Temperature Creep Deformation Research Articles

Si-Ti-C-O繊維/SiC基複合材料の高温クリープ変形(クリープ,OS.14 先進材料の力学)

The present work investigates the high temperature creep deformation of Si-Ti-C-O fiber/SiC Matrix composites. Since an examination is performed in the high temperature atmosphere, the surface of this composite material is covered with the glass sealant for oxidization prevention. In this study, tensile creep testing was conducted at 1200℃ in air. For creep stresses between 80 and 160MPa, creep rate decreased continuously with time. Generally steady-state creep rate, dε_<cr>/dt, is represented by Bailey-type and the stress exponent is constant. However, in this composite material, the stress exponent decreased with creep time. Therefore, a new creep deformation formula was proposed by considering the time dependent stress exponent. Using this formula, the effect of loading rate on stress/strain behavior was examined. The estimated curve based on strain hardening agreed with the experimental results. The creep deformation generated in the high temperature and a short-term was influenced by hardening, and had appeared as loading rate dependability.

The influence of interfacial dislocation arrangements in a fourth generation single crystal TMS-138 superalloy on creep properties

The morphologies of (001) γ/γ′ interfacial dislocation networks are studied through TEM observations. The lattice misfit has an important relation with creep property for superalloy during high temperature creep deformation. The fourth generation superalloy TMS-138 possesses superior creep properties based on its fine interfacial dislocation networks. The networks have two typical characteristics: closely spaced dislocations and stable square morphology during creep deformation. Such arranged dislocations can effectively prevent the slipping dislocations in the γ phase from moving through the γ/γ′ interface and improve drastically the creep resistance in the fourth generation superalloy TMS-138.

High temperature creep deformation of directionally solidified Al 2O 3/Er 3Al 5O 12

The microstructure of directionally solidified Al 2O 3/Er 3Al 5O 12 (19.5 mol% Er 2O 3) is analyzed and high temperature creep deformation studied using fibers in tension between 1400° C and 1550° C. The directionally solidified Al 2O 3/Er 3Al 5O 12 system is an in situ composite and has a fine eutectic- microstructure with sub-micron phase spacing. The microstructure is elongated in the direction of growth. Transmission electron microscopy observations revealed well-bonded interfaces and scatter within the crystallographic alignment of the constituent phases. The creep resistance of the system was very high, comparable to c-axis sapphire, and failure initiated at the lamella interfaces. The influence of the different elastic and plastic behaviors of the eutectic components on creep is examined. A critical discussion on the origin of the high stress dependence of the creep rate, the existence of steady state creep, and the relevant microscopic deformation mechanisms is presented.

The effect of grain size and stability on ambient temperature tensile and creep deformation in metastable beta titanium alloys

The effect of grain size in the range of 100–500 μm on the ambient temperature tensile and creep deformation behavior was investigated in a metastable Ti–9.4 wt% Mn alloy at 95% yield stress. It was observed that, as grain size increases the creep strain increases, the slip lines become coarser and the density of slip increases. An interrupt creep test showed that new slip lines were generated with time and most of the deformation occurred during the first few hours of testing. The effect of β-phase stability was studied by comparing the creep and tensile behavior of Ti–9.4 wt% Mn in this study, with previously reported results obtained for Ti–14.8 wt% V and Ti–13.0 wt% Mn at ambient (room) temperature. The Molybdenum Equivalency, which is a measure of the stability of these alloys, are 9.9, 14.3, and 19.9, respectively. The main mode of deformation in Ti–9.4 wt% Mn alloy was observed to be slip. The modes of deformation changed with the increase in stability from slip accompanied by Stress Induced Plate formation to only slip. It was also found that metastable ω-phase was present in lower stable alloys, irrespective of the observed mode of deformation. At 95% yield stress, the amount of creep strain in 200 h was found to increase with a decrease in stability of the β-phase.

Tensile and creep behavior of cryomilled Inco 625

The tensile and creep behavior of a cyromilled Inconel 625 alloy have been investigated. The microstructure is duplex with grain sizes ranging from 200 nm at the smallest to about 10 μm at the largest. Normal work hardening is observed in uniaxial tension and the stress-strain behavior follows a power law. Deformation of this material is accomplished by dislocation motion as evidenced by TEM examination of deformed samples. The primary source of strengthening comes from grain size refinement. Additional factors such as solid solution strengthening contribute to a lesser extent. Analysis of the high temperature creep behavior reveals that cryomilled Inconel 625 exhibits characteristics of structure controlled (Class II) as well as mobility controlled (Class I) creep behavior. The true activation energy for creep for both structure controlled and mobility controlled creep exceeds the value for lattice self-diffusion in Ni. This is explained in terms of the simultaneous deformation of second phase particles along with the Ni matrix during high temperature creep deformation.

