The effect of grain size on the deformation resistance of nickel

The effect of the grain sizel of commerical nickel on the lower yield point, _y, and flow stress, _f , has been investigated. From the relationship between _y andl ^–1/2 and between _f andl ^–1/2, and also by extrapolation, the parameters ₁( _i ^f ) and k_y(kf), which occur in Petch's well-known expression, were determined. It was found that the values of these parameters depend on the previous history of the samples. It is suggested that the more marked dependence of the deformation resistance of nickel on grain size arising from certain thermal treatments is due to the segregation of impurities to the grain boundaries. It is shown that this is in accord with the presence of grain-boundary hardening and with its dependence on quenching temperature.     

Determining the effect of grain size and maximum induction upon coercive field of electrical steels

Although theoretical models have already been proposed, experimental data is still lacking to quantify the influence of grain size upon coercivity of electrical steels. Some authors consider a linear inverse proportionality, while others suggest a square root inverse proportionality. Results also differ with regard to the slope of the reciprocal of grain size–coercive field relation for a given material. This paper discusses two aspects of the problem: the maximum induction used for determining coercive force and the possible effect of lurking variables such as the grain size distribution breadth and crystallographic texture. Electrical steel sheets containing 0.7% Si, 0.3% Al and 24 ppm C were cold-rolled and annealed in order to produce different grain sizes (ranging from 20 to 150 μm). Coercive field was measured along the rolling direction and found to depend linearly on reciprocal of grain size with a slope of approximately 0.9 (A/m)mm at 1.0 T induction. A general relation for coercive field as a function of grain size and maximum induction was established, yielding an average absolute error below 4%. Through measurement of B₅₀ and image analysis of micrographs, the effects of crystallographic texture and grain size distribution breadth were qualitatively discussed.     

Crystallographic study of grain refinement in low and medium carbon steels

In order to clarify and articulate the long-standing problems associated with the role of various compounds in grain refinement of as-cast steels, a comprehensive crystallographic study on grain refiners in a number of low carbon steels has been conducted using the edge-to-edge matching (E2EM) model, which has been successfully applied to explain and predict effective grain refiners in light metals. Five commonly investigated compounds, namely NbO, CeS, TiN, Ce₂O₃ and TiC, in steels were examined. According to the extent of crystallographic matching, the predicted grain refining potency of these five grain refiners is ranked in the order of NbO > CeS > TiN > Ce₂O₃ > TiC, which is consistent with previously reported experimental results. Four different orientation relationships between δ-ferrite and these grain refiners were predicted. One of them has been verified by previously published experimental data. The similarity and the advantages of the E2EM model over conventional Bramfitt’s model were also discussed.     

The effect of grain size on the dispersion of the volume plasmon in Al-Mg-alloys

Dispersion measurements on the volume plasmon in fine dispersed Al-Mg-alloys of the two phase α + β structure show one or two plasmon peaks, depending on wavector k. The relative intensities of the two peaks are k-dependent.     

Fe含量和粒径对Fe/Cu颗粒膜结构和磁性的影响

采用共蒸发法制备不同组分的Fe/Cu颗粒膜,将样品分两组进行退火和不退火处理. 根据测量及分析,确定了不同成分的Fe/Cu颗粒膜的相组成和晶体结构;找出了 Fe/Cu颗粒膜矫顽力与粒径的关系,利用此关系由自发形核理论可知,提高功率,快速蒸镀薄膜,可得到细密颗粒的Fe/Cu颗粒膜,从而降低矫顽力,减少磁滞损耗.     

