1. Name of Experiment: Microscopic inspection of pure metals and solid solutions. 2. The Objective of the Experiment: To study the different shapes and sizes of grains and the flaws found in casts

1. Baghdad University
College of Engineering
Department of Mechanical Engineering
Name of Experiment
" Microscopic inspection of pure metals and solid solutions. "
Preparation:
Saif al-Din Ali Madi
The second phase
Group "A "

2. 1. Name of Experiment:
Microscopic inspection of pure metals and solid solutions.
2. The Objective of the Experiment:
To study the different shapes and sizes of grains and the flaws found in casts
Casting (metalworking)
Molten metal before casting
Casting iron in a sand mold
In metalworking and jewellery making, casting is a process in which a liquid
metal is somehow delivered into a mold that contains a hollow cavity (i.e., a 3-
dimensional negative image) of the intended shape. The metal and mold are
then cooled, and the metal part (the casting) is extracted. Casting is most
often used for making complex shapes that would be difficult or uneconomical
to make by other methods

3. Expendable mold casting:
Expendable mold casting is a generic classification that includes sand, plastic,
shell, plaster, and investment (lost
mold casting involves the use of temporary, non
Sand casting
Main article: Sand casting :
Sand casting is one of the most popular and simplest types of casting, and has
been used for centuries. Sand casting allows for smaller batches than
permanent mold casting and at a very reasonable cost. Not only does this
method allow manufacturers to create products at a low cost, but there are
other benefits to sand casting, such as very small
allows for castings small enough fit i
enough only for train beds (one casting can create the entire bed for one rail
car). Sand casting also allows most metals to be cast depending on the type of
sand used for the molds.
Sand casting requires a lead time
produc on at high output rates (1
large-part production. Green (moist) sand has almost no part weight limit,
whereas dry sand has a prac cal part mass limit of 2,300
6,000 lb). Minimum part weight ranges from 0.075
sand is bonded together using clays, chemical binders, or polymerized oils
(such as motor oil). Sand can be recycled many times in most operations and
requires little maintenance.
Expendable mold casting:
Expendable mold casting is a generic classification that includes sand, plastic,
shell, plaster, and investment (lost-wax technique) moldings. This method of
g involves the use of temporary, non-reusable molds
Main article: Sand casting :
Sand casting is one of the most popular and simplest types of casting, and has
been used for centuries. Sand casting allows for smaller batches than
mold casting and at a very reasonable cost. Not only does this
method allow manufacturers to create products at a low cost, but there are
other benefits to sand casting, such as very small-size operations. The process
allows for castings small enough fit in the palm of one's hand to those large
enough only for train beds (one casting can create the entire bed for one rail
car). Sand casting also allows most metals to be cast depending on the type of
sand used for the molds.
Sand casting requires a lead time of days, or even weeks sometimes, for
produc on at high output rates (1–20 pieces/hr-mold) and is unsurpassed for
part production. Green (moist) sand has almost no part weight limit,
whereas dry sand has a prac cal part mass limit of 2,300–2,700 k
6,000 lb). Minimum part weight ranges from 0.075–0.1 kg (0.17–
sand is bonded together using clays, chemical binders, or polymerized oils
(such as motor oil). Sand can be recycled many times in most operations and
tenance.
Expendable mold casting is a generic classification that includes sand, plastic,
wax technique) moldings. This method of
Sand casting is one of the most popular and simplest types of casting, and has
been used for centuries. Sand casting allows for smaller batches than
mold casting and at a very reasonable cost. Not only does this
method allow manufacturers to create products at a low cost, but there are
size operations. The process
n the palm of one's hand to those large
enough only for train beds (one casting can create the entire bed for one rail
car). Sand casting also allows most metals to be cast depending on the type of
of days, or even weeks sometimes, for
mold) and is unsurpassed for
part production. Green (moist) sand has almost no part weight limit,
2,700 kg (5,100–
–0.22 lb). The
sand is bonded together using clays, chemical binders, or polymerized oils
(such as motor oil). Sand can be recycled many times in most operations and

4. Plaster mold casting
Main article: Plaster mold casting :
Plaster casting is similar to sand casting except that plaster of Paris is
substituted for sand as a mold material. Generally, the form takes less than a
week to prepare, after which a produc on rate of 1–10 units/hr·mold is
achieved, with items as massive as 45 kg (99 lb) and as small as 30 g (1 oz)
with very good surface finish and close tolerances.[4] Plaster cas ng is an
inexpensive alternative to other molding processes for complex parts due to
the low cost of the plaster and its ability to produce near net shape castings.
The biggest disadvantage is that it can only be used with low melting point
non-ferrous materials, such as aluminum, copper, magnesium, and zinc.
Shell molding
Main article: Shell molding :
Shell molding is similar to sand casting, but the molding cavity is formed by a
hardened "shell" of sand instead of a flask filled with sand. The sand used is
finer than sand casting sand and is mixed with a resin so that it can be heated
by the pattern and hardened into a shell around the pattern. Because of the
resin and finer sand, it gives a much finer surface finish. The process is easily
automated and more precise than sand casting. Common metals that are cast
include cast iron, aluminum, magnesium, and copper alloys. This process is
ideal for complex items that are small to medium-sized

5. 3. Devices Used for Experiment:
A. Microscope
b. Specimens for microscopic study
C. Specimens for macroscopic study

