Industrial Engineering Chapter 11 Firing Leads Shrinkage Weight Ratio These Materials Beneficial The The Part Resulting

Chapter 11

Properties and Processing of Metal

Powders, Ceramics, Glasses,

Composites, and Superconductors

Questions

Powder metallurgy

11.1 Explain the advantages of blending different

metal powders.

(a) Powders can be mixed to obtain special

physical, mechanical, and chemical char-

11.2 Is green strength important in powder-metal

processing? Explain.

Green strength is very important in powder-

11.3 Give the reasons that injection molding of metal

Powder-injection molding has become an im-

portant process because of its versatility and

economics. Complex shapes can be obtained at

high production rates using powder metals that

11.4 Describe the events that occur during sintering.

In sintering, a green P/M part is heated to a

11.5 What is mechanical alloying, and what are its

advantages over conventional alloying of met-

als?

and eventually are mechanically bonded and

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11.6 It is possible to infiltrate P/M parts with vari-

ous resins, as well as with metals. What possi-

ble benefits would result from infiltration? Give

11.7 What concerns would you have when electro-

plating P/M parts?

low current density. Thus, only the sur-

11.8 Describe the effects of different shapes and sizes

of metal powders in P/M processing, comment-

ing on the magnitude of the shape factor of the

At low compaction pressures, the density of

P/M parts is low and at high compacting

11.10 Should green compacts be brought up to the

sintering temperature slowly or rapidly? Ex-

11.11 Explain the effects of using fine vs. coarse pow-

the voids between marbles or tennis balls in a

box (see also Fig. 3.2). The larger voids result

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11.12 Are the requirements for punch and die mate-

rials in powder metallurgy different than those

for forging and extrusion, described in Chapter

6? Explain.

abrasive resistance is a major consideration in

ble 3.6 on p. 114). Processes such as isostatic

11.13 Describe the relative advantages and limita-

tions of cold and hot isostatic pressing, respec–

allurgical bonding, and good mechanical prop-

11.14 Why do mechanical and physical properties de-

pend on the density of P/M parts? Explain.

will have more and larger voids. The modulus

of elasticity decreases with increasing voids be-

11.15 What type of press is required to compact pow-

ders by the set of punches shown in Fig. 11.7d?

The operation shown in Fig. 11.7d would re-

quire a double-action press, so that independent

movements of the two punches can be obtained.

This is usually accomplished with a mechanical

11.16 Explain the difference between impregnation

infiltration is the media (see Section 11.5). In

by surface tension and fills the voids in the

porous structure of the part. The lubricant

11.17 Explain the advantages of making tool steels by

P/M techniques over traditional methods, such

special tooling to produce the part. However,

perature depend on the type of powder metal

used? Explain.

of the material melting temperature on an ab-

solute scale. As for the compacting pressure, it

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11.19 Name various methods of powder production

By the student. Refer to Fig. 11.2. Brieﬂy:

11.20 Are there any hazards involved in P/M process-

ing? If any, what are their causes?

the major one is that powder metals can be

explosive (particularly aluminum, magnesium,

titanium, zirconium, and thorium). Thus,

11.21 What is screening of metal powders? Why is it

sizes. This is done in order to have good control

11.22 Why is there density variations in compacted

metal powders? How is it reduced?

tional resistance of the punch and die sur-

faces, or by adding lubricants that reduce inter-

11.23 It has been stated that P/M can be competitive

with processes such as casting and forging. Ex-

plain why this is so, commenting on technical

fittings, small toys) are economical and not as

tion 10.12.4 as a rapid prototyping technique.

What similarities does this process have with

the processes described in this chapter?

rial transfer is obtained from a laser and not by

11.26 Describe the major differences between ceram-

quire extensive answers that can be tabulated

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11.27 Explain why ceramics are weaker in tension

ever, the ﬂaws in the material do not cause

11.28 Why do the mechanical and physical properties

of ceramics decrease with increasing porosity?

11.29 What engineering applications could benefit

from the fact that, unlike metals, ceramics gen-

erally maintain their modulus of elasticity at

elevated temperatures?

manner of producing the parts. Engineering

applications that require high and reliable me-

11.31 List the factors that you would consider when

replacing a metal component with a ceramic

for example, the following factors:

tic and have a smaller distribution of

strength. Thus, a major concern is

whether or not a material is suitable for

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doping (see pp. 159 and 605), resulting in two or

static fatigue can be important.

11.34 Explain the difficulties involved in making large

ceramic components. What recommendations

would you make to overcome these difficulties?

