Grain Size Ratio Research Articles

Temperature dependent grain growth of forsterite–nickel mixtures: Implications for grain growth in two-phase systems and applications to the H-chondrite parent body

Abstract Grain growth experiments in the system forsterite (Fo) + nickel (Ni) have been performed on two analogue mixtures of ordinary chondrites, with volume % of Fo:Ni (95:5) and (80:20). These two mixtures have been studied at temperatures of 1390 °C and 1340 °C, at an oxygen fugacity ( f O 2 ) three orders of magnitude below the Ni–NiO buffer, for durations between 2 h and 10 days. Microstructures and grain size distributions show that grain growth is normal and that for durations >10 h the Zener relation is verified (i.e., the ratio of Fo and Ni grain size is independent of time). Comparison with results previously obtained at 1440 °C shows a similar grain growth exponent ( n ∼ 5 ) for both phases, consistent with growth of forsterite by grain boundary migration, limited by the growth-rate of nickel. The details of size distribution frequencies and the value of grain-growth exponent indicate that the nickel grains, which pin forsterite grain boundaries, grow by diffusion along one-dimensional paths (i.e., along forsterite triple junctions). The derived activation energies for nickel and forsterite are 235 ± 33 kJ / mol and 400 ± 48 kJ / mol respectively. Within the framework of the Zener relation, this unexpected difference of activation energy is shown to be related to temperature-dependent variations in the ratio of Ni and Fo grain-size that are consistent with observed variations in Fo–Ni–Fo dihedral angle. These data thus indicate that the presence of all phases should be taken into account when considering the activation energy of growth rate of individual phases. As an application, the experimentally derived growth law for metal has been used in conjunction with temperature–time paths taken from models of the thermal history of the H-chondrite parent body to estimate the grain size evolution of metal in H-chondrites. A remarkably self-consistent picture emerges from experimentally derived grain-growth laws, textural data of metal grains in well characterised H-chondrite samples, and geochemically constrained temperature–time paths, providing the potential to use textural data of metal as a window into the thermal history of chondritic samples.

Grain size of Lake Qinghai sediments: Implications for riverine input and Holocene monsoon variability

Grain-size compositions of lake sediments can provide direct information on changes in transporting mechanism and sedimentary environment. Various grain-size parameters have been employed to reconstruct hydrological conditions within the lake and dust influx from outside the lake. Here we present the grain-size results of a 5-m core retrieved from Lake Qinghai, northeastern Tibetan Plateau in order to address the links between Holocene depositional process and climatic change. Our results indicate that two parameters (skewness and grain-size ratio of 8–50/2–8μm) are sensitive to hydrodynamic changes in Lake Qinghai, which are further linked to the strength of the Asian summer monsoon. Variations of these two parameters reveal that summer monsoon intensity weakened gradually from early to late Holocene, superimposed by persistent centennial variability with dominant periods at 0.35, 0.23 and 0.12 kyr. Comparison of grain-size variations with solar activities and North Atlantic cooling events reveals that solar forcing likely plays an important role in driving centennial monsoon variability.

Application of Micro Wear Testing in Investigations of Super Coarse WC-Co Type Sintered Carbides

The mico-wear abrasion test has recently become a popular method for the measurements of wear resistance of both coated and solid materials. It provides insight into abrasion micromechanisms and quantitative information (wear coefficient) of the tested samples. The investigated super coarse WC-Co composite (WC particles average size of 6-10 μm) reveals the biggest fracture resistance within the whole size range of sintered carbides, at the certain expense of hardness. Super coarse grades are used, among other, as coal mining tools and rock cutting/driling bits. In this work, ball-cratering wear tests were performed using 1 μm diamond particles as the abrasion medium; the abrasives used produced well-defined craters. The worn areas were observed and measured using optical and electronic microscopy, the wear coefficient was calculated based on the increasing sliding distance method. It was found that super coarse sinters abraded with 1 μm diamond grains were more wear resistant than the more fine grained counterparts. This result is attributed to the influence of the large size ratio of WC particles and diamond grains and consequent stronger WC embeding in the metal matrix.