Effect of initial grain size on texture evolution and magnetic properties in nonoriented electrical steels

The magnetic properties of nonoriented electrical steels are influenced by the grain size and crystallographic texture. The technologies used to control the grain size in nonoriented electrical steels are approaching their limits. However, there is still some room for improvement of the magnetic properties through texture control. Hot-band annealing is known to be one of the most effective processing stages for texture modification. In this study, two types of initial grain sizes prior to cold rolling are obtained by different hot-band annealing. The effect of initial grain size on texture evolution and magnetic properties in nonoriented electrical steels containing 2% Si is examined. The specimens having different initial grain sizes have significantly different textures in the cold-rolled state and the annealed state. During the recrystallization stage, new grains formed in the coarse-grained specimens have stronger Goss but weaker γ-fibre texture than those in the fine-grained specimens. During the grain growth after complete recrystallization, the coarse-grained specimens still have weaker γ-fibre texture than the fine-grained specimens. The magnetic induction of the coarse-grained specimens is always higher at the same temperature than that of the fine-grained specimens. The core loss of the coarse-grained specimens is lower at the same temperature than that of fine-grained specimens. However, the improvement of the core loss becomes less pronounced as the annealing temperature increases.     

The effect of inclusion size on grain boundary wetting in Al-Sn alloys

The wetting behavior of liquid metal was studied for the Al-Sn system with particular reference to low Sn concentrations. It was shown that for Sn concentrations below 5 wt-%, liquid grain boundary films break up into separate inclusions, the wetting angle of which increases with decreasing inclusion size. Possible explanations for this phenomenon are discussed, and it is concluded that the wetting angle is not a fixed constant according solely to Young's equation, but that a correction factor is required for small inclusions.     

Effect of hot-band grain size and intermediate annealing on magnetic properties and texture of non-oriented silicon steels

The combination of the large hot-band grain size and an intermediate annealing with partial recrystallization in non-oriented silicon steel was tested in this paper. The magnetic properties of these samples were compared to the literature, indicating the favorable effect of both factors.     

Experimental and modeling studies of grain size and moisture content effects on radon emanation

Some models have already been developed to explain the effect of moisture content on the radon emanation fraction of soil. For this purpose, “microscopic” soil models, which are easy to deal with mathematically but cannot take grain size into consideration, have been designed. These previous models consist basically of two opposite grain surfaces and pores between the grains. In the present study, in order to study the effect of not only moisture content but also grain size, we present a simple modeling approach based on two “macroscopic” soil models: (1) a single-grain model and (2) a multiple-grain model. The latter model represents a configuration of spherical grains packed in a simple cubic structure. Based on these soil models and general assumptions, the radon emanation fraction was calculated as a function of grain size or moisture content by Monte Carlo simulation. The results for the multiple-grain model show that the radon emanation fraction is markedly increased with grain sizes ranging from 10 to 100 μm and reaches a constant value of 50% when moisture content is 0% and the radium is uniformly distributed on the grain surface. Moreover, a drastic increase is seen at smaller grain sizes with increasing moisture content. From these results, we concluded that the calculation of radon emanation depends greatly on the pore size between a Ra-bearing grain and a neighboring grain. The validity of the model was also evaluated by comparison to experimental data.     

The grain size effect on the magnetic properties in NiZn ferrite and the quality factor of the inductor

Polycrystalline ferrite materials with the chemical composition of Ni_0.49Zn_0.49Co_0.02Fe_1.90O_x have been fabricated using the conventional ceramic sintering method. Grain sizes have been adjusted from ∼2.2 to ∼13.5 μm with changing sintering conditions. From the measurements of the complex permeability, it is suggested that the permeability is dominated only by the spin rotation at mono-domain state and both domain wall and spin rotation contribute at multi-domain state. At mono-domain state, the core loss has been drastically decreased similar to the other work. The measurement result for the loss angle indicates that the low loss state can be maintained up to the higher magnetic field with smaller grain size in spite of the mono-domain state. The simplified wire-wounded type inductors have been also fabricated and characterized. The results have shown that the inductor fabricated with the smaller grain size has a better performance in the quality value under relatively higher current.     

The effect of grain size distribution on the frequency dependence of the ultrasonic attenuation in polycrystalline materials

An expression has been derived for the effect of the grain size distribution in polycrystalline materials on the frequency dependence of the ultrasonic attenuation. It has been shown that two specimens with the same mean grain size can have significantly different ultrasonic attenuations if their grain size distributions are different and that no unique solution in terms of the grain size exists for a particular ultrasonic attenuation against frequency curve. Qualitative agreement has been found between the theory and some of the experimental data available.     

