Fine-grain Material Research Articles

Preparation of fine-grain aluminum alloy by spinning method and its corrosion resistance test

Due to the lack of shear resistance, the implanted materials in the aluminum alloy will lead to obvious wear. The emergence of fine-grained aluminum alloy materials can perfectly solve the above problems. Therefore, in this paper, the fine-grain aluminum alloy material is prepared by the spinning method, and the corrosion resistance test is carried out. The experimental results show that there is no significant difference in weight loss and surface morphology between aluminum alloy and fine-grain aluminum alloy immersed in normal saline and D-Hand’s solution for 30 days. The experimental results show that the fine-grained aluminum alloy has the basic conditions for in vivo implantation, which lays a foundation for the development of a new generation of in vivo implantation materials.

Hot deformation behavior and processing map development of Mg/Al2O3 composite: A case study of extrusion ratio effects

The hot deformation behavior of 2.5 wt.% submicron alumina reinforced magnesium composite manufactured by a new casting method was examined to assess the impact of extrusion ratio and initial microstructure on the hot workability of Mg/Al2O3 composite. The thermomechanical experiments were performed at strain rates from 0.001 s−1 to 0.05 s−1 and the temperature ranging from 523 K to 673 K. The processing map was developed using power dissipation efficiency in terms of temperature and strain rate. Results revealed that the higher extrusion ratio yields finer grain size and a more homogenous distribution of alumina particles resulting in lower flow stress and activation energy. Stable regions with more power efficiency (57%) and less instability were observed in materials that experienced higher strain. Based on the microstructural observation, dynamic recrystallization as the main restoration mechanism occurred at composite with a higher extrusion ratio and finer grains in all conditions. It was deduced that the enhanced workability of fine-grain material is confirmed by steady flow stress and safe zones of the processing map. It was also revealed that twinning–twinning intersection and flow localization are the main reasons for unstable flow in both samples with unlike grain sizes.

Mechanisms of the preferential cleavage of Ti2AlNb-based alloy: The influence of grain size and local plasticity

An in-depth understanding on the preferential cleavage of the matrix B2 phase, with an ordered body-centered cubic (BCC) structure, is pivotal to improve the processability of Ti2AlNb-based alloys. This research employed in-situ micro tensile tests, multiscale microstructure characterizations, and crystal plasticity simulations to study the grain-size dependent cleavage of the alloy with a full B2 phase. The material was intentionally prepared with two grain sizes differing by order of magnitude, i.e., the millimeter-level coarse grain (CG) and the micron-level fine grain (FG). The experimental results showed that the cleavage of CGs always occurred on the {100} planes, even when the loading direction was much less favorable for the cleavage of these planes, whereas the cleavage of FGs took place on both {100} and {110} planes. The investigation demonstrated that the plastic deformation takes a critical role in selecting cleavage planes. Full-field crystal plasticity simulations demonstrated that, for the CGs, the plastic deformation associated with cleavage on {100} planes is less than that associated with cleavage on {110} planes, indicating a less plastic deformation-induced blunting effect with cleavage on {100} planes. For the FG material, however, the existence of plentiful grain boundaries (GBs) leads to significantly heterogeneous plastic deformation, local stress distribution deviating from the imposed global stress, and hot spots of stress and strain concentration at GB triple junctions. These local plasticity heterogeneities enable the possibility for cleavage on both the {100} and {110} planes.

Welding-induced yield strength heterogeneity in X100Q: Modelling and characterisation

Yield strength (YS) heterogeneity in X100Q high strength low alloy (HSLA) steel welded joints is a key factor which influences fatigue life performance. The effects of welding-induced microstructural changes are investigated using a mechanistic YS model, which enables understanding of the key strengthening mechanisms which give rise to YS heterogeneity in X100Q. The model is used to predict YS in parent metal, physically-simulated fine-grain heat-affected zone material, and inter-critical heat-affected zone material, incorporating cooling rate effects. The model successfully predicts the measured welding-induced YS heterogeneity, with high-angle boundary (HAB) and precipitate strengthening mechanisms as dominant factors.