Phase and Microstructural Evolution, and Densification Behaviour of Kaolin Powder Compacts

ABSTRACTTwo types of kaolin clay samples of different origins were studied using X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy and thermogravimetric/differential thermal analysis. Mineralogical and morphological characteristics of die-pressed kaolin samples were investigated. Kaolinite was identified as the major mineral phase; however, other minerals, e.g. illite and quartz were also present as subordinates. The transformation heats during heating were quantified from DTA measurements and phase changes were followed by XRD analyses. The present results indicated a series of phase transformations as the kaolin was fired at elevated temperatures. The formation of mullite was detected by XRD at a temperature as low as 1100°C. Microstructural evolution investigations showed that mullite needles were formed within the powder compacts during sintering. Size and aspect ratio of the mullite grains increased with the increase of firing temperature. The powder compacts showed anisotropic shrinkage after sintering, mainly due to preferred orientation of the kaolin flakes within the powder compacts. The density was found to be increasing with increase of firing temperature until 1300°C.

Utilization of soil properties to understand the vertical distribution of dioxins in the soil of Bien Hoa airbase, Vietnam

During the Vietnam War, Bien Hoa airbase was utilized by the US military in the storage and transport of Agents Orange, White, and Blue, which are herbicides/defoliants used during the war. These chemicals used were highly contaminated with dioxins, which were still unknown at that time as carcinogenic chemicals. Thus, accidental spills as well as deliberate disposal of contaminated items within the airbase caused the advertent dioxin problem of the airbase. The relationships of soil properties and dioxin distribution have not yet been considered at this site. Therefore, the objective of this paper was to clarify these relationships using soil samples from boring cores drilled from three areas of the airbase. Dioxins concentrations, total organic carbon (TOC), loss on ignition (LOI), and grain size distribution were analyzed. The results showed that dioxin concentration increased with the increase in TOC. Silty clay with higher TOC of 0.49 % presented the highest toxicity equivalency quantity (TEQ) of 3300 pg-TEQ/g-dw at borehole BH01. Similarly, at BH02, silty clay with the highest TOC of 0.42 % showed the highest TEQ of 760 pg-TEQ/g-dw. The analyzed results of this research also presented a relationship between the TEQ and particle size. It seems to show that the higher concentration of dioxins was found with a ratio of coarse grain size to fine grain size approximately 1:1. However, correlation between dioxins and LOI was not clearly observed. This indicates that mobility of dioxins is sensitive to the TOC of soils.

Cellular automata simulations of grain growth in the presence of second-phase particles

In this article, we studied the grain growth kinetics in the presence of second-phase particles by using a 2D cellular automata (CA) model with deterministic rules. The curvature-driven grain growth mechanism was adopted in the CA model and an expanded method for the computation of curvature along a grain boundary was used. Simulations in real time and space were performed for various particle sizes, volume fractions of particles, and initial grain sizes, and their effects on the microstructure evolution and final limiting grain size were discussed. A modified Zener relation was proposed to predict the limiting grain size by introducing two items: one describes the effect of initial grain size and the other describes the effect of the ratio of initial grain size to particle size. The proposed relation shows a good fit to the simulated limiting grain sizes for different cases.

Atomistic mechanisms of fatigue in nanotwinned metals

We investigate the fatigue behavior of nanotwinned Cu using a combination of molecular statics and molecular dynamics simulations. The presence of nanoscale twins is found to enhance fatigue crack growth resistance. For the twin-free nanocrystalline samples, the fatigue crack propagates by linking the nanovoids that are formed ahead of the crack tip. In the case of the nanotwinned samples, however, it advances as the crack tip alternately blunts and re-sharpens due to dislocation emission and slip. Both detwinning and crack closure are observed in the path of the fatigue crack in nanotwinned samples with a high density of twin boundaries. As the twin number per grain (quantified by the ratio of the mean grain size to the twin boundary spacing d/λ) increases, detwinning increases the dissipated energy of fatigue cracking, leading to enhanced fatigue resistance. The atomistic simulations show that fatigue crack growth in nanotwinned Cu conforms to Paris’ law. In conjunction with the experimental results, we obtain a quantitative estimation of the Paris’ law exponent (∼4.0), which is in agreement with the theoretical predictions from the damage accumulation model.

