Lowell D. Outland
IET307
Material Science
IET 307: Materials Science
HW 2 (based on chapter 4),
Due on September 16’Th (Friday, before 11.55 PM), 2011
100 points (Cite external references wherever used)
1. What are Solid solutions? Explain interstitial and Substitutional solid solutions
(10points).
Solid solutions are formed when impure atoms are added to the host material,
while maintain the crystal structure.
Substitutional is when the impure atoms replace the host atoms
Interstitial is when the impure atoms fill the spaces in between the host atoms
2. Explain in a paragraph each; (in detail along with schematic diagrams of the
equipment) optical microscopy, electron microscopy and scanning probe microscopy
respectively? (10 points).
Optical Microscopy – the light microscope is used for this. For opaque materials
light must be reflected of the surface of the material, and only the surface can be seen.
The surface of these materials must be carefully prepared in order to get the best
results. As the light reflects differently on each crystalline structure these structures can
be examined. The following image was obtained from www.olympus.ims.com and
illustrates the basic principles of this type of microscope. The optical microscope can
magnify up to approximately 2000 times.
Electron Microscopy – with electron microscopy there are two types of modes,
Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM).
The image produced by the TEM is formed by an electron beam that passes through a
specimen. These specimens must be in the form of extremely thin foils. With this type of
microscopy one can achieve magnifications of up to 1,000,000X. With the SEM the
Lowell D. Outland
IET307
Material Science
surface of a specimen to be examined need not be polished, etched or made into thin
foils. It must however be electrically conductive. Therefore on nonconductive materials a
thin metallic coating needs to be applied. This type of microscopy has a magnification
range from 10 to in excess of 50,000.
Scanning Probe Microscopy- This is a relatively new concept. There are several
different varieties of this microscope. This differs from optical and electron microscopy
in the terms that it does not use reflected light or electrons to produce an image, instead
this microscope generates a topographical map on an atomic scale. Some of the
features of this microscope are,1) magnification of up to 10 9X with greater resolutions,
2) three dimensional images are provided, and 3) some SPM’s can operate in a variety
of environments(such as in a vacuum or under water).
3. What makes plain carbon steel harder than pure iron? (5 points)
Carbon steel is harder because the carbon steel alloy is a more dense material
giving it a greater bonding strength.
4. An ASTM grain size determination is being made from a photomicrograph of a metal
at a magnification of 100X. What is the ASTM grain-size number of the metal if there
are 64 grains per square inch? (10 points).
Using the formula: n = log N / log 2
(log64/log2)+1 = 7 The ASTM grain size is 7.
5. Calculate the energy for vacancy formation in silver, given that the equilibrium
number of vacancies at 8000C (1073 K) is 3.6 * 1023 m-3. The atomic weight and
density (at 8000 C) for silver are, respectively, 107.9 g/mol and 9.5 g/cm3. (10 points)
= 1.10 eV/atom
6. What is the composition, in weight %, of an alloy that consists of 15 atomic % Au and
85 atomic % Pb? (10 points)
C1 = M1/M1+M2 x100
C1 = (107.87/(107.87+207.19))x100
C2 = (207.19/(107.87+207.19))x100
C1 = 34.23 Au
C2 = 65.76 Pb
Lowell D. Outland
IET307
Material Science
7. In structural applications, why do we use alloys rather than pure metals? (5 points)
As a general rule alloys are normally stronger than pure metals.
8. Pure copper is strengthened by addition of small concentration of Be. What
mechanism of strengthening is this related to? (5 points).
Precipitation hardening.
9. A slab of steel is transformed into a car chassis. Does this process involve plastic or
elastic deformation? (5 points)
In order for the chassis to maintain its shape plastic deformation would have to
be used.
10. Why would metals behave as brittle materials without dislocations? (5 points)
Without dislocations the crystals are aligned is a row making the metal more
brittle than if they were not aligned.
11. What is added to an alumina crystal to turn it into a ruby crystal? (5 points)
To turn an alumina crystal into a ruby crystal you need to add a small amount of
chromium, this gives it the red coloring.
12. Sterling silver consists of approximately 93 wt% silver and 7 wt% copper. Discuss all
the ways by which the addition of 7 wt% copper is beneficial. (5 points)
The copper enhances the strength of the silver while keeping its natural
resistance to corrosion.
13. Describe the structure of a grain boundary. Why are grain boundaries favorable
sites for the nucleation and growth of precipitates? (5 points)
The grain boundary is a boundary separating two small grains and having
different crystallographic orientations.
Lowell D. Outland
IET307
Material Science
14. What are edge and screw dislocations? (5 points)
An edge dislocation is a linear defect associated with the lattice distortion close
to the end of an extra half plane of atoms within a crystal.
A screw dislocation is a linear defect created when normally parallel planes are
joined together to form a helical ramp.
15. What are a solute and a solvent? Give 5 examples of a solute and a solvent from
our daily lives? (5 points)
A salute is the component that makes up the smallest portion of a solution.
A solvent is the component that makes up the largest portion of a solution, and
dissolves the solute.
Examples include:
Salute
Solvent
Kool Aid
Water
Paint
Thinner
Laundry detergent
Water
Sodium Bicarbonate
Water
Cocoa
Milk