Impact Of Grain Size Distribution Research Articles

Probing the impact of grain size distribution on the deformation behavior in fine-grained austenitic stainless steel: A critical analysis of unimodal structure versus bimodal structure

This study investigated the effect of grain size distribution on the deformation behavior in fine-grained (FG) austenitic stainless steels (γ-SSs). Commercial Cr–Mn–N γ-SS was selected as the coarse-grained (CG) specimen, which was cold rolled and then annealed at 1000 °C for 60 s and 700 °C for 3600 s to obtain FG specimens with similar grain sizes but different grain size distributions. The CG specimens annealed at 1000 °C for 60 s and 700 °C for 3600 s were referred to as unimodal-FG and bimodal-FG specimens, respectively. The tensile properties revealed that the yield strength was enhanced from 383 MPa to 685 MPa when the grain size was refined from CG (10.7 μm) to FG (∼1.8 μm). Moreover, the bimodal-FG specimen exhibited a higher total elongation of 48% than 36.5% for the unimodal-FG specimen. Transmission electron microscopy, electron backscatter diffraction and X-ray diffraction were used to identify the microstructural characteristics during tension. The results indicated that the main deformation mechanisms of γ-SSs specimens during tension were dislocation generation and accumulation at the initial stage, deformation twinning at the intermediate stage, and deformation-induced martensite (DIM) at the final stage. Compared with the unimodal-CG counterpart, grain refinement in the unimodal-FG specimens restricted the formation of DIM due to the increased austenite stability. A newly discovered phenomenon was that the bimodal-FG specimens promoted the formation of geometrically necessary dislocation (GND) and DIM compared to the unimodal-FG, which was due to the uneven deformation in grains located on hetero-boundaries (HBs). Moreover, the bimodal-FG specimen was preferentially formed DIM on HBs, especially in the smaller grains side rather than inside larger grains due to the higher stress concentration in smaller grains.

Impact of grain size distribution on the magnetic deterioration due to cutting of electrical steel sheets

Efforts to increase the power density and continuous power of electric machines have intensified the request for tailored non-grain oriented electrical steel grades. Possible measures to optimize electrical steel grades are the use of thinner gauges as well as grades with tailor-made microstructural properties. However, these grades are developed mainly focusing on the magnetic and mechanical properties, neglecting the detrimental and strongly material-dependent processing effect on the magnetic properties of electrical steel, especially the cutting influence. In this paper, the microstructure-dependence of the magnetic material deterioration due to guillotine cutting is studied on ten industrial non-grain oriented electrical steels with thicknesses between 0.1mm and 0.35mm, all of which the chemical composition, grain structure and texture is known. This allows a consideration of the interdependence of material thickness, microstructure, alloy content with the cutting effect. The magnetic deterioration is characterized on a single-sheet-tester with samples in rolling as well as transverse direction. The grain size distribution and homogeneity is evaluated and linked to magnetic-loss and magnetization-curve deterioration by means of statistical methods. As a result sheet-thickness-dependent microstructures are evaluated with respect to their cutting influence.

Permeability and physical properties of semi-compacted fine-grained sediments – A laboratory study to constrain mudstone compaction trends

Permeability and physical properties of fine-grained clastic sediments show a wide range of variations. Despite rather intensive research, the impact of grain size distribution and mineralogical composition of individual rock constituents is not thoroughly investigated. We performed mechanical compaction of brine-statured reconstituted borehole cuttings and synthetic quartz-clay mixtures to study the evolution of properties in fine-grained clastic sediments during burial. The primary objective was to examine whether the hydraulic and physical properties of fine-grained sediments could be described and constrained by binary quartz-clay mixtures. The synthetic binary mixtures were prepared by mixing quartz with non-swelling (kaolinite) and strongly-swelling (smectite) clays, which can represent the endmember properties within the clay minerals. In addition to vertical permeability, physical and seismic properties, stress-dependence of permeability, and two-phase relative permeability of brine-oil system were investigated. Experimental results show that grain size distribution and mineralogical composition control the vertical permeability. A well-constrained porosity-permeability bound is defined, where the compaction trends of pure quartz and quartz-smectite 15:85 (wt %) mixtures describe the maximum and minimum boundaries, respectively. The quartz-clay mixtures, however, fail to provide bounds to constrain the broad range of variations in physical and seismic properties of reconstituted aggregates, and consequently natural mudstones. It is crucial to incorporate microstructure into the permeability prediction models because the experiments indicated that the microscale characteristics control the macroscale fluid flow properties.

