High-temperature Plastic Flow Research Articles

Hot processing map and high temperature deformation behaviour of TB17 Ti alloy

The thermal compression experiments of TB17 titanium alloy under different thermal deformation process parameters were carried out using a thermal simulation compressor. The high-temperature plastic flow behaviour of the alloy was studied. It was found that with the decrease of the deforming temperature and the increase of the strain rate, the flow stress increased, and the discontinuous yield phenomenon occurred in hot deformation. The larger the strain rate, the more obvious the discontinuous yield phenomenon. The thermal activation energy Q decreased with the increase of strain, and the average value of activation energy Q is 209.54 KJ / mol. The constitutive equation of high-temperature plastic flow of TB17 titanium alloy was established. The predicted values of this equation are in good agreement with the experimental values. The average error is 3.987 %, and the correlation coefficient is 0.9972, which has high accuracy. Based on the Prasad criterion, the hot processing map of TB17 titanium alloy was constructed. It was found that the flow instability zone was mainly concentrated in the high strain rate region. The flow instability zone was determined to be 795 °C ~ 895 °C, 0.046s-1 ~ 1s-1, and the stable deformation zone was mainly located in the region with high temperature and low strain rate. The optimum processing parameter range is 860 °C ~ 895 °C, 0.001 s-1 ~ 0.025 s-1.

Athermal effect of flash event on high-temperature plastic deformation in Y2O3-stabilized tetragonal ZrO2 polycrystal

This study experimentally demonstrates the athermal effect of a flash event under a DC electric field on high-temperature plastic deformation in a dense, fine-grained 3 mol% Y2O3-stabilized tetragonal ZrO2 polycrystal (3Y-TZP). A high-temperature three-point flexural test in the conventionally sintered 3Y-TZP body with an average grain size of 0.36 µm was conducted under a flash event with a current density of 67 mA·mm−2 at a furnace temperature between 900 °C and 1300 °C. The flash event significantly enhanced the high-temperature plastic flow in the 3Y-TZP body, even though subtracting the effect of specimen temperature rise by Joule heating, while grain growth during the flexural tests was effectively suppressed under the examined conditions. The athermal effect on the plastic flow was attributed to the reduction in the activation energy for the high-temperature plastic flow.

Kinetic Analysis of High-Temperature Plastic Flow in 2.25Cr-1Mo-0.25V Steel.

High-temperature plastic flow of heat-resistant 2.25Cr-1Mo-0.25V steel was investigated by hot tension (at 500–650 °C) on a Gleeble 3800 machine. The strain rate of hot tension was set as 0.001–1 s−1. The constitutive relation of the steel was modeled by the introduction of the parameters termed “true activation energy” and “threshold stress”. Then, the kinetics of high-temperature plastic flow was analyzed based on an Arrhenius equation modified by a “threshold stress”. The stress exponent of the modified equation was equal to 5. True activation energy was estimated to be 132 kJ·mol−1. According to the slip band model, the basic mechanism behind the hot deformation of the steel was considered to be dislocation climbing, which was governed by grain boundary diffusion. This model proved to be successful in its analysis of the experimental results of hot tension tests.

Constitutive Analysis on High-Temperature Flow Behavior of 3Cr-1Si-1Ni Ultra-High Strength Steel for Modeling of Flow Stress

High-temperature plastic flow is the underlying process that governs the product quality in many advanced metal manufacturing technologies, such as extrusion, rolling, and welding. Data and models on the high-temperature flow behavior are generally desired in the design of these manufacturing processes. In this paper, quantitative constitutive analysis is carried out on 3Cr-1Si-1Ni ultra-high strength steel, which sheds light on the mathematic relation between the flow stress and the thermal-mechanical state variables, such as temperature, plastic strain, and strain rate. Particularly, the hyperbolic-sine equation in combination with the Zener-Hollomon parameter is shown to be successful in representing the effect of temperature and strain rate on the flow stress of the 3Cr-1Si-1Ni steel. It is found that the flow stress of the 3Cr-1Si-1Ni steel is significantly influenced by strain. The strain-dependence on flow stress is not identical at different temperatures and strain rates. In the constitutive model, the influence of strain in the constitutive analysis is successfully implemented by introducing strain-dependent constants for the constitutive equations. Fifth-order polynomial equations are employed to fit the strain-dependence of the constitutive constant. The proposed constitutive equations which considers the compensation of strain is found to accurately predict flow stress of the 3Cr-1Si-1Ni steel at the temperatures ranging from 800 °C to 1250 °C, strain rate ranging from 0.01/s to 10/s, and strain ranging from 0.05 to 0.6.