11.35 Explain why ceramics are effective cutting-tool

materials. Would ceramics also be suitable as

die materials for metal forming? Explain.

p. 454 and Figs. 8.30 and 8.37), chemical inert-

ness, and wear resistance. In ceramic dies for

forming, the main difficulties are that (1) ce-

ramics are brittle, so any tensile or shear load

would lead to crack propagation and failure,

11.36 Describe applications in which the use of a ce-

ramic material with a zero coefficient of thermal

Fig. 11.23 and Section 3.9.5) would have a much

lower probability of thermal cracking when ex-

posed to extreme temperature gradients, such

11.37 Give reasons for the development of ceramic-

matrix components. Name some present and

other possible applications for such large com-

•engines for missiles and reusable space ve-

hicles; and

11.38 List the factors that are important in drying

ceramic components, and explain why they are

important.

Refer to Section 11.9.4. Since ceramic slur-

ries may contain significant moisture content,

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11.39 It has been stated that the higher the coefficient

of thermal expansion of glass and the lower its

perature in the glass, and the more uniform

11.40 What types of finishing operations are typically

performed on ceramics? Why are they done?

tion 11.9.5). Abrasive machining, such as grind-

ing, is done to assure good tolerances and to re-

11.41 What should be the property requirements for

the metal balls used in a ball mill? Explain why

p. 44).

11.43 What properties should plastic sheet have when

11.44 Consider some ceramic products that you are

familiar with and outline a sequence of pro-

ture of a coffee cup:

•The mold is allowed to rest, allowing the

water in the slurry to be absorbed by the

designs, the handle is cast integrally with

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11.47 Injection molding is a process that is used for

plastics and powder metals as well as for ceram-

ics. Why is it suitable for all these materials?

11.48 Are there any similarities between the strength-

ening mechanisms for glass and those for other

metallic and nonmetallic materials described

throughout this text? Explain.

or annealed to relieve surface residual stresses,

compressive residual stresses are induced on

11.49 Describe and explain the differences in the man-

ner in which each of the following ﬂat surfaces

(a) When subjected to an impact load, ordi-

nary window glass will shatter into numer-

ous fragments or shards of various sizes.

and slip casting, (c) extrusion of metals and

extruding polymers, and (d) drawing of metal

The doctor-blade process, shown in Fig. 11.28,

produces thin sheets of ceramic. This process

has, for example, been very cost-effective for

11.52 Describe the methods by which glass sheet is

Fig. 11.32. Basically:

down to the desired thickness.

•In the ﬂoat method, a glass sheet ﬂoats on

11.53 Describe the differences and similarities in pro-

ducing metal and ceramic powders. Which of

these processes would be suitable for producing

glass powder?

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11.54 How are glass fibers made? What application

do these fibers have?

Glass fibers (see pp. 612-613) are bundle drawn

11.56 What are the similarities and differences be-

tween injection molding, metal injection mold-

ing, and ceramic injection molding?

11.57 Aluminum oxide and partially stabilized zirco-

nia are normally white in appearance. Can they

be colored? If so, how would you accomplish

this?

including the susceptibility of ceramics to ﬂaws

in tension and the range of porosity that ce-

ramic parts commonly contain.

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11.59 Estimate the number of particles in a 500-g

sample of iron powder, if the particle size is 50

µm.

m=ρV = (7.86)(6.545×10−8) = 5.14×10−7g

11.60 Assume that the surface of a copper particle is

covered with a 0.1-µm-thick oxide layer. What

is the volume occupied by this layer if the cop-

per particle itself is 75 µm in diameter? What

would be the role of this oxide layer in subse-

quent processing of the powders?

11.61 Determine the shape factor for a ﬂakelike par-

ticle with a ratio of surface area to thickness

or, solving for D,

D=3

r6V

r6(144)

15.17. For the ellipsoid particle, all cross sec-

tions across the three major and minor axes are

where a,b, and care the three semi-axes of the

ellipsoid. Because of arbitrary units, we can

calculate the volume of an ellipsoid with axes

ratios of 5:2:1 as

units,

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11.62 It was stated in Section 3.3 that the energy in

brittle fracture is dissipated as surface energy.

We also noted that the comminution process

for powder preparation generally involves brit-

tle fracture. What are the relative energies in-

volved in making spherical powders of diame-

ters 1, 10, and 100 µm, respectively?

process parameters: µ= 0 to 1, k= 0 to 1, and

D= 5 mm to 50 mm.

The key equation is Eq. (11.2) on p. 680:

px=poe−4kx/D

The results are plotted in three graphs, for

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11.3.1. Therefore, the expression for the pres-

11.67 For the ceramic described in Example 11.7, cal-

shrinkages during drying and firing are 8% and

Because the linear shrinkage during firing

Vd

=0.91

1.24 = 0.73,or 73%

Consequently, the porosity of the dried

Ld

or

Since L= 20 mm,

or Lo= 23.23 mm.

11.68 What would be the answers to Problem 11.67

if the quantities given were halved?

Vd=Vf/(1 −0.035)3= 1.112Vf

part is (1 – 0.86) = 0.14, or 14%.

Ld

= 0.035

0.965 = 20.73 mm

and thus

havior.

The plots are given below.

