冶金学概论(铸造基础理论)超赞培训材料

show DBTT deform more easily at high T lower diffusion rate – good creep resistance properties are anisotropic

FCC


HCP

Melting Point - Strength
Pure
Production methods effect grain size and orientation Grain size and orientation can effect isotropy

Phase Diagrams
Phase Diagrams

Phase diagrams describe the phases present in any mixture of two elements at standard pressure over the range of temperatures exceeding the melting point

Cubic, tetragonal, orthorhombic, rhombohedral, hexagonal, monoclinic, triclinic

Further symmetries result in 14 different space, or Bravais, lattices

Eutectic (L + ) – Pb-Sn system Peritectic ( + L ) – Fe-C system

Partial Solid Miscibility
Partial Solid Miscibility
Partial Solid Miscibility

Annealed Metals
Melting points grouped by crystal structure Room temperature strength correlates to melting point At same fraction of MP, all metals have similar strength


Terminology – liquidus, solidus Lever Rule
Partial Solid Miscibility
One element is soluble in the other only to a certain extent Basis for precipitation hardening At intermediate concentrations in the liquid state, a three-phase reaction occurs
Magnesium Aluminum Copper Iron Titanium
321
650 660 1085 1538 1668
70
90 45 209 207 235
Chromium
Tungsten
BCC
BCC
1875
3410
282
945
0.011
0.006
Melting Point - Strength

Alpha-iron (RT – 911º C) Delta-iron (1392°C – MT) Vanadium Molybdenum Chromium Tungsten
Hexagonal Close Packed

Packing factor varies with plane of interest Anisotropic Examples

Single Crystal Materials
Atoms in Bravais lattice arranged in same direction (crystallographic orientation) Show isotropy/anisotropy of Bravais lattice Difficult to produce in large components Important in creep-resistant applications (turbine blades)
Three-phase reactions also occur in solid state Analogous to liquid state reactions

Eutectiod ( + ) – Fe-C system Peritectiod ( + )

Solid State Reactions
319 – T6 D5506
78
77 77
Single Crystals vs. Polycrystals
Single Crystals vs. Polycrystals
Most discussion so far has concerned single crystals The tendencies related thus far are amplified or negated in polycrystalline materials
2.70
4.51 7.87 7.19 8.64 8.92 19.25
Magnesium
Tungsten Chromium Iron Copper Aluminum Cadmium
52
49 39 26 23 16 8
Density – Strength:Weight
Alloy
AZ91D 319 – T6 356 – T6 380 - F TiAl4
Assume everything happens in equilibrium NOTHING happens in equilibrium, but we’ll deal with that later….

Complete Solid Miscibility


Elements are completely soluble at all concentrations Example: Cu-Ni system
RT Density
1.81 2.79 2.69 2.71 4.49
Alloy
TiAl4 AZ91D 380 - F 1040 Q & T 1040
Specific Strength
223 126 116 102 79
1040 Q & T
D5506 1040
7.63
7.15 7.84
356 – T6
Pure Annealed Metals Melting points grouped by crystal structure Room temperature strength correlates to melting point At same fraction of MP, all metals have similar strength Worked and Alloyed Metals These rules are thrown out the window, as we shall see….
Bravais Lattices
Crystal Geometry

Most engineering metals have BCC, FCC, or HCP Bravais lattices
Face-Centered Cubic



Highest atomic packing factor Properties are fairly isotropic Examples
Metallurgical Fundamentals
Metallurgical Fundamentals


Байду номын сангаас

Crystal Geometry Metallic Properties Plastic Deformation Single Crystals vs. Polycrystals Phase Diagrams Strengthening Mechanisms Softening Processes Topics on Solidification Diffusion

Polycrystalline Materials

Made up of groups of single crystals (grains)

10 – 100 microns
Each crystal has it’s own crystallographic orientation Regions between crystals (grain boundaries) have higher energy due to local distortion of atomic order
Polycrystals (cont.)
Random crystallographic orientation results in isotropy Common engineering metals are polycrystalline


Ease of production, isotropic properties
Density
Density Important consideration for design Values for metals range 1.74 g/cc for magnesium to 19.30 g/cc for gold Values for non-metals (polymers & elastomers) generally 1.0 to 3.0 g/cc Specific Strength or Better design criteria

Aluminum Copper Nickel Gold Silver Gamma-iron (911 – 1392º C)
Body-Centered Cubic



Lower atomic packing factor Properties are fairly isotropic Examples
Crystal Geometry
Crystal Geometry

Crystalline solids have periodic, ordered 3-D arrays These arrays can be described in terms of a unit cell Seven basic crystal systems – interatomic distances and angles
Melting Point - Strength
Metal RT Melting UTS Crystal Point (C) (MPa) Structure (RT)
HCP
HCP FCC FCC BCC HCP
RT / MP
0.062
0.031 0.030 0.018 0.013 0.012
Cadmium
Strengthening Mechanisms
Deformation
When subject to stress, interatomic distance increases – elastic deformation Beyond the elastic limit (yield point), no further increase in interatomic distance Additional deformation is due to atomic movement – plastic deformation

Titanium Magnesium Cobalt Zinc Cadmium Zirconium
Metallic Properties
Structure - Properties

Similar crystal structure = similar properties BCC
Stiffness
Density – Strength:Weight
Element
Magnesium
RT Density
1.74
Element
Titanium
Specific Strength
52
Aluminum
Titanium Iron Chromium Cadmium Copper Tungsten