Impact of grain size and grain size distribution on the resistivity of metal nanocrystalline systems

The grain size effect of the resistivity in the metal nanocrystalline systems is known to stem mainly from grain boundaries. In this letter, we propose a semi-quantum model based on transfer-matrix approach to calculate the resistivity. In accord with the above results, the impact of grain size distribution on the resistivity of 2D and 3D metal nanocrystalline is surveyed. The findings show the change of the resistivity is associated with the number of grain boundaries per mean free path.

Plastic Deformation Modes in Mono- and Bimodal-Type Ultrafine-Grained Austenitic Stainless Steel

An attempt was made to track plastic tensile deformation modes operating in bulk ultrafine-grained austenitic stainless steel with mono- (maximum at ~0.6 μm) and bimodal-type (minimum at ~0.5 μm and maximum at ~1.65 μm) grain size distributions produced by cyclic thermal processing. Post tensile deformation electron backscatter diffraction studies were conducted to analyse the impact of grain size distribution on plastic deformation characteristics. The study revealed extensive strain localisation in the monomodal-type grain size distribution, leading to poor strain-hardening behaviour. On the other hand, the bimodal-type distribution disclosed a conventional dislocation-mediated deformation mechanism operating in the coarse grains, while it was restricted to initial small strains in ultrafine austenite grains. The subsequent deformation process in these ultrafine austenite grains was dictated by nucleation and autocatalytic growth of strain-induced α′-martensite. The observed martensitic transformation of ultrafine austenite grains in preference to coarse grains was attributed to activation of local ‘grain to grain’ interactions.

Impact of grain size distribution on the multiscale mechanical behavior of nanocrystalline materials

A macro–micro scale transition model based on self-consistent approximation is proposed to explore the effect of grain size and grain size distribution, along with the strain rate, on the mechanical response of nanocrystalline (nc) materials. The representative volume element (RVE) is composed of grains supposed to follow an elastic–viscoplastic behavior, and randomly distributed with a grain size distribution following a log-normal statistical function. The grain interior and grain boundary are not taken as two independent phases with different volume fractions, but as an integral object to sustain deformation mechanisms of grain-boundary sliding, grain-boundary diffusion and grain-interior plasticity. Numerical results for the case of nc copper are shown to be in good agreement with available experimental data. The predictions firstly display that not only the mean grain size plays an important role but also the grain size dispersion has a slight impact on the flow stress. A decrease of the yield stress with an increasing of the grain size dispersion occurs. Secondly, the strain rate sensitivity has strong effect on the mechanical behavior of nc materials and the effect increases with decreasing the grain size. Lastly, deviations of the internal stress and local strain from the overall stress and macroscopical strain occur, respectively. Local plastic strains and internal stresses, developing within the RVE, have been recorded and discussed. Using the present model, we have also studied the failure behavior of nc materials.

On the impact of grain size distribution on the plastic behaviour of polycrystalline metals

Recent experimental studies have reported improved combinations of strength and uniform elongation in ultrafine-grained polycrystals with bi-modal grain size distributions. Despite these results, the extent to which the grain size distribution affects macroscopic tensile response, particularly at large strains, is unclear. This issue is examined here for polycrystals with varying grain sizes and grain size distributions using a grain size dependent constitutive model within the viscoplastic self-consistent formalism. The evolution of the macroscopic and grain-level stresses and strains has been monitored as a function of the width and mean of the grain size distribution. As an example of highly heterogeneous structures, the stress–strain response of a number of bi-modal microstructures have been examined and compared with their uni-modal counterparts.

Impact of Grain Size Distribution of Gate Poly-Si on PMOSFET Performance

We studied the impact of grain size distribution of poly-Si gate on PMOSFET performance. It was found from voltage capacitance characteristic that the smaller grain size causes boron concentration to be depleted at gate dielectric film interface. Moreover, grain size affects the ultra thin gate dielectric film too. Boron is more penetrated to ultra thin gate dielectric film as initial grain size gets larger. The penetrated boron degrades hole mobility at channel region in PMOSFET. It was found for the first time that highest PMOSFET performance can be obtained by optimizing the grain size of gate poly-Si, which strongly impacts on the hole mobility as well as the depletion of boron concentration at gate dielectric film interface.

Impact of Grain Size Distribution of Gate Poly-Si on PMOSFET Performance

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