a function of the quenching temperature, quenching cycles and specimen thickness by the water-quenching technique. It is shown that the residual strength of the quenched specimens decreases with increasing the quenching temperature and specimen thickness, but the residual strength is hardly affected by the quenching cycles. Moreover, the thermal shock resistance to heating was investigated by the instantaneous heating method. It was found that the residual strength of the heated specimens decreases gradually with increasing the heating temperature. The thermal shock damage was proposed to originate from the propagation of cracks at the necks (the bonded parts between SiC particles). However, the pores may arrest the propagating cracks and then impair this damage. Therefore, the in situ reaction bonded porous SiC ceramics exhibit excellent thermal shock resistance.

Material failure modes, part III: A brief tutorial on corrosion-related material failure modes

This article is the final installment of a three-part series on material failure modes recently published in the MaterialEASE section of AMPTIAC Quarterly. Part One introduced the concept of material failure modes and covered fracture, ductile failure, elastic deformation, creep, and fatigue. Part Two continued the discussion with brief descriptions of impact, spalling, wear, brinelling, thermal shock, and radiation damage. This article completes the series on material failure modes, covering uniform, galvanic, crevice, pitting, intergranular, and erosion corrosion; selective leaching/dealloying; hydrogen damage; stress-corrosion cracking; and corrosion fatigue. The three articles taken together make a valuable desk reference for any professional making material selection and design decisions.

Erosion wear mechanisms of coal–water–slurry (CWS) ceramic nozzles in industry boilers

Al 2O 3/(W, Ti)C ceramic composites were prepared for the use of coal–water–slurry (CWS) nozzles in industry boilers. The erosion rates of the CWS ceramic nozzles were measured. Eroded bore surfaces of the nozzles was examined by scanning electron microscopy. Finite element method (FEM) was used as a means of numerically evaluating temperature, temperature gradient, thermal stress and its distribution inside the ceramic nozzle. Results showed that the primary wear mechanisms of the CWS ceramic nozzle exhibited polishing action in the inner center hole and thermal shock damage with chipping at exit. The temperature, temperature gradient and thermal stress at exit surfaces of the CWS ceramic nozzle were higher than those of other parts of the nozzle. Greater temperature gradient and higher thermal stress were the main reason that caused the failure of the exit surface of the CWS ceramic nozzle.

Material failure modes, part II: A brief tutorial on impact, spalling, wear, brinelling, thermal shock, and radiation damage

A number of material failure modes were introduced in this article, including impact, spalling, wear, brinelling, thermal shock, and radiation damage. These mechanisms can affect metals, polymers, ceramics, and composites in various applications and in many different environments. Thus, it is important to take these failure modes into consideration during the design phases of a component or system in order to make appropriate materials selection decisions.

Derivation of Simple Evaluation Method for Thermal Shock Damage on Accelerator Materials Caused by Out-of-control Beam Pulses and its Application to J-PARC

In high-intensity proton accelerator facilities, a failure of an electromagnet that steers beam pulses may result in thermal shock damage to the accelerator material by injecting an out-of-control pulse. It is important that a Machine Protection System (MPS) is appropriately designed to prevent this damage in the facilities such as the Japan Proton Accelerator Research Complex (J-PARC). In this study, a simple evaluation method for the allowable injection time before the operation of the MPS was derived from the relation between the thermal stress and the yield stress of materials. As the first step in the derivation, the upper limit of heat generation was formulated for various kinds of materials without beam experiments. Second, the allowable injection time was evaluated on the basis of the upper limit of heat generation, assuming a Gaussian distribution in the beam current density. The derived evaluation method was then applied to J-PARC. The allowable injection time ranged from 1.5 to 330 μs for the incident energy above 25 MeV. This time was longer than the beam pulse width for the 3-GeV RCS ring, and some beam-transport lines. On the other hand, the injection of the whole pulse was not permitted for the other accelerating systems of J-PARC.

Thermal Shock Damage of a 3D‐SiC/SiC Composite

Thermal shock of a three‐dimensional (3D) SiC/SiC composite prepared by chemical vapor infiltration (CVI) process was conducted using water quenched method. Thermal shock damage of the composite was assessed by SEM characterization and measurement mechanical properties using three‐point flexure after quenching. After quenched from 1200°C to 25°C water for 100 cycles, the composite retained 80% of the original flexural strength in the longitudinal direction while cracked through the width direction. Thermal shock damage of the composite was analyzed by thermal stress analysis based on the braiding structure of the composite as well as the distribution and shape of flaws referred to residual pores in the matrix. The braided structure and the dimension difference resulted in the anisotropy of mechanical properties and the matrix pores configuration of the composite, which led to the thermal shock damage anisotropy of the composite.

Thermal Shock Resistance of Cordierite-Mullite Refractory Composites

The design of composite materials leads to the development of multi-component systems where each constituent has a specific function in the material, from technological and/or application points of view. Examples of such composite systems are the cordierite-mullite refractory materials investigated in this contribution. Two different commercially available compositions were selected for evaluation of the influence of microstructure on fracture behaviour under thermal shock conditions. The materials were exposed to water-quench tests from 1250°C and subsequently the fracture toughness was evaluated using the chevron notched specimen technique. The results were compared to those obtained on as-received materials. Microstructural damage was also studied applying fractographic techniques with the aim to gain knowledge on the thermal shock damage mechanisms acting in the materials.

