Subsequent Recrystallization Research Articles

Influence of Wavy Bending on Microstructure and Mechanical Properties of a Rolled AZ31 Sheet

In the present work, cross-wavy bending at room temperature was carried out to tailor the microstructure and stretch formability of rolled AZ31 sheets. Wavy bending processing generates profuse {10–12} twins and a tilt basal texture. Subsequent recrystallization annealing causes grain coarsening and enhances the intensity of twin-orientation. The combined use of wavy bending and annealing can maintain high tensile ductility and remarkably enhances the stretch formability of rolled AZ31 sheet. It can be mainly attributed to the non-basal texture in the wavy bent sheet which increases the thinning capability during in-plane tension.

Formation of Hollow Gold Nanocrystals by Nanosecond Laser Irradiation

The irradiation of spherical gold nanoparticles (AuNPs) with nanosecond laser pulses induces shape transformations yielding nanocrystals with an inner cavity. The concentration of the stabilizing surfactant, the use of moderate pulse fluences, and the size of the irradiated AuNPs determine the efficiency of the process and the nature of the void. Hollow nanocrystals are obtained when molecules from the surrounding medium (e.g., water and organic matter derived from the surfactant) are trapped during laser pulse irradiation. These experimental observations suggest the existence of a subtle balance between the heating and cooling processes experienced by the nanocrystals, which induce their expansion and subsequent recrystallization keeping exogenous matter inside. The described approach provides valuable insight into the mechanism of interaction of a pulsed nanosecond laser with AuNPs, along with interesting prospects for the development of hollow plasmonic nanoparticles with potential applications related to gas and liquid storage at the nanoscale.

Insight into picosecond kinetics of insulator surface under ionizing radiation

We found experimentally and theoretically that MgO, CaF2, and Y3Al5O12 (YAG) irradiated with fast ions demonstrate a noticeably different surface response. Striking differences follow from the kinetics of nanodroplets ejection. Protrusion of the hot materials and subsequent recrystallization in MgO and CaF2 recover transient damage in the surface region, forming a spherically shaped nanohillock. YAG demonstrated almost no recovery of the transient disorder, forming an amorphous hillock. These differences are attributed to complex interplay between the mobilities of atoms in the hot region and surface tensions.

ОСОБЕННОСТИ ФОРМИРОВАНИЯ ЗОН ЛОКАЛИЗОВАННОЙ ДЕФОРМАЦИИ ПРИ ГОРЯЧЕЙ ОСАДКЕ СПЛАВА ВТИ-4 И ПОСЛЕДУЮЩЕМ ОТЖИГЕ

Textural and macrostructural changes in the intermetallic titanium alloy VTI-4 based on the orthorhombic phase (Ti2AlNb) during hot high-rate compression and subsequent recrystallization annealing where studied. The main attention is paid to the formation features of localized deformation bands (LDB) in the central zone of the compressed sample, which are one of the signs of unstable and nonuniform deformation. It is shown that recrystallization annealing after hot compression does not eliminate the LDB and the compression texture. Reasons for this behavior of the material are studied applying the analysis of the solid solution state.

Redistribution of germanium during dynamic recrystallization of sphalerite

Abstract Rare metals are essential to the development of the “green” technologies that are at the core of low-carbon societies. In nature, these metals are frequently present in trace amounts scattered in base metal ore deposits, but the physico-chemical processes that are responsible for their concentration into strategic minerals are still poorly understood. Based on laser-induced breakdown spectroscopy (LIBS), coupled with electron backscattered diffraction (EBSD) analysis, this study shows that plastic deformation and subsequent syntectonic recrystallization of sphalerite (zinc sulfide, ZnS) led to the spatial redistribution of germanium (Ge): from a background level of a few hundreds of parts per million in undeformed primary sphalerite to tens of weight-percent in neocrystallized Ge minerals. During dynamic recrystallization, Ge is likely released from the crystal lattice of parent sphalerite and subsequently concentrated in Ge minerals, leaving behind a Ge-depleted, recrystallized sphalerite matrix. Identifying how rare metals concentrate through deformation and syntectonic recrystallization at the mineral scale is essential to understand the spatial redistribution and localization at the deposit scale. This study highlights the importance of coupling in situ chemical mapping analysis with macro- and microstructural characterization when targeting rare metals in deformed ore.

