Effect Of Grain Size Variation Research Articles

Investigating acoustic emission during macro-indentation of AZ 31 magnesium alloy

Accelerated mechanical characterization is crucial for enabling the rapid assessment of mechanical properties during process optimization or material development. This article introduces an innovative approach, combining profilometer-based indentation plastometry (PIP) with a real-time acoustic emission (AE) monitoring system. This approach assists in comprehensively assessing both mechanical properties and the underlying deformation mechanisms during indentation through AE emission. In this study, we investigate the effect of grain size variation on acoustic emission in AZ31 magnesium alloy during PIP indentation. Our findings demonstrate that PIP-inferred yield strength is notably higher (68 MPa) for samples with smaller grain sizes (70 µm) compared to those with large grain sizes (98 µm), with a yield strength of 46 MPa. Moreover, AE-energies are notably lower in samples with smaller grain sizes as opposed to those with larger grain sizes. To further gain insight into the dominant deformation mechanism, a non-supervised cluster analysis, in conjunction with electron backscattered diffraction (EBSD) analysis, reveals that the major deformation systems are basal dislocation glide 0001112̅0 and extension twinning 101̅2101̅1.

3D DEM simulations of the variability of rock mechanical behaviour based on random rock microcracks

In this study, to investigate the variability of mechanical parameters of rock, a three-dimensional (3D) discrete element model (DEM) with the consideration of random microcracks was proposed. The random microcracks follow the negative power-law distribution with upper and lower limits of microcrack size. The results showed that coefficient of variations (COVs) and average values of elastic modulus, Poisson's ratio, unconfined compression strength and tensile strength of Lac du Bonnet granite are well matched through the present model. The present simulations indicate that the large COVs were induced by the interconnected large microcracks. The parametric study clearly indicates that the random microcracks significantly affect COVs, while the effect of grain size variation can be ignored. The size of microcracks determines the variability of mechanical parameters, and the volume density of microcracks can significantly influence the COVs. The correlation between the fractal dimension of microcrack size distribution and COVs is not linear. The increasing variability of microcrack density can result in the increase of COVs. Finally, a calibration procedure was proposed to determine the present model's parameters.

On the role of grain size variation on pitting corrosion and passive film behavior of Alloy 600H

AbstractIn this work, the effect of grain size variation on the pitting corrosion as well as the passivation behavior of the Alloy 600H has been critically assessed by various electrochemical techniques. The grain size modifications have been achieved by a series of thermal and thermo‐mechanical processing. The potentiodynamic polarization study has revealed that the coarse‐grained specimens exhibit higher corrosion and pitting resistance than the fine‐grained ones. This has been attributed to the greater extent of random high‐angle grain boundary (RHAGB) surface area in the fine‐grained specimens, which acted as favorable locations for pit initiation. The electrochemical impedance spectroscopy (EIS) result has indicated the formation of more imperfect (nonstoichiometric) passive layers in fine‐grained specimens due to the predominant presence of high energy and defective RHAGBs surface. Moreover, the Mott–Schottky analysis has revealed that the fine‐grained specimens generate higher defect densities at the interfaces, which leads to passive film instability due to increased mobility of cation interstitial and cation vacancies at the interfaces.

An experimental investigation on the combined effect of plastic deformation and grain size variation on the acoustic nonlinearity parameter.

The combined effect of grain size variation and plastic deformation on the acoustic nonlinearity parameter has been investigated in an austenitic stainless-steel material of grade 304. The nonlinear behavior of this parameter with grain growth has deviated to linear fit with deformation. This is due to the interaction of elastic waves with the strain-induced dislocation substructure in the grains. The normalized mean square strain of the deformed specimens has been estimated through angle dispersive x-ray diffraction studies using a synchrotron source, and this has been correlated with the change in the acoustic non-linearity parameter with deformation. The nonlinearity parameter is found to be very sensitive to the plastic deformation even in the presence of grain size variations. The results infer that the variations in the nonlinearity parameter can be used to have an estimate of the extent of localized deformations often occurring during the fabrication of metallic components.

