High-temperature Deformation Experiments Research Articles

High-temperature creep of olivine single crystals, 2. dislocation structures

Dislocation structures and densities in experimentally deformed single crystals of San Carlos olivine were examined using the oxidation-decoration technique. The high-temperature deformation experiments were conducted at various temperatures ( T), differential stresses (σ), and oxygen fugacities ( ƒ o 2 ); the samples were buffered against either orthopyroxene (opx) or magnesiowustite (mw) solid-state powders and compressed along one of the three 45° orientations. In samples that were deformed and subsequently quenched under load, seven distinct dislocation structures were observed. (a) For samples compressed parallel to [110] c at 16 < σ < 50 MPa and ƒ o 2 = 10 −6 atm , two different dislocation arrangements were identified. For opx-buffered samples at 1400 < T < 1475° C, the dislocation structure was composed of curved screw segments that had usually cross-slipped and straight edge segments of comparable length. At 1300 < T < 1350° C for opx-buffered samples and at 1350 < T < 1500° C for mw-buffered samples, the dislocation structure is dominated by arrays of very long edge or mixed dislocations with only a few screw dislocations, (b) For both opx-buffered and mw-buffered samples compressed parallel to [101] c at 1340 < T < 1400° C and 30 < σ <60 MPa, the dislocation configurations are characterized by zigzag near-edge dislocations at ƒ o 2 = 10 −5 atm and by straight, cross-slipped screw dislocations plus pinned edge dislocations at ƒ o 2 = 10 −9 atm . (c) For samples compressed parallel to [011] c at T = 1400° C and 70 < σ < 150MPa, the primary dislocations change from long, straight edge dislocations (for ƒ o 2 = 10 −4 atm and opx buffer) to a combination of straight edge dislocations and polygon-shaped half loops (for ƒ o 2 = 10 −4 atm and mw buffer), to gently curved near-edge dislocations (for ƒ o 2 = 10 −9 atm for both solid-state buffers). Abundant long, straight screw dislocations were present in each case for the [011] c samples. All of the above variations in dislocation structure are paralleled by changes in the measured power-law equation that describes the behavior of creep mechanisms of olivine. Thus, the different dislocation structures are associated with different rate-controlling creep mechanisms. For all of the dislocation structures, the dislocation density (ρ) increases with differential stress according to the relation ρ ∞ σ 1.4. Dislocation structures in samples that were deformed and then statically annealed have also been studied. For both [110] c and [011] c samples deformed over a wide range of experimental conditions, the dislocation structures on the slip planes generally consist of short, curved edge or mixed dislocation segments. In [101] 1 samples deformed at low ƒ o 2 , 50 MPa and 1400°C, the dislocation structure was much less altered by annealing than the dislocation structures in [110] c and [011] c samples. The density of dislocations decreased much less for these [101] c samples than for the [110] c and [011] c samples. Due to climb of the edge segments, the straight screw segments found in quenched samples became curved and many low-angle (100) tilt boundaries, connected by straight [100] screw dislocations, developed during the annealing process.

High‐temperature rheology of enstatite: Implications for creep in the mantle

High‐temperature deformation experiments have been performed on oriented single crystals of enstatite at 1 atm under controlled conditions of oxygen fugacity and silica activity. The results indicate that creep on the weakest high temperature slip system in enstatite within the protoenstatite stability field is independent of oxygen fugacity and obeys a power law relation with a stress exponent of n = 3.8±0.5 and activation energy of Q = 820±80 kJ/mol. A decrease in creep rate with increasing aluminum and iron content suggests that aluminum or iron ions play an active role in maintaining charge neutrality within the crystals. The single crystal strengths are greater than those reported for polycrystalline enstatite deforming predominantly on the same slip system, suggesting that the polycrystalline samples may have been water weakened. A comparison of the single crystal results with those for olivine deformed at 1 atm indicates that enstatite is probably stronger than olivine under upper mantle conditions, unless the presence of water results in a greater weakening of enstatite than olivine.