A Selective Reduction Approach to Construct Robust Cu1.81S Truss Structures for High-Performance Sodium Storage

Summary The practical application of transition metal sulfides as anodes for sodium-ion batteries has long been hindered by the design and fabrication of stable electrodes. Here, inspired by architecture, we design a stable electrode based on Cu1.81S micro-truss structures (MTs) for the first time. The key to this “selective reduction” strategy is to engrave Cu1.75S precursors with a truss structure by using an anti-reduction agent (Fe3+ ions), and a subsequent recrystallization process reinforces the truss structure. The Cu1.81S MTs with high structural stability exhibits a pronounced stability enhancement for 1,000 cycles with 77.7% capacity retention and delivers excellent rate performance of 331 mAh g−1 at 3 A g−1. As a new method for designing robust electrode structures, this synthetic strategy is not limited to the synthesis of truss structures. It provides new insights into a new generation of electrode structures and could be applied to the structural design of other batteries.

Interaction of FeII and Si under anoxic and reducing conditions: Structural characteristics of ferrous silicate co-precipitates

The interaction of FeII and Si is at the heart of many critical geochemical processes in diverse natural and engineered environments. The resulting FeII-silicate phases play important roles in regulating the concentrations and bioavailability of FeII and Si, as well as serve as sinks for trace and hazardous elements. Therefore, a detailed understanding of their structural characteristics and the underlying formation mechanisms may provide insights useful to predicting their reactivity and stability under different conditions. In this work, co-precipitates with different Si/FeII ratios (0.5, 1.0 and 2.0) were synthesized under anoxic and reducing conditions at different solution pH (7, 9 and 11). Thermodynamic calculations from solution chemistry data were carried out and co-precipitates were studied using X-ray diffraction (XRD), infrared (IR) spectroscopy and Fe K-edge extended X-ray absorption fine structure spectroscopy (EXAFS). Thermodynamic calculations predict the formation of phyllosilicate phases such as greenalite in all the samples. Solid characterization data, however, reveal significant structural variabilities and phase heterogeneity. Incipient phyllosilicate structures tend to be more pronounced in samples from pH 9 and 11, while at neutral pH conditions, polymeric silicate phases like amorphous SiO2 become predominant. These variabilities are possibly linked to heterogeneous formation processes arising from relative solubility differences between SiO2 and Fe(OH)2. High pH (>8) conditions favor the polymerization of Fe(OH)2 layers which likely serve as templates for layered silicate formation, while neutral pH conditions favor the precipitation of polymeric silicate phases like amorphous SiO2 to which aqueous Fe species may adsorb. In samples from Si/FeII = 0.5, relatively well developed Fe(OH)2 layers were identified from the EXAFS data. Increasing Si/FeII ratios lead to amorphous SiO2 precipitation and inhibition of Fe(OH)2 polymerization, resulting in smaller phyllosilicate domains embedded in a polymeric SiO2 matrix. The results of this work may be useful in interpreting structural variabilities of FeII-Si phases observed both in nature and in engineered environments. Such variabilities may influence subsequent phase recrystallization processes as well as reactivity towards environmentally relevant elements such as radionuclides.

Pyroxene exsolution microstructures in garnet from the Almklovdalen peridotite, SW Norway

