Compressive Creep Properties Research Articles

Mechanical Properties of Lead Alloys in Compression

Some lead alloys have compressive elastic and creep properties that make them potentially useful in certain types of structures, but until now very little useful mechanical property data have been available. Results from short-term compressive stress-strain and from longer-term creep tests are presented for three standard lead alloys and pure lead in a format that it is hoped will be of use to structural designers. The stress-strain results show that work hardening improves the short-term elastic behavior of the lead alloys tested, and indicate that of the alloys tested, copper tellurium alloy is the most stable. The compressive creep results show that it would normally be acceptable to ignore primary creep and just include secondary creep in analyses. Two forms of creep equations are presented for use in analyses, but care is needed when using these, since in certain cases they can produce a strain rate value significantly different from that measured.

Solid-solution hardening of Ir by Pt and Ni

To understand the solid-solution hardening effect of Pt and Ni to Ir, compressive strength and compressive creep properties were investigated for Ir–Pt, Ir–Ni, and Ir–Pt–Ni alloys. The solid-solution hardening effect of Ni was higher than that of Pt because the atomic size difference was larger in the Ir–Ni alloy than in the Ir–Pt alloy.

Creep behavior of Ni-added Ir 85Nb 15 two-phase refractory superalloys at 1800 °C

To provide information relevant to Ir-based two-phase alloys for future ultra-high-temperature applications, the compression creep properties for the Ni-added Ir 85Nb 15 alloys were investigated at 1800 °C under 137 MPa. The results show that Ni addition has a significant effect on the creep resistance of the Ir 85Nb 15 two-phase refractory superalloy.

Reactive infiltration processing and secondary compressive creep of NiAl and NiAl-W composites

Reactive infiltration processing was used to fabricate bulk NiAl and fiber-reinforced NiAl composites. Homogenous, pore-free materials were obtained by chemical reaction between nickel and aluminum after complete infiltration with liquid aluminum of preforms of nickel wires (containing tungsten wires for the composites) with low surface-to-volume ratio, high permeability, and regular infiltration paths. Reactively-processed, monolithic NiAl exhibited compressive creep properties at 715 °C and 1025 °C in good agreement with those of conventionally processed NiAl. The compressive creep behavior of NiAl composites reinforced with 5 to 20 vol pct W was also characterized at the same temperatures. At 715 °C, the NiAl-W composites exhibited secondary creep with little primary and tertiary creep, while at 1025 °C, the composites displayed all three stages. Microstructurally, secondary creep was characterized by pure uniaxial compression of tungsten fibers. The measured composite secondary creep rates could be predicted reasonably well with the role-of-mixtures isostrain model developed for composites where both phases undergo creep deformation using tensile creep data measured on the as-received tungsten fibers.

Compressive creep properties of lead alloys

The visco-elastic properties of lead can be used to advantage in some forms of structure to reduce undesirable load transfer. As part of an investigation of this topic a programme of compressive creep testing of lead and lead alloy specimens was undertaken and this paper reports the results from this testing. The materials tested were 99.99% lead, 0.06% copper lead, 0.06% copper 0.04% tellurium lead, and 1.2% antimony lead, and work-hardened specimens were tested at temperatures between 5°C and 60°C and at stress levels up to 12.5 N/mm 2. Strain–time results from these tests are presented and from the measured secondary strain rates, values for the Norton power factor n and the creep activation energy Q c were calculated.

1300 K creep behavior of [001] oriented Ni–49Al–1Hf (at.%) single crystals

A study of the 1300 K compressive and tensile creep properties of [001]-oriented NiAl-1Hf (D209) single crystals has been undertaken. Neither post homogenization cooling treatment, minor chemical variations within an ingot or from ingot-to-ingot, nor testing procedure had a significant effect on mechanical behavior; however a heat treatment which dissolved the initial G-phase precipitates and promoted formation of Heusler particles led to a strength reduction. Little primary creep was found utilizing direct measurement of strain, and a misorientation of 18 deg from the [001] did not reduce the creep strength. The effects of heat treatments on properties and a comparison of the flow stress-strain rate data to those predicted by the Jaswon-Cottrell solid solution hardening model indicate that the 1300 K strength in NiAl-1Hf single crystals is mainly due to precipitation hardening mechanisms.

