Creep Of Metals Research Articles

Review of Second Harmonic Generation Measurement Techniques for Material State Determination in Metals

This paper presents a comprehensive review of the current state of knowledge of second harmonic generation (SHG) measurements, a subset of nonlinear ultrasonic nondestructive evaluation techniques. These SHG techniques exploit the material nonlinearity of metals in order to measure the acoustic nonlinearity parameter, $$\beta $$ . In these measurements, a second harmonic wave is generated from a propagating monochromatic elastic wave, due to the anharmonicity of the crystal lattice, as well as the presence of microstructural features such as dislocations and precipitates. This article provides a summary of models that relate the different microstructural contributions to $$\beta $$ , and provides details of the different SHG measurement and analysis techniques available, focusing on longitudinal and Rayleigh wave methods. The main focus of this paper is a critical review of the literature that utilizes these SHG methods for the nondestructive evaluation of plasticity, fatigue, thermal aging, creep, and radiation damage in metals.

A review of the changes of internal state related to high temperature creep of polycrystalline metals and alloys

When polycrystalline metals and their alloys are used at high temperature, creep deformation leads to changes in their internal state. The change in internal state manifests itself in many ways, but the two ways that concern us in this review are (i) the creation of internal stress arising from the strain incompatibility between grains and/or the formation of cell/sub-grain structures and (ii) a change in the material resistance. This review aims to provide a clear separation of these two concepts by exploring the origin of each term and how it is associated with the creep deformation mechanism. Experimental techniques used to measure the internal stress and internal resistance over different length-scales are critically reviewed. It is demonstrated that the interpretation of the measured values requires knowledge of the dominant creep deformation mechanism. Finally, the concluding comments provide a summary of the key messages delivered in this review and highlight the challenges that remain to be addressed.

Effect of Creep on Stress and Strain at the Tip of Stress Corrosion Cracking in High Temperature Water Environments

Stress and strain at the crack tip are main mechanical parameters which estimate the stress corrosion cracking rate in metals, and the creep of metals in high temperature and high pressure environment will lead to the redistribution of stress and strain nearby the crack tip. The effects of creep on stress and strain nearby the crack tip are discussed by using 1T-CT specimen and finite element method in this study. The investigated results indicate that both increasing of temperature and stress intensity factor would induce the equivalent creep strain increases at the crack tip.

Effect of Creep on Thermal Stresses in ZrO<sub>2</sub>/Ti Functionally Graded Thermal Barrier Coatings

This study numerically investigates the effect of creep on thermal stress states and design of ZrO2/Ti functionally graded thermal barrier coatings (FG TBCs) based on a mean-field nonlinear micromechanical approach, which takes into account the time-independent and dependent inelastic deformation, such as plasticity of metals, creep of metals and ceramics, and diffusional mass flow at the ceramic/metal interface. The effect of creep on micro-stress states in the FG TBCs has been examined in terms of the compositional gradation patterns. The suitable compositional gradation patterns have been proposed for typical thermo-mechanical boundary conditions with different creep abilities of constitute phases in the FG TBCs.

Results of studying creep and long-term strength of metals at the Institute of Mechanics at the Lomonosov Moscow State University (To Yu. N. Rabotnov’s Anniversary)

Basic results of experimental and theoretical research of creep processes and long-term strength of metals obtained by researchers of the Institute of Mechanics at the Lomonosov Moscow State University are presented. These results further develop and refine the kinetic theory of creep and long-duration strength proposed by Yu. N. Rabotnov. Some problems arising in formulating various types of kinetic equations and describing experimental data for materials that can be considered as statically homogeneous materials (in studying the process of deformation and rupture of such materials, there is no need to study the evolution of individual cracks) are considered. The main specific features of metal creep models at constant and variable stresses, in uniaxial and complex stress states, and with allowance for one or two damage parameters are described. Criterial and kinetic approaches used to determine long-term strength under conditions of a complex stress state are considered. Methods of modeling the metal behavior in an aggressive medium are described. A possibility of using these models for solving engineering problems is demonstrated.