We report the occurrence of oriented pyroxenes in garnets within a garnetite and an orthopyroxenite from the Almklovdalen peridotite body located in the central-western part of the Western Gneiss Region (WGR), SW Norway. The garnetite sample is a non-deformed clot or aggregate that contains optically strongly birefringent purple garnets up to several centimetres in size. The microstructure is defined by millimetre-sized olivine and orthopyroxene grains that partially decorate garnet–garnet grain boundaries, but also occur as inclusions within individual garnets. Additionally, garnet has acicular to lamellar shaped inclusions that are dominantly 40–60 μm thick, up to 600 μm long and seem to have their longest crystal-shape axis oriented in four directions within the garnet host mineral. Individual lamellae are composed of orthopyroxene (dominantly) or clinopyroxene or both. Usually, these early minerals (interstitials, inclusions and host) are severely replaced by kelyphite, amphibole and chlorite. The garnet-orthopyroxenite sample is less altered and shows substantial dynamic recrystallisation. Porphyroclastic orthopyroxenes have abundant chromite and clinopyroxene lamellae while porphyroclastic garnets preserve oriented lamellae of pyroxene that are similar to those of the garnetite sample. These lamellae in cogenetic garnet and pyroxene indicate an origin by exsolution during cooling from temperatures ≥1500 °C at lithospheric mantle depth. Dynamically recrystallised pyroxenes lack oriented inclusions. Garnets of both samples are pyrope-rich (55–79 mol%) and have moderate CaO (4.0–5.7 wt%) and Cr2O3 (0.95–2.90 wt%) contents. Application of classical thermobarometry on the lamellae-bearing mineral assemblages suggests equilibration at metamorphic conditions of circa 2.9 GPa and 730 °C. This P–T estimate is consistent with a cratonic geotherm with 38mWm−2 surface heat flow. In contrast, the dynamically recrystallised mineral assemblage has orthopyroxene with a very low Al2O3 content (0.28 wt%) indicating equilibration at circa 4.1 GPa and 770 °C, i.e. within the stability field of diamond. The microstructures, the chemistry and metamorphic conditions of the minerals in the Almklovdalen garnetite and garnet-orthopyroxenite resemble those of similar rocks with Archaean majoritic garnet precursors that occur in the northwestern part of the WGR. Accordingly, these mantle fragments are interpreted to have been derived from the same depth interval (circa 90-110 km) within the mantle hanging wall of cratonic Laurentia before they have been incorporated into the subducted Baltic crust. Subsequent shared prograde diamond-grade partial recrystallisation implies that the early Scandian tectonic history across the WGR had much more in common than previously recognised. Another implication is that former majoritic garnet was once spatially widespread throughout the E Greenland lithosphere.

Effect of Pre-compression on Microstructure Evolution of AQ80 Magnesium Alloy in Forward Extrusion and Twist Deformation

A magnesium alloy, Mg-8Al-0.5Zn-0.2Ag-0.2Mn (AQ80), was extruded by forward extrusion and twist deformation (FETD) at 370°C with 0% and 6% pre-compression. The effect of pre-compression on microstructure and texture of the AQ80 Mg alloy during FETD was systematically investigated. Compared with the 0% pre-compression FETD-ed sample, the 6% pre-compression FETD-ed sample shows a more uniform and finer microstructure and a weaker texture. The effects of pre-twinning on the microstructure and texture during FETD were also investigated. It was found that many {10–12} tension twins were implanted into the as-cast AQ80 Mg alloy by the 6% pre-compression treatment, providing sufficient nucleation sites for subsequent dynamic recrystallization. Combined with microstructure evolution analysis, it can be concluded that the texture development is strongly influenced by the twinning and basal slip during FETD extrusion.

Early-Transition-Metal Complexes of Functionalized Nonagermanide Clusters: Synthesis and Characterization of [Cp2(MeCN)Ti(η1-Ge9{Si(TMS)3}3)] and K3[Cp2Ti(η1-Ge9{Si(TMS)3}2)2

Anionic clusters with a homoatomic [Ge9] core are species with Ge atoms in low oxidation states. In this study their reaction with early-transition-metal complexes was investigated. We report the syntheses of Ti(III) complexes of silylated [Ge9] Zintl clusters, which are rare examples of molecular complexes with Ge-Ti interactions. The neutral species [Cp2(MeCN)Ti(η1-Ge9{Si(TMS)3}3)] (1) was obtained by the reaction of K[Ge9{Si(TMS)3}3] with [Cp2TiCl]2 in toluene as dark orange crystals, whereas the reaction of K2[Ge9{Si(TMS)3}2] with [Cp2TiCl]2 in thf and subsequent recrystallization from toluene resulted in dark green crystals of K3[Cp2Ti(η1-Ge9{Si(TMS)3}2)2] (2). Compound 2 contains the trianion [Cp2Ti(η1-Ge9{Si(TMS)3}2)2]3- (2a), which can be described either as a [Cp2Ti]+-bridged [Ge9{Si(TMS)3}2]2- dimer or as a heavily distorted tetrahedral Ti(III) complex bearing two germanide cluster ligands. Both compounds display donor-acceptor interactions between single Ge vertex atoms of the [Ge9] clusters and Ti(III). Compounds 1 and 2 were characterized by single-crystal X-ray diffraction, EPR spectroscopy, and elemental analysis.

