Properties and Processing of Powder Metals, Ceramics, Glasses, and Composites

1
CHAPTER 11

• Properties and Processing of Powder Metals,
  Ceramics, Glasses, and Composites
• (??????)

2
Typical Applications for Metal Powders

• Material density in P/M is controllable
• 70 of P/M part production is for automotive
  applications

3
Powder-Metallurgy
Figure 11.1 (a) Examples of typical parts made
by powder-metallurgy processes. (b) Upper trip
lever for a commercial irrigation sprinkler, made
by P/M. This part is made of unleaded brass
alloy it replaces a die-cast part, with a 60
savings. Source Reproduced with permission from
Success Stories on P/M Parts, 1998. Metal Powder
Industries Federation, Princeton, New Jersey,
1998. (c) Main-bearing powder metal caps for 3.8
and 3.1 liter General Motors automotive engines.
Source Courtesy of Zenith Sintered Products,
Inc., Milwaukee, Wisconsin.
4
Making Powder-Metallurgy Parts
Figure extra Outline of processes and operations
involved in making powder-metallurgy parts.
5
Particle Shapes in Metal Powders
Figure 11.2 Particle shapes in metal powders,
and the processes by which they are produced.
Iron powders are produced by many of these
processes.
6
Powder Particles
Figure extra (a) Scanning-electron-microscopy
photograph of iron-powder particles made by
atomization. (b) Nickel-based superalloy (Udimet
700) powder particles made by the rotating
electrode process see Fig. 17.5b. Source
Courtesy of P. G. Nash, Illinois Institute of
Technology, Chicago.

• Particle sizes 0.1? to 1000? distribution
• Shapes aspect ratio(largest/smallest), shape
  factor(surface/volume)

7
Atomization and Mechanical Comminution
Figure 11.3 Methods of metal-powder production
by atomization (a) melt atomization (b)
atomization with a rotating consumable electrode.

• Reduction of metal oxides
• Electrolytic deposition
• Decomposition of metal carbonyls
• Mechanical alloying
• Precipitation, chips by machining, vapor
  condensation

8
Equipment for Blending Powders
Figure extra Some common equipment geometries
for mixing or blending powders (a) cylindrical,
(b) rotating cube, (c) double cone, and (d) twin
shell. Source Reprinted with permission from R.
M. German, Powder Metallurgy Science. Princeton,
NJ Metal Powder Industries Federation, 1984.

• Under controlled condition ?? contamination,
  deterioration
• High shape factor ? explosive Al, Mg, Ti, Zr, Th

9
Compaction
Figure 11.6 (a) Compaction of metal powder to
form a bushing. The pressed powder part is
called green compact. (b) Typical tool and die
set for compacting a spur gear. Source Metal
Powder Industries Federation.

• Green compact as-
  pressed
• - shape
• - (green) density
• - contact of particles
• Compressibility ?? green density

10
Density Effects
Figure 11.7 (a) Density of copper- and
iron-powder compacts as a function of compacting
pressure. Density greatly influences the
mechanical and physical properties of P/M parts.
Source F. V. Lenel, Powder Metallurgy
Principles and Applications. Princeton, NJ
Metal Powder Industries Federation, 1980. (b)
Effects of density on tensile strength,
elongation, and electrical conductivity of copper
powder. IACS means International Annealed Copper
Standard for electrical conductivity.
11
Density Variations in Dies
Figure 11.8 Density variation in compacting
metal powders in various dies (a) single-action
press (b), (c) and (d) double-action press.
Note in (d) the greater uniformity of density,
from pressing with two punches with separate
movements, compared with (c). (e) Pressure
contours in compacted copper powder in a
single-action press. Source P. Duwez and L.
Zwell.

• Uniform density by multiple punches (d)

(Fig. 11.9)
12
Compacting Pressures for Various Metal Powders
13
Mechanical Press
Figure extra A 7.3 MN (825 ton) mechanical press
for compacting metal powder. Source Courtesy of
Cincinnati Incorporated.
14
Hot and Cold Isostatic Pressing
Figure 11.10 Schematic diagram of cold isostatic
pressing, as applied to forming a tube. The
powder is enclosed in a flexible container around
a solid core rod. Pressure is applied
isostatically to the assembly inside a
high-pressure chamber. Source Reprinted with
permission from R.M. German, Powder Metallurgy
Science. Princeton, NJ Metal Powder Industries
Federation, 1984.

