Aspects of Grain Size Strengthening in Polycrystals

2001 ◽  
Vol 683 ◽  
Author(s):  
Dilip Chandrasekaran ◽  
Kjell Pettersson
Keyword(s):  
Experimental Data ◽  
Grain Size ◽  
Simple Model ◽  
Grain Boundaries ◽  
Yield Point ◽  
Strengthening Effect ◽  
Petch Relationship ◽  
Sharp Yield Point

ABSTRACTThe strengthening effect of grain boundaries is well established and observed experimentally as the Hall-Petch relationship. In this paper different mechanisms proposed in the literature to explain the observed Hall-Petch effect are reviewed critically. The fundamental implications of the different approaches are discussed with reference to experimental data for two different classes of materials;-Materials with locked dislocations, i.e. with a sharp yield point behaviour.-Materials without locked dislocations, i.e. with a smooth yielding behaviour.It is shown that a simple model (Bergström) can be used to understand the grain size strengthening in the latter class of materials while more work is needed to quantitatively understand the behaviour of materials showing a sharp yield point.

What is Behind the Inverse Hall-Petch Behavior in Nanocrystalline Materials?

2006 ◽  
Vol 976 ◽  
Author(s):  
Christopher Carlton ◽  
P. J. Ferreira
Keyword(s):  
Grain Size ◽  
Yield Strength ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Critical Value ◽  
Petch Relationship ◽  
And Diffusion ◽  
Critical Grain Size

AbstractAn inverse Hall-Petch effect has been observed for nanocrystalline materials by a large number of researchers. This result implies that nanocrystalline materials get softer as grain size is reduced below a critical value. Postulated explanations for this behavior include dislocation based mechanisms and diffusion based mechanisms. In this paper, we report an explanation for the inverse Hall-Petch effect based on the statistical absorption of dislocations by grain boundaries, showing that the yield strength is both dependent on strain rate and temperature, and that it deviates from the Hall-Petch relationship at a critical grain size.

Modeling of Thermal Conductivity of Polycrystalline GaN Films

2003 ◽  
Vol 764 ◽  
Author(s):  
D. Kotchetkov ◽  
A. A. Balandin
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Grain Size ◽  
Grain Boundaries ◽  
Theoretical Investigation ◽  
Interface Structure ◽  
Hopping Transport ◽  
Model Predictions ◽  
Size Dispersion ◽  
Transport Approach

AbstractWe present preliminary results of a theoretical investigation of the thermal conductivity of polycrystalline GaN films. It is assumed that grain boundaries play a major role in limiting the thermal conductivity, which is calculated using the phonon-hopping transport approach. The effect of the grain size, size dispersion, and inter-grain interface structure on the thermal conductivity values is analyzed. The obtained results are compared with available experimental data for polycrystalline films and model predictions for crystalline GaN films.

Interfacial studies in Nb3Sn superconductors

1991 ◽  
Vol 49 ◽  
pp. 590-591
Author(s):  
Ernest L. Hall ◽  
Lee E. Rumaner ◽  
Mark G. Benz
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Flux Pinning ◽  
Size Control ◽  
High Magnetic Fields ◽  
Type Ii ◽  
Reaction Interface ◽  
Liquid Diffusion ◽  
Type Ii Superconductor ◽  
Grain Size Control

The intermetallic compound Nb3Sn is a type-II superconductor of interest because it has high values of critical current density Jc in high magnetic fields. One method of forming this compound involves diffusion of Sn into Nb foil containing small amounts of Zr and O. In order to maintain high values of Jc, it is important to keep the grain size in the Nb3Sn as small as possible, since the grain boundaries act as flux-pinning sites. It has been known for many years that Zr and O were essential to grain size control in this process. In previous work, we have shown that (a) the Sn is transported to the Nb3Sn/Nb interface by liquid diffusion along grain boundaries; (b) the Zr and O form small ZrO2 particles in the Nb3Sn grains; and (c) many very small Nb3Sn grains nucleate from a single Nb grain at the reaction interface. In this paper we report the results of detailed studies of the Nb3Sn/Nb3Sn, Nb3Sn/Nb, and Nb3Sn/ZrO2 interfaces.

