Glossary - Lent 2013 Flashcards
(168 cards)
1
Q
Annealing
A
Holding a sample at an elevated temperature, to bring the microstructure closer to stable equilibrium
2
Q
Austenite
A
The cubic close packed allotrope of iron found between 912C and 1394C for pure iron. Also called the gamma phase
3
Q
Cast iron
A
Any of a wide range of Fe-C alloys, with a carbon content of 2-4wt%. The carbon content is higher than for steels
4
Q
Cementite
A
Iron carbide Fe3C often found in cast irons and steels although it is a metastable phase. (Graphite is actually the stable C-rich phase in the Fe-C system)
5
Q
Coherent interface
A
An interface between 2 crystalline phases such that the 2 lattices match perfectly at the interface. Such an interface is typically of low free energy (see Semi-coherent & Incoherent interfaces)
6
Q
Cooling curve
A
A plot of a sample temperature vs. time cooling. Changes in the cooling rate indicate phase transformations
7
Q
Common-tangent construction
A
The algorithm for calculating the compositions of 2 phases co-existing in equilibrium, based on the relevant free energy vs. composition curves
8
Q
Component
A
The different elements or chemical compounds which make up a system. The composition of a phase or the system can be described by giving the relative amount of each component
9
Q
Coring
A
Variation of solute content in a phase arising when solidification is too rapid to permit a uniform composition to be achieved by solid-state diffusion
10
Q
Dendrite
A
A branched tree-like form of crystal commonly found when metals solidify, often originating because of solute accumulation or depletion around the growing crystal
11
Q
Diffusion
A
Transport of atoms in a liquid or solid in which the diffusing atom moves relative to its neighbours
12
Q
Diffusion coefficient (Diffusivity, D)
A
A temperature dependent coefficient which describes the rate of diffusion. Has units of m^2s^-1
13
Q
Displacive Phase Transition
A
The transition between 2 phases which are related by small atomic displacements (see Reconstructive Phase Transition)
14
Q
Driving force
A
The difference in free energy driving a transformation
15
Q
Enthalpy, H
A
A thermodynamic extensive variable, defined so that the changes in H are given by the heat input at constant pressure. (H= U + PV)
16
Q
Entropy, S
A
A thermodynamic extensive variable, describing the degree of disorder of a system. For natural (spontaneous) changes, total entropy (of the system and its surroundings) always increases. In statistical mechanics, the entropy is related to the number of configurations of the system, Ω by S = klnΩ
17
Q
Equilibrium
A
A state of a system in which there is no driving force for infinitesimal change. Different types of equilibrium are distinguished by the stability of the system to small and large perturbations (see Metastable, Neutral, Stable and Unstable equilibrium)
18
Q
Eutectic
A
Relating to the transformation in which one liquid phase transforms to 2 solid phases on cooling. Is locally the lowest freezing point in the system
19
Q
Eutectoid
A
Relating to the transformation in which one solid phase transforms to 2 solid phases on cooling.
20
Q
Ferrite
A
The body centred cubic allotrope of iron - at lower temperature (below 912C in pure iron) labelled as alpha, at higher temperature (above 1394C in pure iron) as delta
21
Q
First order Transformation
A
A transformation from one phase to another in which the first derivatives of the free energy (e.g. entropy & volume) are discontinuous
22
Q
Free energy
A
Gibbs free energy is used to analyse equilibrium at constant pressure, Helmholtz free energy at constant volume
23
Q
Freezing range
A
The temperature over which freezing occurs in solidification of a liquid with more than one component. It is the interval between the liquidus and solidus
24
Q
Gibbs free energy, G
A
The thermodynamic potential which is minimised for equilibrium at constant pressure. Defined by G = H - TS
25
Glass
The phase formed when a liquid is cooled into a state of solid-like viscosity without crystallisation. Can be a material with any of the common bonding types (covalent, ionic, metallic, van der Waals)
26
Glass-ceramic
A fine-grained, almost totally crystalline product obtained by annealing a glass
27
Heterogeneous nucleation
Nucleation which occurs because of the presence of heterogeneities (see Homogeneous nucleation)
28
Homogeneous nucleation
Nucleation which occurs in a uniform phase without any influence of heterogeneities (see Heterogeneous nucleation)
29
Ideal solution
A solution in which the enthalpy of mixing is zero and the entropy of mixing has its ideal value
30
Incoherent interface
An interface between 2 crystalline phases at which there is no lattice matching. Such an interface will typically have a high free energy (see Coherent and Semi-coherent interfaces)
31
Intergrowth
A mixture of 2 phases, usually on a fine scale, formed when they grow cooperatively from a 3rd phase. Typical product of eutectic and eutectoid transformations
32
Internal energy, U
The potential energy and kinetic energy of a system. Changes in U are given by heat input at constant volume
33
Isothermal transformation diagram
Also known as a time-temperature-transformation (TTT) diagram. Temperature is plotted vertically, and the isothermal annealing time for a given fraction of transformation is plotted horizontally, usually on a logarithmic scale