Analytical and Experimental Investigation for Tensile and Compressive Creep of the A3003P Aluminium Alloy Used for Plate-Fin Heat Exchanger.

Analytical and experimental analysis for tensile and compressive creep properties of fine and coarse-grained aluminium alloy, A3003P, used for plate-fin heat exchanger are presented for temperatures from 400°C to 600°C and stresses between 0.255 MPa and 6.370 MPa. Investigation for parameters' effect on the behaviour of the time-dependent flow of material was carried out. For analytical investigation, the grain-size mechanism was applied to both tension and compression creep tests. Creep-strain rate increases with increasing both temperature and stress, while decreasing with coarse grain size. For loading mode, experimental results showed lower creep strain in compression than in tension for all stresses investigated. Nevertheless, numerical analysis showed identical behaviour for both tension and compression. Good agreement was found between the experimentally determined creep strain and analytical predictions at lower stress levels. However, at higher stresses considerable deviations from the experimental results were recorded for the analytical findings. Though the grain-size mechanism is applicable in case of tension for pure aluminium, modification becomes necessary when compression is applied.

Creep of metals containing high volume fractions of unshearable dispersoids—Part II. Experiments in the AlAl 2O 3 system and comparison to models

The tensile and compressive creep properties of coarse- and fine-grained dispersion-strengthened aluminum with 25 vol.% submicron alumina dispersoids are presented for temperatures between 335°C and 500°C and stresses between 30 MPa and 110 MPa. For all stresses investigated, the minimum creep rate is higher in tension than in compression, because cavitation is the main deformation mechanism in tension. In compression, however, dislocation creep is the dominant deformation mechanism at all stresses for the large-grained material and at high stresses for the fine-grained material, while diffusional creep dominates in the fine-grained material at low stresses. The apparent stress exponents for both diffusional creep and dislocation creep are much higher than for unreinforced aluminum, indicating that the dispersoids strongly inhibit both mechanisms. The threshold stresses determined experimentally for dislocation creep are significantly higher than those predicted by existing climb or detachment models, which consider the interaction of a single dislocation with dispersoids. Since transmission electron microscopy reveals that several dislocations typically interact with a single dispersoid, the modified threshold stress model presented in the theoretical companion article [1] is applicable, whereby the stress of dislocation pile-ups upon the threshold-controlling dislocation is taken into account. Good agreement is found between the experimentally determined threshold stresses and theoretical predictions from that model. The same model can also satisfactorily explain the very high measured values of the apparent activation energy.

Compressive Creep and Creep Failure of 8Y2O3/3Al2O3‐Doped Hot‐Pressed Silicon Nitride

The compressive creep properties of hot‐pressed Si3N48Y2O3—3Al2O3 (wt%) have been investigated in the temperature range of 1543–1603 K in air. The stress exponent, n, of the power creep law was determined to be 1.5, and the activation energy was determined to be 650 kJ/mol. Transmission electron microscopy observations showed that grain‐boundary sliding occurred with cavitation formation in the grain‐boundary glassy phase. The quasi‐steady‐state creep results were consistent with that of the diffusion‐controlled solution—diffusion—precipitation creep mechanism, and the distinguished failure mechanism was cavitation creep damage controlled by the viscosity of the boundary glassy phase. The compressive creep failure time, obtained at 1573 K, in the stress range of 175–300 MPa, followed the MonkmanGrant relation, indicating that cavity growth was mainly controlled by the creep response of the material.

Microstructure and plasticity of two molybdenum-base alloys (TZM)

In two different commercial Mo-base alloys (TZM), produced by vacuum melting and by powder metallurgy respectively, microstructural differences (particle size and chemistry, grain and subgrain sizes, dislocation density) have been found which affect the observed mechanical properties of the material. The compression-creep properties at 1423 K show a negligibly small creep rate at a stress of approximately 200 MPa. Trapping of dislocations by particles is proposed to be the controlling deformation mechanism during creep. The microstructure and fatigue properties of TZM welds were also investigated. Friction welds showed the best mechanical properties. Fatigue measurements in load control at room temperature and 1123 K show that the endurance limit of the vacuum-melted alloy is higher than that of the powder-metallurgically processed alloy.

