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ME 350 Ch 6, 7 Metals

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Title: ME 350 Ch 6, 7 Metals


1
ME 350 Ch 6, 7 Metals Ceramics
  • Ch6 - Metals
  • Alloys
  • Binary Phase Diagrams
  • Metal Types and Designations
  • Ch 7 - Ceramics
  • Types
  • Characteristics

2
Alloys
  • An alloy a mixture or compound of two or more
    elements, at least one of which is metallic
  • Two main categories
  • Solid solutions - An alloy in which one element
    is in another to form a
    single-phase structure
  • Intermediate phases - When the amount of the
    dissolving element in the alloy exceeds the
    limit of the base metal, a second phase
    forms in the alloy
  • A any homogeneous mass of
    material, in which the grains all have the same
    crystal lattice structure

3
Two Forms of Solid Solutions
  • solid solution - atoms of solvent element
    are replaced in its unit cell by dissolved
    element
  • solid solution - atoms of dissolving
    element fit into vacant spaces between base metal
    atoms in the lattice structure
  • In both forms, the alloy structure is generally
    than either of the component elements

4
Two Forms of Solid Solutions
5
Types of Intermediate Phases
  • Metallic compounds consist of a metal and
    nonmetal, such as Fe3C ( )
  • Intermetallic compounds - two metals that form a
    compound, such as Mg2Pb
  • In some alloy compositions, the intermediate
    phase is mixed with the primary solid solution to
    form a two-phase structure
  • Some two-phase alloys are important because they
    can be heat treated for much higher strength than

6
Phase Diagrams
  • A graphical means of representing the phases of a
    metal alloy system as a function of composition
    and temperature
  • A phase diagram for two elements (at atmospheric
    pressure) is called a

7
Inverse Lever Rule - Example
Solid phase composition Liquid phase
composition
Liquid
2000 1500 1000
a Liquid
Temperature C
Solid phase proportion Liquid phase
proportion
a
0 10 20 30 40 50 60
70 80 90
A
8
  • Nickel-Copper Binary Phase Diagram
  • A melt is formed with 35 Ni and 65 Cu, it is
    slowly cooled from 1300C to 1270C
  • initial solid is Ni, initial liquid
    is Ni
  • middle solid is Ni
    middle liquid is Ni
  • at end solid is Ni

9
Inverse Lever Rule Example 2
Solid phase composition Liquid phase
composition
2000 1500 1000
Temperature C
Solid phase proportion Liquid phase
proportion
0 10 20 30 40 50 60
70 80 90
A
10
Iron-Carbon Phase Diagram
? a Fe3C
11
Solubility Limits of Carbon in Iron
  • Ferrite phase can dissolve only about carbon
    at 723?C (1333?F)
  • Austenite can dissolve up to about carbon at
    1130?C (2066?F)
  • The difference in solubility between alpha and
    gamma provides opportunities for strengthening by
    heat treatment

12
Steel and Cast Iron Defined
  • an iron-carbon alloy containing from
    0.02 to 2.1 carbon
  • an iron-carbon alloy
    containing from 2.1 to about 4.3 carbon
  • Steels and cast irons can also contain other
    alloying elements besides carbon

13
Eutectic and Eutectoid Compositions
  • composition of Fe-C system 4.3
    C
  • Phase changes from solid (? Fe3C) to liquid at
    1130?C (2066?F)
  • composition of Fe-C system
    0.77 C
  • Phase changes from ? to ? above 723?C (1333?F)
  • Below 0.77 C, called steels
  • From 0.77 to 2.1 C, called steels

14
Carbon Content in Steel
15
AISI-SAE Designation Scheme
  • Specified by a 4-digit number system 10XX, where
    10 indicates plain carbon steel, and XX indicates
    carbon in hundredths of percentage points
  • For example, 1020 steel contains C
  • Developed by American Iron and Steel Institute
    (AISI) and Society of Automotive Engineers (SAE),
    so designation often expressed as AISI 1020 or
    SAE 1020

16
AISI-SAE Designation Scheme
  • AISI-SAE designation uses a 4-digit number
    system YYXX, where YY indicates alloying
    elements, and XX indicates carbon in hundredths
    of points
  • Examples
  • 13XX - Manganese steel
  • 20XX - Nickel steel
  • 31XX - Nickel-chrome steel
  • 40XX - Molybdenum steel
  • 41XX - steel