Shear modulus and damping ratio of sand-granulated rubber mixtures

Recycled waste tires when mixed with soil can play an important role as lightweight materials in retaining walls and embankments, machine foundations and railroad track beds in seismic zones. Having high damping characteristic, rubbers can be used as either soil alternative or mixed with soil to reduce vibration when seismic loads are of great concern. Therefore, the objective of this work was to evaluate the dynamic properties of such mixtures prior to practical applications. To this reason, torsional resonant column and dynamic triaxial experiments were carried out and the effect of the important parameters like rubber content and ratio of mean grain size of rubber solids versus soil solids (D 50,r/D 50,s) on dynamic response of mixtures in a range of low to high shearing strain amplitude from about 4×10-4% to 2.7% were investigated. Considering engineering applications, specimens were prepared almost at the maximum dry density and optimum moisture content to model a mixture layer above the ground water table and in low precipitation region. The results show that tire inclusion significantly reduces the shear modulus and increases the damping ratio of the mixtures. Also decrease in D 50,r/D 50,s causes the mixture to exhibit more rubber-like behavior. Finally, normalized shear modulus versus shearing strain amplitude curve was proposed for engineering practice.

Erosion difference of growth and nucleation sides of free-standing diamond films prepared by DC arc plasma jet CVD

Solid particle erosion behaviors of the nucleation and growth surface of free-standing diamond films as a function of erosion time were studied by a laboratory designed blast type erosion apparatus. The surface roughness and the transmission loss were used to evaluate the extent of erosion performance. Results showed that the erosion damage features generated by impact appeared after erosion for 5s and 30s for nucleation and growth surface of diamond films respectively, and primarily occurred at grain boundaries in the form of micro-cracks. Then the local chipping of small sections on the border of cracks was followed resulting in material removal. The threshold erosion time, to maintain the transmission at 10.6μm still above 60%, was 60s and 300s for nucleation and growth surface of diamond films. The growth surface of diamond films exhibited about 5 times higher erosion resistance for ending up with relatively lower surface roughness and transmission loss compared with the nucleation surface, which was in accordance with the ratio of grain sizes.

Study of Work-Function Variation for High-<inline-formula> <tex-math notation="LaTeX">$\kappa $ </tex-math></inline-formula>/Metal-Gate Ge-Source Tunnel Field-Effect Transistors

The work-function variation (WFV) in high- $\kappa $ /metal-gate (HK/MG) Ge-source tunnel FETs (TFETs) is evaluated using technology computer-aided design simulations. By matching the simulation results with the plot for the ratio of the average grain size to the gate area (i.e., the RGG plot), we find that the slope in the RGG plot for the TFET can be significantly altered depending on three main factors, namely, the gate width, average grain size, and equivalent oxide thickness. In addition, it is verified that the variation of channel potential affects the WFV-induced threshold voltage variation in HK/MG Ge-source TFETs.

Forming micro channels on aluminum foils by using flexible die forming process

A flexible die forming process is proposed to form aluminum micro channels with channel widths not larger than 1mm. Three micro channel dies and two different polyurethanes (40A and 90A) were used to form micro channels on the annealed and as-received aluminum foils (50 and 75μm). For understanding the influences of size effects, polyurethane hardness and channel width on forming micro channels, a series of experiments were conducted. Through using different annealing conditions, different grain sizes were obtained such that different T/D, the ratio of thickness and average grain size, could be obtained. T/D ratio is used as a parameter to model the size effects in the two models proposed in this paper. These two models can predict the depths of the micro channels formed by the proposed process, so they can be used by industry as a design tool for product design, process design and development, annealing process, etc.

Microstructural evolution in bitaxial crack‐seal veins: A phase‐field study

AbstractBitaxial crack sealing by epitaxial crystal growth is the most common vein‐forming process in Earth's crust, but the details of the microstructural processes in these are not well understood. Here we model the evolution of bitaxial crack‐seal quartz veins in two and three dimensions, using the phase‐field method. Our numerical simulations show the influence of different parameters, such as the obliquity of crack opening and crack location, grain size, and orientations on the evolving vein microstructure. We examine the underlying growth competition observed during epitaxial growth of quartz. Results show many similarities with natural microstructures such as stretched crystals and compare well with the previous numerical findings. As the ratio of crack aperture and matrix grain size for the present studies is chosen to be sufficiently large for growth competition to occur before complete sealing, it leads to the formation of crystal fragments along the crack‐opening trajectory. We explain how such fragment trails act as potential indicators of the opening of crack‐seal veins, if they are confirmed to be common in natural microstructures. Finally, we highlight the importance of accounting for the third dimension in the numerical simulations by analyzing the evolution of fluid connectivity in 2‐D and 3‐D during the sealing process.

