High-pressure Deformation Research Articles

Exothermic Effects in Mixtures of Several Low-Molecular Organic Compounds with 50 wt % Aluminum after High-Pressure Plastic Deformation

DSC and thermogravimetry show that the thermal decomposition of anthracene, adamantane, melamine, pentaerythritol, cyanuric, aspartic and succinic acids is followed by endothermic effects. It is found that the enthalpies of endothermic processes vary from 500 J g−1 (for adamantane) to 1900 J g−1 (for pentaerythritol) and depend on the elemental composition of the organic compounds. The plastic deformation of the mixtures of the organic compounds containing 50 wt % of aluminum is done at a pressure of 1 GPa in a high-pressure apparatus of the anvil type. Endothermic peaks are registered in the thermograms of mixtures containing anthracene, melamine, and cyanuric acid in the temperature range of the decomposition of the organic compounds; exothermic peaks are registered in the thermograms of mixtures containing adamantane, succinic acid, pentaerythritol, and aspartic acid. Exothermic processes related to the oxidation and nitriding of aluminum are registered in the thermograms of all mixtures in the temperature range of 400–800°С. The total enthalpies of exothermic processes in deformed samples are determined. They vary from 1.9 kJ g−1 (for the mixture containing melamine) to 36.0 kJ g−1 (for the mixture containing pentaerythritol). The dependences of the results from DSC and thermogravimetric studies on the gaseous medium used in measuring (air, nitrogen, or argon) are determined.

Nanoparticles Observed in a Shear Fracture of Dolomite and a Probable Formation Mechanism.

Nanoparticles have been extensively found in brittle faults or ductile shear zones, and their formation is closely related to shear movement along the fault plane. However, the formation mechanisms of these nanoparticles are not yet clear. In this study, dolomite samples were triaxially compressed, at a confining pressure of 200-300 MPa, a temperature between 27 °C and 900 °C and a strain rate of approximately 10-5s-1, with a Paterson designed gas medium high-temperature and high-pressure deformation apparatus (HTPDA). Samples deformed at room temperature were characterized by universal microcracks and undulatory extinctions in some grains; when at a temperature between 300 °C and 500 °C, well-developed mechanical twins dominated the microstructure, while at a temperature ≥800 °C, displacements of twin lamellae along a cleavage and a well-developed fracture zone could be seen. Nanoparticles of different shapes were discovered on the slip surfaces of a shear fracture or in microcracks by field emission scanning electron microscopy (FESEM). Nanoparticles on deformed samples under low differential stress were usually of sporadic spherical shapes and uneven distribution; while deformed samples under high differential stress had more dense distributions that were identified. Moreover, grain-overlap and nanofine granulation could be recognized in high strain samples. Based on a mechanical data analysis and microstructural observations, it was suggested that the initial formation of nanoparticles was macroscopically determined by the differential stress subjected to the host rocks, and had nothing to do with temperature; whereas the aggregation morphology of the nanoparticles was related to the temperature during the formation and evolution processes of the nanoparticles.

Structure Transformation of Dispersionstrengthened Vanadium Alloys under Conditions of High-Pressure Torsion and Room-Temperature Tensile Deformation

A comparative study of the features of microstructure transformation in dispersion strengthened vanadium alloys of the V–Me(Cr, W)–Zr system under conditions of deformation by torsion under pressure and tension at room temperature is carried out. It is found out that suppression of dislocation plasticity in the high-strength state favors the formation of an anisotropic submicrocrystalline structure both during torsion deformation and in the region of strain localization in the case of tension at room temperature. It is shown that one of the main mechanisms of crystal fragmentation under these conditions is a dislocation-disclination mechanism, whose realization requires structural states with nonzero values of the curvature rotor or a high continual density of disclinations.

Atomic Disordering and BCC → FCC Transformation in the Heusler Compound Ni54Mn20Fe1Ga25 Subject to High-Pressure Torsional Megaplastic Deformation

The Heusler compound with the L21 Ni54Mn20Fe1Ga25 structure subject to high-pressure torsional megaplastic deformation was first systematically studied by in situ methods of X-ray phase analysis and transmission and scanning electron microscopy. It was established that the torsional shear deformation at room temperature reduces the polycrystalline structure of the compound to a nanocrystalline and partially amorphous state. It was revealed that, as the pressure increases from 3 to 5 GPa and the degree of deformation increases from 2 to 5 revolutions, total atomic disordering and sequential structural-phase transformation according to the scheme B2(bcc) → A2(bcc) → A1(fcc) occur. It is shown that annealing at a temperature of 570 K and below causes devitrification of the amorphous phase and annealing at a temperature of 620 K and above causes the restoration of the L21 structure. The dimensional effect of suppressing the thermoelastic martensitic transformation is revealed in the nanostructured austenitic L21 alloy with grains smaller than 80 nm when cooled to 120 K. The capability of the thermoelastic martensitic transformation and of the shape memory is restored in a submicrocrystalline ultrafine-grained alloy after its recrystallization annealing at temperatures above 600 K.