1400 and 1500 K compressive creep properties of an NiAlAlN composite

Compressive creep properties of an NiAl/AlN(p) composite produced by a reaction milling process were investigated at 1400 and 1500 K and at slow strain rates, to investigate the relative strength of this composite at high temperatures, and to determine if the consolidation technique affects the 1400 K creep properties. Results indicate that the stress exponent of the NiAl/AlN(p) composite was similar to that for unreinforced NiAl. However, the activation energy for the composite was found to be more than twice that measured in the unreinforced matrix. Oxidation did not affect the composite at 1400 K, but a significant attack was observed in a sample subjected to fast deformation at 1500 K.

Influence of grain size on the creep behavior of HfC-dispersed NiAl

Rapid solidification technology has been utilized to produce a NiAl-4(wt.%)HfC composite containing about 0.3 vol.% HfC as dispersed 50 nm particles. Study of the 1300 K compressive creep properties demonstrated that the initial, small grain size microstructure was unstable under slow strain rate deformation conditions. The grain growth which occurred during testing led to considerable strengthening. Subsequent measurements of the creep properties of the coarse grained specimens revealed that this strength was achieved by a large increase in the activation energy for deformation without any change in the stress exponent. Based on this work it is concluded that large grain microstructures will be required for optimum elevated temperature creep properties in dispersed NiAl.

The effect of TiN and TiC dispersoids on the high-temperature deformation mechanisms of Si 3N 4

The compression creep properties of pressureless sintered Si 3N 4 matrix, Si 4N 4−(TiN + TiC) and Si 3N 4−N composites, and of a hot pressed Si 3N 4−TiC composite were studied in air between 1260 and 1340°C. Creep characteristics have been compared in relation to microstructure. The addition of soft TiC particles resulted in better mechanical strength, particularly in the creep ductility. The deformation of Si 3N 4TiC, dominated by a more refractory vitreous phase, was slower than for the other composites. Further, based on a comparison of creep parameters obtained experimentally in this work and on the nature of dispersoids, deformation mechanisms are proposed.

Compressive and Flexural Creep Behavior of Carbon Fiber/PEEK Composites

The present study deals with the compressive and flexural creep properties of polyetheretherketone (PEEK), a high temperature semicrystalline thermoplastic. The compressive and flexural modes are important from a practical viewpoint, and yet rather limited viscoelastic data exist presently for testing in the two modes. The creep compli ance results of the unreinforced PEEK and the carbon fiber/PEEK composites are reported for temperatures ranging from 120°C to 160°C. Transverse compressive and cross-ply [±45°] s flexural compliances, the matrix dominated properties, displayed a significant viscoelastic behavior. The unidirectional 0° samples, on the other hand, displayed only a very limited time dependent response since the composite properties in the longitudinal direction are controlled by the almost elastic response of the fibers. The time-dependent experimental compliance values for the composites are compared to the results predicted from a micromechanics model and the classical lamination theory in conjunction with the quasi-elastic methodology.

