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Texture (crystalline)
Encyclopedia
In materials science
, texture is the distribution of crystallographic orientations of a polycrystalline
sample. A sample in which these orientations are fully random is said to have no texture. If the crystallographic orientations are not random, but have some preferred orientation, then the sample has a weak, moderate or strong texture. The degree is dependent on the percentage of crystals having the preferred orientation. Texture is seen in almost all engineered materials, and can have a great influence on material properties. Also, geologic rocks show texture due to their thermo-mechanic history of formation processes.
One extreme case is a complete lack of texture: a solid with perfectly random crystallite orientation will have isotropic properties at length scales sufficiently larger than the size of the crystallites. The opposite extreme is a perfect single crystal, which has anisotropic properties by geometric necessity.
) in Scanning Electron Microscope
s. Qualitative analysis can be done by Laue photography, simple X-ray diffraction or with the polarized microscope. Neutron
and synchrotron high-energy X-ray
diffraction allow access to textures of bulk material and in-situ analysis, whereas laboratory x-ray diffraction instruments are more appropriate for thin film textures.
Texture is often represented using a pole figure
, in which a specified crystallographic
axis (or pole) from each of a representative number of crystallites is plotted in a stereographic projection, along with directions relevant to the material's processing history. These directions define the so-called sample reference frame and are, because the investigation of textures started from the cold working of metals, usually referred to as the rolling direction RD, the transverse direction TD and the normal direction ND. For drawn metal wires the cylindrical fiber axis turned out as the sample direction around which preferred orientation is typically observed (see below).
) which can be achieved through evaluation of a set of pole figures or diffraction spectra. Subsequently, all pole figures can be derived from the 
.
The
is defined as the volume fraction of grains with a certain orientation 
.
The orientation
is normally identified using three Euler angles
. The Euler angles then describe the transition from the sample’s reference frame into the crystallographic reference frame of each individual grain of the polycrystal. One thus ends up with a large set of different Euler angles, the distribution of which is described by the
.
The orientation distribution function,
, cannot be measured directly by any technique. Traditionally both X-ray diffraction and EBSD may collect pole figures. Different methodologies exist to obtain the 
from the pole figures or data in general. They can be classified based on how they represent the 
. Some represent the 
as a function,
sum of functions or expand it in a series of harmonic functions. Others, known as discrete methods, divide the
space in cells and focus on determining the value of the 
in each cell.
In wire
and fiber
, all crystals tend to have nearly identical orientation in the axial direction, but nearly random radial orientation. The most familiar exceptions to this rule are fiberglass
, which has no crystal structure
, and carbon fiber
, in which the crystalline anisotropy is so great that a good-quality filament will be a distorted single crystal with approximately cylindrical symmetry (often compared to a jelly roll
). Single-crystal fibers are also not uncommon.
The making of metal sheet
often involves compression in one direction and, in efficient rolling operations, tension in another, which can orient crystallites in both axes by a process known as grain flow. However, cold work destroys much of the crystalline order, and the new crystallites that arise with annealing
usually have a different texture. Control of texture is extremely important in the making of silicon steel sheet for transformer
cores (to reduce magnetic
hysteresis
) and of aluminium cans (since deep drawing
requires extreme and relatively uniform plasticity
).
Texture in ceramic
s usually arises because the crystallites in a slurry
have shapes that depend on crystalline orientation, often needle- or plate-shaped. These particles align themselves as water leaves the slurry, or as clay is formed.
Casting
or other fluid-to-solid transitions (i.e., thin-film deposition) produce textured solids when there is enough time and activation energy for atoms to find places in existing crystals, rather than condensing as an amorphous solid
or starting new crystals of random orientation. Some facet
s of a crystal (often the close-packed planes) grow more rapidly than others, and the crystallites for which one of these planes faces in the direction of growth will usually out-compete crystals in other orientations. In the extreme, only one crystal will survive after a certain length: this is exploited in the Czochralski process
(unless a seed crystal
is used) and in the casting of turbine
blades and other creep
-sensitive parts.
resistance, weldability
, deformation behavior, resistance to radiation damage
, and magnetic susceptibility
can be highly dependent on the material’s texture and related changes in microstructure
. In many materials, properties are texture-specific, and development of unfavorable textures when the material is fabricated or in use can create weaknesses that can initiate or exacerbate failures. Parts can fail to perform due to unfavorable textures in their component materials. Failures can correlate with the crystalline textures formed during fabrication or use of that component.. Consequently, consideration of textures that are present in and that could form in engineered components while in use can be a critical when making decisions about the selection
of some materials and methods
employed to manufacture parts with those materials. When parts fail during use or abuse, understanding the textures that occur within those parts can be crucial to meaningful interpretation of failure analysis
data.
