Static Annealing Research Articles

Micro structure and texture evolution during super plastic deformation of Mg–Re extruded alloy

Microstructure and texture evolution during super plastic deformation of Mg–Gd–Y–Zr extruded rods were investigated in the study. For the purposes, the tensile tests under super plastic deformation condition were conducted at different strain levels. The static annealing tests were performed to reveal the micro structural evolution only influenced by thermal load. Grain structure analysis proves that initial grain refinement during the preheating stage is driven by store energy inherited from extrusion deformation. Microstructure and texture analysis suggests that deformation mechanisms are initial grain boundary sliding and subsequent slip creep. Moreover, the β phases (Mg5 (Gd, Y)) on (sub) grain boundaries hinder grain boundary sliding and continuous dynamic recrystallization. Macro-texture evolution shows that texture components varied according to the transition of deformation mechanisms. Micro-texture measurement using EBSD proves that β phase has undergone severe deformation before elongation-to-failure.

XRD study of intercalation in statically annealed composites of ethylene copolymers and organically modified montmorillonites. 1. Two-tailed organoclays

Ethylene copolymers with different polar comonomers, such as vinyl acetate, methyl acrylate, glycidyl methacrylate, and maleic anhydride, have been used to prepare polymer/clay nanocomposites by static annealing of their mechanical mixtures with different organoclays containing two long alkyl tails. The nanostructure of the products and the dispersion of the silicate particles have been monitored by X-ray diffraction and microscopic analyses. The effect of the preparation conditions has also been addressed through the characterization of selected samples with similar composition prepared by melt compounding or solution blending. The results show that intercalation of the copolymer chains occurs rapidly within the galleries of most of the investigated organoclays, independent of whether shear stress is applied to the molten mixtures. Solution blending, though leading to effective and uniform dispersion of clay primary particles within the polymer bulk, resulted unable, without subsequent thermal treatments, to lead to intercalation. However, the micron-sized polymer/clay mixtures prepared from solution change even more rapidly into intercalated nanocomposites upon static melting. Most of the polymer/organoclay couples gave thermodynamically stable intercalated/exfoliated structures. Nevertheless, the highest levels of exfoliation, together with excellent dispersion of the clay particles, have been obtained for the nanocomposites prepared by melt compounding from polymer–clay couples with optimal match of polar characteristics.

Development of Microstructure and Texture Heterogeneities during Static Annealing of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si Alloy Preformed by Hot Working

The effect of annealing temperature on the development of microstructure and texture in an α+β titanium alloy Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) preformed by hot working was investigated with the aid of electron back-scattered diffraction and X-ray diffraction measurements. It is shown that considerable microstructure and texture heterogeneities were developed in the cross-section of the hot-worked rod due to the non-uniform deformation. Subsequent annealing at 940 °C and 990 °C led to homogeneous microstructures with globular α grains, whereas a typical lamellar α+β microstructure was obtained after annealing at 1040 °C. In the latter case, the Burgers orientation relationship was well preserved between the two phases in a single colony. The α lamellar within a given colony depicted similar crystallographic orientations and the boundary α grains shared the orientation of one of the neighboring α lamellar. In contrast, subsequent annealing had very limited effect on the main features of the textures, indicating strong inheritance of the texture heterogeneity in annealing. It is thus crucial to control the hot working process in order to achieve a high level of texture homogeneity in the final parts.

Ti-6Al-4V Recycled from Machining Chips by Equal Channel Angular Pressing

Ti-6Al-4V machining chips have been recycled into fully dense material by a solid-state process based on equal channel angular pressing (ECAP). The as-recycled material possessed a refined microstructure and contained a series of oxide layers associated with the boundary of each machining chip. The chip boundaries were observed to dissolve into interstitial solid solution following static annealing. A series of static heat treatments within the temperature range 700 to 1000°C, for durations of between 1 and 20 hours, were performed. The effect of thermomechanical processing on microstructure and mechanical properties is discussed and compared to the as-recycled and commercially available materials.