Creep and microstructure of TiC particulate Si3N4-based composites

The compressive creep properties of Si3N4/TiC composite, in comparison with those of Si3N4 matrix and Si3N4/TiN, were studied in temperature range 1260–1340°C at stresses between 100 and 300 M Pa. The creep curves and the stress dependence of the creep rate showed that a diffusional creep, with a stress exponent n = 1, was dominant up to 1340°C and 300 M Pa. Although the creep rate was greater than that of the matrix, a significant increase of creep ductility was obtained. Furthermore, the microstructural development under applied processing conditions was examined. The TiC dispersoid, added to improve the toughness and strength of Si3N4, was found to be ‘chemically’ reactive with the Si3N4 matrix. The reaction products, composed of TiC0·5N0·5 and SiC crystals, were observed in the vicinity of TiC/Si3N4 interfaces. The matrix grain refinement, desirable interfaces and a modification of the glassy film were suggested to affect both the creep rate and creep ductility. Das Kriechverhalten von Si3N4-Verbundwerkstoffen wurde im Temperaturbereich von 1260 bis 1340°C bei Drücken von 100 bis 300 M Pa untersucht und mit dem von reinem Si3N4 und Si3N4/TiN verglichen. Bis 1340°C und 300 M Pa zeigten die Kriechkurven und die Spannungsabhängigkeit der Kriechgeschwindigkeit diffusionsgesteuertes Kriechen mit einem Spannungsexponent von n = 1. Obwohl die Kriechgeschwindigkeit größer war als die der Matrix, zeigte sich eine beträchtliche Zunahme der Kriechverformung. Desweiteren wurde die Gefügeentwicklung unter den angewandten Prozeßbedingungen untersucht. Es zeigte sich, daß die zur Erhöhung der Zähigkeit und der Festigkeit des Si3N4 zugegebenen TiC-Teilchen mit der Si3N4-Matrix reagierten. Die Reaktionsprodukte, bestehend aus TiC0·5N0·5 und SiC Kristallen, konnten in der Umgebung der TiC/Si3N4 Grenzflächen nachgewiesen werden. Auf den Einfluß einer reduzierten Korngröße des Matrixmaterials, der Bindungsverhältnisse an den Korngrenzen und einer Veränderung der Zusammensetzung der vorhandenen Glasphase auf die Kriechgeschwindigkeit wie auch auf die Verformung während des Kriechens wird eingegangen. Les propriétés du fluage en compression du composite Si3N4/TiC, comparativement à celles de la matrice Si3N4 et du Si3N4/TiN, ont été étudiées dans une plage de température 1260–1340°C, sous des contraintes allant de 100 à 300 M Pa. L'étude de la déformation et de sa vitesse pour différentes contraintes montre qu'un fluage diffusion, avec un exposant de contrainte n = 1, est dominant jusqu'à 1340°C et sous 300 M Pa. Bien que la vitesse de fluage soit plus grande que celle de la matrice, la ductilité augmente de façon significative. En outre, le développement de la microstructure dans les conditions appliquées au cours du processus d'élaboration a été examiné. Les particules de TiC, ajoutées pour améliorer la résistance mécanique et la ténacité, sont ‘chimiquement’ réactives avec la matrice de Si3N4. Des produits de réaction, composés par des cristaux de TiC0·5N0·5 et de SiC, ont été observés prés de l'interface TiC/Si3N4. La réduction de taille de grain de la matrice, la cohésion des interfaces et le changement de composition du film vitreux sont considérés affecter la vitesse et la ductilité de fluage.

Rheological Properties of Grain Dust

ABSTRACT EXPERIMENTS were conducted to determine the rheological properties of grain dust collected from the dust control systems of commercial grain elevators. The moisture content of the dust samples ranged from 9 to 15%. Bulk densities of grain dust ranged from 180 to 350 kg/m3 at loose-fill conditions and from 400 to 660 kg/m3 at a pressure of 120 kPa. The compression creep and stress relaxation properties of grain dust can be described by Burger's model and the generalized Maxwell model represented by three Maxwell elements, respectively. A functional relationship expressing bulk density of grain dust as a function of pressure was obtained. The hysteresis loss of grain dust during loading and unloading cycles increased and the degree of elasticity decreased when moisture content increased.

Compression Creep Properties of Reduced Forage

Compression Creep Properties of Reduced Forage

On the mechanisms of tertiary creep in face centred cubic metals

Using a constant stress machine, the compressive creep properties of a copper-aluminium alloy and a dilute nickel alloy have been studied. This data has been compared with the results of tensile creep tests also carried out under constant stress. It is shown that a stage of accelerating creep in compression (in the absence of recrystallisation) is associated with non-homogeneous deformation due to barrelling of the specimen after extensive deformation. The tertiary stage observed in tensile creep is accounted for by the increase in recovery rate throughout this stage. Also, cavities present on the grain boundaries do not cause an acceleration of the creep rate under compressive creep conditions even when the cavities continue to grow in compression. It is concluded that the thermodynamic stability of grain boundary cavities is an important factor in determining their effect on the creep rate.