Mineralogical and Geochemical Characterization of Gold Mining Tailings and Their Potential to Generate Acid Mine Drainage (Minas Gerais, Brazil)

For more than 30 years, sulfide gold ores were treated in metallurgic plants located in Nova Lima, Minas Gerais, Brazil, and accumulated in the Cocoruto tailings dam. Both flotation and leaching tailings from a deactivated circuit, as well as roasted and leaching tailings from an ongoing plant, were studied for their acid mine drainage potential and elements’ mobility. Detailed characterization of both tailings types indicates the presence of fine-grain size material hosting substantial amounts of sulfides that exhibit distinct geochemical and mineralogical characteristics. The samples from the ongoing plant show high grades of Fe in the form of oxides, cyanide, and sulfates. Differently, samples from the old circuit shave higher average concentrations of Al (0.88%), Ca (2.4%), Mg (0.96%), and Mn (0.17%), present as silicates and carbonates. These samples also show relics of preserved sulfides, such as pyrite and pyrrhotite. Concentrations of Zn, Cu, Au, and As are higher in the tailings of the ongoing circuit, while Cr and Hg stand out in the tailings of the deactivated circuit. Although the obtained results show that the sulfide wastes do not tend to generate acid mine drainage, leaching tests indicate the possibility of mobilization of toxic elements, namely As and Mn in the old circuit, and Sb, As, Fe, Ni, and Se in the tailings of the plant that still works. This work highlights the need for proper management and control of tailing dams even in alkaline drainage environments such as the one of the Cocoruto dam. Furthermore, strong knowledge of the tailings’ dynamics in terms of geochemistry and mineralogy would be pivotal to support long-term decisions on wastes management and disposal.

A new quartz for

Quartz grains extracted from aeolian sand (<i>LexCal2014</i>) are tested for suitability as transfer material for radiation source calibration. After thermal pre-treatment, this quartz exhibits luminescence and dose-response properties which appear appropriate for transfer calibration purposes with little dependence of recovered β-dose on preheat temperature in the single aliquot (SAR) procedure and satisfying performance in β-dose recovery (0.98−1.00 given/measured β-dose for various experiments). Additional support is obtained by SARA and interpolation procedures, where OSL-data from γ-dosed <i>LexCal2014</i> is interpolated on data obtained for zeroed <i>LexCal2014</i> quartz, which is β-irradiated by the source to be calibrated. Initial results on fine-grain material agree with the coarse grain results presented. The γ-dose of 3.00 ± 0.07 Gy is administered in a scatter-free geometry at the IAEA/WHO Secondary Standard Dosimetry Laboratory (SSDL) of the Helmholtz Zentrum München, with absorbed dose calculations obtained by Monte Carlo simulations.

High temperature behavior of severely deformed AA 5083 through equal channel lateral extrusion

Describing the high temperature behavior of a fine-grained AA 5083 aluminum alloy using an improved constitutive model is the focus of this paper. Dual Equal Channel Lateral Extrusion (DECLE) was utilized to create fine-grain microstructure in AA 5083 aluminum alloy. EBSD confirmed the formation of fine-grain microstructure after 5 passes of DECLE. The hot deformation behavior of the DECLEd alloy was assessed by hot compression tests at temperatures of 200–275 °C and strain rates of 10−4-10−1 s−1. The material constants, A, n and Q, in the hyperbolic-sine constitutive equation were calculated at peak stresses. The results suggested that the grain size affects the values of α and n, while the activation energy (Q) is more or less independent of the grain size. The values of α and n for the fine-grain material were obtained as 0.004357 (MPa−1) and 9.97, respectively. These calculated values (α and n) are respectively lower and higher than those reported for a coarse-grain one in the literature. This result was related to the high flow stress of the refined microstructure. The value of Q showed that the dislocation-dispersoid interactions are the rate-controlling mechanism during hot deformation. By iterating the calculation of constants at various strains, a strain-compensated constitutive equation was proposed for the prediction of flow stress over a wide range of strain. Finally, the processing maps were developed for the AA 5083 alloy at various strains.

Beneficiation of 6-0 mm fine-grain oil shale using vibrating air-dense medium fluidized bed separator

The throughput of oil shale is gradually increasing because of the high value it provides for different applications. However, during oil shale mining, a large amount of fine-grain (6-0mm) material is produced. As the 6-0mm material has higher oil content and better combustion performance, it can be effectively utilized by performing beneficiation through physical sorting to reduce impurities and upgrade the oil shale grade. In this paper, the physical properties of fine-grain (6-0mm) oil shale were analyzed. The beneficiation of 6-0mm oil shale using a vibrating air-dense medium fluidized bed was proposed. The effects of the vibration intensity Γ, gas velocity v, and bed height h on the beneficiation efficiency were systematically investigated. The distribution characteristics of the oil content in the upper, middle, and lower layers of the bed under the optimum operating parameters were studied. Under the optimum operating parameters (v=1.46cm/s, h=85mm, Γ=10.87), the oil content in the upper layer material of the bed is uniform and the fluctuation of the oil content is gentle with better stability. The distribution of the oil content in the middle layer is disorderly, the fluctuation range expands further, and the stability is the worst. The oil content distribution in the lower layer material is uniform with a very small range of fluctuation, and the oil content distribution in the bed material is stable. The yields and oil content of the concentrate are 31.34% and 10.68%, while those of tailings are 68.66% and 0.92%, and the separating accuracy (probable error) is 0.125g/cm3. In conclusion, 6-0mm oil shale can be effectively beneficiated by the vibrating air-dense fluidized bed separator and it can be recycled and utilized efficiently.