Slip traces caused by plastic deformation during recrystallization of thin metal sheets

1994 ◽  
Vol 52 ◽  
pp. 620-621
Author(s):  
H. Lin ◽  
D. P. Pope
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Sample Thickness ◽  
List Type ◽  
Metal Sheets ◽  
Second Phases ◽  
Slip Traces ◽  
Series Of Experiments ◽  
Cold Rolled ◽  
Individual Grains

During a study of mechanical properties of recrystallized B-free Ni3Al single crystals, regularly spaced parallel traces within individual grains were discovered on the surfaces of thin recrystallized sheets, see Fig. 1. They appeared to be slip traces, but since we could not find similar observations in the literature, a series of experiments was performed to identify them. We will refer to them “traces”, because they contain some, if not all, of the properties of slip traces. A variety of techniques, including the Electron Backscattering Pattern (EBSP) method, was used to ascertain the composition, geometry, and crystallography of these traces. The effect of sample thickness on their formation was also investigated.In summary, these traces on the surface of recrystallized Ni3Al have the following properties:1.The chemistry and crystallographic orientation of the traces are the same as the bulk. No oxides or other second phases were observed.2.The traces are not grooves caused by thermal etching at previous locations of grain boundaries.3.The traces form after recrystallization (because the starting Ni3Al is a single crystal).4.For thicknesses between 50 μm and 720 μm, the density of the traces increases as the sample thickness decreases. Only one set of “protrusion-like” traces is visible in a given grain on the thicker samples, but multiple sets of “cliff-like” traces are visible on the thinner ones (See Fig. 1 and Fig. 2).5.They are linear and parallel to the traces of {111} planes on the surface, see Fig. 3.6.Some of the traces terminate within the interior of the grains, and the rest of them either terminate at or are continuous across grain boundaries. The portion of latter increases with decreasing thickness.7.The grain size decreases with decreasing thickness, the decrease is more pronounced when the grain size is comparable with the thickness, Fig. 4.8.Traces also formed during the recrystallization of cold-rolled polycrystalline Cu thin sheets, Fig. 5.

scholarly journals ODS EUROFER Steel Strengthened by Y-(Ce, Hf, La, Sc, and Zr) Complex Oxides

Metals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1148 ◽  
Author(s):  
Roman Husák ◽  
Hynek Hadraba ◽  
Zdeněk Chlup ◽  
Milan Heczko ◽  
Tomáš Kruml ◽  
...  
Keyword(s):  
Grain Size ◽  
Yield Strength ◽  
Complex Oxides ◽  
Oxide Dispersion Strengthened ◽  
Interparticle Spacing ◽  
Oxide Dispersion ◽  
Strengthening Effect ◽  
Dispersion Strengthening ◽  
Doping Element ◽  
Average Grain Size

Oxide dispersion-strengthened (ODS) materials contain homogeneous dispersions of temperature-stable nano-oxides serving as obstacles for dislocations and further pinning of grain boundaries. The strategy for dispersion strengthening based on complex oxides (Y-Hf, -Zr, -Ce, -La) was developed in order to refine oxide dispersion to enhance the dispersion strengthening effect. In this work, the strengthening of EUROFER steel by complex oxides based on Y and elements of the IIIB group (lanthanum, scandium) and IVB group (cerium, hafnium, zirconium) was explored. Interparticle spacing as a dispersoid characteristic appeared to be an important factor in controlling the dispersion strengthening contribution to the yield strength of ODS EUROFER steels. The dispersoid size and average grain size of ODS EUROFER steel were altered in the ranges of 5–13 nm and 0.6–1.7 µm, respectively. Using this strategy, the yield strength of the prepared alloys varied between 550 MPa and 950 MPa depending on the doping element.

scholarly journals Microstructural evolution during high-temperature tensile creep at 1,500°C of a MoSiBTiC alloy