• Pressure 400MPa ( up to 1000MPa)

• Hot isostatic pressing
  compaction sintering

15
Capabilities Available from P/M Operations
Figure 11.11 Capabilities, with respect to part
size and shape complexity, available from various
P/M operations. P/F means powder forging.
Source Metal Powder Industries Federation.
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Figure 11.12 Schematic illustration of hot
isostatic pressing. The pressure and
temperature variation vs. time are shown in the
diagram. Source Preprinted with permission
from R.M. German, Powder Metallurgy Science.
Princeton, NJ Metal Powder Industries
Federation, 1984.

• Common condition 100MPa at 1100oC 100 density,
  good metallurgical bonding, good
  mechanical properties
• Relatively expensive ? superalloy components

17
Powder Rolling
Figure extra An example of powder rolling.
Source Metals Handbook (9th ed.), Vol. 7.
American Society for Metals.

• Other compacting methods
• - Forging repressing, upsetting
• - Extrusion
• - Injection molding
• - Pressureless compaction only by
  gravity
• - Ceramic molds ? investment casting

18
Sintering

• Heated in a controlled atmosphere to a
  temperature below its melting point, but
  sufficiently high to allow bonding of individual
  particles

Figure 11.13 Schematic illustration of two
mechanisms for sintering metal powders (a)
solid-state material transport (b) liquid-phase
material transport. R particle radius, r
neck radius, and r neck profile radius.

• Different metals alloying ? particles
  with low melting point melt

19
Sintering Temperature and Time for Various Metals

• Diffusion
• Plastic flow

• Grain growth
• Pore shrinkage

• Bond strength

• Evaporation of volatile materials in the compact
• Recrystallization

• Increase of sintering time(temperature) ?
  increase of elongation and dimensional
  change from die size(Fig. 11.14)

20
Mechanical Property Comparison for Ti-6Al-4V

• Sintered density ? mechanical properties
• - green density
• - sintering temperature (7090 of melting
  point) and time
• - furnace atmosphere

21
Mechanical Properties of Selected P/M Materials
22
Examples of P/M Parts
Figure 11.16 Examples of P/M parts, showing poor
designs and good ones. Note that sharp radii and
reentry corners should be avoided and that
threads and transverse holes have to be produced
separately by additional machining operations.

• Secondary and finishing operations
• - impregnating fluid (oil)
• - infiltration slug of low-melting point
  metal
• - heat treating
• - machining
• - finishing deburring, coating,

23
Forged and P/M Titanium Parts and Potential Cost
Saving

• Spray deposition (Osprey process Fig. 11.15) ?
  spray of atomized metal on a cooled preform
  mold

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Characteristics of Ceramics Processing
25
Steps in Making Ceramic Parts
Figure extra Processing steps involved in making
ceramic parts.
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Processing of Ceramics
Figure 11.23 Methods of mechanical comminution,
to obtain fine particles (a) roll crushing, (b)
ball mill, and (c) hammer milling.

• Raw materials clay(fine-grained sheet-like
  structure), SiO2
• Oxide ceramics Al2O3, ZrO2
• Other ceramics WC, TiC, SiC, CBN, TiN, Si3N4,
  cermets Sialon(Si3N4 Al2O3 TiC yttrium
  oxide)

27
Slip-Casting
Figure 11.24 Sequence of operations in
slip-casting a ceramic part. After the slip has
been poured, the part is dried and fired in an
oven to give it strength and hardness. Source
F. H. Norton, Elements of Ceramics.
Addison-Wesley Publishing Company, Inc. 1974.
28
Extruding and Jiggering
Figure 11.26 (a) Extruding and (b) jiggering
operations. Source R. F. Stoops.

• Plastic forming extrusion, injection molding,
  molding, jiggering
• Pressing dry pressing, wet pressing, isostatic
  pressing, hot pressing(pressure
  sintering)

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Shrinkage

• Drying and firing 15-20 of original moist
  size

Figure 11.27 Shrinkage of wet clay caused by
removal of water during drying. Shrinkage may be
as much as 20 by volume. Source F. H. Norton,
Elements of Ceramics. Addison-Wesley Publishing
Company, Inc. 1974.

• Finishing after firing grinding, lapping,
  ultrasonic, .