Plastic deformation and development of antigorite crystal preferred orientation in high-pressure serpentinites

We have inferred the deformation mechanisms of antigorite by high-resolution EBSD mapping of samples from Cerro del Almirez ultramafic massif (Betic Cordillera, SE Spain). Textural relations and phase diagram calculations constrain the foliation development conditions to the subduction prograde path at up to 600–630°C and 1.6–1.9GPa. Deformation was followed by static annealing of antigorite at ca. 680°C. The Crystal Preferred Orientation (CPO) of antigorite is characterised by a strong alignment of (001) poles normal to the foliation plane and a weaker, but clear, parallelism between [100] axes and the macroscopic lineation defined by the elongation of magnetite aggregates. Analysis of misorientations across subgrains shows predominance of [010] rotation axis, consistent with activation of the [100](001) slip system. However, tilt subgrain boundaries subparallel to (100), probably formed by edge dislocations of this system, are subsidiary. Most subgrain boundaries are subparallel to (001) planes. They are interpreted as (001) twins wherein continuing viscoplastic deformation resulted in a slight increase of the misorientation between the twins. Modelling of the evolution of the antigorite CPO using a lower bound approach and considering different deformation regimes and sets of basal and non-basal slip systems has shown that intensities of [100] and [010] maxima reflect the relative strength of the antigorite [100](001) and [010](001) systems. Activation of other basal or non-basal slip systems does not change significantly the CPO patterns, but results in less concentrated CPO. 3D transpression models better reproduce the CPO of natural antigorite serpentinites. We propose that the widespread occurrence of strong CPO in high-pressure antigorite serpentinite is consistent with deformation by dislocation creep with dominant glide on [hk0](001), together with the activation of twinning, implying that a power law rheology would better account for the mechanical behaviour of antigorite serpentinite deep in the subduction channel and mantle wedge.

Microstructural stability of ultrafine-grained niobium–zirconium alloy at elevated temperatures

The present study reports on microstructural evolution upon static annealing treatment and elevated-temperature low-cycle fatigue (LCF) of an ultrafine-grained (UFG) body-centered cubic (bcc) niobium–zirconium (NbZr) alloy, processed by equal channel angular processing (ECAP) at room temperature.UFG NbZr showed recovery and recrystallization at homologous temperatures, which are in the same range as those of another UFG bcc material, i.e. interstitial free (IF) steel. Unlike the UFG IF steel, the UFG NbZr featured a distinct plateau of decreased hardness due to recovery at temperatures below the recrystallization limit. This was attributed to the absence of dynamic recovery during ECAP due to the low homologous temperature of Th=0.11 (Th=0.16 for IF steel) at room temperature processing.Strain-controlled elevated-temperature LCF tests performed in vacuum revealed stable cyclic deformation response up to 600°C (Th=0.32). At higher temperatures, but still below the static recrystallization limit (≈900°C, Th=0.43), cyclic softening, rapid decrease of mean stress and premature failure were observed. As compared to the UFG IF steel, cyclic stability is preserved up to higher Th due to the stabilizing effect of solid solution alloying elements, i.e. mainly Zr.In the case of the UFG IF steel, localized grain coarsening at the crack tip caused premature failure upon elevated-temperature LCF below the static recrystallization temperature. The more stable microstructure in the UFG NbZr did not show any localized alterations in the vicinity of the crack tip, but instead slightly coarsened throughout the whole gauge length.In combination with the results obtained on the UFG IF steel in previous studies, a comprehensive summary of the microstructural evolution of UFG bcc materials at elevated temperatures is presented.

An experimental investigation of the interactions between reaction-driven and stress-driven melt segregation: 2. Disaggregation at high melt fraction

To investigate the coupling between stress-driven melt segregation and reaction-driven melt infiltration, we performed static annealing and torsional deformation experiments on couples constructed from a melt-rich basaltic source and melt-poor olivine + orthopyroxene + chromite + basalt sink. In this study (the second of two companion papers), the melt source is almost completely molten with ϕ = 0.8–0.9, well above the rheologically critical melt fraction. We deformed two geometries of source/sink couples with the source either as the core or the outer ring of a cylinder. Our experiments demonstrate (1) that deformation significantly enhances the rate of melt infiltration from the source into the sink and (2) that combined reaction and deformation promote greater strain localization than does deformation alone. Deformation and melt infiltration enhance disaggregation at the interface of the source and sink. The implication of these coupled interactions is that deformation and melt-rock reaction may enhance the corrosion (or ‘stoping’) rates of the wall rocks of magma chambers and intrusions in the crust and upper mantle.