Extraterrestrial Soils and Space Agriculture

Extraterrestrial Soils and Space Agriculture

A new method to predict the metadynamic recrystallization behavior in a typical nickel-based superalloy

The metadynamic recrystallization (MDRX) behaviors of a typical nickel-based superalloy are investigated by two-pass hot compression tests and four conventional stress-based conventional approaches (offset stress method, back-extrapolation stress method, peak stress method, and mean stress method). It is found that the conventional stress-based methods are not suitable to evaluate the MDRX softening fractions for the studied superalloy. Therefore, a new approach, ‘maximum stress method,’ is proposed to evaluate the MDRX softening fraction. Based on the proposed method, the effects of deformation temperature, strain rate, initial average grain size, and interpass time on MDRX behaviors are discussed in detail. Results show that MDRX softening fraction is sensitive to deformation parameters. The MDRX softening fraction rapidly increases with the increase of deformation temperature, strain rate, and interpass time. The MDRX softening fraction in the coarse-grain material is lower than that in the fine-grain material. Moreover, the observed microstructures indicate that the initial coarse grains can be effectively refined by MDRX. Based on the experimental results, the kinetics equations are established and validated to describe the MDRX behaviors of the studied superalloy.

Superconducting cavity material for the European XFEL

Analysis of the strategy for superconducting cavity material procurement and quality management is done on the basis of the experience with the cavity production for the European x-ray free electron laser (EXFEL) facility. An adjustment of the material specification to EXFEL requirements, procurement of material, quality control (QC), documentation, and shipment to cavity producers have been worked out and carried out by DESY. A multistep process of qualification of the material suppliers included detailed material testing, single- and nine-cell cavity fabrication, and cryogenic radiofrequency tests. Production of about 25 000 semi-finished parts of high purity niobium and niobium-titanium alloy in a period of three years has been divided finally between companies Heraeus, Tokyo Denkai, Ningxia OTIC, and PLANSEE. Consideration of large-grain (LG) material as a possible option for the EXFEL has resulted in the production of one cryogenic module consisting of seven (out of eight) LG cavities. LG materials fulfilled the EXFEL requirements and showed even 25% to 30% higher unloaded quality factor. A possible shortage of the required quantity of LG material on the market led, however, to the choice of conventional fine-grain (FG) material. Eddy-current scanning (ECS) has been applied as an additional QC tool for the niobium sheets and contributed significantly to the material qualification and sorting. Two percent of the sheets have been rejected, which potentially could affect up to one-third of the cavities. The main imperfections and defects in the rejected sheets have been analyzed. Samples containing foreign material inclusions have been extracted from the sheets and electrochemically polished. Some inclusions remained even after 150 μm surface layer removal. Indications of foreign material inclusions have been found in the industrially fabricated and treated cavities and a deeper analysis of the defects has been performed.

Review of ingot niobium as a material for superconducting radiofrequency accelerating cavities

As a result of collaboration between Jefferson Lab and niobium manufacturer Companhia Brasileira de Metalurgia e Mineração (CBMM), ingot niobium was explored as a possible material for superconducting radiofrequency (SRF) cavity fabrication. The first single cell cavity from large-grain high purity niobium was fabricated and successfully tested at Jefferson Lab in 2004. This work triggered research activities in other SRF laboratories around the world. Large-grain (LG) niobium became not only an interesting alternative material for cavity builders, but also material scientists and surface scientists were eager to participate in the development of this technology. Many single cell cavities made from material of different suppliers have been tested successfully and several multi-cell cavities have shown performances comparable to the best cavities made from standard fine-grain niobium. Several 9-cell cavities fabricated by Research Instruments and tested at DESY exceeded the best performing fine grain cavities with a record accelerating gradient of Eacc=45.6MV/m. The quality factor of those cavities was also higher than that of fine-grain (FG) cavities processed with the same methods. Such performance levels push the state-of-the art of SRF technology and are of great interest for future accelerators. This contribution reviews the development of ingot niobium technology and highlights some of the differences compared to standard FG material and opportunities for further developments.

