Concise Dictionary of Materials Science Part 1 pdf

Structure and Characterization
of Polycrystalline Materials
MATERIALS
SCIENCE
CONCISE DICTIONARY
OF
© 2003 by CRC Press LLC
A
α-Al
2
O
3

Pure alumina. Polycrystalline Al
2
O
3
is known as corundum and single
crystals as sapphire. Its crystal structure can be described as consisting
of two sublattices: an FCC sublattice of O
2–
ions and a sublattice of Al
3+
ions occupying two thirds of the octahedral sites in the first one.
α-Fe
Allotropic form of iron having BCC crystal structure and existing at tem
-
peratures below 910°C at atmospheric pressure.
α isomorphous Ti system

Ti–X alloy system in which the alloying element X
is the
α
-stabilizer, i.e., it raises the temperature of the
β

↔ α
polymorphic
transformation.
α-phase [in Ti alloys]
A solid solution of alloying elements in α-Ti.
α′-martensite

See titanium martensite.
α″-martensite

See titanium martensite.
α-stabilizer

In physical metallurgy of Ti alloys, an alloying element increasing
the thermodynamic stability of α-phase and thereby raising the β/(α + β)
transus in the corresponding phase diagram. In physical metallurgy of
steels, it is referred to as ferrite-stabilizer.
α-Ti

Allotropic form of titanium having a hexagonal crystal structure and exist
-
ing at temperatures below 882°C at atmospheric pressure. The axial ratio
of its lattice c/a = 1.58, i.e., a little smaller than in an ideal HCP structure.
α Ti alloy

Titanium alloy in which α-phase is the only phase constituent after
air-cooling from the β-field in the phase diagram concerned. Alloys with
a small fraction of β-phase (∼5 vol%) are usually related to the same
group and are called near-α alloys. All the α alloys contain α-stabilizers.
(
α
+
β
)
brass
Brass with two phase constituents: a copper-based substitutional
solid solution (α-phase) and an electron compound (β-phase).
(
α
+
β
)
Ti alloy
Alloy whose phase constituents are α- and β-phases after air-
cooling from the (α + β)-field in the phase diagram concerned. Slow
cooling of these alloys from the β-field results in a microstructure com
-
prising grain-boundary allotriomorphs of the α-phase (known as “pri-
mary” α) and packets of similarly oriented α-platelets with the β-phase
layers between the platelets.
A
1
/Ae
1 te

mperature
In the Fe–Fe
3
C diagram, the temperature of an eutectoid
reaction corresponding to the PSK line in the diagram. Since the reaction,
on cooling, starts at a certain undercooling (see nucleation), the temper
-
© 2003 by CRC Press LLC