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View over a village near Geumgang(Riv.), Gongju
Ave Maria, Caccini
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Sheet Glass Formation
Processing of Glasses
Figure extra (a) Continuous process for drawing
sheet glass from a molten bath. Source W. D.
Kingery, Introduction to Ceramics. Wiley, 1976.
(b) Rolling glass to produce flat sheet.
Figure 11.28 The float method of forming sheet
glass. Source Corning Glass Works.

• Float glass fire polished smooth surface ?
  no further polishing/grinding

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Glass Tubing
Figure 11.29 Manufacturing process for glass
tubing. Air is blown through the mandrel to keep
the tube from collapsing. Source Corning Glass
Works.

• Mandrel rotating
• Air is blown through the mandrel ?? tube
  collapse

• Drawing of continuous fibers multiple orifices
  with speeds as high as 500 m/s ? fibers as
  small as 2?
• Short glass fibers by centrifugal spraying
  process

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Steps in Manufacturing a Glass Bottle Blowing
Figure 11.30 Stages in manufacturing an ordinary
glass bottle. Source F.H. Norton, Elements of
Ceramics. Addison-Wesley Publishing Company,
Inc. 1974.
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Glass Molding
Figure 11.31 Manufacturing a glass item by
pressing glass in a mold. Source Corning Glass
Works.
Figure 11.32 Pressing glass in a split mold.
Source E.B. Shand, Glass Engineering Handbook.
McGraw-Hill, 1958.
35
Centrifugal Glass Casting
Figure extra Centrifugal casting of glass.
Television-tube funnels are made by this process.
Source Corning Glass Works.

• TV picture tubes
• Missile nose cones

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Residual Stresses
Figure 11.33 Residual stresses in tempered glass
plate, and stages involved in inducing
compressive surface residual stresses for
improved strength.

• Large amount of energy stored from residual
  stresses ? shatters into a large number of
  pieces when broken

• Chemical tempering exchange of ions in bath of
  molten KNO3, K2SO4, NaNO3 ? compressive
  stresses on the surface

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• Rapid-Prototyping Operations

38
Rapid Prototyping Examples
Figure extra (a) Examples of parts made by rapid
prototyping processes. (b) Stereolithography
model of cellular phone.
39
Stereo-lithography
Figure extra The computational steps in
producing a stereolithography file. (a)
Three-dimensional description of part. (b) The
part is divided into slices (only one in 10 is
shown). (c) Support material is planned. (d) A
set of tool directions is determined to
manufacture each slice. Shown is the extruder
path at section A-A from (c), for a
fused-deposition-modeling operation.
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Fused-Deposition-Modeling
Figure extra (a) Schematic illustration of the
fused-deposition-modeling process. (b) The FDM
5000, a fused-deposition-modeling-machine.
Source Courtesy of Stratysis, Inc.
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Common Support Structures
Figure extra (a) A part with a protruding
section which requires support material. (b)
Common support structures used in
rapid-prototyping machines. Source P.F. Jacobs,
Rapid Prototyping Manufacturing Fundamentals
of Stereolithography. Society of Manufacturing
Engineers, 1992.
42
Stereolithography
Figure extra Schematic illustration of the
stereolithography process. Source Ultra Violet
Products, Inc.
43
Example of Stereolithography
Figure extra A two-button computer mouse.
44
Selective Laser Sintering
Figure extra Schematic illustration of the
selective laser sintering process. Source After
C. Deckard and P.F. McClure.
45
Solid-Base Curing
Figure extra Schematic illustration of the
solid-base-curing process. Source After M.
Burns, Automated Fabrication, Prentice Hall, 1993.
46
Three-Dimensional Printing
Figure extra Schematic illustration of the
three-dimensional-printing process. Source
After E. Sachs and M. Cima.
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Laminated-Object Manufacturing
Figure extra (a) Schematic illustration of the
laminated-object-manufacturing process. Source
Helysis, Inc. (b) Crankshaft-part example made
by LOM. Source After L. Wood.
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Investment Casting
Figure extra Manufacturing steps for investment
casting that uses rapid--prototyped wax parts as
blanks. This approach uses a flask for the
investment, but a shell method can also be used.
Source 3D Systems, Inc.
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Sand Casting Using Rapid-Prototyped Patterns
Figure extra Manufacturing steps in sand casting
that uses rapid-prototyped patterns. Source 3D
Systems, Inc.
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Sand Casting (continued)
Figure extra
51
Rapid Tooling
Figure extra Rapid tooling for a
rear-wiper-motor cover