High-temperature creep of olivine single crystals, 1, mechanical results for buffered samples : J Geophys Res V96, NB2, Feb 1991, P2441–2463

To investigate the rheological behavior of the Earth's upper mantle, over 100 high-temperature deformation experiments have been performed on single crystals of San Carlos olivine in controlled chemical environments at a total pressure of 0.1 MPa. Constitutive equations have been determined which describe the dependence of creep rate on applied stress, temperature and oxygen fugacity in terms of power law relations. In addition, the effects of orthopyroxene activity and loading orientation on the creep behavior have been investigated. For samples of each of three compression directions, [101]c, [011]c and [110]c, buffered by orthopyroxene or magnesiowustite, either two or three power law equations are required to describe the dependence of strain rate at fixed stress on temperature and oxygen fugacity over the full range of experimental conditions. It is proposed that in each power law regime a different creep mechanism controls the creep rate. For all of the experimental conditions, the activation energy for creep is independent of the stress level and the stress exponent is constant at 3.5±0.1. Activation energies for the various creep mechanisms varied from 230 to 1000 kJ/mol; and oxygen fugacity exponents lie in the range −0.03 to 0.4. From the constitutive equations determined based on the power law equations for all of the creep mechanisms, e˙-T-fo2 deformation maps were constructed at a stress of 1 MPa for olivine.

Palaeostress estimation using calcite twinning: experimental calibration and application to nature

By means of high-temperature deformation experiments on calcite rocks of different grain sizes, we have established the relationships between differential stress and twinning incidence, twin density and volume fraction, and the way that these relationships depend on grain size. Both twinning incidence and volume fraction increase with grain size at a constant level of differential stress. Log twin density is proportional to stress but is independent of grain size. At a given grain size, volume fraction of twinning increases non-linearly with differential stress. Twinning activity measured by twinning incidence increases linearly with stress. The behaviour of each of these parameters is independent of temperature, strain and strain rate. These relationships can be used as a basis for the estimation of palaeostress values in naturally deformed calcite rocks. This is illustrated by a study of twinning activity in limestones close to thrust faults in the Cantabrian zone of the Variscan orogenic belt in northwestern Spain. High peak differential stresses were measured, ranging from 150 to 250 MPa. Using the Turner Dynamic Analysis technique, however, it is clear that shear stresses resolved parallel to the fault planes were very low. The attainment of high stress differences when the resistance to faulting was low is attributed either to bending forces induced during the motion of the non-planar surfaces relative to each other or to the stress peak being attained prior to the localization of deformation onto the fault surfaces.

Anisotropic grain growth in quartz aggregates under stress and its implication for foliation development

Fine-grained quartz aggregates show significant grain growth during high-temperature (700-1000 °C) and high-pressure (400 MPa) deformation experiments when water is present. Flattening of grains that exceeds the deformation-induced flattening and a resultant clear foliation are found in the samples recrystallized at relatively low temperatures and high strain rates (i.e., high deviatoric stresses). The distribution of water as inferred from the distribution of pore space is also anisotropic in these samples. In contrast, the samples recrystallized at relatively high temperatures and low strain rates (i.e., low deviatoric stresses) show small grain flattening and almost isotropic water distribution. The observed very large flattening under high stress indicates a significant contribution of anisotropic grain growth. Because the anisotropy of grain growth is correlated with the anisotropy of water distribution, we suggest that the observed foliation under high stress is due to anisotropic grain growth caused by enhanced mass transport through water. Foliation caused by this mechanism will be related to the stress orientation.

High-temperature yield behavior in NaCl-structure oxides

High-temperature (T > 0.5 T /SUB m/ ) deformation experiments have been performed on several NaClstructure oxides. Alkaline-earth oxides such as MgO are stoichiometric compounds, while the transition-metal oxides NiO, CoO, FeO, and MnO are all metal deficient and may be written in the form M/sub 1//sup -/deltaO. The deviation from stoichiometry delta is a function of temperature T and oxygen partial pressure p(O/sub 2/) and is achieved primarily by creation of metal vacancies and chargecompensating electron holes. Deformation experiments performed at nearly constant strain rates epsilon have been carried out on NiO, CoO, and FeO. The deviation from stoichiometry ranges from delta slip systems, and during compression at high temperatures they develop a steady-state stress /tau/ /SUB s/ at which the work-hardening rate is zero. At this stress, work hardening is balanced by a recoverymore » mechanism.« less