Instantaneous creep in face-centered cubic metals at ultralow strain rates by a high-resolution strain measurement

Instantaneous creep in face-centered cubic metals, 5N Al (99.999%), 2N Al (99%) and 4N Cu (99.99%) with different grain sizes, was firstly investigated by sudden stress-change experiments at ultralow strain rates $\dot \varepsilon $ ⩽ 10−10 s−1 and temperature T < 0.32 T m. The experimental results indicate that the observed instantaneous creep is strongly dependent on grain size, the concentration of impurity, and stacking fault energy. Creep in high-purity aluminum, 5N Al, with a very large grain size, d g > 1600 μm, shows non-viscous behavior, and is controlled by the recovery of dislocations in the boundary of dislocation cells. On the other hand, for 5N Al with a small grain size, d g=30 μm, and low-purity aluminum, 2N Al, with d g= 25 μm, creep shows viscous behavior and may be related to ‘low temperature grain boundary sliding’. For high-purity copper, 4N Cu, with d g= 40 μm and lower stacking fault energy, creep shows a non-viscous behavior, and is controlled by the recovery process of dislocations. For all of the samples, creep shows anelastic behavior.

Influence of preliminary ultrasonic treatment upon the steady-state creep of metals of different stacking fault energies

This paper addresses the issue of the ultrasound effects upon the creep deformation of metals with different levels of stacking fault energy. The influence of preliminary ultrasound irradiation time upon the steady state creep rate is considered. Synthetic theory of irrecoverable deformation is taken as a mathematical apparatus. The analytical results show good agreement with experimental data.

New insight into crack formation during corrosion of zirconium-based metal-oxide systems

Zirconium alloys are typically used in nuclear pressurized water reactors (PWR) as fuel cladding tubes due to their chemical stability and their mechanical strength at operating temperatures (≈300°C). However, the corrosion of Zr-based cladding tubes is one of the factors limiting the burn-off rate in PWRs. It is commonly accepted that the corrosion kinetics involves a periodic succession of growth where the oxide thickness varies parabolically with time. As the oxide thickens, a cracking structure forms. The oxide appears striated with periodic layers of cracks running parallel to the metal/oxide interface. This cracking structure has been experimentally related to the periodicity of the oxide growth. In the present work, a finite-element study is used to investigate the development of stresses in the oxide under the combined influence of molar volume expansion during oxide formation, metal/oxide interface geometry and metallic substrate creep. The generation of tensile stresses capable of initiating the cracks that are observed experimentally is explored.

Influence of Annealing Temperature in the Course of Mechanical-Thermal Treatment upon the Steady-State Creep Rate of Metals

AbstractThe influence of annealing temperature in the course of mechanical-thermal treatment on the steady-state creep of metals is discussed and modeled. The synthesis theory of irrecoverable deformation is taken as a mathematical apparatus. Results obtained in terms of the generalized synthetic theory give good agreements with experimental data.

Loading Surface in the Course of Mechanical-Thermal Treatment and Steady-State Creep of Metals

Abstract: Kinetics of the loading surface of a material gives precious information on the level of the hardening of the material. This paper is concerned with the evolution of the loading surface during successive actions, such as: (i) plastic deformation, (ii) annealing of the pre-strained specimen, and (iii) secondary creep of the treated material. The analysis of the loading surface is carried out in terms of the synthetic theory of irrecoverable deformation. Keywords: loading surface; mechanical-thermal treatment; creep and plastic strain; synthetic theory of irrecoverable deformation

Loading Surface in the Course of Mechanical-Thermal Treatment and Steady-State Creep of Metals

Loading Surface in the Course of Mechanical-Thermal Treatment and Steady-State Creep of Metals

Influence of the Creep of Metals on the Service Life of Reactors for the Magnesium-Thermal Production of Titanium

The influence of plastic deformation (creep) of corrosion-resistant 10Kh23N18, 04Kh18N10Т, and AISI 321 steels on the decrease in the thickness of the shell wall and the intensification of corrosion fracture processes is investigated. The comparative evaluation of the materials used in the retort production is performed. It is shown that the application of 10Kh23N18 steel with improved creep characteristics increases the service life of the retorts from 35 to 43 cycles.

Design of ZrO&lt;sub&gt;2&lt;/sub&gt;/Ti Functionally Graded Thermal Barreir Coatings Based on a Nonlinear Micromechanical Approarch

This study presents a design process of ZrO2/Ti functionally graded thermal barrier coatings (FG TBCs) based on a mean-field nonlinear micromechanical approach developed by Tsukamoto [1], which takes into account the time-independent and dependent inelastic deformation, such as plasticity of metals, creep of metals and ceramics, and diffusional mass flow at the ceramic/metal interface. The effect of compositional gradations on micro-stress states in the FG TBCs has been examined. The suitable compositional gradations have been proposed for typical thermo-mechanical boundary conditions in terms of thermal-stress relaxations, thermal-shielding and light-weight characteristics.