Tailoring the texture on demand became an important task in thin film technology. In the case of oxide compounds intended for transparent conducting film
s or surface acoustic wave
(SAW) devices, for instance, the polar axis should be aligned along the substrate normal. Another example is given by cables from high-temperature superconductors that are being developed as oxide multilayer systems deposited on metallic ribbons. The adjustment of the biaxial texture in YBa2Cu3O7 layers turned out as the decisive prerequisite for achieving sufficiently large critical currents.
The degree of texture is often subjected to an evolution during thin film growth and that most pronounced textures are only obtained after the layer has achieved a certain thickness. Thin film growers thus require information about the texture profile or the texture gradient in order to optimize the deposition process. The determination of texture gradients by x-ray scattering, however, is not straightforward, because different depths of a specimen contribute to the signal. Techniques that allow for the adequate deconvolution of diffraction intensity were developed only recently.
Materials science
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...
, texture is the distribution of crystallographic orientations of a polycrystalline
Polycrystalline
Polycrystalline materials are solids that are composed of many crystallites of varying size and orientation. The variation in direction can be random or directed, possibly due to growth and processing conditions. Fiber texture is an example of the latter.Almost all common metals, and many ceramics...
sample. A sample in which these orientations are fully random is said to have no texture. If the crystallographic orientations are not random, but have some preferred orientation, then the sample has a weak, moderate or strong texture. The degree is dependent on the percentage of crystals having the preferred orientation. Texture is seen in almost all engineered materials, and can have a great influence on material properties. Also, geologic rocks show texture due to their thermo-mechanic history of formation processes.
One extreme case is a complete lack of texture: a solid with perfectly random crystallite orientation will have isotropic properties at length scales sufficiently larger than the size of the crystallites. The opposite extreme is a perfect single crystal, which has anisotropic properties by geometric necessity.
Characterization and representation
Texture can be determined by various methods. Some of them allow a quantitative analysis of the texture; others are only qualitative. Among the quantitative techniques, the most widely used is X-ray diffraction using texture goniometers, followed by EBSD-method (electron backscatter diffractionElectron backscatter diffraction
Electron backscatter diffraction , also known as backscatter Kikuchi diffraction is a microstructural-crystallographic technique used to examine the crystallographic orientation of many materials, which can be used to elucidate texture or preferred orientation of any crystalline or polycrystalline...
) in Scanning Electron Microscope
Scanning electron microscope
A scanning electron microscope is a type of electron microscope that images a sample by scanning it with a high-energy beam of electrons in a raster scan pattern...
s. Qualitative analysis can be done by Laue photography, simple X-ray diffraction or with the polarized microscope. Neutron
Neutron diffraction
Neutron diffraction or elastic neutron scattering is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material: A sample to be examined is placed in a beam of thermal or cold neutrons to obtain a diffraction pattern that provides information of...
and synchrotron high-energy X-ray
High energy X-rays
High energy X-rays or HEX-rays are very hard X-rays, with typical energies of 80 keV - 1000 keV , about one order of magnitude higher than conventional X-rays . They are produced at modern synchrotron radiation sources such as the beamline ID15 at the European Synchrotron Radiation Facility...
diffraction allow access to textures of bulk material and in-situ analysis, whereas laboratory x-ray diffraction instruments are more appropriate for thin film textures.
Texture is often represented using a pole figure
Pole figure
A pole figure is a graphical representation of the orientation of objects in space. For example, pole figures in the form of stereographic projections are used to represent the orientation distribution of crystallographic lattice planes in crystallography and texture analysis in materials...
, in which a specified crystallographic
Crystallography
Crystallography is the experimental science of the arrangement of atoms in solids. The word "crystallography" derives from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write.Before the development of...
axis (or pole) from each of a representative number of crystallites is plotted in a stereographic projection, along with directions relevant to the material's processing history. These directions define the so-called sample reference frame and are, because the investigation of textures started from the cold working of metals, usually referred to as the rolling direction RD, the transverse direction TD and the normal direction ND. For drawn metal wires the cylindrical fiber axis turned out as the sample direction around which preferred orientation is typically observed (see below).
Common Textures
There are several textures that are commonly found in processed materials. They are named either by the scientist that discovered them, or by the material they are most found in. These are given in miller indices for simplification purposes.- Cube component: (001)[100]
- Brass component: (110)[-112]
- Copper component: (112)[11-1]
- S component: (123)[63-4]
Orientation distribution function
The full 3D representation of crystallographic texture is given by the orientation distribution function () which can be achieved through evaluation of a set of pole figures or diffraction spectra. Subsequently, all pole figures can be derived from the .The
is defined as the volume fraction of grains with a certain orientation .The orientation
is normally identified using three Euler anglesEuler angles
The Euler angles are three angles introduced by Leonhard Euler to describe the orientation of a rigid body. To describe such an orientation in 3-dimensional Euclidean space three parameters are required...