2020 ◽  
Vol 39 (1) ◽  
pp. 136-145 ◽  
Author(s):  
Sojiro Uemura ◽  
Shiho Yamamoto Kamata ◽  
Kyosuke Yoshimi ◽  
Sadahiro Tsurekawa
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Grain Boundary Sliding ◽  
Primary Creep ◽  
Tensile Creep ◽  
Tertiary Creep ◽  
Continuous Dynamic Recrystallization ◽  
Continuous Dynamic ◽  
Creep Regime

AbstractMicrostructural evolution in the TiC-reinforced Mo–Si–B-based alloy during tensile creep deformation at 1,500°C and 137 MPa was investigated via scanning electron microscope-backscattered electron diffraction (SEM-EBSD) observations. The creep curve of this alloy displayed no clear steady state but was dominated by the tertiary creep regime. The grain size of the Moss phase increased in the primary creep regime. However, the grain size of the Moss phase was found to remarkably decrease to <10 µm with increasing creep strain in the tertiary creep regime. The EBSD observations revealed that the refinement of the Moss phase occurred by continuous dynamic recrystallization including the transformation of low-angle grain boundaries to high-angle grain boundaries. Accordingly, the deformation of this alloy is most likely to be governed by the grain boundary sliding and the rearrangement of Moss grains such as superplasticity in the tertiary creep regime. In addition, the refinement of the Moss grains surrounding large plate-like T2 grains caused the rotation of their surfaces parallel to the loading axis and consequently the cavitation preferentially occurred at the interphases between the end of the rotated T2 grains and the Moss grains.

scholarly journals Study on the erosion of Mo/ZrO2 alloys in glass melting process

2020 ◽  
Vol 39 (1) ◽  
pp. 595-598
Author(s):  
Cui Chaopeng ◽  
Zhu Xiangwei ◽  
Li Qiang ◽  
Zhang Min ◽  
Zhu Guangping
Keyword(s):  
Grain Size ◽  
Corrosion Resistance ◽  
Powder Metallurgy ◽  
Hydrothermal Synthesis ◽  
Grain Boundaries ◽  
Electrode Material ◽  
Glass Melting ◽  
Melting Process ◽  
Fine Grain ◽  
Conventional Electrode

AbstractThe Mo/ZrO2 electrode was prepared by combining hydrothermal synthesis with powder metallurgy, and this new electrode material has a totally different microstructure from the conventional electrode. The grain size of the new electrode was fine, and the size of ZrO2 in the alloy reached 200 nm. According to the results, the Mo–ZrO2 electrode has better performance, because the erosion occurs along the grain boundaries. Meanwhile, the new electrode, based on its fine grain, can effectively improve the corrosion resistance of the electrode.

scholarly journals Effect of Rare Earth Ce on Deep Stamping Properties of High-Strength Interstitial-Free Steel Containing Phosphorus

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1473
Author(s):  
Hao Wang ◽  
Yanping Bao ◽  
Chengyi Duan ◽  
Lu Lu ◽  
Yan Liu ◽  
...  
Keyword(s):  
Solid Solution ◽  
Grain Size ◽  
Rare Earth ◽  
High Strength ◽  
Rolling Process ◽  
P Element ◽  
Second Phase ◽  
Strengthening Effect ◽  
Interstitial Free ◽  
If Steel

The influence of rare earth Ce on the deep stamping property of high-strength interstitial-free (IF) steel containing phosphorus was analyzed. After adding 120 kg ferrocerium alloy (Ce content is 10%) in the steel, the inclusion statistics and the two-dimensional morphology of the samples in the direction of 1/4 thickness of slab and each rolling process were observed and compared by scanning electron microscope (SEM). After the samples in each rolling process were treated by acid leaching, the three-dimensional morphology and components of the second phase precipitates were observed by SEM and energy dispersive spectrometer (EDS). The microstructure of the sample was observed by optical microscope, and the grain size was compared. Meanwhile, the content and strength of the favorable texture were analyzed by X-ray diffraction (XRD). Finally, the mechanical properties of the product were analyzed. The results showed that: (1) The combination of rare earth Ce with activity O and S in steel had lower Gibbs free energy, and it was easy to generate CeAlO3, Ce2O2S, and Ce2O3. The inclusions size was obviously reduced, but the number of inclusions was increased after adding rare earth. The morphology of inclusions changed from chain and strip to spherical. The size of rare earth inclusions was mostly about 2–5 μm, distributed and dispersed, and their elastic modulus was close to that of steel matrix, which was conducive to improving the structure continuity of steel. (2) The rare earth compound had a high melting point. As a heterogeneous nucleation point, the nucleation rate was increased and the solidification structure was refined. The grade of grain size of products was increased by 1.5 grades, which is helpful to improve the strength and plasticity of metal. (3) Rare earth Ce can inhibit the segregation of P element at the grain boundary and the precipitation of Fe(Nb+Ti)P phase. It can effectively increase the solid solution amount of P element in steel, improve the solid solution strengthening effect of P element in high-strength IF steel, and obtain a large proportion of {111} favorable texture, which is conducive to improving the stamping formability index r90 value.