34
Lamella(e)
Thin plate(s)
35
Lever rule
The algorithm for calculating the relative proportions of 2 phases, based on their compositions and overall composition
36
Line compound
A compound of very limited composition range which appears as a vertical line on a phase diagram of T vs. Composition. Such a compound is stoichiometric
37
Liquidus
The locus of the equilibrium temperature for solidification to start as a function of composition (see Solidus)
38
Martensite
A phase formed from austenite by a diffusionless transformation if the eutectoid transformation to pearlite is avoided on cooling. A martensitic transformation also refers, more generally, to any diffusionless shear transformation
39
Mechanical mixture
A mixture of phases in which each retains its separate identity. The free energy of the mixture is the weighted sum of the free energies of the constituent phases
40
Metastable equilibrium
Applies to a system which is stable against small fluctuations but not against large (see Equilibrium)
41
Microstructure
The arrangement of phases and other structural features that make up a solid material
42
Neutral equilibrium
Applies to a system in which there is no variation of potential with any change (see Equilibrium)
43
Pearlite
Fine eutectoid intergrowth of ferrite and cementite found in steels and cast irons
44
Phase
A portion of a system whose structure, properties and composition are homogeneous and which is physically distinct from other parts of the system
45
Phase separation
As a single phase solution is cooled, it may develop a free energy composition curve which has 2 minima, It will then separate into 2 isostructural phases
46
Precipitation
Formation of one phase in another of different chemical composition
47
Pro-eutectoid
Applied to a phase appearing by precipitation in advance of a eutectoid transformation. The precipitate phase is one of the phases in the eutectoid intergrowth
48
Reconstructive Phase Transition
A complete rearrangement of the structural topology involving the breaking and remaking of bonds.
49
Quench
A rapid cooling of a sample intended to avoid a phase transformation
50
Semi-coherent interface
An interface between 2 crystalline phases at which areas of perfect lattice matching are separated by dislocations. The dislocations act to relieve strain energy when lattice spacings in the interface plane are not the same in the 2 phases
51
Sintering
Particle coalescence in a powder by diffusion, accomplished by thermal treatment
52
Solidus
The locus of the equilibrium temperature for solidification to finish as function of composition (see Liquidus)
53
Solution
A mixture of components which is one phase. Contrasted with a mechanical mixture
54
Solvus
The temperature-composition locus showing the onset of precipitation. Indicates the limits of solubility
55
Stable equilibrium
Applies to a system which is stable against all fluctuations. It has the lowest possible free energy (see Equilibrium)
56
Steel
Any of a wide range of Fe-C alloys with a carbon content of ~0.1 - 1.4wt%. The carbon content is less than for cast irons
57
Stoichiometric
Obeying a strict chemical formula
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Supercooling
Below an equilibrium temperature the temperature interval in which the higher temperature phase is preserved in a metastable state (also called undercooling)
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System
The matter which is the subject of a thermodynamic analysis. In metallurgy, often an alloy which can exist as one or more phases
60
Texture
The preferred crystallographic orientation of grains in a material
61
Tie-line
Horizontal line on a temperature vs composition phase diagram the ends of which indicate phase compositions which co-exist in equilibrium
62
Transformation/Transition
These terms are used interchangeably here to denote a change in phase
63
Twins
Regions within a crystal with the same composition and structure, but different crystallographic orientation, and showing a specific orientation relationship between them
64
Unstable equilibrium
Applies to a system which is unstable against all fluctuations (see Equilibrium)
65
Widmannstatten
The characteristic pattern of precipitation of one solid phase in another, in which plate like precipitates have specific orientations governed by the symmetry of the matrix phase
66
Beam stiffness (Σ)
Product of Young's Modulus and moment of Inertia, characterising the resistance to deflection when subjected to a bending moment
67
Bending moment (M)
Turning moment generated in a beam by set of applied forces. The bending moment is balanced at each point along the beam by the moment of the internal stresses
68
Brittle fracture
Fracture not involving gross plastic flow, although some local plastic deformation may occur at the tip of the crack
69
Burgers vector (b)
Vector giving magnitude and direction of lattice displacement generated by passage of a dislocation. It is a lattice vector for a perfect dislocation
70
Climb
Movement of an edge dislocation by absorption or emission of a vacancy
71
Critical resolved shear stress (
Value of resolved shear stress at which slip occurs on a specified slip system
72
Cross-slip
Movement of a screw dislocation from one permissible slip plane on to another, usually in order to bypass an obstacle
73
Curvature (