0.4

0.2

0

UTS/UTS0

10.80.60.40.20

Porosity

=

5

0.4

0.2

0

E/E0

10.80.60.40.20

182

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1

0.8

0.6

0.4

0.2

k/k0

10.80.60.40.20

Porosity

11.70 Plot the total surface area of a 1-g sample of

mass of each particle is:

or A= (2.22 cm3)D−1, where Dis in cm (µm

Spherical particles will be in the sub-mm sizes

(tens to hundreds of microns), while other

shapes can approach a few mm in average di-

ameter.

11.72 A coarse copper powder is compacted in a me-

chanical press at a pressure of 20 tons/in2. Dur-

tional 8%. What is the final density of the part?

shrinks an additional 8% during sintering, the

11.73 A gear is to be manufactured from iron powder.

Fig. 11.6a, the required pressure for this den-

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1.4 g/cm3. Therefore, the volume of powder

required is

V=m

11.75 The axisymmetric part shown in the accompa-

nying figure is to be produced from fine copper

11.76 What techniques, other than the powder-in-

tube process, could be used to produce super-

conducting monofilaments?

(a) coating of silver wire with superconduct-

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11.79 Calculate the thermal conductivities for ceram-

ics at porosities of 1%, 5%, 10%, 20%, and 30%

for ko= 0.7 W/m-K.

Inserting the values into the equation, we ob-

5 0.665

20 0.56

11.80 A ceramic has ko= 0.65 W/m-K. If this ce-

ramic is shaped into a cylinder with a porosity

For the remainder of the problem, use X=

x/L. The average porosity is then given by

= 0.0167

ity is:

¯

k=ko1−¯

P= (0.65)(1 −0.0167)

11.81 Assume that you are asked to give a quiz to stu-

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much as possible. There are many similarities

the hub and the gear root should be as large

as possible. Explain the reasons for this design

11.85 How are the design considerations for ceramics

different, if any, than those for the other mate-

rials described in this chapter?

11.86 Are there any shapes or design features that

are not suitable for production by powder met-

allurgy? By ceramics processing? Explain.

11.87 What design modifications would you recom-

mend for the part shown in Problem 11.75?

11.88 The axisymmetric parts shown in the accompa-

nying figure are to be produced through P/M.

(a) (b)

Some considerations are:

(a) Part (a):

•The part has very thin walls, and it

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pressed parts.

(b) Part (b): Same as in (a)

(c) Part (c): Same as in (a), and the ﬂanges

should comply with the recommendations

11.89 Assume that in a particular design, a metal

beam is to be replaced with a beam made of

ceramics. Discuss the differences in the behav-

ior of the two beams, such as with respect to

strength, stiffness, deﬂection, and resistance to

temperature and to the environment.

By the student. This is an open-ended problem

that can be answered in a number of ways by

the students. They can, for example, consider

a cantilever, where the deﬂection at the end of

the cantilever is,

y=−P l3

3EI

and then compare materials that would give

the same deﬂection for different beam heights,

widths, or volumes. One could also consider

the lightest weight cantilever that could sup-

port the load or one that would have a small

deﬂection under the load. Students are encour-

11.90 Describe your thoughts regarding designs of in-

ternal combustion engines using ceramic pis-

associated with such designs. For example, lu-

bricants (see Section 4.4.4) typically are formu-

11.91 Assume that you are employed in technical

sales. What applications currently using non-

P/M parts would you attempt to develop?

What would you advise your potential cus-

tomers during your sales visits? What kind of

questions do you think they would ask?

that requires knowledge of parts that are and

are not currently produced by P/M. It would be

advisable for the instructor to limit the discus-

sion to a class of product, such as P/M gears.

In this case, the questions that would be asked

of customers include:

(a) Are you aware of the advantages of P/M

processes?

(b) Are you aware of the tribological advan-

tages of P/M parts?

(c) Are you interested in unique alloys or

blends that can only be achieved with

P/M technologies?

(d) Is it beneficial to achieve a 5-10% weight

savings using porous P/M parts?

Typical anticipated questions from the cus-

tomer could include:

(a) Is there a cost or performance advantage?

(b) We have had no failures, so why should we

change anything?

11.92 Pyrex cookware displays a unique phenomenon:

it functions well for a large number of cycles

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11.93 It has been noted that the strength of brittle

materials, such as ceramics and glasses, are very

sensitive to surface defects such as scratches

the direction of the scratch. As a comparison,

even a highly heat-treated aluminum plate (i.e.,

11.94 Make a survey of the technical literature and

describe the differences, if any, between the

fibers for communications applications are for-

11.95 Describe your thoughts on the processes that

these products. Some examples are:

(a) Small ceramic statues are usually made by

slip casting, then fired to fuse the particles

11.96 As described in this chapter, one method of

producing superconducting wire and strip is by

the green part before or during drawing, and its

implications; inhomogeneous deformation that

for constant-thickness parts, as opposed to the

sarily based on the axisymmetric nature of the

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