Proposal of new damage model for thermal shock based on dynamic fracture on the brittle materials

In the current paper, we propose that the mechanical resistance of the brittle materials under dynamic loading can be used to predict the thermal shock damage resistance via a new proposed damage criterion. The increase of the mechanical resistance based on high loading rate has been investigated by experimental methods for ‘Lead Crystal Glass’ including the static and dynamic loadings by universal ‘INSTRON’ and ‘split Hopkinson pressure bars (SHPB)’. The relationship between the measured static and dynamic strengths of materials has been compared and developed via Tuler and Butcher’s dynamic criterion. ‘Modified Brazilian disk (MBD)’ specimens are used to obtain indirect tensile stress concentration at notch tip. The fracture process under various loading rates has been observed by optical and scanning electronic microscope (SEM) to study the fracture phenomenon according to the high loading rate effect for Lead Crystal Glass. The dynamic stress due to high loading rates can be considered as the thermal stress during thermal shock phenomenon with high heat convection coefficient values which leads to high gradient temperature, low duration time and intrinsic damage feature like cracks and flakes for concerned material. The transient thermal stress analysis has been carried out by numerical method for MBD specimen subjected to rapid cooling condition. The numerical results and experimental dynamic resistance of selected material are utilized to develop a new semi-empirical damage criterion based on the continuum damage mechanics (CDM) including dynamic material resistance, critical thermal shock time which corresponds to maximum transient thermo-mechanical stress and heat convection coefficient evolution according to the thermal shock severity.

Derivation of Simple Evaluation Method for Thermal Shock Damage on Accelerator Materials Caused by Out-of-control Beam Pulses and its Application to J-PARC

Derivation of Simple Evaluation Method for Thermal Shock Damage on Accelerator Materials Caused by Out-of-control Beam Pulses and its Application to J-PARC

Wear behavior of ceramic nozzles in coal water slurry burning

In this paper, Al 2O 3/(W,Ti)C ceramic composite and WC/Co cemented carbide were prepared for the use of nozzle materials in coal water slurry (CWS) burning. The wear behavior of nozzles made from these materials was compared by determining the cumulative volume loss and the erosion rates. Results showed that the hardness of the nozzles plays an important role with respect to its erosion wear in CWS burning processing. The Al 2O 3/(W,Ti)C nozzles possessing high hardness exhibited lower erosion rates, while the WC/Co cemented carbide nozzles with a low hardness showed higher erosion rates under the same test conditions. Examination of eroded bore surface of the nozzles showed that wear of the WC/Co cemented carbide nozzle occurred by a preferential removal of the metal binder followed by pluck out of the exposed WC grains, while the primary wear mechanisms of Al 2O 3/(W,Ti)C ceramic nozzle exhibited polishing action in the hole and thermal shock damage with chipping at the bore exit.

Alumina forming high temperature silicides and carbides

Aluminium containing heat-resistant silicides and ternary carbides (Maxthal ®), have been evaluated in terms of their high temperature behaviour in various atmospheres including vacuum. The novelty of these materials is in their ability to form a stable and adherent protective alumina scale at low partial pressures of oxygen as well as in air. Recently developed heating elements, for oxidising and reducing atmospheres, made of molybdenum aluminosilicide (Kanthal Super ER) have been evaluated by thermogravimetric analysis (TGA) studies in air and other atmospheres. The performance up to 1575 °C has been evaluated at vacuum levels down to 10 −4 mbar. In addition to its remarkable thermal shock resistance, damage tolerance and machinability, Ti 2AlC (Maxthal ®) showed a parabolic and stable oxide growth rate up to 1400 °C in air. Cyclic testing confirmed that the oxide layer is adherent to the bulk. It has been concluded that both Maxthal ® and Kanthal Super ER are capable of operating in air, up to 1400 and 1575 °C, respectively.

Fratura de refratários

A fratura de refratários é considerada sob o ponto de vista tradicional de resistência mecânica além da perspectiva da mecânica da fratura. Resistência mecânica e tenacidade à fratura são relacionadas por meio do tamanho dos agregados em refratários, o que ilustra a importância dos aspectos microestruturais dos agregados refratários na resistência. O método de análise da integral-J e a técnica experimental da separação de cunha (wedge-spliting) são revisados devido ao fato destes serem convenientes para explicar o caráter não-linear da curva força-deslocamento para refratários. Este último aspecto é associado ao conceito de curva-R crescente, que é discutido sob o ponto de vista fenomenológico. Curvas-R crescentes estão diretamente relacionadas ao agregado refratário através dos mecanismos de tenacidade que são ativos na zona de processo de trinca, tanto na frente como atrás da trinca em propagação. Os processos de tenacificação de refratários são responsáveis pelas regiões não-lineares das curvas ou diagramas de tensão-deformação e força-deslocamento e das curvas-R crescentes. O dano por choque térmico, originalmente apresentado sob o ponto de vista convencional de resistência mecânica é abrangido no conceito de curva-R crescente. Concluiu-se que a natureza dos agregados de refratários, bem como seu tamanho e distribuição, tem importância decisiva no fenômeno de fratura em refratários. Isso é devido ao papel crucial que agregados assumem na região de propagação da trinca. A distribuição do agregado deve ser o foco do arranjo microestrutural para melhores características de fratura, quando todos os outros fatores são de igual importância ao refratário como um todo.

Fracture behaviour of magnesia and magnesia–spinel composites before and after thermal shock

Microstructural changes, as a consequence of the thermal expansion mismatch between magnesia and spinel phases, and fracture behaviour of magnesia and spinel composites have been investigated as a function of spinel content (10, 20, 30 wt.%). Fracture surfaces of magnesia showed mostly transgranular fracture; for the composites, however, the amount of intergranular fracture increased with increasing spinel content. This change in fracture behaviour is thought to be the main reason for the increase in the work of fracture, γWOF. The 30% spinel composite was found to exhibit both the greatest resistance to crack propagation, and the greatest resistance to thermal shock damage, with the highest retained strength after quenching.