. The Euler angles then describe the transition from the sample’s reference frame into the crystallographic reference frame of each individual grain of the polycrystal. One thus ends up with a large set of different Euler angles, the distribution of which is described by the
.The orientation distribution function,
, cannot be measured directly by any technique. Traditionally both X-ray diffraction and EBSD may collect pole figures. Different methodologies exist to obtain the from the pole figures or data in general. They can be classified based on how they represent the . Some represent the as a function,sum of functions or expand it in a series of harmonic functions. Others, known as discrete methods, divide the
space in cells and focus on determining the value of the in each cell.Origins
Wire
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...
and fiber
Fiber
Fiber is a class of materials that are continuous filaments or are in discrete elongated pieces, similar to lengths of thread.They are very important in the biology of both plants and animals, for holding tissues together....
, all crystals tend to have nearly identical orientation in the axial direction, but nearly random radial orientation. The most familiar exceptions to this rule are fiberglass
Fiberglass
Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...
, which has no crystal structure
Amorphous solid
In condensed matter physics, an amorphous or non-crystalline solid is a solid that lacks the long-range order characteristic of a crystal....
, and carbon fiber
Carbon fiber
Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...
, in which the crystalline anisotropy is so great that a good-quality filament will be a distorted single crystal with approximately cylindrical symmetry (often compared to a jelly roll
Jelly roll
Jelly roll or Jelly Roll may refer to:* Swiss roll, a pastry* Jelly Roll Morton, a jazz musician* Jelly roll, a slang term for a lover, intercourse, or the sex organs* Jelly Roll , in hip hop...
). Single-crystal fibers are also not uncommon.
The making of metal sheet
Sheet metal
Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material...
often involves compression in one direction and, in efficient rolling operations, tension in another, which can orient crystallites in both axes by a process known as grain flow. However, cold work destroys much of the crystalline order, and the new crystallites that arise with annealing
Annealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
usually have a different texture. Control of texture is extremely important in the making of silicon steel sheet for transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
cores (to reduce magnetic
Magnetism
Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...
hysteresis
Hysteresis
Hysteresis is the dependence of a system not just on its current environment but also on its past. This dependence arises because the system can be in more than one internal state. To predict its future evolution, either its internal state or its history must be known. If a given input alternately...
) and of aluminium cans (since deep drawing
Deep drawing
Deep drawing is a sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. It is thus a shape transformation process with material retention. The process is considered "deep" drawing when the depth of the drawn part exceeds...
requires extreme and relatively uniform plasticity
Plasticity (physics)
In physics and materials science, plasticity describes the deformation of a material undergoing non-reversible changes of shape in response to applied forces. For example, a solid piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the...
).
Texture in ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
s usually arises because the crystallites in a slurry
Slurry
A slurry is, in general, a thick suspension of solids in a liquid.-Examples of slurries:Examples of slurries include:* Lahars* A mixture of water and cement to form concrete* A mixture of water, gelling agent, and oxidizers used as an explosive...
have shapes that depend on crystalline orientation, often needle- or plate-shaped. These particles align themselves as water leaves the slurry, or as clay is formed.
Casting
Casting
In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...
or other fluid-to-solid transitions (i.e., thin-film deposition) produce textured solids when there is enough time and activation energy for atoms to find places in existing crystals, rather than condensing as an amorphous solid
Amorphous solid
In condensed matter physics, an amorphous or non-crystalline solid is a solid that lacks the long-range order characteristic of a crystal....
or starting new crystals of random orientation. Some facet
Facet
Facets are flat faces on geometric shapes. The organization of naturally occurring facets was key to early developments in crystallography, since they reflect the underlying symmetry of the crystal structure...
s of a crystal (often the close-packed planes) grow more rapidly than others, and the crystallites for which one of these planes faces in the direction of growth will usually out-compete crystals in other orientations. In the extreme, only one crystal will survive after a certain length: this is exploited in the Czochralski process
Czochralski process
The Czochralski process is a method of crystal growth used to obtain single crystals of semiconductors , metals , salts, and synthetic gemstones...
(unless a seed crystal
Seed crystal
A seed crystal is a small piece of single crystal/polycrystal material from which a large crystal of the same material typically is to be grown...
is used) and in the casting of turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
blades and other creep
Creep (deformation)
In materials science, creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strength of the material....
-sensitive parts.