Room temperature creep deformation and its effect on yielding behaviour of a line pipe steel with discontinuous yielding

A study was conducted to understand post-yield creep behaviour and its effect on the subsequent tensile behaviour of X-52 line pipe steel at room temperature. As a result of the carbon-locking effect, this steel exhibits a distinct yield point followed by a range of discontinuous yielding. Although normally not observed during re-loading after the first yielding, there was a yield point during re-loading following the exhaustion of creep deformation at a stress equal to the lower yield strength. The re-appearance of the yield point after creep deformation is related to the dislocation locking effect, rather than a carbon locking effect. The creep deformation following the initial loading to the region of discontinuous yielding is dependent on both the initial loading strain rate and the initial loading strain. Higher loading strain rate results in a higher dislocation velocity and a larger number of mobile dislocations at the start of creep, causing larger creep deformation. Smaller initial loading strain causes more creep deformation, but the total strain including the initial loading strain and the subsequent creep strain is insensitive to the initial loading strain.

Description of Temperature Dependence and Creep Deformation of 60 Sn-40 Pb Solder Alloys.

This paper shows the temperature effect on the deformation of 60 Sn-40 Pb solder alloys and a simulation using a constitutive model for viscoplasticity. First, a series of tests, such as creep, pure tension, and cyclic tension-compression loading were conducted to clarify the temperature effect on the deformation of 60 Sn-40 Pb solder alloys. The test results showed that the deformation of the solder alloys has a large temperature dependence. Simulations of the temperature effect on the deformation were also conducted by a constitutive model previously proposed. The parameters used in the model can be determined simply from pure tension and cyclic tension-compression loading tests at several temperatures. It was also found that the constitutive model describes not only the temperature effect on the pure tension and the cyclic tension-compression loading but also the creep curves after cyclic tension-compression preloading.

Accelerated Coarsening of MX Carbonitrides in 12%Cr Steels during Creep Deformation

MX carbonitrides (M=Nb, V, Ta/X=C, N), which are finely dispersed in the matrix of 12%Cr ferritic heat resistance steels, increase the creep strength of the steels by the precipitation strengthening mechanism. However, MX particles usually coarsen during high temperature creep deformation, and this results in a decrease of creep strength. In order to clarify the coarsening process of MX particles in 12%Cr steels (10.5Cr-0.1C-(Nb, V, Ta)), TEM samples were prepared from the grip portion (creep stress free zone) and the gauge portion (stress zone) of ruptured creep test pieces. The changes of MX particle radii in the gauge portion were considerably larger than that in the grip portion, indicating that creep stress accelerated Ostwald ripening of the particles in the gauge portion. The Ostwald ripening equation was modified by introducing the effective diffusion coefficient as a sum of the lattice diffusion coefficient and dislocation diffusion coefficient, based on an assumption that Nb and V might diffuse not only by the lattice diffusion mechanism but also by the dislocation diffusion mechanism. The effect of dislocation diffusion in the gauge portion was larger than that in the grip portion because dislocations in the gauge portion were moved by creep stress, and a rate of solute atoms diffusing along the dislocations might be increased. The coarsening process of MX particles in the gauge portion could be simulated successfully by means of a modified ripening equation.

A model for viscous flow creep in ceramics containing secondary crystalline phases

Many structural ceramics (e.g., Si{sub 3}N{sub 4}) contain an intergranular amorphous phase which results from liquid phase sintering. This amorphous phase is present both at the multigrain junctions and as thin films at two-grain boundaries. High temperature creep deformation of these materials may occur by viscous flow of the amorphous phase from grain boundaries in compression to those in tension. Several models have been developed to describe this process, based on the assumption of either square or hexagonal grains. All these models assumed that the grain size and grain boundary film thickness were uniform throughout the material. In polycrystalline material, however, a large range of grain size distribution is usually observed and secondary crystalline phases (SP) may also exist. The effect of grain size distribution on the viscous flow process has been analyzed recently by Dey et al. They argued that the presence of large grains can cause very high local stress concentrations. Since a residual glass film always remains along matrix/SP grain boundaries (heterophase boundaries) and is generally 2 or 3 times thicker than that along homophase boundaries (between matrix grains), a new model considering this heterogeneity is required to describe viscous flow creep in ceramics containing secondary crystallinemore » phases.« less

Description of Temperature Dependence and Creep Deformation of 60 Sn-40 Pb Solder Alloys.