In-situ LA-ICP-MS and EMP trace element analyses of hematite: Insight into the geochemical signature of the Neoproterozoic Urucum iron formation, Brazil

Hematite hosted in iron formations (IFs) is widely held as a transformation of (bio)chemical precipitates, which may register depositional conditions and sources responsible for the origin of these enigmatic rocks. Consequently, this is an attractive target to mineral-specific geochemical investigations aiming at distinguishing primary signatures from ore-related transformations and terrigenous contamination. This study reports in situ Electron Microprobe (EMP) and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) analyses of hematite grains from the Neoproterozoic Urucum IF, Jacadigo-Boqui Gr. The hematite grains were divided into three main morpho-textural types: (i) anhedral, micro-crystalline hematite (Hm1); (ii) coarser, subhedral to euhedral, microspecular (Hm2) and (iii) microplaty (Hm3) hematite. Factor analysis (FA) was used to trace underlying relationships among the trace elements (TEs). The identified factors were correlated to: (i) substitutions in the hematite structure (F3a, MgO-MnO-Al2O3-TiO2; and F1b, Al-Ti-V); (ii) mineral inclusions (F1a, SiO2; F2a, P2O5-CaO-MgO; and F2b, Mg-Mn-Sr); (iii) hydrogenous and diagenetic incorporation (F3b, Th-Zr-Cu and Ba-REE; F4b, Si-U-Hf). The TE compositions are broadly consistent in all hematite types; this trend suggests limited post-depositional overprinting. Nearly isochemical signatures show that transformation of ferrihydrite to hematite and the subsequent recrystallization of this mineral were dominated by solid-state processes under high Eh. Elements exclusively incorporated in the hematite structure (Al, Ti, V) did not show significant fractionation with increasing recrystallization. Replacement and solution precipitation also occurred, albeit to a lesser extent. The recrystallization of Hm1 to Hm2 and Hm3 was likely controlled by texture and assisted by pressure and fluid circulation. Warm, alkaline, basin brines were also responsible for the dissolution of gangue minerals, particularly chert. Consequently, elements associated with mineral inclusions (Si, P, Ca, Mg, Mn, and Sr) decrease in abundance from Hm1 to Hm2 and Hm3. Ptygmatic quartz veinlets and chert dissolution pods attest to silica leaching and volume reduction leading to hypogene enrichment. Supergene enrichment resulted in ubiquitous secondary porosity, but generally did not affect the composition of the hematite grains. Non-CHARAC Zr/Hf ratios suggest active HFSE fractionation processes. Super-chondritic ratios record basin seawater enriched in Zr as a consequence of the fractionation of Hf onto amorphous silica, registered by sub-chondritic Zr/Hf ratios and a correlation between Si and Hf in factor F4b. Distinctively seawater-like REE pasterns suggest a common precursor hydrogenous phase. Consistent true negative Ce anomalies and generally low Th/U ratios, together with the relatively common occurrence of hematite peloids, suggest that the precursor ferrihydrite particles were deposited and accumulated near the water-sediment interface, in a well-oxygenated shallow water setting. This implies the existence of a discrete chemocline separating the deep ferruginous waters from oxygenated shallow waters.

Study of potential recrystallization nuclei in the cold-rolled microstructure of an electrical steel by electron backscatter diffraction

Strain induced boundary migration (SIBM) is widely recognized to be the main mechanism corresponding to recrystallization in metals of low or medium amount of deformation. The nucleation process in recrystallization of heavily deformed metals is, however, less understood for key issues such as how the nuclei are formed and where they are located. The evolution of texture from deformation to recrystallization cannot thus be explained well. In this study, an attempt was conducted to identify the potential recrystallization nuclei (PRN) in the cold-rolled microstructure of an electrical steel by electron backscatter diffraction (EBSD). This work demonstrates that the SIBM mechanism can be the main mechanism corresponding to recrystallization nucleation in a heavily deformed steel. The same area in both the cold-rolled and partially recrystallized states was analysed using EBSD to obtain the correlation between the recrystallized grains and the cold-rolled substructures. The deformed grains having high stored energy were first selected, followed by identifying substructures surrounded entirely or partly by high angle boundaries in these heavily deformed grains. The deformation induced grains having low intra-granular misorientation of 2° or less exhibit a very similar orientation distribution to that of the recrystallized grains and are proposed to be the PRN in subsequent recrystallization.

