Mean grain size determination in marbles by ultrasonic velocity techniques

Grain size determinations by various ultrasonic techniques have been considered by several researches. In this paper, we have studied mean grain size determination of some marbles by using ultrasonic velocity measurements. We have represented ultrasonic velocity–grain size size master graph. Using this graph, we have compared mean grain size of marble samples by optic microscope images.     

Evaluation of mean grain size using the multi-scale ultrasonic attenuation coefficient

An evaluation model based on the multi-scale ultrasonic attenuation coefficient was developed to control both systematic error and random error. AISI 304 stainless steel was used to validate the presented model. Wavelet transformation was used to obtain the variation of ultrasonic signal over time and scale. Particle swarm optimization was utilized to correlate the coefficient with grain sizes. The model shows the attenuation of all scales increased with the grain size, and ultrasound attenuates faster on smaller scales. Compared with the ultrasonic velocity method and the traditional attenuation method, the proposed method has less systematic error and random error.     

Grain size influence on ultrasonic velocities and attenuation

During the last two decades, ultrasonic testing was developed as an efficient tool for materials characterization. Acoustical waves by their passage through materials, carry out a multitude of information contained in the signal on the mechanical and physical properties of the material under inspection. In this paper, an experimental study on steel samples has been performed to study the evolution of some ultrasonic parameters such as wave velocities and attenuation coefficients as function of the steel grains size. The experimental results obtained are discussed and analyzed in order to develop an ultrasonic non-destructive technique to grains size determination.     

Evaluating the grain size in curved components using the ultrasonic attenuation method with diffraction correction

Ultrasonic wave propagation in curved components was simulated based on the Multi-Gaussian beam theory to eliminate the negative influence of the surface curvature and water path on grain size attenuation evaluation. The multi-frequency weighted attenuation evaluation model with diffraction correction was introduced into the measured attenuation spectrum to control the systematic error. The experimental results show that for 6 blocks with different curvatures and the same mean grain size, the relative error was reduced from 15.41% to 4.28% by using the presented method, and the standard deviation of the error was 15.92% of that of the traditional method.     

Mechanisms for grain size hardening and softening in Zn

An analysis of the rate-controlling mechanisms corresponding to effect of grain size d=10⁻⁹ to 10⁻³ m on the flow stress of Zn at 300K and s⁻¹ was performed. Three grain size regimes were indicated: Regime I, d≈10⁻⁶–10⁻³ m, Regime II, d≈10⁻⁶–10⁻⁸ m and Regime III, d<10⁻⁸ m. Grain size hardening occurred in Regimes I and II and grain size softening in Regime III. The intersection of pyramidal forest dislocations by basal dislocations was concluded to be the rate-controlling mechanism in both Regimes I and II, the major effect of the grain size being on the forest and gliding dislocation densities. The absence of twinning and a dislocation cell structure distinguished Regime II from I. The grain size softening observed in Regime III is in better accord with grain boundary shear than with grain boundary diffusion creep.     

Process monitoring of moulding compounds by ultrasonic measurements in a compression mould

Current research addresses ultrasonic quality sensor utilisation for inline cure monitoring, to control and analyse compression moulding. In this investigation, an ultrasonic impulse transmission method was applied to directly monitor changes in the mechanical properties of moulding compounds throughout the whole cure cycle. These measurements were performed during the processing using transducers which were designed to operate at elevated temperature and pressure in a compression mould. Measurements of ultrasound velocity and variation of attenuation coefficient of longitudinal waves were performed following the cure cycle. Ultrasonic measurements were used to investigate the influence of different types of moulding compounds, artificial weathering at elevated temperatures, filler volume, moisture content as well as amount of hardener on the curing process.     