Fatigue and Fracture Behaviors of Nickel-Based Forging GH4169 Superalloy and Optimization of Model Parameters

The aim of this paper was to identify the high-temperature low-cycle fatigue (HTLCF) performances and optimize model parameters of nickel-based GH4169 superalloy. Microanalysis revealed that fatigue lives of specimens obtained from different regions of inhomogeneous radical forging disc were determined by their microstructures, such as the uniformity ratio of grain size and the distribution of δ phase along the grain boundary. Typical fatigue characteristics of all specimens were investigated after HTLCF tests through the analysis on fracture morphologies and secondary cracks. Then, an evolution and optimization process of model parameters in ɛ-N curves was proposed.

The influence of axial compressive stresses on the formability and scattering of process parameters in micro-hydroforming processes of tubes

Feasible product geometries manufactured with micro-hydroforming, as well as process stability are crucially influenced by the microstructure of the used tube material. The higher ratio of grain size to tube wall thickness d k / t 0 in micro-hydroforming, compared to conventional tube hydroforming, leads to an increase of scattering of process parameters and instabilities. This paper presents experimental and theoretical results for the micro-hydroforming of tubes made from stainless steel and from platinum with a focus on the correlations between the microstructure of the workpiece material, the stress state during forming and the resulting stability of the forming process. Investigated tube dimensions were 800 µm outer diameter and 40 µm wall thickness of the steel tubes, respectively 1650 µm and 76 µm of the platinum tubes. The average ratio d k / t 0 was about 0.3 for the steel material and about 0.9 for the platinum alloy. It has been shown that superimposed axial stresses are suitable to reduce the restricting influence of an increased ratio d k / t 0 and to improve the forming result as well as the process stability.

Impact of Current Flow Shape in Tapered (Versus Rectangular) FinFET on Threshold Voltage Variation Induced by Work-Function Variation

Depending on the real fin shape in a FinFET (i.e., rectangular versus tapered fin), the impact of the current flow shape in both rectangular and tapered FinFETs on threshold voltage variation induced by work-function variation is investigated by performing extensive 3-D TCAD simulations. It is found that if a FinFET has two independent (versus single and bulky) current flow in the channel, the extended gate area should be (should not be) included in calculating the ratio of average grain size to gate area (RGG) to agree with a previously validated FinFET RGG plot. Depending on the current flow shape in a FinFET, the RGG calculation should be refined.

The Prediction Methods for Potential Suspended Solids Clogging Types during Managed Aquifer Recharge

The implementation and development of managed aquifer recharge (MAR) have been limited by the clogging attributed to physical, chemical, and biological reactions. In application field of MAR, physical clogging is usually the dominant type. Although numerous studies on the physical clogging mechanism during MAR are available, studies on the more detailed suspended clogging types and its prediction methods still remain few. In this study, a series of column experiments were inducted to show the process of suspended solids clogging process. The suspended solids clogging was divided into three types of surface clogging, inner clogging and mixed clogging based on the different clogging characteristics. Surface clogging indicates that the suspended solids are intercepted by the medium surface when suspended solids grain diameter is larger than pore diameter of infiltration medium. Inner clogging indicates that the suspended solids particles could transport through the infiltration medium. Mixed clogging refers to the comprehensive performance of surface clogging and inner clogging. Each suspended solids clogging type has the different clogging position, different changing laws of hydraulic conductivity and different deposition profile of suspended solids. Based on the experiment data, the ratio of effective medium pore diameter (Dp) and median grain size of suspended solids (d50) was proposed as the judgment index for suspended solids clogging types. Surface clogging occurred while Dp/d50 was less than 5.5, inner clogging occurred while Dp/d50 was greater than 180, and mixed clogging occurred while Dp/d50 was between 5.5 and 180. In order to improve the judgment accuracy and applicability, Bayesian method, which considered more ratios of medium pore diameter (Dp) and different level of grain diameter of suspended solids (di), were developed to predict the potential suspended solids types.