Migration of fluids and melts in subduction zones and general aspects of thermophysical modeling in geology

Modeling of fluid-magmatic systems in a suprasubduction mantle wedge is considered for the case of Kamchatka with reference to data on peridotites from other known subduction and oceanic rock complexes. This modeling has to take account of magma storage in several intermediate reservoirs at different depths, up to six such reservoirs, as in the case of Avacha Volcano. Comparison of available data on melt inclusions in spinels indicates crystallization of the Avacha peridotites in magmatic systems progressively decreasing in temperature (>1200 °C → 1100 °C → 900 °C) and pressure (from 13.8 to 4.5 kbar) in intermediate reservoirs at depths of 30-40 and 15-20 km. The Avacha harzburgites do not belong to primary oceanic mantle as they lack both signatures of high-temperature plastic flow and effects of mantle melts known for sheared mantle peridotites from ophiolite suites. The vP/vS ratio estimated from jointly analyzed P- and S-wave velocities (vP and vs, respectively), an important indicator for seismic tomographic reconstructions of subduction zones, allows discriminating between regions saturated mainly with liquid (melts) and gas phases beneath volcanoes. Only specially tested tomographic data can provide reliable reference for modeling of mantle wedge processes.

High-temperature plastic flow of a precipitation-hardened FeCoNiCr high entropy alloy

In this work, we systematically investigated flow behavior of a high entropy alloy (HEA) strengthened by coherent γ′ precipitates in the temperature range of 1023–1173K. In contrast to the single-phase FeCoNiCrMn HEA, this precipitate-hardened alloy, i.e., (FeCoNiCr)94Ti2Al4, exhibited large reduction of the steady-state strain rate (by ~2 orders of magnitude) or drastic enhancement in flow stress, indicating significant improvement in high-temperature properties. Our results showed that the deformation could be divided into two regimes. At temperatures below 1123K, coherent γ′ precipitates effectively blocked the dislocation motion, thus resulted in a threshold stress effect. Above 1123K, however, γ′ particles dissolved and the deformation was controlled by the ordinary dislocation climb mechanism. In addition, we conducted transmission electron microscopy to characterize dislocation-precipitate interaction to provide microstructural evidences to support our conclusion of the specific deformation mechanisms in the two temperature regimes.

The structural evolution of dunite and chromite ore from the Kharcheruz Massif, the Polar Urals

The Kharcheruz block of the Syumkeu ultramafic massif is a southern fragment of the Khadata ophiolitic belt, which closes the ophiolites of the Polar Urals in the north. The block, striking in the latitudinal direction, is sheetlike in shape and primarily composed of dunite with nearly latitudinal zones of chromite mineralization. The dunites are subject to ductile deformation various in intensity, and this variability is displayed in their heterogeneous structure and texture. The following microstructural types are distinguished by the variety and intensity of their deformation: protogranular → mesogranular → porphyroclastic → porphyrolath → mosaic. The petrostructural patterns of olivines pertaining to the above types reflect conditions of ductile deformation. Protogranular dunite is formed as a product of pyroxene decomposition in mantle harzburgite accompanied by annealing recrystallization at a temperature above 1000°C. Mesogranular dunite is formed as a product of high-temperature plastic flow by means of translation sliding in olivine and diffuse creep at a temperature dropping from 1000 to 650°C and at a low rate ( 10–6 s–1). Dunite is deformed by means of syntectonic recrystallization and subordinate translation gliding. Linear zones of disseminated mineralization undergo destruction thereby, with the formation of lenticular chromitite bodies from which ductile olivine is squeezed out with the formation of densely impregnated and massive ores.