Extreme value analysis of tail departure from log-normality in experimental and simulated grain size distributions

Grain size data were taken from four three- and two-dimensional microstructures, including simulated grain growth, thin film and superalloy data sets. Probability plots revealed approximately log-normal distributions for experimental grain size data sets, but with systematic differences in the upper tails. A simulated grain size data set obtained from Potts model growth exhibited strong deviation from log-normality. A peaks-over-threshold analysis was applied to quantify the differences in the upper tails. Potts model simulation of normal grain growth shows the shortest tail, whereas the thin film data showed the longest tail (i.e. closest to log-normal), with an intermediate tail shape in the superalloy.     

Ultrasonic velocity measurements for estimation of grain size in austenitic stainless steel

Ultrasonic velocity measurements have been used to estimate average grain size in an AISI type 316 stainless steel. For precise ultrasonic transit time measurements, the pulse-echo-overlap technique has been used. Master graphs relating ultrasonic velocity with metallographically obtained grain size have been generated. Using these graphs, grain sizes in new specimen have been obtained. The results indicate that grain size can be predicted with good confidence level using ultrasonic velocity measurements. Shear waves are found to be more sensitive for grain size measurement, as compared to longitudinal waves. The grain size estimated by velocity measurements is found to be more accurate when compared to that obtained by attenuation measurements.     

标准砂在磨料粒度组成检测中的作用分析

磨料粗磨粒粒度组成检测的基本方法为筛分法。本文通过对磨料粒度组成检测时筛分条件对筛分结果的影响进行分析，得出标准砂在粒度组成检测中的两个作用：一是用来选择高精度的试验筛，二是对筛分结果进行校正，达到准确检测粒度组成，统一检测结果的目的。同时论述了标准砂的校正原理，并以实例对标准砂的作用进行了论证。     

Structure and composition heterogeneity of a FeAl alloy prepared by one-step synthesis and consolidation processing and their influence on grain size characterization

This paper aims to characterize a bulk dense FeAl (47 at.%) alloy synthesized and consolidated by one-step current-activated pressure-assisted processing of nanocrystalline elemental powders. The end-product was analyzed using a combination of scanning (SEM) and transmission electron microscopies (TEM), electron back-scattering diffraction (EBSD) as well as electron probe microanalysis (EPMA). Special attention was paid to verify the grain size (32–89 nm) previously determined by X-ray diffraction peak profile analysis. It has been found that this material displays equiaxed grains (0.8–4 μm in size) and contains limited structural defects like subgrains and dislocations. The EPMA result reveals that a variability in Al content (36–47 at.%) is present within the synthesized FeAl phase. Thus, the local variation of lattice parameters resulting from this heterogeneity accounts for the broadening of X-ray diffraction peaks instead of the common idea that the broadening is due to the small grain size. The formation mechanisms of the structure and the composition heterogeneity are also discussed and related to the combustion reaction process.     

Comparative effect of grain size and texture on the corrosion behaviour of commercially pure titanium processed by equal channel angular pressing

The effect of grain size and texture on the corrosion properties of commercially pure titanium was investigated. Equal channel angular pressing (ECAP) was used to produce different grain size and various crystallographic orientations. Electrochemical impedance spectroscopy was employed to measure the corresponding surfaces’ general corrosion resistance. Samples with the (0 0 0 2) planes parallel to the surface were found to offer the highest corrosion resistance, regardless of their grain size.     

Predicting grain refinement by cold severe plastic deformation in alloys using volume averaged dislocation generation

Grain refinement during severe plastic deformation (SPD) is predicted using volume averaged number of dislocations generated. The model incorporates a new expansion of a model for hardening in the parabolic hardening regime, in which the work hardening depends on the effective dislocation-free path related to the presence of non-shearable particles and solute–solute nearest-neighbour interactions. These two mechanisms give rise to dislocation multiplication in the form of generation of geometrically necessary dislocations and dislocations induced by local bond energies. The model predicts the volume averaged number of dislocations generated and considers that they distribute to create cell walls and move to existing cell walls/grain boundaries, where they increase the grain boundary misorientation. The model predicts grain sizes of Al alloys subjected to SPD over two orders of magnitude. The model correctly predicts the considerable influence of Mg content and content of non-shearable particles on the grain refinement during SPD.