Correlation between grain size variation and hydrogen embrittlement in a cost-effective Fe40Mn40Ni10Cr10 austenitic medium entropy alloy

The effect of grain size variation (11 μm, 34 μm) on the hydrogen-induced tensile properties degradation of a Co-free cost-effective Fe40Mn40Ni10Cr10 austenitic medium entropy alloy was investigated using a slow strain rate test. Despite improving both strength and ductility with decreasing the grain size in non-charged conditions, the fine-grain alloy showed a higher relative elongation loss after electro-chemical hydrogen charging. The larger ductility loss in the fine-grain alloy was ascribed to the fast propagation rate of major intergranular cracks and the drastic strain hardening rate drop of the alloy under hydrogen charging. The Schmid factor analysis showed that the enhanced dislocation activity in the fine-grain alloy compared with coarse-grain one was responsible for rapid hydrogen transfer to the grain boundaries, fast dislocation pile-up behind the grain boundaries, and, consequently, more severe hydrogen embrittlement. The significant stress concentration near the grain boundaries and fast intergranular crack propagation were recognized to be the main reason for premature fracture in fine-grain alloy.

Alteration trends and geochemical source region characteristics preserved in the fluviolacustrine sedimentary record of Gale crater, Mars

Abstract The Mars Science Laboratory’s Chemistry and Camera (ChemCam) instrument suite on-board the Curiosity rover has analysed ∼1200 sedimentary targets during the mission up to sol 1482. These targets have included sedimentary rock, diagenetic features (e.g., fracture-associated alteration halos, mineral veins, nodules, and erosion resistant raised ridges), active aeolian fines, soils and float. We have isolated ChemCam geochemical trends relating to diagenetic features and alteration products from those of the sedimentary rock in order to identify the compositional characteristics of Gale crater’s sediment source regions. The effects of grain size variation on sedimentary unit geochemistry have been taken into account by grouping and analysing geological units according to grain size. With obvious diagenetic features removed from the database, and predominately isochemical aqueous alteration inferred for the Mt Sharp Group samples, we propose that source region composition is a stronger source of geochemical change between the Bradbury and Mt Sharp Groups than open-system alteration. Additionally, a lack of correlation between the Chemical Index of Alteration (CIA) values and SiO2, MgO or FeOT indicates that the slight increase in chemical weathering of the Mt Sharp Group sediments was insufficient to overprint sediment source compositional signatures. This has led to the identification of five unique igneous endmember compositions which we hypothesise to have contributed to Gale crater’s stratigraphic record. These endmembers are: (1) a subalkaline basalt, compositionally similar to the tholeiitic Adirondack Class basalts of Gusev crater, and dominant within the finer grained units up to the base of Mt Sharp; (2) a trachybasalt, mostly identified within conglomerate units from the Darwin waypoint to the base of Mt Sharp; (3) a potassium-rich volcanic source, determined from strong potassium enrichment and a high abundance of sanidine that is most dominant in the fluvial sandstones and conglomerates of the Kimberley formation; (4) a highly evolved, silica-rich igneous source that correlates with the presence of tridymite, and is recorded in the lacustrine mudstone of Mt Sharp’s Marias Pass locality; and, (5) a fractionated, relatively SiO2-rich subalkaline basalt, seen to have influenced the composition of mudstone deposited in the lower part of the Mt Sharp Group. Endmembers (1), (2), (3), and (4) have previously been identified at specific waypoints along the rover’s traverse, but we show that their influence extends throughout Gale’s stratigraphic record. The occurrence of detected endmembers is also strongly correlated with stratigraphic position, which suggests changing sediment source regions with time. We conclude that Gale sediment provenances were much more varied than suggested by the largely homogenous, globally-distributed Martian basalt inferred from orbit, showing that complex magmatic assemblages exist within the ancient highland crust surrounding Gale.