Reciprocal of the radius of curvature adopted by a beam subject to a bending moment. Also equal to the through-thickness gradient of strain in the beam
74
Deformation twinning
Mode of plastic deformation involving the co-operative shear of atomic arrays into a new orientation of the same crystal structure (reflecting the parent orientation across the twin plane). Also termed mechanical twinning
75
Dislocation line
Boundary between slipped and unslipped regions of a crystal
76
Dispersion Strengthening
Raising of yield stress via obstacles to dislocation glide that are thermally stable
77
Ductile fracture
Fracture involving gross plastic flow
78
Edge dislocation
Dislocation with a Burgers vector normal to the dislocation line
79
Engineering strain (ε)
Normal strain, given by ratio of change in length to original length. Also called nominal strain. (See true strain)
80
Engineering stress (σ)
Normal stress, given by the ratio of applied force to original sectional area. Also called nominal stress. (see true stress)
81
Fracture energy (G[subscript c])
Energy per unit area required to extend a crack. Also termed the critical strain energy release rate
82
Fracture toughness (K[subscript c])
Critical value of the stress intensity factor, characterising the resistance of a material to crack propagation
83
Frank's rule
A dislocation reaction will occur only if the energy of the product dislocation(s) is less than that of the reacting dislocation(s). The energy of a dislocation is proportional to the square of its Burgers vector
84
Frank-Read source
A mechanism by which dislocations can multiply
85
Glide
Motion of a dislocation on its slip plane by small cooperative movements of atoms close to the dislocation core
86
Glissile dislocation
A dislocation which is able to glide
87
Griffith criterion
Energy based condition for fracture
88
Hooke's Law
Stress is proportional to strain during elastic deformation
89
Jog
A step in a dislocation that does not lie in the slip plane
90
Kink
A step in a dislocation that lies in the slip plane
91
Martensitic transformation
Phase transformation occurring via cooperative shear of atomic arrays into a new crystal structure
92
Mixed dislocation
Dislocation in which the Burgers vector is neither parallel nor perpendicular to the dislocation line
93
Neutral axis (of a beam)
Axis (strictly, a plane) parallel to the length of a beam, along which there is no change in length on bending
94
Normal strain (ε)
Deformation in which change in length is parallel to original length
95
Normal stress (σ)
Stress induced by a force acting normal to the sectional area to which it is applied
96
OILS rule
Non-graphical method to find the slip system with the highest Schmid factor in a cubic crystal
97
Orowan bowing
The bowing of dislocations between precipitates that cannot be cut
98
Partial dislocation
A dislocation for which the Burgers vector is smaller than a lattice vector
99
Perfect dislocation
A dislocation for which the Burgers vector is a lattice vector
100
Primary slip system
Slip system which first becomes active. Normally the one with the highest Schmid factor
101
Resolved shear stress (tau subscript r)
Component of shear stress acting on a slip plane and parallel to a slip direction in that plane
102
Schmid factor (cos theta cos fi)
Geometrical factor relating resolved stress to normal stress along the tensile axis in a single crystal under tension or compression
103
Schmid's law
Slip initiates at a critical value of resolved shear stress
104
Screw dislocation
Dislocation with a Burgers vector parallel to its dislocation line
105
Second moment of area (I)
Parameter dependent on sectional shape, characterising the resistance a beam offers to deflection under an applied bending moment. Also called the moment of inertia
106
Sessile dislocation
A dislocation which is unable to glide
107
Shear modulus (G)
Constant of proportionality between shear stress and shear strain
108
Beam stiffness (Σ)
Product of Young's Modulus and moment of Inertia, characterising the resistance to deflection when subjected to a bending moment
109
Bending moment (M)
Turning moment generated in a beam by set of applied forces. The bending moment is balanced at each point along the beam by the moment of the internal stresses
110
Brittle fracture
Fracture not involving gross plastic flow, although some local plastic deformation may occur at the tip of the crack
111
Burgers vector (b)
Vector giving magnitude and direction of lattice displacement generated by passage of a dislocation. It is a lattice vector for a perfect dislocation
112
Climb
Movement of an edge dislocation by absorption or emission of a vacancy
113
Critical resolved shear stress (tau subscript c)
Value of resolved shear stress at which slip occurs on a specified slip system
114
Cross-slip
Movement of a screw dislocation from one permissible slip plane on to another, usually in order to bypass an obstacle
115
Curvature (kappa)
Reciprocal of the radius of curvature adopted by a beam subject to a bending moment. Also equal to the through-thickness gradient of strain in the beam
116
Deformation twinning
Mode of plastic deformation involving the co-operative shear of atomic arrays into a new orientation of the same crystal structure (reflecting the parent orientation across the twin plane). Also termed mechanical twinning
117
Dislocation line
Boundary between slipped and unslipped regions of a crystal
