Thermal Shock Damage Research Articles

Elevated Temperature Fatigue Behavior of Tungsten Fiber Reinforced Superalloy Composites

The low-and high-cycle fatigue behavior of three different fiber-reinforced superalloy (FRS) composite materials were evaluated. Each composite material contained 40 vol% unidirectionally aligned continuous length tungsten-1.5 wt% ThO2 fibers. The metal matrices were Waspaloy, Type 316L stainless steel, and Incology 907. Fatigue tests were conducted at 871°C in a helium atmosphere under load control with a load ratio (minimum stress/maximum stress) of 0.2. The composites were found to have excellent elevated temperature fatigue strength. The fibers played a major role in controlling the fatigue strength of the composites. Fatigue crack fronts were found to be retarded by the fibers. The cracks tended to branch at the fiber/matrix interface and grew by a sliding mode along the interface. Matrix surface cracks induced by thermal shock damage had little influence on the fatigue strength of the FRS composites.

Thermal shock behaviour of ceramics and ceramic composites

AbstractTremendous efforts have been devoted to the studies of ceramic materials under transient thermal conditions over the past four decades. Such studies are becoming increasingly more important as advanced ceramic materials are demanded for applications at higher temperatures and more severe transient thermal conditions. In this paper, the theoretical and experimental studies on the thermal shock behaviour of monolithic ceramics and ceramic composites are reviewed; a survey of the experimental techniques that have been developed for characterising thermal shock damage is also included. It is shown that such studies for the monolithic ceramics have been extensive. The theoretical analyses are based primarily on the behaviour of monolithic ceramics and have been successfully applied to explain experimental phenomena and predict the thermal shock behaviour of monolithic ceramics. However, similar studies of the thermal shock resistance of ceramic composites, especially continuous fibre reinforced composi...

Thermal shock resistance of composites of alumina and partially stabilized zirconia

The ZrO 2 martensitic transformation (tetragonal-tomonoclinic) and the attendant volume expansion and the related microcracking effects can be used to improve substantially the fracture energy and/or strength in alumina composites and the resistance of the materials to thermal stresses by rapid cooling and heating [1]. The thermal shock resistance of ceramics is of particular importance in a variety of applications. To meet the needs of these various applications, a number of thermal shock (R) parameters based on material properties have been generated. The basis of this approach is to analyse thermal stress failure in terms of the relationship between the usual thermomechanical properties of materials. This has led to the generation of a series of thermal shock parameters: R, R', R", R'", R'' and ATe. Of these, R, R' and R" are thermal shock fracture resistance parameters and R'" and R .... are thermal shock damage resistance parameters. The fracture resistance parameters apply to crack initiation problems, whereas the damage resistance parameters apply to crack propagation problems. ATe is called the critical temperature difference, at which the remaining strength of the material suddenly drops considerably [2-5]. The physical and mechanical properties of the composites of 20wt% alumina and remainder zirconia-3 mol% yttria (TZ-3Y20A; Tosoh Corporation, Tokyo, Japan) for both the as-sintered condition (sintered at 1500 °C for 2 h) and the sintered + hot isostatically pressed (HIPed) condition (sintered at 1500 °C for 2 h and subsequently HIPed at 1450 °C and 190 MPa for 1 h) are summarized in Table I.

Evaluation of Thermal Shock Resistances for Structural Ceramics.

An evaluation of thermal shock resistances for structural ceramics was conducted by employing various types of Vickers-indented specimens with different Biot moduli. Then, examination of the correlations between thermal shock resistances obtained by the author's method and usual thermal shock resistances, such as thermal shock fracture resistance and thermal shock damage resistance, was conducted. As a result, the correspondence between the minimum thermal shock condition required for the onset of propagation of generated microcracks and the thermal shock fracture resistance was recognized by conducting repeated thermal shock tests using thicker SiC specimens which have larger Biot moduli. The amount of crack growth per thermal shock cycle implies the same meanings as thermal shock damage resistance for various structural ceramics.

Crack Growth in Castable Refractory due to Thermal Shock Fatigue: An Acousto-Ultrasonic Study

Thermal shock fatigue crack growth in an alumino-silicate castable refractory has been studied using the non-destructive method of acousto-uitrasonic signal analysis. Acousto-ultra- sonic signal parameters supported by strength measurement studies and microscopic observations, indicated initiation, growth and interlinking of microcracks with increasing cycles of thermal shock fatigue. Equations have been proposed to monitor degradation of strength from acousto-uitrasonic measurements. The study reveals that acousto-ultrasonics is a very useful approach for non-destructive qualitative as well as quantitative evaluation of thermal shock damage in refractories.