17
Stainless Steel (SS)
  • Highly alloyed steels designed for corrosion
    resistance
  • Principal alloying element is , usually
    greater than 15
  • forms a thin impervious oxide film that
    protects surface from corrosion
  • Nickel (Ni) is another alloying ingredient in
    certain SS to increase
  • Carbon is used to strengthen and harden SS, but
    high C content reduces corrosion protection since
    chromium carbide forms to reduce available free
    Cr

18
Designation Scheme for Stainless Steels
  • Three-digit AISI numbering scheme
  • First digit indicates general type, and last two
    digits give specific grade within type
  • Examples
  • Type 302 Austenitic SS
  • 18 Cr, 8 Ni, 2 Mn, 0.15 C
  • Type 430 Ferritic SS
  • 17 Cr, 0 Ni, 1 Mn, 0.12 C
  • Type 440 Martensitic SS
  • 17 Cr, 0 Ni, 1 Mn, 0.65 C

19
Cast Irons
  • Iron alloys containing from carbon and from
    1 to 3 silicon
  • Most important is
  • Other types include ductile iron, white cast
    iron, malleable iron, and various alloy cast
    irons
  • Ductile and malleable irons possess chemistries
    similar to the gray and white cast irons,
    respectively, but result from special processing
    treatments

20
Cast Iron Chemistries C Si
21
Designations of Aluminum Alloys
  • Alloy group Wrought code Cast code
  • Aluminum ? 99.0 purity 1XXX 1XX.X
  • Copper alloy 2XXX 2XX.X
  • Manganese alloy 3XXX
  • Silicon alloy 4XXX 4XX.X
  • Zinc alloy 7XXX 7XX.X
  • Tin alloy 8XX.X

22
Magnesium and Its Alloys
  • alloys of the structural metals
  • Available in both wrought and cast forms
  • Relatively easy to machine
  • In all processing of magnesium, small particles
    of the metal (such as small metal cutting chips)
    oxidize rapidly, and care must be taken to avoid
    hazards

23
Copper Alloys
  • Strength and hardness of copper is relatively
    low to improve strength, copper is frequently
    alloyed
  • - alloy of copper and tin (typical ? 90 Cu,
    10 Sn), widely used today and in ancient times
    (i.e., )
  • - alloy of copper and zinc (typical ? 65 Cu,
    35 Zn).
  • Highest strength alloy is beryllium-copper (only
    about 2 Be), which can be heat treated to high
    strengths and used for springs

24
Titanium
  • Coefficient of thermal expansion is relatively
    low among metals
  • Stiffer and stronger than Al
  • Retains good strength at elevated temperatures
  • Pure Ti is reactive, which presents problems in
    processing, especially in molten state
  • At room temperature Ti forms a thin adherent
    oxide coating (TiO2) that provides excellent
    corrosion resistance

25
Zinc and Its Alloys
  • Low melting point makes it attractive as a
    casting metal, especially die casting
  • Also provides corrosion protection when coated
    onto steel or iron
  • The term steel refers to steel coated with
    zinc
  • Widely used as alloy with copper ( )

26
Refractory Metals
  • Metals capable of enduring high temperatures -
    maintaining high strength and hardness at
    elevated temperatures
  • Most important refractory metals
  • Other refractory metals
  • Columbium
  • Tantalum

27
Superalloys
  • High-performance alloys designed to meet
    demanding requirements for strength and
    resistance to surface degradation at high service
    temperatures
  • Many superalloys contain substantial amounts of
    , rather than consisting of one base metal
    plus alloying elements
  • Operating temperatures often around 1100?C
    (2000?F)
  • Applications gas turbines - jet and rocket
    engines, steam turbines, and nuclear power plants
    (all are systems in which operating efficiency
    increases with higher temperatures)

28
Three Groups of Superalloys
  • Iron-based alloys - in some cases iron is less
    than 50 of total composition
  • Alloyed with Ni, Cr, Co
  • Nickel-based alloys - better high temperature
    strength than alloy steels
  • Alloyed with Cr, Co, Fe, Mo, Ti
  • Cobalt-based alloys - ? 40 Co and ? 20 chromium
  • Alloyed with Ni, Mo, and W
  • In virtually all superalloys, including iron
    based, strengthening is by precipitation hardening