On the Nature of Grain Boundaries in Nanocrystalline Diamond

MRS Bulletin ◽  
1998 ◽  
Vol 23 (9) ◽  
pp. 36-41 ◽  
Author(s):  
P. Keblinski ◽  
D. Wolf ◽  
F. Cleri ◽  
S.R. Phillpot ◽  
H. Gleiter
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Active Sites ◽  
Critical Role ◽  
Diamond Films ◽  
Structural Disorder ◽  
Nanocrystalline Diamond ◽  
High Wear Resistance ◽  
Atomic Structures ◽  
Nanocrystalline Diamond Films

The low-pressure synthesis of rather pure nanocrystalline diamond films from fullerene precursors suggests that for a small enough grain size the diamond structure may be energetically preferred over graphite. Because of the small grain size of typically about 15 nm in these films, a significant fraction of the carbon atoms is situated in the grain boundaries (GBs). The surprisingly high wear resistance of these films even after the substrate is removed and their high corrosion resistance suggest that the grains are strongly bonded. Grain-boundary carbon is also believed to be responsible for the absorption and scattering of light in these films, for their electrical conductivity, and for their electron-emission properties. In spite of all these indications of a critical role played by GB carbon in achieving the remarkable properties of nanocrystalline diamond films, to date the atomic structures of the GBs are essentially not known.It is well-known that the electronic and optical properties of polycrystalline silicon films are significantly affected by the presence of GBs. For example GBs can provide active sites for the recombination of electron-hole pairs in photovoltaic applications. Also, in electronic devices such as thin-film transistors, GBs are known to play an important role. Because of silicon's strong energetic preference for sp3 hybridization over other electronic configurations, the structural disorder in silicon GBs is accommodated by a distortion of the tetrahedral nearestneighbor bonds and in the extreme by the creation of dangling bonds—that is, of three-coordinated Si atoms each having one unsaturated, bound electron in an otherwise more or less tetrahedrally coordinated environment.

scholarly journals Structural and Electrical Studies on ZnO-Based Thin Films by Laser Irradiation

2016 ◽  
Vol 2016 ◽  
pp. 1-6 ◽  
Author(s):  
Shanyue Zhao ◽  
Yinqun Hua ◽  
Ruifang Chen ◽  
Jian Zhang ◽  
Ping Ji
Keyword(s):  
Thin Films ◽  
Grain Size ◽  
Electrical Properties ◽  
Grain Boundaries ◽  
Laser Irradiation ◽  
Nonlinear Coefficient ◽  
Acceptor State ◽  
Xrd Pattern ◽  
Electrical Studies ◽  
Structural And Electrical Properties

The effects of laser irradiation on the structural and electrical properties of ZnO-based thin films were investigated. The XRD pattern shows that the thin films were highly textured along thec-axis and perpendicular to the surface of the substrate. Raman spectra reveal that Bi2O3segregates mainly at ZnO-ZnO grain boundaries. After laser irradiation processing, the grain size of the film was reduced significantly, and the intrinsic atomic defects of grain boundaries and Bi element segregated at the grain boundary were interacted frequently and formed the composite defects of acceptor state. The nonlinear coefficient increased to 24.31 and the breakdown voltage reduced to 5.34 V.

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