Inhomogeneous deformation and recrystallization behavior of through-thickness tantalum sheet under one-cycle clock-rolling

Effects of low clock rolling passes on through-thickness deformation and recrystallization behavior of the Ta sheet have been investigated. The clock-rolled samples with one cycle (8 passes) were systematically examined under different thickness layers. X-ray diffraction (XRD) and X-ray diffraction line profile analysis (XLPA) showed that the extremely inhomogeneous texture evolution generated and the bulk stored energy existed in the through-thickness clock-rolled Ta sheet after 8 passes. The electron backscatter diffraction (EBSD) results revealed the misorientation of the grains in the deformed samples, indicating that grain subdivision in the surface and center layer was more serious than that in the quarter layer. High intensities misorientation indicates the presence of microshear bands in the surface and center layer. During annealing, the difference of the stored energy and the fragmentation of deformation microstructure along the thickness led to a heterogeneous driving force for the nucleation of the grains, resulting in subsequent different recrystallization rate in the different regions of the sample.

Influence of pre-recovery on recrystallization behavior, microstructure and mechanical properties of twin-roll cast AA6016 sheet

Pre-recovery (PR) treatment and the subsequent recrystallization of twin-roll cast (TRC) AA6016 (Al-1.04Si-0.5Mg-0.4Fe-0.16Mn) sheet are performed. The effects of PR on the recrystallization behavior, grain structure and mechanical properties are investigated. Results reveal that the refinement and homogeneity of the recrystallization grain structure first increase and then decrease when the PR temperature (PRT) is increased. This attributes to the fact that the PR enhances the sub-grain coalescence nucleation (SGCN) when PRT reaches 160 °C. As the PRT exceeds 160 °C, the SGCN is prevented by the concurrent precipitation, and the number of nuclei decreases, resulting in a coarse and inhomogeneous grain structure. Additionally, mechanical anisotropy (Δr) of the sheet is weakened by the PR. In particular, the Δr after PR treatment at 160 °C is 0.01, which is significantly smaller than that of the sheet without PR treatment (0.26). The microstructural refinement and high grain structure homogeneity improve the mechanical properties of the TRC AA6016 sheet.

Research of grain size homogeneity effect on sheet stamping ability characteristics of Al2Mg and Al6Mg alloys

The quality of products made of sheet aluminum alloys strongly depends on the technological features of the sheet stamping process, as well as on the structure of sheet semi-finished products. The grain size and grain structure uniformity are among the key structural features that influence stampability. A method is proposed and the homogeneity of the grain structure is evaluated. Stampability of Al2Mg and Al6Mg aluminium alloys was evaluated based on measurements of the spring back index, minimum bending radius, stamping ratio, and Martens strain index. Cold work (with a strain degree of 20 %) and subsequent recrystallization annealing at temperatures of 250, 350 and 450 °C for 1 h were used to obtain a grain structure of (26,8 Ѓ} 7,4)÷(126 Ѓ} 43) μm (Al6Mg alloy) and (120 Ѓ} 11)÷(264 Ѓ} 130) μm (Al2Mg alloy) in size. As a result of processing, the effect of the initial grain size was revealed: the coarser structure of the Al2Mg alloy led to a larger grain size after strain and annealing. It was found that an increase in the grain size in both alloys leads to an increase in the Martens index and a decrease in the stamping ratio, which indicates higher stampability of the alloys in the drawing operations of sheet stamping. In the Al2Mg alloy, an increase in the grain size leads to a decrease in the spring back index by 1,5–1,7 times, and an increase in the minimum bending radius. In the Al6Mg alloy, an increase in the grain size leads to an increase in the spring back index by 1,1–1,2 times, and a decrease in the minimum bending radius. The Al6Mg minimum bending radius remains higher compared to Al2Mg regardless of the grain size. Grain size inhomogeneity in the Al6Mg alloy causes an increase in the Martens index and minimum bending radius, and a decrease in the stamping ratio. In the Al2Mg alloy, grain size inhomogeneity causes an increase in the Martens index and minimum bending radius, and a decrease in the stamping ratio. For the spring back index, the increase in grain size inhomogeneity causes a high scatter of data. In the Al6Mg alloy, the low annealing temperature led to the preservation of the non-recrystallized structure, which influenced the decrease in stampability.