Effect of pre-existing crystallographic preferred orientation on the rheology of Carrara marble

Localized deformation during high temperature plastic flow is frequently attributed to mechanical weakening caused by grain size reduction and, in some cases, by the development of a crystallographic preferred orientation (CPO). This study aims to investigate experimentally the contribution of CPO development to the strain weakening seen in Carrara marble samples during large strain torsion experiments at temperatures in the range 600–800 °C at constant strain rate and confining pressure. The starting material shows little or no CPO. Samples were treated in three steps. First, they were deformed to achieve a well-developed CPO and recrystallized to a finer grain size. Second, the samples were annealed at 727 °C for 5 h to grow the grains to approximately their original size and shape while maintaining a reasonably strong CPO. Finally, the samples were deformed again, under the same conditions as the first step. Re-deformed samples showed a strain weakening lower than during the first step. We infer that this strength difference is caused primarily by the CPO developed during the first deformation event. This implies that CPO development is an important process that contributes to strain weakening during flow of Carrara marble and likely of other rock types as well.

연속주조 압출 ZK60A 합금의 고온 기계적 특성

Abstract Continuous casting is a process where molten metal is solidified into a semi-finished billet on a large scale with either a rectangular or round cross section for subsequent processing. The use of continuous casting provides an opportunity for producing material on a practical industrial scale with lower cost than conventional casting. In the current study, the material was fabricated by continuous casting and subsequent extrusion. Tensile tests were conducted on continuous cast ZK60A after extrusion over a range of strain rates at temperatures from 473K to 623K. The alloy exhibits a quasi-superplastic behavior with a maximum recorded elongation of ~250% at 523K when tested with an initial strain rate of 10 -5 /s. The experiments give a strain rate sensitivity exponent of 0.3~0.4 and an activation energy of 108 kJ/mol. From the current investigation, it was found that the high-temperature plastic flow of the ZK60A is controlled by a dislocation viscous glide mechanism.

Grain Boundary Nanostructure and High Temperature Plastic Flow in Polycrystalline Oxide Ceramics

High temperature creep and superplastic flow in high-purity, polycrystalline oxide ceramics is very sensitive to a small amount of doping by various oxides. The doping effect is attributed to change in grain boundary diffusivity owing to grain boundary segregation of the doped cations. The doping effect on the grain boundary diffusivity is caused mainly by change of chemical bonding state in the vicinity of the grain boundary segregated with the doped cations. In other words, controlling of grain boundary nanostructure based on the doping process will be a useful way to develop new high-performance functional ceramics in the near future.

Structure of melt flow channels in the mantle

Structural events during the formation of the mantle peridotite section in the Voikar-Syn’ya massif of the Polar Urals are considered. The structural units of the mantle section were formed during several deformation stages. Dunite bodies in restitic peridotites were formed in the course of deformation that completed the formation of large-scale folds of high-temperature plastic flow of mantle material. The final stage of deformation accompanied by migration of melt through harzburgite occurred in the shallow mantle in the setting of suprasubduction spreading related to the ascent of a mantle diapir. The rate of plastic deformation was relatively low. As a result, the intracrystal translation gliding of dislocations in olivine was the main mechanism in both harzburgite and dunite. The paths of focused melt flow are marked by dunite veins and associated pyroxenite and chromitite. It is suggested that stress concentration in fold hinges and their abrupt relaxation with formation of orthogonal network of weakened zones with high permeability was one of the possible mechanisms of the formation of melt conduits. The dispersed melt ascending from a great depth spontaneously migrated toward these zones. The distribution and structure of chromitite bodies reflect multistage formation of dunite, nonstationary dynamics of melt flow through restite, and abrupt variations of local stress fields in the areas adjacent to melt conduits.