Deep crustal source of gneiss dome revealed by eclogite in migmatite (Montagne Noire, French Massif Central)

AbstractIn orogens worldwide and throughout geologic time, large volumes of deep continental crust have been exhumed in domal structures. Extension‐driven ascent of bodies of deep, hot crust is a very efficient mechanism for rapid heat and mass transfer from deep to shallow crustal levels and is therefore an important mechanism in the evolution of continents. The dominant rock type in exhumed domes is quartzofeldspathic gneiss (typically migmatitic) that does not record its former high‐pressure (HP) conditions in its equilibrium mineral assemblage; rather, it records the conditions of emplacement and cooling in the mid/shallow crust. Mafic rocks included in gneiss may, however, contain a fragmentary record of a HP history, and are evidence that their host rocks were also deeply sourced. An excellent example of exhumed deep crust that retains a partial HP record is in the Montagne Noire dome, French Massif Central, which contains well‐preserved eclogite (garnet+omphacite+rutile+quartz) in migmatite in two locations: one in the dome core and the other at the dome margin. Both eclogites record P ~ 1.5 ± 0.2 GPa at T ~ 700 ± 20°C, but differ from each other in whole‐rock and mineral composition, deformation features (shape and crystallographic preferred orientation, CPO), extent of record of prograde metamorphism in garnet and zircon, and degree of preservation of inherited zircon. Rim ages of zircon in both eclogites overlap with the oldest crystallization ages of host gneiss at c. 310 Ma, interpreted based on zircon rare earth element abundance in eclogite zircon as the age of HP metamorphism. Dome‐margin eclogite zircon retains a widespread record of protolith age (c. 470–450 Ma, the same as host gneiss protolith age), whereas dome‐core eclogite zircon has more scarce preservation of inherited zircon. Possible explanations for differences in the two eclogites relate to differences in the protolith mafic magma composition and history and/or the duration of metamorphic heating and extent of interaction with aqueous fluid, affecting zircon crystallization. Differences in HP deformation fabrics may relate to the position of the eclogite facies rocks relative to zones of transpression and transtension at an early stage of dome development. Regardless of differences, both eclogites experienced HP metamorphism and deformation in the deep crust at c. 310 Ma and were exhumed by lithospheric extension—with their host migmatite—near the end of the Variscan orogeny. The deep crust in this region was rapidly exhumed from ~50 to <10 km, where it equilibrated under low‐P/high‐T conditions, leaving a sparse but compelling record of the deep origin of most of the crust now exposed in the dome.

Development of a Stress Sensor for In-Situ High-Pressure Deformation Experiments Using Radial X-Ray Diffraction

We developed a stress sensor for in-situ deformation experiments using synchrotron radial X-ray diffraction. This stress sensor provided nearly diffraction-plane-independent stress that, when used in series with a sample, reduced the uncertainty of the average stress estimation acting on a sample. Here, we present the results of a study where pyrope was used as a stress sensor. Using a Deformation-DIA (D-DIA) high-pressure deformation apparatus, pyrope, olivine and alumina were deformed in the same run/cell assembly placed in series along the compression direction. Deformation experiments were conducted at pressures between 4 and 5 GPa and temperatures between 730 and 1273 K with strain-rates between 10−5 and 10−6 s−1. Stresses estimated from various (hkl) planes in pyrope were nearly the same; i.e., pyrope is plastically isotropic with ≤10 % variation with (hkl). However, stresses from various (hkl) planes in olivine and alumina varied by approximately a factor of 3. Comparisons between average stresses inferred from pyrope and those from different diffraction planes in olivine and alumina showed that the average stress in these materials evolved from low-end stress, estimated from various (hkl) planes at small strain, to high-end stress at a large strain. This suggests that the rate-controlling slip system in these materials changes from the soft to the hard slip system with strain.