29
How to Enhance Mechanical Properties
  • adding additional elements to
    increase the strength of metals
  • - strain hardening during deformation
    to increase strength (also reduces ductility)
  • Strengthening of the metal occurs as a byproduct
    of the forming operation
  • - heating and cooling cycles performed
    on a metal to beneficially change its mechanical
    properties
  • Operate by altering the microstructure of the
    metal, which in turn determines properties

30
Ch7 - Three Basic Categories of Ceramics
  • ceramics - clay products such as
    pottery, bricks, common abrasives, and cement
  • ceramics - more recently developed
    ceramics based on oxides, carbides, etc., with
    better mechanical or physical properties than
    traditional ceramics
  • - based primarily on silica and
    distinguished by their noncrystalline structure

31
Strength Properties of Ceramics
  • Ceramics are substantially stronger in
    than in or in bending
  • Ceramics fail by much more readily
    than metals
  • grain size generally increases strength

32
Oxide Ceramics
  • Most important oxide ceramic is
  • also has good hot hardness, low thermal
    conductivity, and good corrosion resistance

33
Carbide Ceramics
  • Silicon carbide ( ), tungsten carbide (
    ), titanium carbide ( ), tantalum carbide (
    ), and chromium carbide ( )
  • WC, TiC, and TaC are valued for their hardness
    and in applications requiring these
    properties (e.g., cutting tools)
  • WC, TiC, and TaC must be combined with a metallic
    binder such as or in order
    to fabricate a useful solid product

34
Nitrides
  • Important nitride ceramics are silicon nitride
    (Si3N4), boron nitride (BN), and titanium nitride
    (TiN)
  • Properties usually electrically
    insulating, TiN being an exception
  • Applications
  • Silicon nitride components for gas turbines,
    rocket engines, and melting crucibles
  • Boron nitride and titanium nitride cutting tool
    materials and coatings

35
Glass Ceramics
  • is the main component in glass
    products, usually comprising 50 to 75 of total
    chemistry
  • It naturally transforms into a glassy state (
    ) upon cooling from the liquid, whereas most
    ceramics crystallize upon solidification
  • Glass-ceramics are a class of ceramic material
    that contain crystalline phase with
    very small grain size (0.1 - 1µm) and are usually
    .
  • They can contain sodium oxide (Na2O), calcium
    oxide (CaO), aluminum oxide (Al2O3), magnesium
    oxide (MgO), potassium oxide (K2O), lead oxide
    (PbO), and boron oxide (B2O3)

36
Advantages of Glass-Ceramics
  • Efficiency of processing in the glassy state
  • Close dimensional control over final shape
  • Good mechanical and physical properties
  • High strength (stronger than glass)
  • Absence of porosity low thermal expansion
  • High resistance to thermal shock
  • Applications
  • Cooking ware
  • Heat exchangers
  • Missile radomes

37
Graphite
  • Form of carbon with a high content of crystalline
    carbon in the form of layers
  • Bonding between atoms in layers is covalent and
    strong, but parallel layers are bonded to each
    other by weak van der Waals forces
  • Structure makes graphite anisotropic properties
    vary significantly with direction
  • As a powder it is a lubricant, but in traditional
    solid form it is a refractory
  • As a fiber, it is a high strength structural
    material (e.g., fiber reinforced plastics)

38
Diamond
  • Carbon is a cubic crystalline structure with
    covalent bonding between atoms very high
    hardness
  • Applications cutting tools and grinding wheels
    also used in dressing tools to sharpen grinding
    wheels
  • Synthetic diamonds fabricated by heating graphite
    to around 3000?C (5400?F) under very high
    pressures

39
Boron
  • Semi-metallic element in same periodic group as
    aluminum
  • Properties , semiconducting properties,
    and very high modulus of elasticity) in
    fiber form
  • Applications B2O3 in certain glasses, as a
    nitride (cBN) for cutting tools, and in nearly
    pure form as a fiber in polymer matrix composites

40
Guide to Processing Ceramics
  • Processing of ceramics can be divided into two
    basic categories
  • Molten ceramics - major category of molten
    ceramics is glassworking (solidification
    processes)
  • Particulate ceramics - traditional and new
    ceramics (particulate processing)
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