Effect of Crystallization on High-Temperature Plastic Flow and Ductility in Pre-Annealed Zr-Al-Ni-Cu Bulk Metallic Glass

High-temperature plastic flow and tensile ductility in pre-annealed Zr65Al10Ni10Cu15 bulk metallic glass are examined in a supercooled liquid region. The specimen annealed at 673K for 1.8ks before the tensile test exhibits uniform deformation, and large elongation of 1100% is obtained in the tensile test at 673K and in a constant true strain rate of 1×10-2s-1. In the specimen, initial stress decreases in comparison with that of the specimen without annealing, but apparent strain hardening arise during deformation. SEM analysis after the deformation reveals that the cavitation is very limited even at the fracture tip. XRD and TEM analyses reveal that icosahedral phase is observed only in gage section but not in grip section after the deformation. The limited cavitation due to the accommodation of stress concentration through the grain boundary amorphous phase possibly makes a positive contribution to the large elongation in the annealed specimen, as well as the neck stability due to the strain hardening by the interaction between the icosahedral phase particles increasingly crystallized by the local strain.

カチオン複合添加 TZP の高温変形と添加量依存性

カチオン複合添加 TZP の高温変形と添加量依存性

正方晶 ZrO<sub>2</sub> 多結晶体の高温変形における TiO<sub>2</sub> 及び GeO<sub>2</sub> 添加量依存性

The doping dependence of high temperature plastic flow behavior in TiO2-doped, GeO2-doped and TiO2 and GeO2 co-doped tetragonal ZrO2 polycrystal (TZP) was systematically examined at 1400°C in air under an initial strain rate of 1.3×10-4 s-1. The amount of dopant cations was in the range of 0.2-4 mol%. The flow stress in the TZP decreases with the increasing doping amount in TiO2 and/or GeO2-doped TZP, but levels off over a 3 mol% addition in the GeO2-doped and TiO2-GeO2 co-doped TZP. The doping dependence of the flow stress in the TiO2-GeO2 co-doped TZP is close to that in the GeO2-doped TZP rather than to that in the TiO2-doped TZP; the flow stress in the GeO2-doped and TiO2-GeO2 co-doped TZP is significantly lower than that in the TiO2-doped TZP. The doped cations tend to segregate in the vicinity of the grain boundaries in TZP. The doping dependence of the flow stress is probably related to the amount of the grain boundary segregation of the dopant cations; the grain boundary segregation of the dopant cations is supposed to enhance the grain boundary atomic diffusion in the TZP, and hence the flow stress consequently decreases. On the other hand, elongation to failure in the TZP is highly improved by the TiO2 and/or GeO2 doping. The improved high temperature ductility of the TZP is attributed to the flow stress reduction due to the TiO2 and/or GeO2 doping.

608 Zr-Al-Ni-Cu基金属ガラスの高温変形挙動に及ぼす結晶化の影響(OS-4 機械的性質)

608 Zr-Al-Ni-Cu基金属ガラスの高温変形挙動に及ぼす結晶化の影響(OS-4 機械的性質)

High temperature plastic flow and grain boundary chemistry in oxide ceramics

High temperature plastic flow or grain boundary failure in oxide ceramics such as Al2O3 and tetragonal ZrO2 polycrystal (TZP) is sensitive to small levels of doping by various cations. For example, high temperature creep deformation in fine-grained, polycrystalline Al2O3 is highly suppressed by 0.1 mol% lanthanoid oxide or ZrO2-doping. An elongation to failure in superplastic TZP is improved by 0.2–3 mol% GeO2-doping. A high-resolution transmission electron microscopy (HRTEM) observation and an energy-dispersive X-ray spectroscopy (EDS) analysis revealed that the dopant cations tend to segregate along the grain boundaries in Al2O3 and TZP. The dopant effect is attributed to change in the grain boundary diffusivity due to the grain boundary segregation of the dopant cations. A molecular orbital calculation suggests that ionicity is one of the most important parameters to determine the high temperature flow stress, and probably, the grain boundary diffusivity in the oxide ceramics.