Solid-Phase ortho-Hydroxylation of 2,4-Di-tert-butylphenol and Its Derivatives

Direct phenol–catechol conversion has been realized as a result of the solid-phase reaction of 2,4-di-tert-butylphenol with cuprous oxide under high pressure and shear deformation on the Bridgman anvils. The yield of 3,5-di-tert-butylcatechol in this reaction was about 85%. When cupric oxide was used in the solid-phase process, oxidative coupling of the starting phenol took place, resulting in quantitative formation of tetra-tert-butyl-ortho-bisphenol. The reaction of 6-substituted derivatives of 2,4-di-tert-butylphenol with cuprous oxide was used as an example to demonstrate the possibility of substitutive ortho-hydroxylation yielding 7–20% of pyrocatechols.

Studies of Deep Earth Rheology Based on High-Pressure Deformation Experiments Using D111-Type Apparatus

Studies of Deep Earth Rheology Based on High-Pressure Deformation Experiments Using D111-Type Apparatus

Tuneable Magneto-Resistance by Severe Plastic Deformation

Bulk metallic samples were synthesized from different binary powder mixtures consisting of elemental Cu, Co, and Fe using severe plastic deformation. Small particles of the ferromagnetic phase originate in the conductive Cu phase, either by incomplete dissolution or by segregation phenomena during the deformation process. These small particles are known to give rise to granular giant magneto-resistance. Taking advantage of the simple production process, it is possible to perform a systematic study on the influence of processing parameters and material compositions on the magneto-resistance. Furthermore, it is feasible to tune the magneto-resistive behavior as a function of the specimens’ chemical composition. It was found that specimens of low ferromagnetic content show an almost isotropic drop in resistance in a magnetic field. With increasing ferromagnetic content, percolating ferromagnetic phases cause an anisotropy of the magneto-resistance. By changing the parameters of the high pressure torsion process, i.e., sample size, deformation temperature, and strain rate, it is possible to tailor the magnitude of giant magneto-resistance. A decrease in room temperature resistivity of ~3.5% was found for a bulk specimen containing an approximately equiatomic fraction of Co and Cu.

Collapsing Cavities and Converging Shocks in Non-Ideal Materials

Summary As modern hydrodynamic codes increase in sophistication, the availability of realistic test problems becomes increasingly important. In gas dynamics, one common unrealistic aspect of most test problems is the ideal gas assumption, which is unsuited to many real applications, especially those involving high pressure and speed metal deformation. Our work considers the collapsing cavity and converging shock test problems, showing to what extent the ideal gas assumption can be removed from their specification. It is found that while most materials simply do not admit simple (that is scaling) solutions in this context, there are infinite-dimensional families of materials which do admit such solutions. We characterize such materials, derive the appropriate ordinary differential equations and analyze the associated nonlinear eigenvalue problem. It is shown that there is an inherent tension between boundedness of the solution, boundedness of its derivatives and the entropy condition. The special case of a constant-speed cavity collapse is considered and found to be heuristically possible, contrary to common intuition. Finally, we give an example of a concrete non-ideal collapsing cavity scaling solution based on a recently proposed pseudo-Mie–Gruneisen equation of state.

High-pressure deformation and amorphization in boron carbide

Icosahedral boron-rich solids fall second in hardness to diamondlike structures and have been the subject of intense investigations over the past two decades, as they possess low density, high thermal, and mechanical stability at high temperatures, and superior industrial manufacturability. A common deleterious feature called “presssure-induced amorphization,” limits their performance in high-velocity projectile applications. This article discusses spectral characteristics of amorphized states of boron carbide, a common icosahedral boron-rich ceramic, with the goal of understanding the mechanistic layout of pressure-induced amorphization. Mystery has surrounded the appearance of new peaks in Raman spectrum of pressure-induced amorphized boron carbide, but to date, no convincing explanation exists on their origin. Shock studies of boron carbide have proposed phase transformation at high pressures, but to date, no conclusive evidence has been corroborative to prove the existence of new high-pressure phases. We propose a new rationale toward deciphering the amorphization phenomenon in boron carbide centered on a thermodynamic approach to explain atomic interactions in amorphous islands. Quantum mechanical simulations are utilized to understand the impact of stresses on Raman spectra, while results from molecular dynamics (MD) simulations of volumetric compression are used to understand thermodynamic aspects of amorphization. Atomic-level nonbonded interactions from the MD potential are utilized to demonstrate origins of the residual pressure. Combining these efforts, the present study deciphers the connection between deformation behavior of boron carbide at high pressure and its mysterious amorphous Raman spectrum. The approach highlights the importance of meticulously incorporating multiscale modeling considerations in determining accurate material behavior of ultrahard materials.

