single-domain particle Magnetic particle whose minimum linear size is smaller than the domain wall thickness; because of this, it consists of one magnetic domain.. Thus, in a single-dom
Trang 1silica Silicon dioxide SiO2 Interatomic bond in silica is partially covalent and
partially ionic ( see electronegativity ) It has three polymorphic modifica-tions: cristobalite, tridymite, and quartz, with the transformation
temper-atures 1470 (cristobalite ↔ tridymite) and 867°C (tridymite ↔ quartz)
In all of the modifications, Si atoms are arranged at the centers of tetra-hedra formed by O atoms
simple lattice See primitive lattice
single crystal Body consisting of one crystal only There are no grain boundaries
in single crystals, although subboundaries and sometimes twin boundaries
can be found
single-domain particle Magnetic particle whose minimum linear size is smaller
than the domain wall thickness; because of this, it consists of one magnetic domain If several domains were present in such a particle, the particle’s free energy would be increased In the particle, the energy of the magnetic
poles at its surface is the lowest in the case of the largest pole spacing Thus, in a single-domain particle of an elongated shape, the orientation
of its magnetization vector is determined not only by its magnetic crys-talline anisotropy, but also by its shape anisotropy If elongated
single-domain particles are oriented predominately along the same direction in
a body, the latter possesses a magnetic texture and excellent hard-magnetic
properties
single slip Dislocation glide motion over a single slip system characterized by
the maximum Schmid factor.
sintering Procedure for manufacturing dense articles from porous particulate
compacts (porosity in green compacts usually is between 25 and 50 vol%) resulting from spontaneous bonding of adjacent particles The main driv-ing force for sinterdriv-ing is a decrease of an excess free energy associated with the phase boundaries Sintering is fulfilled by firing the compacts
at high temperatures (up to ∼0.9 Tm), and is always accompanied by their shrinkage and densification (i.e., a decrease in porosity) Shrinkage evolves primarily through coalescence of neighboring particles under the influence of the capillary force in the neck between the particles The
pore healing also contributes to shrinkage Densification during sintering
is accomplished by both the surface diffusion and the grain-boundary diffusion It is essential for densification that the pores remain at the grain boundaries, because the pores inside the grains can be eliminated by slow bulk diffusion only, whereas the grain-boundary pores “dissolve,” via the splitting out of vacancies and their motion to sinks, by much more rapid
grain-boundary diffusion Thus, the theoretical density can be achieved
in cases in which the abnormal grain growth is suppressed and the rate
of normal grain growth is low (for details of microstructure evolution in
the course of sintering, see solid-state sintering) Sintering can be accel -erated in the presence of a liquid phase (see liquid-phase sintering) or by pressure application during firing (see hot pressing)
size distribution Histogram displaying the frequency of grains (or particles) of
different sizes The shape of grain size distribution after normal grain
Trang 2silica Silicon dioxide SiO2 Interatomic bond in silica is partially covalent and
partially ionic ( see electronegativity ) It has three polymorphic modifica-tions: cristobalite, tridymite, and quartz, with the transformation
temper-atures 1470 (cristobalite ↔ tridymite) and 867°C (tridymite ↔ quartz)
In all of the modifications, Si atoms are arranged at the centers of tetra-hedra formed by O atoms
simple lattice See primitive lattice
single crystal Body consisting of one crystal only There are no grain boundaries
in single crystals, although subboundaries and sometimes twin boundaries
can be found
single-domain particle Magnetic particle whose minimum linear size is smaller
than the domain wall thickness; because of this, it consists of one magnetic domain If several domains were present in such a particle, the particle’s free energy would be increased In the particle, the energy of the magnetic
poles at its surface is the lowest in the case of the largest pole spacing Thus, in a single-domain particle of an elongated shape, the orientation
of its magnetization vector is determined not only by its magnetic crys-talline anisotropy, but also by its shape anisotropy If elongated
single-domain particles are oriented predominately along the same direction in
a body, the latter possesses a magnetic texture and excellent hard-magnetic
properties
single slip Dislocation glide motion over a single slip system characterized by
the maximum Schmid factor.
sintering Procedure for manufacturing dense articles from porous particulate
compacts (porosity in green compacts usually is between 25 and 50 vol%) resulting from spontaneous bonding of adjacent particles The main driv-ing force for sinterdriv-ing is a decrease of an excess free energy associated with the phase boundaries Sintering is fulfilled by firing the compacts
at high temperatures (up to ∼0.9 Tm), and is always accompanied by their shrinkage and densification (i.e., a decrease in porosity) Shrinkage evolves primarily through coalescence of neighboring particles under the influence of the capillary force in the neck between the particles The
pore healing also contributes to shrinkage Densification during sintering
is accomplished by both the surface diffusion and the grain-boundary diffusion It is essential for densification that the pores remain at the grain boundaries, because the pores inside the grains can be eliminated by slow bulk diffusion only, whereas the grain-boundary pores “dissolve,” via the splitting out of vacancies and their motion to sinks, by much more rapid
grain-boundary diffusion Thus, the theoretical density can be achieved
in cases in which the abnormal grain growth is suppressed and the rate
of normal grain growth is low (for details of microstructure evolution in
the course of sintering, see solid-state sintering) Sintering can be accel -erated in the presence of a liquid phase (see liquid-phase sintering) or by pressure application during firing (see hot pressing)
size distribution Histogram displaying the frequency of grains (or particles) of
different sizes The shape of grain size distribution after normal grain
Trang 3Taylor factor Quantity averaging the influence of various grain orientations on
the resolved shear stress, τr, in a polycrystal:
σ = Mτr
(M is the Taylor factor, and σ is the flow stress) The averaging is fulfilled
under the supposition that the deformations of the polycrystal and its grains are compatible Reciprocal Taylor factor can be used for polycrys
-tals instead of Schmid factor, whose magnitude is defined for a single grain only In a nontextured polycrystal with FCC structure, reciprocal
Taylor factor is 0.327
temper carbon In malleable irons, graphite clusters varying in shape from flake
aggregates to distorted nodules
tempered martensite Microconstituent occurring in quenched steels upon the
tempering treatment at low temperatures Due to the precipitation of ε -carbides, the lattice of tempered martensite is characterized by a tetra-gonality corresponding to ∼0.2 wt% carbon dissolved in the martensite
See steel martensite
tempering of steel martensite Alterations in the phase composition under the
influence of tempering treatment They are the following Up to ∼200°
C, as-quenched martensite decomposes into tempered martensite and ε-
(or η-) carbide (in low- to medium-carbon steels) or χ-carbide (in
high-carbon steels) Above ∼300°C, cementite precipitates from the tempered martensite, whereas the latter becomes ferrite and the ε- and η- (χ-)
carbides dissolve In steels alloyed with carbide-formers, the alloying elements inhibit the carbon diffusion and displace all the previously
men-tioned phase transitions to higher temperatures In addition, at tempera-tures ∼600°C, the diffusion of the substitutional alloying elements becomes possible, which leads to the occurrence of special carbides
accompanied by cementite dissolution The phase transformations described are accompanied by the following microstructural changes in martensite and ferrite Crystallites of tempered martensite retain the shape
of as-quenched martensite Ferrite grains, occurring from tempered
mar-tensite, do not change their elongated shape and substructure until