Reconstructing the setting for deposition of distal tephra in the Sea of Japan Basin: A catastrophic eruption of Baitoushan Volcano

This paper presents a detailed analysis of the attitude and accumulation of fine-grain ash material from the Baegdusan-Tomakomai bed (B-Tm) on the seafloor; this material was deposited after a powerful explosion of the ultraplinian type that occurred around 938 AD. It was found that, provided one has a large digital array of grain-size analyses that characterizes both areal and vertical variability in the bed and makes use of advanced mathematical data-processing techniques (division of the grain-size distribution into subpopulations, a trend analysis of transport pathways, and so on), one can derive new information concerning the character of the eruption, its location, the pathways of aerial and marine transport, and the condition of the atmosphere and water at the time of the eruption. It was found that the grain-size distributions for the tephra in the bed in question contain information on two explosive episodes that lasted 10 days each that took place under the conditions of atmospheric circulation typical of spring (the earlier episode) and of autumn (the later episode). For both of these episodes we determined the most likely areas of ash deposition on the marine water surface. We also identified a complex structure of the areas of concentrated particle distribution on the basin bottom that reflected a vortical water structure in the Sea of Japan during the eruption.

The Effect of Heat Treatment on Creep Resistance of Castings from the Modified Superalloy MAR-247

mpact of heat treatment on durability has been evaluated in this study in conditions of high-temperature creep of castings made from nickel superalloy MAR-247 post production rejects. Castings made in the processes of modification and filtration when pouring into moulds were subject to solubilization (1185°C/2 h) with subsequent ageing (870°C/20 h). It has been found on the basis of performed tests that in conditions of high-temperature creep at temperature 980°C with stress σ = 150 MPa the resistance of specimens of coarse-grain structure was significantly higher when compared to fine-grain material. The conditions of initiation and propagation of cracks in these specimens were analysed with consideration of morphological properties of material macro-, micro-and substructure. Moreover, it has been proven that creep resistance of heat treated MAR-247 superalloy significantly improves when compared to its condition after the process of modification only. Macrostructural changes in the MAR-247 superalloy that determine the increase of superalloy creep resistance after solubilization and ageing, as observed in the tests, were also examined.

Provenance of terrigenous detritus of the surface sediments in the Bering and Chukchi Seas as derived from Sr and Nd isotopes: Implications for recent climate change in the Arctic regions

Strontium and Nd isotope analysis of the detrital fractions extracted from the marginal sea sediments in the Arctic was applied to examine regional and temporal changes in the inflow and transportation of terrigenous material in the Chukchi and Bering Seas over the past 100 years. Regional distributions of the Sr and Nd isotopes of the surface sediments show higher Sr isotope ratios and lower Nd isotope ratios in the Chukchi Sea (87Sr/86Sr=0.7106–0.7150; εNd=–10.1 to –8.3), and lower Sr isotope ratios and higher Nd isotope ratios in the eastern Bering Sea (0.7045–0.7109; –8.6 to +3.0). In addition, the Rb and Sr contents and REE patterns (e.g., Eu/Eu⁎) changed noticeably across the Bering Strait. These variations mean that the sediments in the Bering and Chukchi Seas have clearly distinct sources. The terrigenous detritus in the Chukchi Sea is mainly derived from northeastern Siberia (87Sr/86Sr=0.711; εNd=–9) and Bering Strait inflow (essentially from the Yukon River), and additionally from the Mackenzie River basin including the Canadian Shield (0.732–0.734; –14). The detritus in the eastern Bering Sea mainly consists of two components: the continental material from the Yukon River basin mainly underlain by Mesozoic and Paleozoic rocks in the Alaskan mainland (0.708–0.709; –9 to –8), and the Aleutian-arc volcanics (0.703; +6 to +10) transported northward by the Alaska Coastal and Bering Shelf Waters. The eastern Bering sediments over the past 100 years show slight variations of the Sr isotope ratio and relatively wide variations of the Nd isotope ratio, and the variations and trends of the time-series of the northeastern Bering Sea in the Sr–Nd isotope diagram are probably controlled by changes in the grain size of the detritus from the Yukon River basin. Some of the εNd time-series show periodic fluctuations correlating with the annual mean surface air temperature (SAT) for the Arctic: the εNd value is low in the high SAT period, and high in the low SAT period. In the warm period, the Yukon River was likely to supply a higher amount of the fine-grain material with a relatively low εNd value such as surficial overburden, probably because partial melting of continental glaciers and permafrosts in the Alaskan mainland increased. More detailed analysis with high time resolution is needed to clearly understand the effects the SAT have on the Arctic continental and marine environments.

