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7/29/2019 Properties and Processing of Powder Metals, Ceramics, Glasses, and Composites
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CHAPTER 11
Properties and Processing of PowderMetals, Ceramics, Glasses, and
Composites()
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Typical Applications for Metal Powders
TABLE 11.1
Application Metals Uses
AbrasivesAerospace
AutomotiveElectrical/electronic
Heat treatingJoining
LubricationMagnetic
ManufacturingMedical/dental
Metallurgical
NuclearOffice equipment
Fe, Sn, ZnAl, Be, Nb
Cu, Fe, WAg, Au, Mo
Mo, Pt, WCu, Fe, Sn
Cu, Fe, ZnCo, Fe, Ni
Cu, Mn, WAg, Au, W
Al, Ce, Si
Be, Ni, WAl, Fe, Ti
Cleaning, abrasive wheelsJet engines, heat shields
Valve inserts, bushings, gearsContacts, diode heat sinks
Furnace elements, thermocouplesSolders, electrodes
Greases, abradable sealsRelays, magnets
Dies, tools, bearingsImplants, amalgams
Metal recovery, alloying
Shielding, filters, reflectorsElectrostatic copiers, cams
Source: R. M. German.
Material density in P/M is controllable
~70% of P/M part production is for automotive applications
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Powder-Metallurgy
Figure 11.1 (a) Examples of typical parts made bypowder-metallurgy processes. (b) Upper trip lever for acommercial irrigation sprinkler, made by P/M. This partis 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 PowderIndustries Federation, Princeton, New Jersey, 1998. (c)Main-bearing powder metal caps for 3.8 and 3.1 literGeneral Motors automotive engines. Source: Courtesy ofZenith Sintered Products, Inc., Milwaukee, Wisconsin.
(a)
(b)
(c)
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Making Powder-Metallurgy Parts
Figure extra Outline of processes and operations involved in making powder-metallurgy parts.
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Particle Shapes in Metal Powders
Figure 11.2Particle shapes inmetal powders, andthe processes by
which they areproduced. Ironpowders areproduced by manyof these processes.
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Powder Particles
Figure extra (a) Scanning-electron-microscopy photograph ofiron-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.
(a) (b)
Particle sizes: 0.1 to 1000: distribution
Shapes: aspect ratio(largest/smallest), shape factor(surface/volume)
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Atomization and Mechanical Comminution
Figure 11.3 Methods of metal-powderproduction by atomization; (a) meltatomization; (b) atomization with arotating consumable electrode.
Reduction of metal oxidesElectrolytic depositionDecomposition of metal carbonylsMechanical alloyingPrecipitation, chips by machining, vapor condensation
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Equipment for Blending Powders
Figure extra Some commonequipment geometries for mixingor blending powders: (a)
cylindrical, (b) rotating cube, (c)double cone, and (d) twin shell.Source: Reprinted withpermission from R. M. German,Powder Metallurgy Science.Princeton, NJ; Metal Powder
Industries Federation, 1984.
Under controlled condition contamination, deteriorationHigh shape factor explosive: Al, Mg, Ti, Zr, Th
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Compaction
Figure 11.6 (a) Compaction ofmetal powder to form a bushing.The pressed powder part is calledgreen compact. (b) Typical tooland die set for compacting a spur
gear. Source: Metal PowderIndustries Federation.
Green compact: as-pressed
- shape- (green) density- contact of particles
Compressibility
green density
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Density Effects
Figure 11.7 (a) Density of copper- and iron-powder compacts as a function of compacting pressure. Densitygreatly 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 ontensile strength, elongation, and electrical conductivity of copper powder. IACS means International AnnealedCopper Standard for electrical conductivity.
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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 puncheswith separate movements, compared with (c). (e) Pressure contours in compacted copper powder in asingle-action press. Source: P. Duwez and L. Zwell.
Uniform density by multiple punches: (d)Dkx
ox epp/4
=
(Fig. 11.9)
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Compacting Pressures for Various Metal
PowdersTABLE 11.3
Metal
Pressure
(MPa)Aluminum
Brass
Bronze
Iron
TantalumTungsten
70275
400700
200275
350800
7014070140
Other materials
Aluminum oxide
CarbonCemented carbides
Ferrites
110140
140165140400
110165
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Mechanical Press
Figure extra A 7.3 MN (825 ton)mechanical press for compactingmetal powder. Source: Courtesy ofCincinnati Incorporated.
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Hot and Cold Isostatic Pressing
Figure 11.10 Schematic diagram ofcold isostaticpressing, as applied to forming a tube. The powder isenclosed in a flexible container around a solid core rod.Pressure is applied isostatically to the assembly inside
a high-pressure chamber. Source: Reprinted withpermission from R.M. German, Powder MetallurgyScience. Princeton, NJ; Metal Powder IndustriesFederation, 1984.