A diagenetic origin for isotopic variability of sediments deposited on the margin of Great Bahama Bank, insights from clumped isotopes

Abstract The clumped isotope temperature proxy has been used to investigate the diagenetic history of carbonate sediments in two cores recovered during ODP Leg 166 on the margin of Great Bahama Bank. While periplatform sediments constitute a tempting archive of paleo ocean chemistry as they are unlikely to be subducted, their primary limitation is a well-documented susceptibility to post-depositional diagenetic reworking. The crystallization temperatures reconstructed using the clumped isotope proxy, as well as the mineralogy and δ13C and δ18O values have been used to determine the relative effects of sediment mixing and sediment recrystallization. Results show that as sediments undergo diagenetic alteration at the seafloor, their initially “warm” clumped isotope composition is overprinted at cooler benthic temperatures. This process appears to occur in an environment with sufficient fluid exchange to overprint carbon isotopes; an observation confirmed in a separate study by analyses of calcium, a similarly rock-buffered element. This early reactive exchange between carbonates and fluids is likely driven by the conversion of metastable aragonite to calcite. This partially occurs within the “flushed zone”, where porewater compositions remain compositionally similar to seawater throughout the upper ∼40 meters of the sediment column. Sediments dominated by open system isotopic compositions correspond to a period of minimal sediment accumulation between 2 and 3 Ma. More deeply buried Miocene sediments of the more platform-proximal Site 1003 show evidence of subsequent recrystallization, incorporating the warmer geothermal TΔ47 values, and more as well as modified water δ18O values, likely driven by co-evolving porewater and carbonate oxygen isotopes. Reconstructed water δ18O values of these deeper sediments at Site 1003 are considerably more positive than the measured modern values, suggesting that porewater δ18O values were more positive during the Miocene. Sediments deposited at the platform distal Site 1006 between the early and middle Miocene did not show evidence for this deeper recrystallization. Differences in diagenetic behavior between the two sites cannot be solely accounted for by differences in sediment accumulation rate. To illustrate this, time-integrated models were constructed which simulated the burial of identically reactive material through the depositional history of each site, the sediments deposited at Site 1006 appear to “stabilize” after an initial phase of neomorphism, whereas the more platform proximal Site 1003 continues to recrystallize during deeper burial, apparently in the presence of a parent fluid with a more positive δ18O value than observed today. We conclude that despite consisting of the same end-member sediment sources, and being spatially separated by less than 30 km, the difference in clumped and oxygen isotopic composition between Sites 1003 and 1006 can be predominantly attributed to differences in the rate and duration of recrystallization during burial.

High-cycle-fatigue induced continuous grain growth in ultrafine-grained titanium

The cyclic deformation behaviour and microstructural stability of severe plastic deformation processed bulk nanostructured (ultrafine-grained, UFG) commercially pure cp-Ti were investigated by using in situ neutron diffraction combined with R = −1 high-cycle-fatigue (HCF) loading at room and cryogenic temperatures. The UFG microstructure was created by equal channel angular pressing (ECAP) and multi-direction forging (MDF). A considerable continuous grain growth was revealed by neutron diffraction for MDF cp-Ti fatigued at 25 °C, as opposed to that at −200 °C. The same HCF fatigue loading at 25 °C only caused very limited grain growth for ECAP cp-Ti. Transmission electron microscopy confirmed the grain growth. Further confirmation of the room-temperature HCF fatigue-induced grain growth was obtained by transmission Kikuchi diffraction based analysis. Novel insights into fatigue induced grain growth mechanism in UFG cp-Ti are thus provided: (i) the thermally activated process plays an important role in grain growth during the room-temperature HCF fatigue; (ii) Continuous dynamic recrystallisation is responsible for the grain growth and dislocation slip or twinning is not essential to trigger such a grain growth; (iii) the anisotropic grain growth behaviour in {0002} grain family can be reconciled by accepting that these grains accumulated highly stored energy during initial severe plastic deformation and the subsequent recrystallisation nucleation occurred at these highly deformed regions.