Effect of Filter Designs on Hydraulic Properties and Well Efficiency

To analyze the effect of filter pack arrangement on the hydraulic properties and the well efficiency of a well design, a step drawdown was conducted in a sand-filled tank model. Prior to the test, a single filter pack (SFP), granule only, and two dual filter packs (DFPs), type A (granule-pebble) and type B (pebble-granule), were designed to surround the well screen. The hydraulic properties and well efficiencies related to the filter packs were evaluated using the Hazen's, Eden-Hazel's, Jacob's, and Labadie-Helweg's methods. The results showed that the hydraulic properties and well efficiency of the DFPs were higher than those of a SFP, and the clogging effect and wellhead loss related to the aquifer material were the lowest owing to the grain size and the arrangement of the filter pack. The hydraulic conductivity of the DFPs types A and B was about 1.41 and 6.43 times that of a SFP, respectively. In addition, the well efficiency of the DFPs types A and B was about 1.38 and 1.60 times that of the SFP, respectively. In this study, hydraulic property and well efficiency changes were observed according to the variety of the filter pack used. The results differed from the predictions of previous studies on the grain-size ratio. Proper pack-aquifer ratios and filter pack arrangements are primary factors in the construction of efficient water wells, as is the grain ratio, intrinsic permeability (k), and hydraulic conductivity (K) between the grains of the filter packs and the grains of the aquifer.

Analysis of carbon nanotube shortening and composite strengthening in carbon nanotube/aluminum composites fabricated by multi-pass friction stir processing

Carbon nanotubes (CNTs) were dispersed into Al matrix by multi-pass friction stir processing (FSP) to fabricate 4.5vol.% CNT/2009Al composites. The maximum strength of the composites was obtained with three-pass FSP and was attributed to the combined effect of CNT cluster reduction, grain refinement, and CNT shortening. A CNT shortening model is proposed to describe the CNT length change with FSP passes. The model indicates that the reciprocal of the CNT length has a linear relationship with the duration of the mechanical effect, which was verified by our and other investigators’ experimental results on various mechanical processes. Based on the concept of the load transfer efficiency of CNTs in the Al matrix, a universal strength model considering the microstructural parameters – the aspect ratio of CNTs, grain size, and concentration of CNT clusters and pores – is proposed to predict the strengthening of the CNT/2009Al composites with and without CNT clusters. The predictions are in good agreement with the experimental results.

Study of High-$k$/Metal-Gate Work Function Variation in FinFET: The Modified RGG Concept

Because the existing ratio of average grain size to gate area (RGG) method is not applicable for calculating the work function variation (WFV) in nonplanar device structures, a modified RGG method is used to quantitatively estimate the WFV in a high-k/metal-gate (HK/MG) FinFET. A plot of the calculated WFV against the RGG for the FinFET with a TiN gate-stack is validated by previous simulation results. The standard deviation of the WFV, σ(WFV), of the nonplanar multigate device structure (e.g., the FinFET) is lower than that of a planar device structure by ~30%.

Study of High-k/Metal-Gate Work-Function Variation Using Rayleigh Distribution

By using a Monte Carlo simulation for the stochastic distribution of grain sizes, the work-function variation (WFV) in high-k/metal-gate (HK/MG) is quantitatively and simply estimated with improved physical validity, with a Rayleigh distribution. Based on the Rayleigh distribution for the grain sizes, the WFV calculation for a TiN gate-stack is validated by previous experimental and simulation results. Additionally, a parameter for the WFV, i.e., ratio of the average grain size to the gate area (RGG), is suggested in this paper. This paves a new path to answer the following questions: 1) to what extent can the grain size of metal-gate materials be minimized to satisfy statistical targets? 2) to what extent can the physical gate area of metal oxide semiconductor field-effect transistors be scaled down whether the total variation is mainly limited by the WFV? Finally, it is concluded that a new HK/MG gate-stack should be developed to have the slope of <; 122 mV in the σ (WFV) versus RGG plot.