Pressure: 400MPa ( up to 1000MPa)
Hot isostatic pressing:compaction + sintering
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Capabilities Available from P/M Operations
Figure 11.11 Capabilities, withrespect to part size and shapecomplexity, available from variousP/M operations. P/F means
powder forging. Source: MetalPowder Industries Federation.
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Figure 11.12 Schematic illustration ofhot 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 metallurgicalbonding, good mechanical properties
Relatively expensive superalloy components
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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
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Sintering
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 = neck profile radius.
Heated in a controlled atmosphere to a temperature below its melting point,
but sufficiently high to allow bonding of individual particles
Different metals:
alloying particles with lowmelting point: melt
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Sintering Temperature and Time for Various Metals
TABLE 11.4
MaterialTemperature
( C)Time(Min)
Copper, brass, and bronze
Iron and iron-graphiteNickel
Stainless steelsAlnico alloys
(for permanent magnets)Ferrites
Tungsten carbideMolybdenum
TungstenTantalum
760900
1000115010001150
1100129012001300
12001500
143015002050
23502400
1045
8453045
3060120150
10600
2030120
480480
DiffusionPlastic flow
Grain growthPore shrinkage
Evaporation of volatile materials in the compactRecrystallization
Bond strength
Increase of sintering time(temperature) increase of elongation and dimensional
change from die size(Fig. 11.14)
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Mechanical Property Comparison for Ti-6Al-4V
TABLE 11.6
Process(*)
Density
(%)
Yield
strength
(MPa)
Ultimate
strength
(MPa)
Elongation
(%)
Reduction
of area
(%)Cast
Cast and forged
Blended elemental (P+S)
Blended elemental (HIP)
Prealloyed (HIP)
100
100
98
> 99
100
840
875
786
805
880
930
965
875
875
975
7
14 40
8
9
14
15
14
17
26
(*) P+S = pressed and sintered, HIP = hot isostatically pressed.
Source: R.M. German.
Sintered density
mechanical properties- green density- sintering temperature (70~90% of melting point) and time- furnace atmosphere
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Mechanical Properties of Selected P/M Materials
TABLE 11.5
Designation
MPIF
type Condition
Ultimate
tensile
strength
(MPa)
Yield
Strength
(MPa) Hardness
Elongation
in 25 mm
(%)
Elastic
modulus
(GPa)
Ferrous
FC-0208 N AS 225 205 45 HRB
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Examples of
P/M Parts
Figure 11.16 Examples of P/M parts, showing poordesigns and good ones. Note that sharp radii and
reentry corners should be avoided and that threadsand transverse holes have to be produced separatelyby additional machining operations.
Secondary and finishing operations- impregnating: fluid (oil)- infiltration: slug of low-melting
point metal- heat treating
- machining- finishing: deburring, coating,
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Forged and P/M Titanium Parts and Potential Cost Saving
TABLE 11.7
Weight (kg)Potential
cost
PartForgedbillet P/M
Finalpart
saving(%)
F-14 Fuselage brace
F-18 Engine mount supportF-18 Arrestor hook support fitting
F-14 Nacelle frame
2.8
7.779.4
143
1.1
2.525.0
82
0.8
0.512.9
24.2
50
2025
50
Spray deposition (Osprey process: Fig. 11.15) spray of atomized metalon a cooled preform mold
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Characteristics of Ceramics Processing
TABLE 11.11
Process Advantages Limitations
Slip casting Large parts, complex shapes; low
equipment cost.
Low production rate; limited dimensional
accuracy.Extrusion Hollow shapes and small diameters;
high production rate.
Parts have constant cross section; limited
thickness.
Dry pressing Close tolerances; high production rate
with automation.
Density variation in parts with high length-to-
diameter ratios; dies require high abrasive-wear
resistance; equipment can be costly.
Wet pressing Complex shapes; high production rate. Part size limited; limited dimensional accuracy;
tooling costs can be high.
Hot pressing Strong, high-density parts. Protective atmospheres required; die life can be
short.
Isostatic pressing Uniform density distribution. Equipment can be costly.
Jiggering High production rate with automation;low tooling cost. Limited to axisymmetric parts; limiteddimensional accuracy.
Injection molding Complex shapes; high production rate. Tooling can be costly.
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Steps in Making Ceramic Parts
Figure extra Processing steps involved in making ceramic parts.
Processing of Ceramics
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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), SiO2Oxide ceramics: Al2O3, ZrO2Other ceramics: WC, TiC, SiC, CBN, TiN, Si3N4, cermets
Sialon(Si3N4 + Al2O3 + TiC + yttrium oxide)
Processing of Ceramics
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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.