Effect of viscosity in ternary polymer blends displaying partial wetting phenomena

Partial wetting in a ternary polymer blend is the thermodynamic state where all three phases meet at a three-phase line of contact. Pickering emulsions, where solid particles situate at the interface of two other phases is a classic example of this state. This paper studies the presence of partial wetting in PE/PP/PS and in PE/PP/PC ternary polymer blends and examines, in particular, the influence of polyethylene viscosity on PS droplet formation at the PE/PP interface. Quantitative analysis of PS droplet growth and coverage at the PE/PP interface during static annealing were obtained by image analysis. A new approach was established to estimate the co-continuous PE/PP coarsening rate and was found to be in agreement with previous studies. In this work it is shown that the polyethylene viscosity can be of significant importance in ternary partial wetting when the interfacial driving force for partial wetting is weak and viscosity directly affects the quantity and size of PS droplets at the interface during annealing. The equilibrium between droplet stability at the interface, as predicted by spreading theory, and the interfacial mobility generated by coarsening determines the PS droplet size and surface coverage at the PE/PP interface. A ternary PE/PP/PC system, which displays a strong partial wetting driving force, was also investigated. The morphology of the blend system studied demonstrated a clear dominance of partial wetting over complete wetting.

Late Cretaceous extensional denudation along a marble detachment fault zone in the Kırşehir massif near Kaman, central Turkey

In the Central Anatolian Crystalline Complex (CACC), 100 km scale metamorphic domains were exhumed in a context of north-south plate convergence during late Cretaceous to Cenozoic times. The timing, kinematics and mechanisms of exhumation have been the focus of previous studies in the southern Niğde Massif. In this study, we investigate the unexplored northern area regarding the tectonic features preserved on the edges of the Kırşehir Massif, based on detailed field-mapping in the Kaman area where high-grade metasediments, non-metamorphic ophiolites and monzonitic plutons are locally exposed together. Close to the contact with the ophiolites, west-dipping foliated marble-rich rocks display mylonites and discrete protomylonites with normal shear senses indicating a general top-to-the W–NW direction. Both of these structures have been brittlely overprinted into cataclastic corridors parallel to the main foliation. The mylonite series and superimposed brittle structures together define the Kaman fault zone. The study of the evolution of calcite deformation fabrics along an EW section supported by Electron Back Scattered Diffraction measurements (EBSD) on representative fabrics indicates that the Kaman fault zone represents an extensional detachment. In Ömerhacılı, in the vicinity of the Baranadağ quartz-monzonite, the metamorphic sequence shows static annealing of the calcite mylonitic fabrics. This evidence suggests that intrusion took place at shallow depth (∼10 km) into an already exhuming metamorphic sequence. As a consequence for the Kaman area, buried metasediments have been rapidly exhumed between 84 and 74 Ma (∼1 km/Ma) where exhumation along a detachment zone, displaying a top-to-the W–NW shear motion, took place in the mid to upper crust prior to magmatic intrusion in the late Campanian. As the intrusion cut through the detachment fault, the main shearing deformation ceased. Brittle tectonics coupled with erosion likely took over during the final unroofing stages at a slower rate (<0.2 km/Ma), until the pertinent rocks reached the Earth’s surface in the late Paleocene.

An experimental study of the effects of surface tension in homogenizing perturbations in melt fraction

Static annealing experiments were conducted on fine-grained samples of a partially molten, olivine-rich rock to explore the role of interfacial tension driven flow in redistributing melt within the sample. A sample of fine-grained olivine + 20% chromite was prepared with an initially homogeneously distributed melt fraction of 0.04. When this sample was deformed in torsion, the melt segregated into distinct melt-rich bands uniformly spaced throughout the sample, as demonstrated in prior studies. Portions of this sample were then statically annealed for different lengths of time to observe the homogenization of the melt distribution. The evolution of the melt distribution in experimental samples was compared to numerical models based on formulations for interfacial tension driven flow that do or do not incorporate the effects of dissolution/precipitation coupled with diffusive mass transfer of components of the solid phase through the liquid phase (dissolution/diffusion/precipitation). The results indicate that, at the grain size and perturbation length scales in these samples, dissolution/diffusion/precipitation in response to the chemical potential gradient arising from the curvature of solid–liquid phase boundaries at triple junctions plays a significant role in accommodating interfacial tension driven flow. These experiments provide a valuable test for theory and allow us to place constraints on the homogenization rate of perturbations in melt fraction in rocks with a relatively simple composition. The results contribute to increasing our understanding of the nature of melt-rich, high-permeability pathways that may facilitate melt extraction from the upper mantle.

Synthesis of cordierite by crystallization from MgO–Al2O3–SiO2 tempered glass

Physicochemical research is conducted to examine the phase formation under dynamic and static annealing of MgO–Al 2 O 3 –SiO 2 tempered glass (composition range adjacent to stoichiometric cordierite). Thirty glass compositions are examined in this system and the range is determined over which single-phase ceramic materials with the lowest possible thermal expansion coefficient are synthesized under specific crystallization conditions.