The magnetic anisotropy of mantle peridotites: Example from the Twin Sisters dunite, Washington

The Twin Sisters dunite massif, Washington State, provides unweathered peridotites for magnetic analysis. These rocks have been chosen to test a new magnetic fabric based on measuring the anisotropy of magnetic susceptibility (AMS) in high-field with a vibrating sample magnetometer. Although the dunites are fresh, they host small quantities of secondary magnetite formed along cracks. Under low-field conditions magnetite masks the magnetic fabric of olivine, and thus the magnetic fabric does not reflect mantle flow deformation. Above the magnetic saturation, at a field of 1 T, the ferrimagnetic component is removed and the high-field slope represents the paramagnetic AMS only. This high-field AMS originates from the magnetocrystalline anisotropy of olivine. The high-field AMS are compared with lattice preferred orientation (LPO) fabric data obtained by electron backscatter diffraction. LPO point distributions are formed by high-temperature plastic flow, and match the high-field measurements. In contrast, girdle LPOs present notable departures from the high-field AMS axes.

Dopant effect on high-temperature plastic flow behavior and grain boundary chemistry in oxide ceramics

The grain boundaries in high-purity oxide ceramics, such as Al 2 O 3 and TZP, are often free from glass phase, and the high-temperature plastic flow or grain boundary failure is sensitive to small levels of doping by various cations. For example, the high-temperature creep strain rate in fine-grained, polycrystalline Al 2 O 3 is highly retarded by 0.1 mol% Lu 3 + or Zr 4 + -doping. The elongation to failure in superplastic TZP is improved by 0.2 - 3 mol% Ge 4 + -doping. Such a dopant effect is attributed to changes of the grain boundary diffusion due to the segregation of dopant cation along the grain boundaries. Quantitative analysis on the atomic structure and chemical bonding state along the grain boundaries by high-resolution electron microscopy, energy-dispersive X-ray spectroscopy, electron energy-loss spectroscopy and molecular orbital calculations will provide theoretical guiding principles to design high-performance oxide ceramics in the near future.

High-Temperature Plastic Flow in Pre-Annealed Zr-Al-Ni-Cu Bulk Metallic Glass in a Supercooled Liquid Region

High-temperature plastic flow in pre-annealed Zr65Al10Ni10Cu15 bulk metallic glass is examined in a supercooled region, in order to clarify the effect of the change in microstructure on high-temperature plastic flow. The specimen without annealing exhibits significant necking, but the elongation of 550% is obtained in the tensile test at 673 K and in a constant true strain rate of 1 � 10 � 2 s � 1 . In contrast, the specimen annealed at 673 K for 1.8 ks before the tensile test exhibits uniform deformation, and large tensile ductility of 1100% is obtained. In the specimen, initial stress decreases in comparison with that of the specimen without annealing, but apparent strain hardening arise during deformation. XRD analysis reveals that no crystalline phase is detected in the specimen without annealing even after deformation. In contrast in the specimen annealed at 673 K for 1.8 ks, the peaks from icosahedral phase are observed only in gage section but not in grip section after deformation. Strain hardening due to the precipitation and growth of icosahedral phase, which is enhanced by deformation, must make a positive contribution to neck stability, and results in the large elongation in the annealed specimen.

High temperature plastic deformation related to grain boundary chemistry in cation-doped alumina

Abstract High temperature plastic deformation in fine-grained, polycrystalline alumina often takes place by diffusional creep or grain boundary sliding in a fairly wide stress and temperature range. Under such conditions, the high temperature creep or plastic flow behavior in alumina is sensitively affected by small amount of cation-doping, even in the dopant level of 0.1 mol% or less. The dopant effect on the plastic deformation in alumina results from a change in chemical bonding state at the grain boundaries due to the dopant cations’ segregation along the grain boundaries. Grain boundary chemistry dominantly affects matter transport phenomena in the grain boundaries and the high temperature mechanical property in alumina.