Thermal Shock Damage Assessment in Ceramics Using Ultrasonic Waves

Structural ceramics are susceptible to microcrack damage by thermal shock. There is a critical temperature for thermal shock damage initiation with damage severity increasing at greater shock temperatures. In this work the applicability of an ultrasonic method to determine the critical temperature and the accumulated damage is demonstrated in alumina. Information is obtained via velocity and attenuation measurements using surface and obliquely incident bulk ultrasonic waves. The elastic anisotropy effect due to preferred crack orientation has been estimated. The critical temperature for the alumina is about 200°C. The damage increases steeply from 200° to 400°C and grows significantly above 400°C. Changes of up to 17% from the original values in the effective shear moduli and up to 45% in the longitudinal effective modulus in the direction transverse to crack orientation are measured at high thermal shock temperatures.

Growth and extraction of flux free YBCO crystals

An improved flux draining technique for the extraction of grown YBCO crystals from its solvent is reported. This simple and efficient technique facilitates in-situ flux separation in the isothermal region of the furnace. Consequently, the crystals are spared from thermal shock and subsequent damage. Flux-free surfaces of these crystals were studied by optical microscopy. Transmission X-ray topographs of the crystals reveal the dislocations present in them as well as the stresses developed as a result of ferroelastic phase transition occurring during cooling.

Computer simulation of the quench-induced strength degradation in glass plates

A computer simulation of the strength degradation of quenched soda-lime glass specimens was performed. The evolution of quench-induced crack growth was studied with (1) no subcritical crack growth effect, and (2) subcritical crack growth included. The computer simulation quanlitatively indicates that the means retained strength exhibits a gradual decrease with increasing quench temperature difference. Subcritical crack growth enhances the thermal shock damage.

Comparison of saturation behavior of thermal shock damage in a variety of brittle materials

The saturation of thermal shock fatigue damage in ceramics composites (as observed by the authors) is compared with the damage saturation behavior for other researchers' data on brittle materials including polymers, dense ceramics, and refractories. The data encompasses a variety of fluid quench media including water, oil, air, and liquid nitrogen. An emperical equation is presented that describes much of the data well. Similarities between mechanical loading fatigue and thermal loading fatigue studies are also discussed.

Strain-amplitude-dependent internal friction and microplasticity in alumina with microcracks

Abstract Internal friction in polycrystalline alumina subjected to thermal shock has been measured as a function of strain amplitude by means of the free-decay method of flexural vibration. The curves of the amplitude dependence show a more rapid rise with increasing thermal shock damage. The data have been analysed on the basis of the phenomenological theory of microplasticity assuming a friction-type hysteresis. Thus the internal friction in alumina with microcracks is transformed into a microplastic strain of the order of 10—9. The stress-strain responses show that the microplastic strain increases nonlinearly with increasing stress under conditions where macroscopic plastic flow can never be observed. The variation in the microplastic flow stress corresponds well to the decrease in the macroscopic fracture strength resulting from the formation of microcracks and crack propagation.

Prediction of a thermal shock damage map for glass plates

A thermal shock damage map to qualitatively predict the effect of thermal quench on a glass plate is proposed based on thermoelastic and thermoviscoelastic stress theory. The map indicates that quenching a glass plate may induce either thermal shock damage and/or residual stresses. The theoretical analysis also generally agrees with experimental results reported for the thermal quench of polycrystalline alumina specimens with a significant glassy phase.

Statistical study of the effect of subcritical crack growth on thermal shock resistance

An experimental study of the effects of subcritical crack growth on thermal shock damage is presented, based on a statistical analysis of the retained strength distribution. Single-quench thermal shock and thermal shock fatigue tests were performed in a room-temperature distilled water bath on glass microscope slides. Experimental results indicate that subcritical crack growth effects are observable in the shock testing of glass slides in terms of systematic shifts in the retained strength distribution.

Solid-state chemistry of alumina-chrome refractories

Incorporating chromium(III) oxide in alumina refractories improves resistance to thermal-shock damage and slag attack. In manufacturing aluminachrome refractories, the chromium(III) oxide can be added to a coarse alumina as a fine chrome ore [1] or to corundum as a purified chrome ore [2]. When preparing ethyl-silicate-bonded alumina-chrome refractories [3] the source of chromium is usually chromium(III) oxide. In our earlier work [4, 5] on alumina-chrome refractories the effect of powder preparation procedures and composition, compaction pressure, and temperature and time of sintering, on the formation of solid solutions in sintered compacts prepared from two aluminium(III) oxide materials (MA95, average particle size 4 #m angular; A17, reactive average particle size 2/~m round) and a chromium(III) oxide material (M100, average particle size 0.4/~m) was studied. These results are summarized in Table I. The low density of some sintered compacts prepared from MA95 material may be due to loss of chromium, which could occur by the reaction

Thermal Shock and Thermal Fatigue Testing

Abstract A method is described for rapidly screening candidate materials used in severe thermal shock applications. The method involves electron beam heating the surface of specimens using a thermal flux equal to that experienced during actual service operation. Two methods of electron beam radiation are described. In one method, the electron beam is swept across a narrow path with the specimen translated across the beam. In the second method, the specimen remained stationary while the electron beam was repeatedly rastered over a square-shaped area. Similarity of thermal shock damage produced on rocket engine turbine blades during thermal shock tests and during engine firings indicates that computer-controlled electron beam radiation can be used for determining thermal shock resistance of turbine blade materials.