An electrochemical analysis of AZ91 Mg alloy processed by plasma electrolytic oxidation followed by static annealing

In this study, the effect of subsequent annealing on the electrochemical response of AZ91 Mg alloy coated via plasma electrolytic oxidation (PEO) was investigated. PEO coating was carried out on the Mg alloy under AC condition in an alkaline silicate electrolyte, and the PEO-coated samples underwent several subsequent annealing treatments at three different temperatures of 100, 150, and 200 °C. The surface morphologies of the coating layers were observed via a scanning electron microscope (SEM) and their constituent compounds were characterized by qualitative observation based on X-ray photoelectron spectroscopy (XPS). In addition, the corrosion protection properties of the PEO-coated sample were examined by electrochemical impedance spectroscopy (EIS) in a 3.5 wt% NaCl solution with a focus on exploring the effect of subsequent annealing on the electrochemical response in a quantitative manner. SEM and XPS observations evidenced that the subsequent annealing at temperatures higher than 150 °C resulted in significant morphological changes due to the dehydration reaction of Mg(OH) 2 to form MgO. Thus, it was found that the sample annealed at 150 °C exhibited a better corrosion resistance than the other samples, which were analyzed by taking an equivalent circuit model into account.

Natural annealing of dynamically recrystallised quartzite fabrics: Example from the Cévennes, SE French Massif Central

Quartzite samples from the SW-Cévennes (French Massif Central) have been investigated in order to reveal the effects of annealing on a previously dynamically recrystallised quartz fabric. The studied quartzite is interlayered with turbiditic micaschist series, and after regional deformation the whole sequence was intruded by the St-Guiral granodiorite at 1–3 kbar and up to 650–700 °C. Recorded crystallographic preferred orientation (CPO) patterns of the dynamically recrystallised quartzite are classified as type I with a monoclinic symmetry and type II with an orthorhombic symmetry. Type I is related to simple shear-dominated deformation and type II to apparent constriction. These two fabric types are consistent with structural observation that a constrictive and coaxial deformation regime controlled the formation of non-cylindrical and refolded folds. In the metamorphic aureole, which produced essentially static annealing, CPO patterns intensify slightly and grain size increases towards the granodiorite until the temperature at which inversion from low- to high quartz is triggered. This inversion caused a volume increase and subsequent intergranular stresses activated slip systems fitting the temperature and water content. This study shows that annealing of dynamically recrystallised quartz crystals can activate previously inactive slip systems, reactivate slip systems and amplify older CPO fabrics. This conclusion identifies limits for the use of annealed quartz fabrics in reconstructing structural histories when earlier dynamic recrystallisation has occured.

The effect of annealing conditions on the intercalation and exfoliation of layered silicates in polymer nanocomposites

Layered silicate nanocomposites based on polyamide 6 and polypropylene have been prepared via static annealing experiments. The evolution of clay dispersion into the polymer matrices was monitored by wide angle X-ray diffraction analysis and transmission electron microscopy. The results have evidenced that the polymer diffusion inside the organoclay galleries is spontaneous and have elucidated the mechanism of nanostructured system formation under static conditions. Indeed, the exfoliation mechanism turned to be a two-step process consisting of polymer intercalation into the clay galleries and progressive layer delamination. Both steps have turned out to depend on thermodynamic and kinetic parameters. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Characterization of HDPE-g-MA/clay nanocomposites prepared by different preparation procedures: Effect of the filler dimension on crystallization, microhardness and flammability

Nanocomposites of maleic anhydride-grafted HDPE (HDMA) and the organoclay Cloisite 20A (20A) have been prepared by melt-compounding, solution-blending and static annealing of polymer/clay powder mixtures. It has been shown that solution-blending of HDMA with 20A fails to produce intercalated composites. Fast intercalation was observed when solution-blending HDMA/clay composites were annealed. The nanocomposites prepared in the melt under shear were found to possess high levels of exfoliation. The dependence of the crystallization behaviour, microhardness and flammability of the composites on the preparation conditions has been studied by differential scanning calorimetry, microhardness tests and determination of limiting oxygen index. The results have shown that the reduction of the flammability and the microhardness of HDMA/20A nanocomposites prepared by melt compounding and composite annealing are higher than those for composites prepared by solution blending. Moreover, a nucleation effect of the clay on the polymer matrix crystallization for some samples has been observed. The results have been interpreted by different levels of clay dispersion and degree of clay intercalation/exfoliation, achieved during different preparation procedures.

