properties and processing of powder metals, ceramics, glasses, and composites

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

properties and processing of powder metals, ceramics, glasses, and composites

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