Effects of non-stoichiometry on the high-temperature deformation of Ni2AITi

Abstract High-temperature deformation experiments have been performed on two non-stoichiometric Ni2AlTi compounds lying roughly on the NiAl-NiTi quasi-binary line in the Ni-Al-Ti ternary system, and the results have been compared with those for the stoichiometric compound. The marked effects of non-stoichiometry on the deformation behaviour are observed only in the Al-rich compound; the deviation from stoichiometry on the Al-rich side produces considerable strengthening of Ni2AlTi and causes the 〈110→ 〈001〉 slip mode transition in crystals with orientations near [111]. In crystals of the Ti-rich compound and in those of the Al-rich compound with orientations away from [111], slip occurs along 〈110〉 directions, as in the stoichiometric compound. The 〈001〉 superlattice dislocations in the Al-rich compound are found to be dissociated into two 1/2〈001〉 superlattice partial dislocations coupled by a ribbon of antiphase boundaries (APB). From the separation of the superlattice partial dislocations, the energy of the APB on {110} in the Al-rich compound is found to be about 115 mjm −2. Assuming that the excess AI atoms in the Al-rich compound are all on the Ti-sublattice, the energy of the APB for the stoichiometric composition is estimated to be higher than 155mJm−2.

Experiments on the origin of slaty cleavage and schistosity

Research Article| May 01, 1976 Experiments on the origin of slaty cleavage and schistosity TERRY E. TULLIS TERRY E. TULLIS 1Department of Geological Sciences, Brown University, Providence, Rhode Island 02912 Search for other works by this author on: GSW Google Scholar Author and Article Information TERRY E. TULLIS 1Department of Geological Sciences, Brown University, Providence, Rhode Island 02912 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1976) 87 (5): 745–753. https://doi.org/10.1130/0016-7606(1976)87<745:EOTOOS>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation TERRY E. TULLIS; Experiments on the origin of slaty cleavage and schistosity. GSA Bulletin 1976;; 87 (5): 745–753. doi: https://doi.org/10.1130/0016-7606(1976)87<745:EOTOOS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The coupled problems of the tectonic significance and mechanism of development of slaty cleavage and schistosity have been studied in high-temperature and pressure deformation experiments. The primary mechanistic question concerns whether preferred orientation of mica in slates and schists develops by rotation of tabular grains or whether it develops by mechanisms that require crystallization or re-crystallization. Most proposed orienting mechanisms predict the same relationship between principal strain directions and preferred orientation. This frustrates attempts to determine the principal orienting mechanisms.Simple theoretical models of rotation of passive planar markers and of isolated rigid ellipsoids in a deforming fluid predict similar relationships between the magnitudes of the strain and the preferred orientation. In room-temperature experiments, these predictions are followed when interactions between adjacent grains are minimal; when interactions are important, the rotation mechanism is less effective.In high-temperature experiments in which phlogopite is syntectonically crystallized from the constituent oxides or fluorophlogopite or biotite is syntectonically recrystallized, the preferred orientations match the predictions of the rotation models. This suggests that crystallization or recrystallization aided the rotation process by reducing mutual grain interference. Textural observations of the recrystallized samples support this interpretation.In all of the deformation experiments, maximum, intermediate, and minimum principal compressive strain directions coincide with maximum, intermediate, and minimum concentrations of poles to mica basal planes, respectively, even for general noncoaxially accumulating strain. These results coupled with studies of natural slates suggest that mica preferred orientations may be used to estimate both magnitudes and directions of finite strain. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Recrystallization behavior in deformed austenite of high strength low alloy (HSLA) steels

High temperature deformation experiments were conducted to monitor the recrystallization process in the austenite phase of a vanadium and columbium-treated HSLA steel alloy. The results show that columbium is much more effective than vanadium in retarding recrystallization. As the austenitizing temperature, above 2000°F, or time is increased the austenite recrystallization in the 1500° to 1700°F hot working temperature range is correspondingly increased. If, following the austenitization, the samples are held in the hot working temperature range for up to 5 min before hot working recrystallization occurs at a much faster rate. Several mechanisms are offered to explain the experimental results.