Void growth in copper during high-temperature power-law creep

Growth of grain boundary voids during high-temperature power-law creep of metals is usually approximated as the growth of a hole in a nonlinearly viscous solid. Using synchrotron tomography, we show that the functional form of the continuum law is valid but that the real growth rates in copper are higher than the prediction of the viscous model by a factor of about 40. Submicrometer resolution tomography showing faceted void shapes as well as the large scatter of individual growth rates suggest that local dislocation glide has significative contribution to void growth.

Design of functionally graded thermal barrier coatings based on a nonlinear micromechanical approach

This study presents the methodology of analysis and design of functionally graded thermal barrier coatings (FG TBCs) consisting of ceramics and metals based on a mean-field micromechanical approach taking into account the time-independent and dependent inelastic deformation, such as plasticity of metals, creep of metals and ceramics, and diffusional mass flow at the ceramic/metal interface. Ni–ZrO 2 systems were numerically studied and the effect of the compositional gradation patterns and time-dependent inelastic deformation on the micro- and macro-stress states in the FG TBCs were examined. The suitable compositional gradation patterns were proposed for typical thermo-mechanical boundary conditions. It was shown that the creep deformation near the ceramic surface can introduce large tensile stresses, potentially leading to thermal fracture, which is possibly reduced by controlling the ability of creep of the ceramics.

Theory of wave propagation in marine sediments.

Saturated, unconsolidated marine sediments support sound waves and shear waves, each of which is dispersive in that its phase speed varies with frequency and the corresponding attenuation scales as the first power of frequency over an extended frequency range. A theory of sound wave and shear wave propagation in unconsolidated marine sediments has recently been developed in which the dissipation is based on a particular form of intergranular interaction involving the molecularly thin layer of pore fluid at grain contacts. As grain-to-grain sliding progresses, the contact is postulated to become progressively stiffer, a phenomenon known as strain-hardening, adapted from the literature on creep in metals and metal alloys. The theory returns algebraic expressions for the phase speed and attenuation of both types of wave, and these expressions depend on frequency as well as the geoacoustic parameters of the sediment. A comparison of the theoretical dispersion relations with data obtained during the ONR-supported SAX99 experiment shows good agreement over the frequency range range from 2–400 kHz. The theoretical expressions also fit measurements, at a fixed frequency, of phase speeds and attenuations versus porosity, overburden pressure, and mean grain diameter. [Research supported by ONR.]

Grain boundary sliding during ambient-temperature creep in hexagonal close-packed metals

Even at ambient temperature or less, below their 0.2% proof stresses all hexagonal close-packed metals and alloys show creep behaviour because they have dislocation arrays lying on a single slip system with no tangled dislocation inside each grain. In this case, lattice dislocations move without obstacles and pile-up in front of a grain boundary. Then these dislocations must be accommodated at the grain boundary to continue creep deformation. Atomic force microscopy revealed the occurrence of grain boundary sliding (GBS) in the ambient-temperature creep region. Lattice rotation of 5° was observed near grain boundaries by electron backscatter diffraction pattern analyses. Because of an extra low apparent activation energy of 20 kJ/mol, conventional diffusion processes are not activated. To accommodate these piled-up dislocations without diffusion processes, lattice dislocations must be absorbed by grain boundaries through a slip-induced GBS mechanism.

Justification of the energy variant of the theory of creep and long-term strength of metals

The hypotheses underlying the energy variant of the theory of creep and long-term strength of metals are formulated and justified experimentally.

Advances in the assessment of creep data during the past 100 years

Many of the classical models representing the creep and rupture behaviour of metals were developed prior to and during the 1950s and 1960s. Nevertheless their subsequent exploitation, in particular for the assessment of large creep property datasets, was initially limited by the capability of the analytical tools available at the time.

Tomographic method for evaluation of apparent activation energy of steady-state creep

A new method for the evaluation of the apparent activation energy of steady-state creep in metals is presented. It is based on in situ monitoring by microtomography the geometry of a specimen subjected to uniaxial load and inhomogeneous temperature distribution. It is shown that microtomography acting as a three dimensional extensometer enables the evaluation of local strain-rates of small material volumes and is an adequate tool for characterization of inhomogeneously deforming specimens. Activation energies obtained with the new method for stainless steel agree within an error of 5% with values obtained according to the classical procedure.