Dynamic compression-induced twins and martensite and their combined effects on the adiabatic shear behavior in a Ti-8.5Cr-1.5Sn alloy

The samples cut from the Ti-8.5Cr-1.5Sn titanium alloy were prepared to explore the combined effects of dynamic compression-induce twins and martensite on the adiabatic shear behavior. The morphologies of the deformed microstructures were examined by means of optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) observations, which revealed a high density of twins and martensite. The volume fraction of these features increased when the strain rate increased from 1000/s to 1500/s, owing to the relatively large driving force associated with twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) effects. Such phenomena resulted in an increase in the unit strain increment (induced by the unit stress increment Δε / Δσ) and the energy absorbed. At strain rates of 2000/s or higher, adiabatic shear failure occurred and the values of Δε / Δσ and the absorbed energy were far greater than that at 1500/s. The twins and martensite around the adiabatic shear bands (ASBs) were broken due to severe local deformation and subsequent dynamic recrystallization. Furthermore, the presence of twins and martensite induced (in general) bifurcation of the ASBs, which played a crucial role in the plasticity of the alloy.

Evidence of austenite memory in PH 15-5 and assessment of its formation mechanism

Austenite memory and subsequent spontaneous recrystallization during austenitization is stated for some types of soft martensitic stainless steels such as X4CrNiMo16-5-1 or 13Cr5Ni but have not been proposed for the commercial alloy PH15-5 until now. However, the understanding of the austenitization behavior is defined to be crucial as it influences grain size, dislocation density of austenite and thus the final mechanical properties of the material.Therefore, this study investigates the austenitization behavior of PH15-5 by means of in-situ high temperature electron back scatter diffraction of continuous austenitization and directly evidences austenite memory also in this alloy. In order to characterize the austenite formation mechanism in detail, dilatometer, in-situ X-ray diffraction and confocal laser scanning microscope experiments have been carried out. Corroborated with thermokinetic DICTRA simulations, a diffusion controlled transformation exhibiting austenite memory is evidenced. The in-situ high temperature electron backscatter diffraction data in comparison with recent literature indicates the inheritance of geometrically necessary dislocations from martensite to austenite. Therefore, a basic model is postulated in order to describe the inheritance of geometrically necessary dislocations due to a diffusion controlled transformation process.

Impurity elements in quartz from gold deposits of the Darasun ore field (Eastern Transbaikalia, Russia): electron paramagnetic resonance data.

The distribution of substitutional Al, Ti, and Ge impurities in quartz samples from the Darasun, Teremkinskoe and Talatui gold deposits, located in the Darasun orefield, were studied using the electron paramagnetic resonance method. Relationship between the isomorphic substitution and the dynamic recrystallization of quartz was studied by optical and scanning electron microscopy.
 Analysis of the plots of interdependency between the concentrations of various substitutional impurities in quartz (isogens) provided an opportunity to detect isomorphic substitution development trends. Two isomorphic substitution stages were recognized, one associated with mineral crystallization and the other, with its subsequent dynamic recrystallization. The first stage leads to Al impurity incorporation into the quartz crystal lattice, and the second, to Ti impurity incorporation. The Ge impurity is the isomorphic substitution catalyst, and its concentrations vary widely. It is noted that the second stage plays a decisive role, because it accounts for the incorporation of the larger part of substitutional impurities. This process is facilitated by the dynamic recrystallization of quartz.
 Four quartz genetic groups, which are described by individual isogens, have been recognized in the Darasun orefield. Two of them correspond to the quartz crystallized from a magmatogenic fluid directly or redeposited with its participation, and the other two correspond to the quartz crystallized from an altered fluid. The facts that substitutional Al concentrations are retained in quartz after redeposition, whereas substitutional Ti impurity concentrations fall dramatically, are demonstrated.
 Mineral formation processes at each gold deposit are discussed. Two types of temperature zoning, the normal and the reverse, have been recognized at the Darasun deposit. Each zoning is characterized by an individual quartz genetic group and the extent of mineralization system closedness. The genetically similar magmatogenic quartz samples found at the Darasun and Talatui deposits attest to the uniformity of mineralization process in the Darasun orefield. The established trends of isomorphic substitution in quartz are applicable in the studies of ore formation histories of gold and other ore deposits.
 Keywords: Darasun; Teremkinskoe; and Talatui deposits of the Darasun orefield; mineral formation; auriferous quartz; dynamic recrystallization; substitutional impurities; genetic analysis; isogens; isomorphic substitution stages; quartz redeposition; temperature zoning; EPR method; scanning electron microscopy