ＴｉＣ‐Ｃｒ３Ｃ２基多元系複合セラミックス工具の耐欠損性

The study was attempted to reason the superiority of TiC-Cr3C2 based multi-component ceramic composites, which have been toughened by multi-toughening mechanism comprising branching and deflection of cracks and micro-cracking, in regard to tool life in intermittent cutting. On the bases of their mechanical properties of various cutting tool materials, the fracture resistance was discussed.It was clarified that the superior tool life of the ceramic composites could be understood according to the large value of thermal shock damage resistance parameter, proposed by D. P. H. Hasselman. It means that it is essential for substantial improvement of fracture resistance in ceramic tools to take place R-curve behaviour at fracture.The possibility of toughening in liquid phase sintering alloys for cutting tool in the same mechanism as the ceramic composites was also clarified in the study.

Thermal fatigue in polycrystalline alumina

Damage accumulation in polycrystalline alumina subjected to cyclic thermal loading was studied via non-destructive elastic modulus and internal friction measurements. These nondestructive techniques were sensitive to cracks formed by thermal loading. Thermal shock damage was observed to saturate as a function of an increasing cumulative number of thermal shock cycles. The observed power law relationship between the damage saturation and thermal shock difference implies a fatigue-like power law relation in stress. The exponent has a value of approximately 12 for the range of ΔT included in this study. Thermal shock damage induced changes in internal friction were found to be a function of a crack damage parameter. These thermal fatigue results of polycrystalline (unreinforced) alumina are also compared to thermal fatigue results for SiC whisker-alumina composites.

Reliability of Soldered Joints: A Description of the State of the Art

In Part 1, background information on mechanical properties and metallurgy of solder alloys and soldered joints has been presented. In this part, mechanisms of damage and degradation of components and soldered joints during soldering, during transport, and during field life are discussed. Thermal shock damage of components and excessive dissolution of metallisations are the major effects during soldering. During transport, fatigue of leads and fracture may be caused by vibration and mechanical shocks respectively. During field life, degradation is governed primarily by low cycle fatigue of the solder and incidentally also by formation of intermetallic diffusion layers between solder and base metals. This article contains an extended illustration of solder fatigue of joints on a variety of component and board types. Finally, the influence of the variety of soldered constructions in electronic circuits on solder fatigue is discussed.

Effect of Grain Size on Mechanical Properties of High-Purity Polycrystalline Magnesia

High-purity polycrystalline magnesia with different microstructures were prepared, and the effects of grain size on their bending strength and thermal shock damage resistance were investigated. The bending strength (δB) increased with decreasing grain size (D: μm), and expressed by following equationn. δB=403D-0.26 (MPa). On the other hand, the thermal shock damage resistance increased linearly with increasing grain size, which was explained by the damage resistance parameter, R′′′=E/σT2(1-ν), where E is Young's modulus, ν is Poisson's ratio and σT is tensile strength. E and ν are unchanged and σT(σB×0.6) decreased with increasing grain size, so R′′′ increased with increasing grain size. Consequently, thermal shock damage resistance increased with increasing grain size.

Cyclic thermal shock in SiC-whisker-reinforced alumina composite

Cyclic thermal shock damage in SiC whisker-alumina ceramic-ceramic composites was monitored non-destructively via elastic modulus and internal friction measurements. Thermal-shock-damage-induced changes in internal friction were found to be a linear function of a crack damage parameter (which in turn is a function of crack density and crack size). The linear relation between internal friction changes and the damage parameter is explained if one assumes that internal friction is proportional to the integrated surface area of damage-induced cracks. Thermal shock damage, as measured by both elastic modulus and internal friction, was observed to saturate as a function of an increasing cumulative number of thermal shock cycles. This saturation damage level increases in proportion to ΔT p , where ΔT is the shock temperature difference. The exponent p has a value of approximately 6 for the range of ΔT included in this study. This power-law relation in ΔT implies a fatigue-like power-law relation in stress (or alternatively, a power-law relation in stress intensity K).

Acoustic emission from crack growth in an advanced zirconia refractory under thermal shock

Crack initiation and growth during the thermal shock tests of a partially stabilized zirconia advanced refractory were investigated by the analysis of acoustic emission (AE) amplitudes. The growth of cracks that were detected by AE was systematically monitored by SEM observations as increasingly severe thermal shocks were applied. The measurements of strength loss after thermal cycling in the ribbon test with various applied temperature differentials correlated with continuous monitoring by acoustic emission and confirmed the effects of microcrack growth on the resistance to thermal shock damage.