Texture and Materials Properties
Material properties such as strength, chemical reactivity, stress corrosion crackingStress corrosion cracking
Stress corrosion cracking is the unexpected sudden failure of normally ductile metals subjected to a tensile stress in a corrosive environment, especially at elevated temperature in the case of metals. SCC is highly chemically specific in that certain alloys are likely to undergo SCC only when...
resistance, weldability
Weldability
The weldability, also known as joinability, of a material refers to its ability to be welded. Many metals and thermoplastics can be welded, but some are easier to weld than others...
, deformation behavior, resistance to radiation damage
Radiation damage
Radiation damage is a term associated with ionizing radiation.-Causes:This radiation may take several forms:*Cosmic rays and subsequent energetic particles caused by their collision with the atmosphere and other materials....
, and magnetic susceptibility
Magnetic susceptibility
In electromagnetism, the magnetic susceptibility \chi_m is a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field...
can be highly dependent on the material’s texture and related changes in microstructure
Microstructure
Microstructure is defined as the structure of a prepared surface or thin foil of material as revealed by a microscope above 25× magnification...
. In many materials, properties are texture-specific, and development of unfavorable textures when the material is fabricated or in use can create weaknesses that can initiate or exacerbate failures. Parts can fail to perform due to unfavorable textures in their component materials. Failures can correlate with the crystalline textures formed during fabrication or use of that component.. Consequently, consideration of textures that are present in and that could form in engineered components while in use can be a critical when making decisions about the selection
Material selection
Material selection is a step in the process of designing any physical object. In the context of product design, the main goal of material selection is to minimize cost while meeting product performance goals. Systematic selection of the best material for a given application begins with properties...
of some materials and methods
Fabrication (metal)
Fabrication as an industrial term refers to building metal structures by cutting, bending, and assembling. The cutting part of fabrication is via sawing, shearing, or chiseling ; torching with handheld torches ; and via CNC cutters...
employed to manufacture parts with those materials. When parts fail during use or abuse, understanding the textures that occur within those parts can be crucial to meaningful interpretation of failure analysis
Failure analysis
Failure analysis is the process of collecting and analyzing data to determine the cause of a failure. It is an important discipline in many branches of manufacturing industry, such as the electronics industry, where it is a vital tool used in the development of new products and for the improvement...
data.
Thin film textures
Pronounced textures occur in thin films. Modern technological devices to a large extent rely on polycrystalline thin films with thickness in the nanometer and micrometer range. This holds, for instance, for all microelectronic and most optoelectronic systems or sensoric and superconducting layers. Most thin film textures may be categorized into two different types: (1) for so-called fiber textures the orientation of a certain lattice plane is preferentially parallel to the substrate plane. (2) In contrast, in biaxial textures also the in-plane orientation of crystallites becomes locked with respect to the sample. The latter phenomenon is accordingly observed in nearly epitaxial growth processes, where the crystallographic axes of the layer tend to align along those of the substrate.Tailoring the texture on demand became an important task in thin film technology. In the case of oxide compounds intended for transparent conducting film
Transparent conducting film
Transparent conducting films are optically transparent and electrically conductive in thin layers.TCFs for photovoltaic applications have been fabricated from both inorganic and organic materials...
s or surface acoustic wave
Surface acoustic wave
]A surface acoustic wave is an acoustic wave traveling along the surface of a material exhibiting elasticity, with an amplitude that typically decays exponentially with depth into the substrate.-Discovery:...
(SAW) devices, for instance, the polar axis should be aligned along the substrate normal. Another example is given by cables from high-temperature superconductors that are being developed as oxide multilayer systems deposited on metallic ribbons. The adjustment of the biaxial texture in YBa2Cu3O7 layers turned out as the decisive prerequisite for achieving sufficiently large critical currents.
The degree of texture is often subjected to an evolution during thin film growth and that most pronounced textures are only obtained after the layer has achieved a certain thickness. Thin film growers thus require information about the texture profile or the texture gradient in order to optimize the deposition process. The determination of texture gradients by x-ray scattering, however, is not straightforward, because different depths of a specimen contribute to the signal. Techniques that allow for the adequate deconvolution of diffraction intensity were developed only recently.
Further reading
- Bunge, H.-J. "Mathematische Methoden der Texturanalyse" (1969) Akademie-Verlag, Berlin
- Bunge, H.-J. "Texture Analysis in Materials Science" (1983) Butterworth, London
- Kocks, U. F., Tomé, C. N., Wenk, H.-R., Beaudoin, A. J., Mecking, H. "Texture and Anisotropy – Preferred Orientations in Polycrystals and Their Effect on Materials Properties" (2000) Cambridge University Press ISBN 052179420X
- Birkholz, M., chapter 5 of "Thin Film Analysis by X-ray Scattering" (2006) Wiley-VCH, Weinheim ISBN 3-527-31052-5