Quantitative three-dimensional characterization of pearlite spheroidization

We investigated the pearlite spheroidization of a 0.8 mass% C–Fe steel under 700 °C static annealing conditions using a combination of computer-aided three-dimensional (3-D) tomography and electron back-scattered diffraction. The holes present in naturally grown cementite lamellae cause shape instability and induce shape evolution of the lamellar structure during spheroidization. 3-D visualization demonstrated that the intrinsic holes play an important role in the initiation and development of pearlite spheroidization. The hole coalescence and expansion causes the break-up up of large cementite lamellae into several long narrow ribbons. Furthermore, the growth mechanism of inter-hole coalescence is related to the ratio of half the inter-hole distance on a cementite lamella to the thickness of that lamella. The driving force for hole growth is either the difference in surface energy or the curvature between the hole edges and the adjacent flat surface of the lamella. The morphologies of cementite ribbons depend on the hole expansion position on cementite lamella, and can change their shape to cylinders or small spheres by Rayleigh’s perturbation process after prolonged spheroidization.

Superplastic deformation mechanism of an ultrafine-grained aluminum alloy produced by friction stir processing

An ultrafine-grained (UFG) Al–4Mg–1Zr alloy with a grain size of ∼0.7 μm with predominantly high-angle boundaries of 97% was produced by friction stir processing (FSP). The UFG Al–4Mg–1Zr retained submicrometer grains even after static annealing at 425 °C, and exhibited excellent superplasticity at 175–425 °C. High strain rate and low-temperature superplasticity of >1200% were observed at 1 × 10 −2–1 × 10 −1 s −1 and 300–350 °C. Even at 425 °C, a superplasticity of 1400% was achieved at 1 s −1. A linear relationship between log ε ˙ opti and T was observed (where ε ˙ opti is the optimum strain rate, and T is the temperature). The analyses on the superplastic data revealed the presence of threshold stress, a stress exponent of 2, an inverse grain size dependence of 2, and an activation energy of 142 kJ mol –1. This indicated that the dominant deformation mechanism was grain boundary sliding, which was controlled by lattice diffusion. Based on this notion, a constitutive equation has been developed. A new superplastic deformation mechanism map for FSP aluminum alloys is proposed.

Heterogeneous enthalpy relaxation in glasses far from equilibrium

We report two fundamental modifications to the Tool–Narayanaswamy–Moynihan (TNM) model on enthalpy relaxation in glasses. Firstly, a generalized stretching function is introduced for the distribution of relaxation times. Secondly, the substantial broadening of the glass transition region due to the hyperquenching process is included. Using the modified model, we have succeeded in accurately modeling the enthalpy response of glasses far from equilibrium to both dynamic heating and static annealing.

Abnormal Grain Growth and Recrystallization in Al-Mg Alloy AA5182 Following Hot Deformation

Abnormally large grains have been observed in Al-Mg alloy AA5182 sheet material after forming at elevated temperature, and the reduced yield strength that results is a practical problem for commercial hot-forming operations. The process by which abnormal grains are produced is investigated through controlled hot tensile testing to reproduce the microstructures of interest. Abnormal grains are shown to develop strictly during static annealing or cooling following hot deformation; the formation of abnormal grains is suppressed during plastic straining. Abnormal grains grow by static abnormal grain growth (SAGG), which becomes a discontinuous recrystallization process when abnormal grains meet to form a fully recrystallized microstructure. Nuclei, which grow under SAGG, are produced during hot deformation by the geometric dynamic recrystallization (GDRX) process. The mechanism through which a normally continuous recrystallization process, GDRX, may be interrupted by a discontinuous process, SAGG, is discussed.

The improvement of strength and ductility in ultra-fine grained 5052 Al alloy by cryogenic- and warm-rolling

The effects of deformation temperatures and post-deformation annealing on mechanical properties, in conjunction with microstructural evolution in the 5052 Al alloy, were investigated. The combination of cryogenic-rolling with warm-rolling effectively increased tensile strength and yield strength without the decrease of ductility through the formation of ultra-fine grains with dynamic recovery in the 5052 Al alloy. And static annealing, as a post-heat treatment, enhanced the ductility. Therefore, ultra-fine grained 5052 Al alloy with high strength and a moderate level of ductility could be made by the combination of cryogenic-rolling with warm-rolling and the additional static annealing process.