scholarly journals Elastic Slow Dynamics in Polycrystalline Metal Alloys

2021 ◽  
Vol 11 (18) ◽  
pp. 8631
Author(s):  
Jan Kober ◽  
Alena Kruisova ◽  
Marco Scalerandi
Keyword(s):  
Granular Media ◽  
Spatial Scales ◽  
Metal Alloys ◽  
Grain Structure ◽  
Slow Dynamics ◽  
Physical Origin ◽  
Reliable Measurement ◽  
Polycrystalline Metal ◽  
Polycrystalline Metals ◽  
External Strain

Elastic slow dynamics, consisting in a reversible softening of materials when an external strain is applied, was experimentally observed in polycrystalline metals and presents analogies with the same phenomenon more widely observed in consolidated granular media. Since the effect is extremely small in metals, precise experimental techniques are needed. Reliable measurement of relative velocity variations of the order of 10−7 is crucial to perform the analysis. In addition, the grain structure and the nature of grain boundaries in metals is very different from that in rocks or concrete. Therefore, linking relaxation elastic effects to the microstructure is needed to understand the physical origin of slow dynamics in metals. Here, interpreting the relaxation phenomenon as a multirelaxation process, we show that it is sensitive to the spatial scale at the microstructural level, up to the point of allowing the identification of the existence of features at different spatial scales, particularly distinguishing damage from microstructural inhomogeneities.

On the Relation between R-Value of a Grain and the Operating Slip Systems of the Grain

2014 ◽  
Vol 626 ◽  
pp. 566-569
Author(s):  
Takeji Abe
Keyword(s):  
Thin Sheet ◽  
Uniaxial Tensile ◽  
Surface Roughening ◽  
Slip Systems ◽  
Polycrystalline Metal ◽  
Polycrystalline Metals ◽  
Thin Sheet Metal ◽  
R Value ◽  
Rate Type ◽  
Active Slip

The r-value is defined as the ratio of the width strain to the thickness strain under uniaxial tensile loading. The r-value can be defined for each grain in polycrystalline metal during plastic deformation. It was pointed out that r-value of a grain affects the surface roughening of polycrystalline metal, and hence also affects the formability of thin sheet metal. On the other hand, it was shown that by using a rate-type constitutive relation for crystal slips the effect of the number of active slip systems on the yield curves is clarified. In the present paper, the relation between r-value of a grain and its operating slip systems in polycrystalline metals is studied.

Results from In-Situ, Real-Time SEM Observations of Grain Growth in Polycrystalline Metal

2004 ◽  
Vol 467-470 ◽  
pp. 875-880 ◽  
Author(s):  
I.M. Fielden
Keyword(s):  
Real Time ◽  
Grain Growth ◽  
Image Sequences ◽  
Growth Behaviour ◽  
Polycrystalline Metal ◽  
Polycrystalline Metals

The development of the converter plate detector has allowed the generation of real-time, in-situ image sequences of evolving microstructures in model and industrial polycrystalline metals. The principal metals investigated were steel, aluminium and gold. The raw video results allow a number of qualitative statements to be made about grain growth behaviour in these systems and some simplistic quantitative statements. However, the sheer volume and variety of data available in the time-stream of micrographs presents its own problems in identifying and extracting the information most useful for rigorous characterisation of the behaviour of a dynamically evolving microstructure. We present and discuss our approach to the analysis of this data and results of that analysis.

