Unlock document.
This document is partially blurred.
Unlock all pages and 1 million more documents.
Get Access
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
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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,
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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?
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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.
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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,
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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-
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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-
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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=ko1−¯
P= (0.65)(1 −0.0167)
11.81 Assume that you are asked to give a quiz to stu-
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
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
© 2008 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited
reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permission(s), write to:
Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.