In this paper, we show the temperature effect on the deformation of 60 Sn-40 Pb solder alloys and its simulation using constitutive model for viscoplasticity. First, we investigate the temperature effect on the deformation of 60 Sn-40 Pb solder alloys from a series of tests, such as creep, pure tension and cyclic tension-compression loading tests. The larger temperature dependence of the solder alloys is found out. Applicability of the constitutive model that has been proposed previously to the temperature dependence of the solder alloys is verified. As a result, the parameters used in the model can be easily determined from the pure tension and the cyclic tension-compression loading test at several temperatures. It also can be found that the constitutive model can describe not only the temperature effect on the pure tension and the cyclic tension-compression loading but also the creep curves after preloading of cyclic tension-compression loading.

A grain boundary sliding model for cavitation, crack growth and fracture in polycrystalline copper

A model is presented for cavity growth, crack propagation and fracture resulting from grain boundary sliding (GBS) during high temperature creep deformation. The theory of cavity growth by GBS was based on energy balance criteria on the assumption that the matrix is sufficiently plastic to accommodate misfit strains produced during the growth of the cavities, and that the cavities were caused to grow as a result of GBS and that sliding would not occur without concurrent cavity growth. This condition then allows shear stress acting on the boundary to do work in opening up the cavity. For elongated cavities, the model predicts a critical stress for fracture of the Griffith type. An equation was derived to establish a link between cavitation and the sliding strain, which was found to describe fairly well the two stages of cavity growth as confirmed by experimental results. Journal of Applied Science and Technology , Vol. 4, Nos. 1 & 2, 1999, pp. 5 - 14

High temperature creep deformation of an Al–Fe–V–Si Alloy

The creep behavior of dispersion-strengthened Al-8.5Fe-1.3V-1.7Si (8009 Al) has been investigated in the temperature range of 573-723 K. The results exhibit a high apparent stress exponent (14-18) and a high apparent activation energy for creep (296 kJ mol(-1)). The creep data were analyzed by incorporating a threshold stress into the power-law creep equation, which leads to a stress exponent of 5 indicating dislocation-climb mechanism. Traditional dislocation creep theories neither lead to correct values nor explain the origin or temperature dependence of the threshold stress, which is much stronger than that attributable to the shear modulus. A good correlation between experimental and theoretical prediction using the dislocation detachment model was obtained by adjusting the structure factor in the creep equation because the dislocation density is not well known. Dislocation/particle interactions as well as dislocation networks and subgrains are frequently observed after creep tests at different conditions. (C) 1999 Elsevier Science S.A. All rights reserved.

On the influence of stress state on rafting in the single crystal superalloy CMSX-6 under conditions of high temperature and low stress creep

Single crystal superalloys have excellent high temperature strength and oxidation resistance and are therefore used as blades in aircraft engines and land based gas turbines. The microstructure of these alloys consists of two phases: (i) a high volume fraction of coherently precipitated {gamma}{prime}-cubes (L1{sub 2}) which strengthen the material separated by (ii) thin channels of face centered cubic (f.c.c.) {gamma}-matrix, as shown. However, microstructural instability (i.e. {gamma}{prime}-coarsening) is observed in these alloys during high temperature creep deformation (T > 900 C). In creep, coarsening of particles is generally considered as a softening process which increases the creep rate of an alloy. However, this process does not always dominate the overall materials response to creep loading. Thus, Mughrabi et al have clearly shown that {gamma}{prime}-coarsening can occur while the overall creep rate decreases. A number of studies on the high temperature creep deformation behavior of various single crystal superalloys have been reported in recent years. To explain rafting the authors here consider the case of a {gamma}/{gamma}{prime}-microstructure with negative misfit, i.e. where the lattice constant of the ordered {gamma}{prime}-phase is smaller than the lattice constant of the {gamma}-phase.