Longitudinal pore alignment in anodic alumina films grown on polycrystalline metal substrates

2013 ◽  
Vol 46 (6) ◽  
pp. 1705-1710 ◽  
Author(s):  
Ilya V. Roslyakov ◽  
Andrey A. Eliseev ◽  
Ekaterina V. Yakovenko ◽  
Alexander V. Zabelin ◽  
Kirill S. Napolskii
Keyword(s):  
Small Angle ◽  
High Sensitivity ◽  
Anodic Alumina ◽  
Grain Structure ◽  
Alumina Film ◽  
Polycrystalline Metal ◽  
Average Pore ◽  
Metal Substrates ◽  
Alumina Films ◽  
Anodic Alumina Film

A quantitative analysis of longitudinal pore alignment in anodic alumina films grown on polycrystalline metal substrates was performed on the basis of small-angle X-ray diffraction mapping. The very high sensitivity of the diffraction pattern to the orientation of the anodic alumina film allowed the average pore alignment within the irradiated area to be determined, with an accuracy better than 0.1°. It is shown that pores deviate from the orientation orthogonal to the metal surface by a small angle that is constant within a single-crystal grain. Strong correlation between the longitudinal pore alignment within the anodic alumina film and the grain structure of the aluminium substrate indicates the important role of the crystallographic orientation of the metal in the pore growth process.

The Challenges Associated with the Formation of Equiaxed Grains during Additive Manufacturing of Titanium Alloys

2018 ◽  
Vol 770 ◽  
pp. 155-164 ◽  
Author(s):  
David H. St John ◽  
Stuart D. McDonald ◽  
Michael J. Bermingham ◽  
Sri Mereddy ◽  
Arvind Prasad ◽  
...  
Keyword(s):  
Mechanical Performance ◽  
Temperature Gradients ◽  
Metal Alloys ◽  
Grain Structure ◽  
Grain Structures ◽  
Columnar Grains ◽  
High Cooling Rates ◽  
Columnar Grain ◽  
Equiaxed Grains ◽  
Equiaxed Grain

It is well established that columnar grain structures usually form when metal alloys are used to additively manufacture components. A challenging goal is to produce an equiaxed grain structure throughout the component to remove anisotropy and refine the grain size in order to improve its mechanical performance. The high cooling rates and associated high temperature gradients are the main reasons for the formation of columnar grains via epitaxial growth of each added layer of material. There appear to be limited strategies for promoting equiaxed nucleation of grains. In addition to cooling rate and temperature gradient, we explore other variables such as the potency of natural or added inoculant particles and the composition of the alloy, and their possible impact on the nucleation of equiaxed grains. Although changing the composition can help, finding a suitably potent nucleant particle is a major challenge. Operating parameters can also influence the microstructure and optimization to produce equiaxed grains may be possible. The limitations of these strategies and possible ways to overcome them are evaluated.

THE EFFECTS OF PLASTIC DEFORMATION ON MAGNETIC PROPERTIES OF POLYCRYSTALLINE METALS

1951 ◽  
Vol 29 (1) ◽  
pp. 21-31
Author(s):  
Ursula M. Martius
Keyword(s):  
Plastic Deformation ◽  
Magnetic Properties ◽  
Magnetic Flux ◽  
Crystallographic Orientation ◽  
Ferromagnetic Behavior ◽  
Polycrystalline Metal ◽  
Polycrystalline Metals ◽  
Ferromagnetic Domains ◽  
Polycrystalline Body ◽  
Crystal Boundaries

Most of the laws of the ferromagnetic behavior of metals and alloys were derived from studies of single crystals. In order to apply these laws to polycrystalline metals the effect of the crystallographic composition of the polycrystalline body has to be taken into account. For this purpose the concept of a "closed flux shell" as a fundamental quality of polycrystalline metal is put forward on the basis of the following trend of thought:One of the most important factors determining the size and arrangement of ferromagnetic domains in a single crystal is the tendency to close the magnetic flux throughout the specimen by a suitable arrangement of these domains. The size of the crystal defines the limits within which the flux can be closed. In a polycrystalline metal, a "crystal" is defined as a region of one crystallographic orientation separated by crystal boundaries from neighboring regions of different orientation. The corresponding unit, as far as ferromagnetic properties are concerned, will be a closed flux shell which may contain many domains but is always a region of closed magnetic flux. Neighboring regions, having different crystallographic orientation, will each also consist of a closed magnetic flux shell. Crystal boundaries are regarded as lattice discontinuities which separate regions of different orientation and at the same time separate different closed flux shells.The consequences of this model and experimental evidence supporting it are discussed. An explanation of the effect of plastic deformation on magnetic properties is suggested by considering the changes in the size of the closed flux shell which will occur during plastic deformation.