Thermally Initiated Processes in Activated Metal–Polymer Composites Obtained by High-Pressure Plastic Deformation of Aluminum-Based Mixtures

The passivating properties of various polymer matrices and processes of their thermal decomposition in the presence of a filler, i.e., active aluminum particles, are studied for an activated metal–polymer composite obtained by vigorous plastic deformation of aluminum powder–polymer mixtures, same as the processes of the further aluminum depassivation and oxidation, when the polymer phase has already been destroyed. For this, mixtures of different polymers with 50 and 80 wt % of aluminum are subjected to plastic deformation under the pressure of 1 and 4 GPa and then are studied using the thermogravimetric method in the temperature range of 20–800°C in air and in nitrogen. A decrease in the sample mass related to polymer decomposition is observed in the range of 20–450°C, while the mass increases due to aluminum oxidation and nitrogenation in the range of 450–800°C. Oxygen activity is lower than nitrogen activity in the low-temperature range and higher in the high-temperature range.

Determination of Frictional Resistances of Deep Drawing Quality Steel Sheets in Bending Under Tension Test

Among many friction tests, the bending under tension (BUT) test simulates the frictional conditions on rounded edge of punch in deep drawing operations. The experimental evaluation of coefficient of friction value has been carried out using a special tribological simulator. Two friction conditions i.e. dry friction and lubrication were analysed. As a test material the deep drawing quality (DDQ) steel sheet commonly used in automotive industry was selected. The mechanical properties of the sheets were selected in the uniaxial tensile test. The experimental results show that the friction coefficient value is very stable after reaching a certain value of sheet deformation. It was found that an increase of rolls surface led to an increase of the sample elongation value at which exists the maximum effectiveness of lubricant. It was also observed that an increase of the amount of sample elongation decreases the sheet surface roughness and friction behaviour changes as a result of high contact pressure and plastic deformation of surface asperities.

Bonding strength of Invar/Cu clad strips fabricated by twin-roll casting process

Abstract Based on traditional twin-roll casting process, Invar/Cu clad strips were successfully fabricated by using solid Invar alloy strip and molten Cu under conditions of high temperature, high pressure and plastic deformation. A series of tests including tensile test, bending test, T-type peeling test and scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) measurements were carried out to analyze the mechanical properties of Invar/Cu clad strips and the micro-morphology of tensile fracture surfaces and bonding interfaces. The results indicate that no delamination phenomenon occurs during the compatible deformation of Invar/Cu in bending test and only one stress platform exists in the tensile stress−strain curve when the bonding strength is large. On the contrary, different mechanical properties of Invar and Cu lead to delamination phenomenon during the uniaxial tensile test, which determines that two stress platforms occur on the stress−strain curve of Invar/Cu clad strips when two elements experience necking. The average peeling strength can be increased from 13.85 to 42.31 N/mm after heat treatment at 800 °C for 1 h, and the observation of the Cu side at peeling interface shows that more Fe is adhered on the Cu side after the heat treatment. All above illustrate that heat treatment can improve the strength of the bonding interface of Invar/Cu clad strips.

High-Pressure Synthesis of High Coercivity Bulk MnAl-C Magnets from Melt-Spun Ribbons

Bulk MnAl-C magnets were prepared via high-pressure compaction of melt-spun ribbons. The e → τ phase transformation (PT) in the melt-spun MnAl and MnAlC ribbons occurs mainly via the massive mode, whereas the displacive mode is not prominent. The massive PT temperatures of the melt–spun MnAl and MnAlC ribbons were measured to be in the range 660–739 K and 700–758 K, respectively. The PT temperatures of the melt-spun MnAlC ribbons are lower than those of water–quenched MnAlC. The annealing process for producing τ-phase from e-phase was optimized based on the measured PT temperature range. As a result, no decomposition of the metastable e/τ-phase MnAl and MnAlC were observed during the optimized high temperature annealing. High-purity τ-phase MnAlC ribbons with high magnetization (122 Am2/kg at 8 T) and low coercivity (0.13 T) were obtained. The coercivity of the bulk MnAlC obtained by high-pressure compaction was significantly enhanced and reached 0.38 T partially due to the grain refinement of the sample during high-pressure deformation.