High temperature creep behaviour of single crystal oxides

The creep resistance of several single crystal oxides is evaluated on the basis of creep data from different sources using a Larson-Miller (L-M) method. The possible creep mechanisms involved in high temperature creep deformation of single crystal oxides are discussed by comparing the collected creep data with theoretical creep models. The high temperature creep of single crystal oxides is generally considered as a diffusion-controlled process: dislocation climb controlled by the lattice diffusion of the slowest moving species (power law) at moderately high stresses, Harper-Dorn creep at low stresses, and power law breakdown at high stresses. The relative comparison of the creep data from different sources using the L-M method and the general analysis about the high temperature creep behaviour indicate that single crystal oxides with a precise stoichiometric composition, complex crystal structure and selected orientation such as [111] oriented YAG (Y3Al5O12),c-axis Al2O3, [110] oriented MgAl2O4 are potential candidates as reinforcements for very high temperature structural applications.

High temperature creep and cyclic deformation behaviour of AISI 316 L(N) austenitic steel and its modelling with unified constitutive equations

Creep tests at constant stress and low cycle fatigue (LCF) tests were performed with a view to investigating and modelling the deformation behaviour of AISI 316 L(N) austenitic stainless steel at 700 °C. All experiments were done on samples taken from two different sheets of the same batch of material. The creep stresses were selected from the high stress range. The results obtained from creep tests on samples from different sheets are compared with each other. The differences between them and the results of a creep test carried out at constant load are indicated. The LCF experiments were strain controlled. The effects of strain rate and strain amplitude on the cyclic hardening behaviour were investigated. The parameters of a set of constitutive equations are determined from these data. The quality of the parameter fit is discussed.

Diffusion-controlled transitory creep in binary oxides

Abstract Valuable information about minority point defects in binary oxides can be obtained by using fast temperature (T) and oxygen partial pressure (Po2) changes during high temperature creep deformation. A creep transient is established after a T or Po2 change, which reflects the evolution of the point defect concentration responsible for the diffusion of the slowest species to the new equilibrium value, allowing us the determination of the chemical diffusion coefficient and the migration energy of these defects.

Grain Size Effect in High Temperature Creep and Superplastic Deformation of Polycrystalline Matrials

Grain Size Effect in High Temperature Creep and Superplastic Deformation of Polycrystalline Matrials

Examination of fracture surfaces of SiC whisker-reinforced alumina after high temperature creep deformation

Examination of fracture surfaces of SiC whisker-reinforced alumina after high temperature creep deformation

Plastic flow and dislocation structures in tantalum carbide: Deformation at low and intermediate homologous temperatures

Dislocation structures and plastic flow in TaC 0.99 have been studied in material deformed by microindentation at 20°C, and in specimens crept at temperatures between 0.37 and 0.43 T m (1300–1500°C). Extensive local plastic deformation occurred during indentation, accomplished mainly by the motion of a 2 <011> edge dislocations gliding on {111}. The resulting defect structure consisted primarily of long screw dislocations, suggesting a relatively high mobility for edge segments and a large Peierls stress for screw dislocation motion. This <110>{111} slip system also operated in specimens crept at 0.37–0.43 T m. Thermal activation apparently increased the mobility of screw segments, resulting in substructures containing mixed dislocations with no preferred orientation. Microstructural observations, and analysis of kinetic data for power-law creep, suggest that intermediate temperature creep deformation of TaC 0.99 occurs mainly by climb-controlled grain boundary sliding with severely limited intergranular accommodation.

低温環境下での一定荷重負荷によるオーステナイト系ステンレス鋼ＳＵＳ３１６ＬＮのひずみ増加の限界応力

Investigation has been conducted on the following subject: low temperature creep deformation behavior of SUS 316LN austenitic stainless steel under constant load which is expected to be the material of superconducting toroidal coil case in Tokamak fusion reactor. Round bar specimens were extracted from SUS 316LN, and several tensile tests were carried out: monotonic loading tests at a room temperature, 77K and 4.2K, and constant loading tests at a room temperature and 77K. Increase in strain under constant load occurs over proportional limit of the material. Critical stress not to allow the increase in strain is 75-100% of 0.01% proof stress at the test temperature. This is the same value as 0.01% proof stress of extremely low rate monotonic loading test when no creep deformation occurs; thus, this is the same value as critical stress where plastic deformation initiates. Based on the result at 77K, the critical stress at 4.2K not to allow the increase in strain under constant load is estimated to be about 90% of 0.01% proof stress at 4.2K, which is about 75% of 0.2% proof stress at 4.2K.