Influence of the grain size on the resistance of micro- and nanocrystalline metals against the neck-like localization of plastic deformation

The “high strength-low plasticity resource” dilemma associated with the macrolocalization of plastic deformation in the form of a neck in a stretched specimen, which leads to ductile failure of the specimen, has been theoretically discussed in the framework of the dislocation-kinetic approach. It has been quantitatively demonstrated using micro- and nanocrystalline metals as an example that their low plasticity resource (a small value of uniform strain before the beginning of the neck formation) and quasi-embrittlement result from the strong increase in the yield strength with a decrease in the grain size and the strain-hardening coefficient due to the annihilation of dislocations in the boundaries and bulk of grains.     

The interaction between Lateral size effect and grain size when scratching polycrystalline copper using a Berkovich indenter

It has been reported previously that, for single and polycrystalline copper (fcc), the indentation size effect and the grain size effect (GSE) can be combined in a single length-scale-dependent deformation mechanism linked to a characteristic length-scale calculable by a dislocation-slip-distance approach (X. D. Hou and N. M. Jennett, ‘Application of a modified slip-distance theory to the indentation of single-crystal and polycrystalline copper to model the interactions between indentation size and structure size effects,’ Acta Mater., Vol. 60, pp. 4128–4135, 2012). Recently, we identified a ‘lateral size effect (LSE)’ in scratch hardness measurements in single crystal copper, where the scratch hardness increases when the scratch size is reduced (A. Kareer, X. D. Hou, N. M. Jennett and S. V. Hainsworth ‘The existence of a lateral size effect and the relationship between indentation and scratch hardness’ Philos. Mag. published online 24 March 2016). This paper investigates the effect of grain size on the scratch hardness of polycrystalline copper with average grain sizes between 1.2 and 44.4 μm, when using a Berkovich indenter. Exactly the same samples are used as in the indentation investigation by Hou et al. (‘Application of a modified slip-distance theory to the indentation of single-crystal and polycrystalline copper to model the interactions between indentation size and structure size effects,’ Acta Mater., Vol. 60, pp. 4128–4135, 2012). It is shown that, not only does the scratch hardness increase with decreasing grain size, but that the GSE and LSE combine in reciprocal length (as found previously for indentation) rather than as a superposition of individual stresses. Applying the same (as indentation) dislocation-slip-distance-based size effect model to scratch hardness yielded a good fit to the experimental data, strongly indicating that it is the slip-distance-like combined length-scale that determines scratch hardness. A comparison of the fit parameters obtained by indentation and scratch on the same samples is made and some distinct differences are identified. The most striking difference is that scratch hardness is over four times more sensitive to grain size than is indentation hardness.     

The effect of grain size of the sample on the determination of the temperature and lattice defects factor by X-ray diffraction

Czechoslovak Journal of Physics - The influence of the particle effect on the distortion of the temperature and lattice defects coefficcient 2M as determined from integrated intensities of X-ray...     

The grain size distribution in nanocomposite films

The grain size distributions and related mechanisms in nanocomposite films with nanostructures comprising a nanocrystalline (nc) phase surrounded by an amorphous (a) matrix under different amorphous phase amounts (V _a) have been analyzed by using a Monte Carlo grain growth model. The results show that with the V _a value increasing to a critical value of ～28%, the grain size distribution approaches lognormality, and it becomes off-lognormal when the V _a value is larger or smaller than ～28%. The simulated results are in a good agreement with the experiment. It is shown that the homogenous or inhomogeneous grain growth mode, determined by the energy exerted on the grain boundary, originates in lognormal or off-lognormal grain size distributions in nanocomposite films. Also, in a system with lognormal grain size distribution, the amorphous phase just covers all grain boundaries (GBs) and the length obtained by summing the boundary circumference of all nanograins is the longest. It is expected that this microstructure can result in exceptional properties of nanocomposite films.