High strength nanocrystalline Cu\u2013Co alloys with high tensile ductility

A supersaturated single-phase Cu–26 at.% Co alloy was produced by high-pressure torsion deformation, leading to a nanocrystalline microstructure with a grain size smaller than 100 nm. The nonequilibrium solid solution decomposed during subsequent isothermal annealing. In situ high-energy X-ray diffraction was used to map changes linked to the separating phases, and the development of a nanoscale Cu–Co composite structure was observed. To gain further information about the relationship of the microstructure and the mechanical properties after phase separation, uniaxial tensile tests were conducted on as-deformed and isothermally annealed samples. Based on the in situ diffraction data, different isothermal annealing temperatures were chosen. Miniaturized tensile specimens with a round cross section were tested, and an image-based data evaluation method enabled the evaluation of true stress–strain curves and strain hardening behavior. The main results are as follows: all microstructural states showed high strength and ductility, which was achieved by a combination of strain-hardening and strain-rate hardening.

Strength of tantalum shocked at ultrahigh pressures

High purity polycrystalline tantalum (Ta) was shocked through 1–3.5 Mbar pressures creating Richtmyer-Meshkov unstable interfaces that were used to determine the dynamic material strength. The experiments were performed on the Omega laser at the University of Rochester Laboratory for Laser Energetics. Prior to shock, the driven surfaces of the tantalum targets where coined with a sinusoidal pattern. The targets were recovered post-shock, and the growth of the sinusoid amplitudes was used to characterize the relative extent of plastic deformation as a function of laser energy. Analogous data were extracted prior to the experiments from phenomenological Von Mises plasticity simulations that considered equation of state tables for Ta. The simulations showed the best agreement with the experiments (less than 5% difference between mean ripple growth measures) for shock pressures ranging from 1.2 to 2.7 Mbar. A fluid model studied as a function of viscosity was also used to qualitatively indicate the sensitivity of the experiments to strength. These results verify the ability to use a phenomenological, equation of state based model to simulate very high-strain rate, high-pressure deformation of tantalum.

Increase in the Saturation Magnetization in a Fe3Al Superstructure under Large Plastic Deformations

The effect of large plastic deformations at room temperature in a Bridgman anvil cell on the specific saturation magnetization of the DO3-type ordered (Fe–24 at % Al) alloy has been revealed. It has been found that torsion at high pressure and certain deformation parameters results in the complete suppression of long-range order in the alloy and in the corresponding increase in the specific saturation magnetization by 11% with respect to the equilibrium state. A theoretical model qualitatively describing the revealed phenomenon has been proposed.

Effect of strain on the intrinsic stacking fault energy of fcc Co: a first-principles study

Although tailoring stacking fault energy (SFE) through the addition of suitable alloying element can improve mechanical properties, the effect of strain must also be included to account for the Co-based alloy design. Using first-principles density-functional-theory calculations, we revealed that there is a strong effect of the strain (volumetric strain, simple strain, and volume conserving) and external pressure on the intrinsic SFE of face-centered cubic (fcc) cobalt. This result indicated a new insight into the Co-based alloys design, especially for application at high pressure and severe plastic deformation. The intrinsic SFE decreased by increasing tensile strain or decreasing pressure, thus the tendency of forming stacking faults increases which improves the mechanical properties. Effect of volumetric (hydrostatic) strain is the strongest indicated that the volume is the dominant factor in determining the SFE and the strain-induced fcc–hcp phase transformation. Different strain methods give different charge transfer between adjacent atoms and then contribute to the variation of the atomic bonding at the specific direction and SFE behavior. Application of external pressure from 0 to 15 GPa increased the elastic constants and elastic modulus of fcc Co and then improved the ductility.

High-pressure, High-temperature Deformation Experiment Using the New Generation Griggs-type Apparatus

In order to address geological processes at great depths, rock deformation should ideally be tested at high pressure (> 0.5 GPa) and high temperature (> 300 °C). However, because of the low stress resolution of current solid-pressure-medium apparatuses, high-resolution measurements are today restricted to low-pressure deformation experiments in the gas-pressure-medium apparatus. A new generation of solid-medium piston-cylinder ("Griggs-type") apparatus is here described. Able to perform high-pressure deformation experiments up to 5 GPa and designed to adapt an internal load cell, such a new apparatus offers the potential to establish a technological basis for high-pressure rheology. This paper provides video-based detailed documentation of the procedure (using the "conventional" solid-salt assembly) to perform high-pressure, high-temperature experiments with the newly designed Griggs-type apparatus. A representative result of a Carrara marble sample deformed at 700 °C, 1.5 GPa and 10-5 s-1 with the new press is also given. The related stress-time curve illustrates all steps of a Griggs-type experiment, from increasing pressure and temperature to sample quenching when deformation is stopped. Together with future developments, the critical steps and limitations of the Griggs apparatus are then discussed.