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Extruding and Jiggering
Figure 11.26 (a) Extruding and (b) jiggering operations. Source: R. F. Stoops.
Plastic forming: extrusion, injection molding, molding, jiggeringPressing: dry pressing, wet pressing, isostatic pressing,
hot pressing(pressure sintering)
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Shrinkage
Figure 11.27 Shrinkage of wet clay caused by removal of water during drying. Shrinkage may be asmuch as 20% by volume. Source: F. H. Norton,Elements of Ceramics. Addison-Wesley PublishingCompany, Inc. 1974.
Drying and firing
Finishing after firing: grinding, lapping, ultrasonic, .
G G
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Ave Maria,Caccini
View over a village near Geumgang(Riv.), Gongju
Processing of Glasses
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Sheet Glass FormationFigure extra (a)Continuous processfor drawing sheetglass from a molten
bath.Source
: W. D.Kingery, Introductionto Ceramics. Wiley,1976. (b) Rollingglass to produce flatsheet.
Figure 11.28 The float method offorming sheet glass. Source: Corning
Glass Works.
g
Float glass: fire polishedsmooth surface no furtherpolishing/grinding
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Glass Tubing
Figure 11.29 Manufacturingprocess for glass tubing. Air isblown through the mandrel to keepthe tube from collapsing. Source:Corning Glass Works.
Mandrel: rotatingAir is blown through themandrel tubecollapse
Drawing of continuous fibers: multiple orifices with speeds as high as 500 m/s
fibers as small as 2Short glass fibers: by centrifugal spraying process
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Steps in
Manufacturing aGlass Bottle: Blowing
Figure 11.30 Stages in manufacturing anordinary glass bottle. Source: F.H.Norton,Elements of Ceramics. Addison-Wesley Publishing Company, Inc. 1974.
Glass Molding
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Glass Molding
Figure 11.31Manufacturing aglass item bypressing glass in amold. Source:
Corning GlassWorks.
Figure 11.32 Pressing glassin a split mold. Source: E.B.Shand, Glass EngineeringHandbook. McGraw-Hill,1958.
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Centrifugal Glass Casting
Figure extra Centrifugal casting of glass.Television-tube funnels are made by thisprocess. Source: Corning Glass Works.
TV picture tubesMissile nose cones
Residual Stresses
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Residual Stresses
Figure 11.33 Residual stresses intempered glass plate, and stagesinvolved in inducing compressivesurface residual stresses forimproved strength.
Large amount of energystored from residualstresses shatters intoa large number ofpieces 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
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Rapid Prototyping Examples
Figure extra (a) Examples of partsmade by rapid prototyping processes.(b) Stereolithography model of cellularphone.
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Stereo-lithography
Figure extra The computationalsteps in producing astereolithography 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) Aset of tool directions is determinedto manufacture each slice. Shownis the extruder path at section A-Afrom (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, afused-deposition-modeling-machine. Source:Courtesy of Stratysis, Inc.
(a) (b)
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Common Support Structures
Figure extra (a) A part with a protruding section which requires support material. (b) Commonsupport structures used in rapid-prototyping machines. Source: P.F. Jacobs, Rapid Prototyping &Manufacturing: Fundamentals of Stereolithography. Society of Manufacturing Engineers, 1992.
S li h h
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Stereolithography
Figure extra Schematicillustration of thestereolithography
process. Source: UltraViolet Products, Inc.
E l f St lith h
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Example of Stereolithography
Figure extra A two-button computermouse.
Selective Laser Sintering
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Selective Laser Sintering
Figure extra Schematic illustration of the selective laser sintering process. Source: After C.Deckard and P.F. McClure.
Solid Base Curing
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Solid-Base Curing
Figure extra Schematic illustration of the solid-base-curing process. Source: After M. Burns,Automated Fabrication, Prentice Hall, 1993.
Th Di i l P i ti
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Three-Dimensional Printing
Figure extraSchematicillustration of thethree-dimensional-
printing process.Source: After E.Sachs and M.Cima.
Laminated-Object Manufacturing
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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.
(a) (b)
Investment
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Casting
Figure extraManufacturing
steps forinvestment castingthat uses rapid--prototyped waxparts as blanks.This approach
uses a flask for theinvestment, but ashell method canalso be used.Source: 3DSystems, Inc.
Sand Casting Using Rapid-Prototyped Patterns
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Figure extra Manufacturing steps in sand casting that uses rapid-prototyped patterns. Source: 3D Systems, Inc.
Sand Casting (continued)
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Figure extra
Rapid Tooling
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Rapid Tooling
Figure extra Rapidtooling for a rear-wiper-motor cover