Investigation of the Effect of Grain Size Variation on Ground Wafer Surface by Grinding Experiment/Simulation

The grinding wheel is comprised by three elements; abrasive grain, bonding material and pore, which are specified by five factors; type of abrasive grain, grain size, type of bonding material, grade of hardness and abrasive grain volume percentage. Regarding the abrasive grain, it is well known that shape and number of cutting edge significantly effects grinding performance such as surface roughness, grinding force and grinding wheel life. In general, abrasive grain size is determined by mean diameter of abrasive grain. However, the abrasive grains in a grinding wheel are randomly scraggly in size and shape. There is no particular aspect to regulate the grain size variation in JIS (Japanese Industrial Standards). This paper investigates the effect of grain size variation on the ground surface topography by actual grinding on silicon wafers and analysis based on grinding simulation. The results reveal that the standard deviation of grain size is a very important index to characterize the grinding performance of a wheel. Smaller standard deviation leads to larger density of effective cutting-edge under the same volume percentage of abrasive grain contained in the wheel. This fact significantly contributes to not only achieve a better surface roughness and more uniform surface integrity, but also shorten the finishing time.

Theoretical analysis on effects of grain size variation

Grinding wheels consist of abrasive grains, bonding materials and porous, which are specified by five factors; type of grain, size of grain, bonding material, bonding strength and grain concentration or volume fraction of grain. The grain size is represented by the mean diameter/radius of grains. However, the abrasives in a grinding wheel are randomly scraggly in size and shape. There is no particular aspect to regulate the variation in grain size. This paper addresses, via a theoretical analysis on the distribution of grain size, the average volume of a grain, the number of grains contained in a specific volume of the wheel, the number and protrusion distribution of grains exposed in a wheel working surface and the fraction of effective grain, when the grain size varies. The effect on the resultant finished surface roughness is also discussed.

Natural age dispersion arising from the analysis of broken crystals: Part II. Practical application to apatite (U–Th)/He thermochronometry

We describe a new numerical inversion approach to deriving thermal history information from a range of naturally dispersed single grain apatite (U–Th)/He ages. The approach explicitly exploits the information about the shape of the 4He diffusion profile within individual grains that is inherent in the pattern of dispersion that arises from the common and routine practice of analysing broken crystals. Additional dispersion arising from differences in grain size and in U and Th concentration of grains, and the resultant changes to helium diffusivity caused by differential accumulation and annealing of radiation damage, is explicitly included. In this approach we calculate the ingrowth and loss, due to both thermal diffusion and the effects of α-ejection, of helium over time using a finite cylinder geometry. Broken grains are treated explicitly as fragments of an initially larger crystal. The initial grain lengths, L0, can be treated as unknown parameters to be estimated, although this is computationally demanding. A practical solution to the problem of solving for the unknown initial grain lengths is to simply apply a constant and sufficiently long L0 value to each fragment. We found that a good value for L0 was given by the maximum fragment length plus two times the maximum radius of a given set of fragments. Currently whole crystals and fragments with one termination are taken into account. A set of numerical experiments using synthetic fragment ages generated for increasingly complex thermal histories, and including realistic amounts of random noise (5–15%), are presented and show that useful thermal history information can be extracted from datasets showing very large dispersion. These include experiments where dispersion arises only from fragmentation of a single grain (length 400μm and radius 75μm, c. 6–50% dispersion), including the effects of grain size variation (for spherical equivalent grain radii between 74 and 122μm, c. 10–70% dispersion) and the combined effects of fragmentation, grain size and radiation damage (for eU between 5 and 150ppm, c. 10–107% dispersion). Additionally we show that if the spherical equivalent radius of a broken grain is used as a measure of the effective diffusion domain for thermal history inversions then this will likely lead to erroneous thermal histories being obtained in many cases. The viability of the new technique is demonstrated for a real data set of 25 single grain (U–Th)/He apatite ages obtained for a gabbro sample from the BK-1 (Bierkraal) borehole drilled through the Bushveld Complex in South Africa. The inversion produces a well constrained thermal history consistent with both the (U–Th)/He data and available fission track analysis data. The advantage of the new approach is that it can explicitly accommodate all the details of conventional schemes, such as the effects of temporally variable diffusivity, zonation of U and Th and arbitrary grain size variations, and it works equally effectively for whole or broken crystals, and for the most common situation where a mixture of both are analysed. For the routine application of the apatite (U–Th)/He thermochronometry technique with samples where whole apatite grains are rare our experiments indicate that 15–20 single grain analyses are typically required to characterise the age dispersion pattern of a sample. The experiments also suggest that picking very short crystal fragments as well as long fragments, or even deliberately breaking long crystals to maximise the age dispersion in some cases, would ensure the best constraints on the thermal history models. The inversion strategy described in this paper is likely also directly applicable to other thermochronometers, such as the apatite, rutile and titanite U–Pb systems, where the diffusion domain is approximated by the physical grain size.