A Study on a Semimicroscopic Formulation of Inelastic Constitutive Equations of Polycrystalline Metals Subjected to a Large Deformation

1989 ◽  
Vol 111 (3) ◽  
pp. 294-298 ◽  
Author(s):  
M. Tokuda ◽  
K. Yamada ◽  
F. Havlicek
Keyword(s):  
Large Deformation ◽  
Constitutive Equations ◽  
Deformation Process ◽  
Grain Shape ◽  
Shape Change ◽  
Strain Range ◽  
Small Strain ◽  
Polycrystalline Metal ◽  
Polycrystalline Metals ◽  
Hardening Mechanisms

Work-hardening mechanisms of a polycrystalline metal significant in a large deformation range are different from those in a small strain range. That is, a texture development and an effect of grain shape change may be typical and important mechanisms in the large deformation process. In this paper, a set of inelastic constitutive equations incorporating two effects are derived theoretically on the basis of crystal plasticity.

Homochirality as the Signature of Extra-Terrestrial Life

1997 ◽  
Vol 161 ◽  
pp. 505-510
Author(s):  
Alexandra J. MacDermott ◽  
Laurence D. Barron ◽  
Andrè Brack ◽  
Thomas Buhse ◽  
John R. Cronin ◽  
...  
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Optical Rotation ◽  
Physical Origin ◽  
Natural Choice ◽  
Rosetta Mission ◽  
Terrestrial Life ◽  
Subsurface Layers ◽  
Solar System Bodies ◽  
Origin Of Homochirality

AbstractThe most characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. We therefore suggest that a search for extra-terrestrial life can be approached as a Search for Extra- Terrestrial Homochirality (SETH). The natural choice for a SETH instrument is optical rotation, and we describe a novel miniaturized space polarimeter, called the SETH Cigar, which could be used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. We believe that homochirality may be found in the subsurface layers on Mars as a relic of extinct life, and on other solar system bodies as a sign of advanced pre-biotic chemistry. We discuss the chiral GC-MS planned for the Roland lander of the Rosetta mission to a comet and conclude with theories of the physical origin of homochirality.

SEM analysis of DC magnetron sputtered beryllium films

1988 ◽  
Vol 46 ◽  
pp. 960-961
Author(s):  
E. F. Lindsey ◽  
C. W. Price ◽  
E. L. Pierce ◽  
E. J. Hsieh
Keyword(s):  
Fine Structure ◽  
Electron Emission ◽  
Secondary Electron ◽  
Low Voltage ◽  
Ion Beam ◽  
Secondary Electron Emission ◽  
Sem Analysis ◽  
Fused Silica ◽  
Grain Structure ◽  
Silica Substrate

Columnar structures produced by DC magnetron sputtering can be altered by using RF biased sputtering or by exposing the film to nitrogen pulses during sputtering, and these techniques are being evaluated to refine the grain structure in sputtered beryllium films deposited on fused silica substrates. Beryllium is brittle, and fractures in sputtered beryllium films tend to be intergranular; therefore, a convenient technique to analyze grain structure in these films is to fracture the coated specimens and examine them in an SEM. However, fine structure in sputtered deposits is difficult to image in an SEM, and both the low density and the low secondary electron emission coefficient of beryllium seriously compound this problem. Secondary electron emission can be improved by coating beryllium with Au or Au-Pd, and coating also was required to overcome severe charging of the fused silica substrate even at low voltage. The coating structure can obliterate much of the fine structure in beryllium films, but reasonable results were obtained by using the high-resolution capability of an Hitachi S-800 SEM and either ion-beam coating with Au-Pd or carbon coating by thermal evaporation.

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