The Harrison Diffusion Kinetics Regimes in Grain Boundary Diffusion: Lattice Monte Carlo Modelling of the Effect of Segregation

The location of the transition points for the three main Harrison’s kinetics regimes (Type-A, B and C) for the measurement of grain boundary diffusivities from tracer concentration depth profiles (self-diffusion) has been extensively studied in (Divinski et al. Zeit. Metallk, 2002, Belova and Murch, Phil. Mag, 2001, 2009; Defect and Diffusion Forum, 2006, 2008, 2009) by making use of the phenomenological Lattice Monte Carlo numerical method. Those locations are mainly dependent on the dimensionality of the problem. For the case of impurity grain boundary diffusion, the segregation effect is very important. In the present study, the influence of segregation on the transition points is investigated for the parallel slab model (2-dimensional) of the grain boundary diffusion problem by making use of the tracer-type solution to the equivalent diffusion problem. It is shown that the Type-B regime is most likely not realized for the cases of fine-grain material with a strong segregation effect present.

The effect of grain size and hardness of Waspaloy on the wear of cemented carbide tools

The effects of grain size and hardness of Waspaloy on the wear of cemented carbide tools were examined by measuring the actual progression of the tool wear in a specific transverse turning operation. Four different conditions of the material from the same batch were studied: fine-grain material in the solution-annealed condition and in the precipitation-hardened condition, as well as large-grain material for the same two conditions. While flank wear, as expected, correlated strongly with hardness, there was basically no effect on the flank wear by the grain size. Notch wear was significant for the large-grain-size material conditions only and was associated with inhomogeneous deformation and burr formation. The deformed layers in the machined surfaces were deeper for the large-grain-size material, but with no obvious effect of hardness.

Surface characteristics and removal mechanism of cemented tungsten carbides in nanoscratching

The surface characteristics and removal mechanism of cemented tungsten carbide materials with different grain sizes in nanoscratching were investigated. The tests with different scratching patterns were used. The results showed that the fine-grain material exhibited different removal characteristics from the coarse-grain one. The roughness of the scratched surface on the fine-grain material was much smaller than that on the coarse-grain material. The removal rate of the coarse-grain material associated with the nanoscratching process was much greater than that of the fine-grain material. The microstructure of the two materials apparently affected their deformation and removal mechanisms involved in the nanoscratching, thus the surface roughness and the removal rate. The results obtained from the lapping experiment supported the findings from the nanoscratching test.

The scenes and spaces of anxiety: Embodied expressions of distress in public and private fora

Psychological treatments of mental health issues have acquired a justifiable notoriety for their tendency to engage in generalisation and reductionism. By contrast, the emergent geographies of exclusion make visible the fine-grain material and spatial contours of the lives of individuals who experience mental health difficulties and distress. However, this can come at the cost of a relative neglect of the psychological. In this paper we propose a set of concepts for facilitating the study of intersecting planes of experience, which demonstrates the interdependency of the spatial, the psychological and the technological. Drawing on empirical work with participants who live with persistent anxiety, we demonstrate how online support networks mediate – that is transduct, intersect and transform – how experiences of anxiety are lived out. Attention to endogenous ‘tactics’ or ‘modes of normativity’ provides an interesting agenda for the emergent engagement of social psychology with social/cultural geography.

Effect of the grain size on the macroscopic response of aluminum to shock loading

Shock tests of two lots of a 1420 aluminum-lithium alloy are performed. The mean grain size is 24 µm in the first lot and 1.6 µm in the second lot obtained by the method of equal-channel angular pressing. Two characteristics of dynamic strength of the material were determined in experiments on the high-velocity impact of flat samples: threshold of dynamic stability with respect to compression on the fore front of the compression pulse and spall strength of the material. The materials of both types have an identical threshold of dynamic stability with respect to compression, whereas the spall strength of the microcrystalline alloy is 20% greater than the spall strength of the polycrystalline alloy. The reason is the consumption of energy on structure formation in the coarse-grain material in passing to a larger-scale structural level (in the case with a fine-grain material, such a structure is available in the initial state). The experiments reveal the presence of a second plastic front whose amplitude is approximately 10% of the first plastic front.