Processing of the chemical components of estuarine sediment by the lugworm, Arenicola marina

The ability of the deposit feeder, Arenicola marina, to process components of oxic estuarine sediment has been examined by comparing the chemical composition of freshly-voided faecal casts and surficial ambient sediment. Analysis of C, H and N, and major metals (Al and Fe) and trace metals (Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Pb) was undertaken on the <63 μm fraction of cast–sediment pairs in order to minimise potential effects of grain size variation among samples. In all cases, C, H and N concentrations were lower in biodeposits than in local sediment, and averaged results suggested digestion of between about 15 and 30% of these elements. Nitric acid-extractable metal concentrations in casts and corresponding sediment samples were, in general, analytically indistinguishable. However, after further data normalisation with respect to Al or Fe, casts exhibited slight metal enrichment, presumably because of the weight loss incurred by digestion of (non-metal-bearing) organic matter and the egestion of metals derived from other sources. A protein known to mimic the digestive fluids of A. marina, bovine serum albumin, released between <0.5% (Al, Fe, Mn and Pb) and 15–25% (Cu, Zn and Cd) of acid-soluble metal from both sediment and cast samples. This suggests that, although A. marina is capable of mobilising certain metals in its gut, they tend to re-combine with particles during the formation or egestion of the cast.

Grain size effects on flow stress in hot compression test

Flow stress data on fine‐grained material are needed for FEM modelling of the final passes in hot rolling. However, a fine grain size may be difficult to retain in reheated specimens for hot compression tests, and the flow stress usually has to be determined using specimens with rather coarse grain sizes. The results for several steels tested in austenitic condition show that the increase in grain size from about 15 μm to 50 μm causes a decrease of 5 − 25% in the mean flow stress (calculated over the strain range of 0 − 0.15) and further coarsening has hardly any influence. The effect of grain size Variation can be described by respective alterations in the strain‐hardening exponent and it can be accounted for by mathematical correction.

EPR studies on donor doped BaTiO 3 grain boundary layer ceramic dielectrics

Donor doped BaTiO 3 ceramics become insulating 5 under controlled conditions with effective dielectric constants >10. The changes in EPR signals indicate that a certain fraction of the donor doped BaTiO 3 is cubic even at room temperature and that the cubic fraction increases with the donor content. X-ray powder diffraction data support the EPR results. The coexistence of both the phases over a range of temperature is characteristic of diffused phase transition. The effect of grain size variation on EPR signal intensities indicate that the boundary layers surrounding the grains may constitute the cubic phase as a result of higher Ba-vacancies and donor contents at the grain boundary layer than in the bulk. Since the acceptor states arising from the Ba-vacancies and the impurities are activated in the cubic phase, they capture electrons from the conduction band, rendering the cubic phase electrically more insulating than the semiconductive tetragonal grain interiors. Thus, the cubic grain boundary layers act as effective dielectric media where the field tends to concentrate.

The role of prior austenite grain size on the tensile ductility and fracture toughness of 18Ni maraging steels

This communication describes the results of an investigation which was undertaken to clarify the contradictory effects of grain size variation on the tensile ductility and fracture toughness of aged 18Ni maraging steel and the possible underlying causes for the fracture mode transitions observed. Varying prior austenite grain size does not effect tensile ductility or fracture toughness. Increasing grain size does result in a decrease in tensile ductility. Fracture mode changes in the aged condition.

Mechanical Constitution of Certain Present-day Egyptian Dune Sands

ABSTRACT A purely graphical and descriptive study is carried out of the results of the mechanical analysis of aeolian sand samples from five aeolian microenvironments of the Suez Canal Zone. These microenvironments are shown to differ by small but significant amounts. Taking into account the geographical environment, the results are found to agree with a deduction from Bagnold's Theory of Saltation, allowing for the effects of grain size variation of the materials taking part in the process.