118
Dispersion Strengthening
Raising of yield stress via obstacles to dislocation glide that are thermally stable
119
Ductile fracture
Fracture involving gross plastic flow
120
Edge dislocation
Dislocation with a Burgers vector normal to the dislocation line
121
Engineering strain (ε)
Normal strain, given by ratio of change in length to original length. Also called nominal strain. (See true strain)
122
Engineering stress (σ)
Normal stress, given by the ratio of applied force to original sectional area. Also called nominal stress. (see true stress)
123
Fracture energy (G[subscript c])
Energy per unit area required to extend a crack. Also termed the critical strain energy release rate
124
Fracture toughness (K[subscript c])
Critical value of the stress intensity factor, characterising the resistance of a material to crack propagation
125
Frank's rule
A dislocation reaction will occur only if the energy of the product dislocation(s) is less than that of the reacting dislocation(s). The energy of a dislocation is proportional to the square of its Burgers vector
126
Frank-Read source
A mechanism by which dislocations can multiply
127
Glide
Motion of a dislocation on its slip plane by small cooperative movements of atoms close to the dislocation core
128
Glissile dislocation
A dislocation which is able to glide
129
Griffith criterion
Energy based condition for fracture
130
Hooke's Law
Stress is proportional to strain during elastic deformation
131
Jog
A step in a dislocation that does not lie in the slip plane
132
Kink
A step in a dislocation that lies in the slip plane
133
Martensitic transformation
Phase transformation occurring via cooperative shear of atomic arrays into a new crystal structure
134
Mechanical twinning
see deformation twinning
135
Mixed dislocation
Dislocation in which the Burgers vector is neither parallel nor perpendicular to the dislocation line
136
Neutral axis (of a beam)
Axis (strictly, a plane) parallel to the length of a beam, along which there is no change in length on bending
137
Nominal strain (ε)
see engineering strain
138
Nominal stress (σ)
see engineering stress
139
Normal strain (ε)
Deformation in which change in length is parallel to original length
140
Normal stress (σ)
Stress induced by a force acting normal to the sectional area to which it is applied
141
OILS rule
Non-graphical method to find the slip system with the highest Schmid factor in a cubic crystal
142
Orowan bowing
The bowing of dislocations between precipitates that cannot be cut
143
Partial dislocation
A dislocation for which the Burgers vector is smaller than a lattice vector
144
Perfect dislocation
A dislocation for which the Burgers vector is a lattice vector
145
Primary slip system
Slip system which first becomes active. Normally the one with the highest Schmid factor
146
Resolved shear stress (
Component of shear stress acting on a slip plane and parallel to a slip direction in that plane
147
Schmid factor (cos(theta)cos(fi))
Geometrical factor relating resolved stress to normal stress along the tensile axis in a single crystal under tension or compression
148
Schmid's law
Slip initiates at a critical value of resolved shear stress
149
Screw dislocation
Dislocation with a Burgers vector parallel to its dislocation line
150
Second moment of area (I)
Parameter dependent on sectional shape, characterising the resistance a beam offers to deflection under an applied bending moment. Also called the moment of inertia
151
Sessile dislocation
A dislocation which is unable to glide
152
Shear modulus (G)
Constant of proportionality
153
Shear strain (
Distortional deformation (an angle) arising from a shear displacement
154
Shear stress (
Stress induced by a force acting parallel to the sectional area to which it is acting
155
Slip system [UVW](hkl)
Combination of slip plane (hkl) and slip direction [UVW], which lies in the (hkl) plane
156
Solution strengthening
Increase in yield stress of a material through the addition of solute atoms, caused by the interaction of these solute atoms with dislocations
157
Stacking fault
A 2d defect in which the sequence of stacking of atomic planes is interrupted
158
Strain energy release rate (G)
Elastic strain energy released per unit of created crack area
159
Strain hardening
see work hardening
160
Stress intensity factor (K)
Parameter characterising the crack driving force, in terms of applied stress level and crack length
161
Surface energy (
Energy per unit area associated with a free surface
162
Thermal expansivity (α)
Ratio of change in length to original length, per unit change in temperature. Also known as Coefficient of Thermal Expansion
163
True strain (ε)
Ratio of change in length to current length. May differ from the engineering strain
164
True stress (σ)
Ratio of force to current sectional area over which it is acting. May differ from engineering stress
165
Twinning plane
Plane within which shear takes place during deformation twinning, which also forms a mirror plane between parent and twin structures
166
Work hardening
Increase in plastic flow stress with strain. Associated with an increase in dislocation density, formation of entanglements, locks etc. Also known as strain hardening
167
Yield point
Point (stress level = σ[subscript y]) at which plastic deformation first occurs
168
Young's modulus (E)
Constant of proportionality between normal stress and normal strain