6. 4, Theory:
A. The different types of grain structure and their properties
solidification is the creation of tiny, stable, solid crystals, or nuclei in the
metal. Cooling the liquid below its equilibrium freezing temperature, or under
cooling, provides the driving force for solidification. For the new solid to be
stable, however, the energy
larger than the energy needed to create the new
Larger clusters of solid atoms are
less surface area per unit volume. Once a cluster reaches a critical size, it
becomes a stable nucleus and continues to grow. The mold walls and any solid
par cles present in the liquid make 6
providing solid surfaces for liquid atoms to solidify upon,
under cooling needed to less than 1co .
single grain, whose shape depends on how neighboring
each other. Thus, greater numbers of nuclei produce a finer (smaller) grain
. The different types of grain structure and their properties
solidification is the creation of tiny, stable, solid crystals, or nuclei in the
metal. Cooling the liquid below its equilibrium freezing temperature, or under
provides the driving force for solidification. For the new solid to be
stable, however, the energy released in forming the new solid volume must be
larger than the energy needed to create the new solid / liquid interface.
Larger clusters of solid atoms are more stable than small ones, since they
less surface area per unit volume. Once a cluster reaches a critical size, it
nucleus and continues to grow. The mold walls and any solid
par cles present in the liquid make 6 nucleation easier. They do this by
providing solid surfaces for liquid atoms to solidify upon, which reduce the
cooling needed to less than 1co . Each nucleus eventually grows into a
single grain, whose shape depends on how neighboring grains impinge upon
r. Thus, greater numbers of nuclei produce a finer (smaller) grain
solidification is the creation of tiny, stable, solid crystals, or nuclei in the liquid
metal. Cooling the liquid below its equilibrium freezing temperature, or under
provides the driving force for solidification. For the new solid to be
released in forming the new solid volume must be
solid / liquid interface.
more stable than small ones, since they have
less surface area per unit volume. Once a cluster reaches a critical size, it
nucleus and continues to grow. The mold walls and any solid
er. They do this by
which reduce the
Each nucleus eventually grows into a
grains impinge upon
r. Thus, greater numbers of nuclei produce a finer (smaller) grain

7. size. A finer grain size is generally beneficial to strength and toughness in the
final product. Nucleation is enhanced by adding alloying elements or other
materials (called grain refiners) that form small solid particles in the liquid.
The seeding of clouds to precipitate rain is a similar process. Dendrites A
casting usually begins with rapid nucleation and growth against the cold mold
walls. This produces a thin chill zone of tiny grains at the casting surface. This
shell of solid metal grows into the remaining liquid as solidification continues.
Due to the combined effects of alloy segregation during freezing, slow
diffusion and shallow temperature gradients in the liquid, the solid / liquid
interface usually does not remain planar. Instead, tree-shaped spikes called
dendrites shoot into the liquid in the direction of heat flow. The dendrites also
grow short, perpendicular secondary arms, Dendrites create a mushy zone
between the solid shell and the liquid, bounded roughly by the liquids and
solidus temperature contours. Certain crystallographic directions in the solid
metal tend to grow faster than others. Thus, some dendrites grow faster than
others into the direction of heat flow. The result of this competition is an array
of parallel aligned dendrites growing away from the randomly-oriented chill
zone. The parallel dendrites eventually form a large region of grains with a
similar orientation, perpendicular to the mold wall, called the internal
columnar zone. These columnar grains are very long and thin, with long
parallel grain boundaries that can be a source of weakness in the final casting.
Grain Structure While columnar grains are growing inward from the mold
walls, other nuclei are simultaneously growing in the central liquid pool. These
central nuclei survive because the first solid to freeze in a typical commercial
alloy has a lower alloy content, and hence a higher melting point, than the
surrounding liquid. The central crystals then grow equally in all directions,
forming roughly round-shaped, equaled grains. Eventually, the growth of the
columnar grains is stopped when7 they impinge on the equaled grains. The
result is a macrostructure consisting of three zones,. The relative proportions
of the chill, columnar, and equaled zones depends on the alloy and thermal
conditions during solidification. Preheated molds decrease the depth of the
chill zone. Conditions that produce large numbers of nuclei in the central zone
tend to result in a large equaled zone with a smaller average grain size. A
lower pouring temperature promotes a larger equaled zone, by making it
easier for nuclei to survive in the center. Alloys with a wide freezing range, or
large difference between the solidus and liquids temperatures, similarly
promote equaled grains. This is because dendrite arms may be broken off by

8. stirring and transported to the center, where they are able to avoid
remolding, due to their different
composition, and act as nuclei. Castings that consist mainly of uniform
equaled grains usually
The image below depicts these zones
B. The different types of solid solutions
Substitution Solid Solution
 . In this type of solid solution, the solute atoms
solvent in the crystal
 .The substitution solid solution are generally ordered at
lower temperatures and disordered at higher
 . Temperature is the deciding factor
 There are two types of substit
1. Ordered Substitution Solid Solution (OSSS)
2. Disordered Substitution Solid Solution (DSSS)
OSSS: In this type, the solute atoms substitute the solvent atoms in
an orderly manner, taking up fixed positions of symmetry in lattice.
This solid solution has uniform distribution of solute and solvent
atoms.
DSSS: In this type, the solute atoms do not occupy any fixed
positions but are distributed at random in the lattice structure of
solvent. The concentration of solute atoms vary consi
lattice structure.
transported to the center, where they are able to avoid
, due to their different
ion, and act as nuclei. Castings that consist mainly of uniform
The image below depicts these zones
. The different types of solid solutions
Substitution Solid Solution
. In this type of solid solution, the solute atoms substitute the atoms of
solvent in the crystal structure of the solvent.
.The substitution solid solution are generally ordered at
lower temperatures and disordered at higher temperatures.
. Temperature is the deciding factor
types of substitution solid solutions:
. Ordered Substitution Solid Solution (OSSS)
. Disordered Substitution Solid Solution (DSSS)
In this type, the solute atoms substitute the solvent atoms in
an orderly manner, taking up fixed positions of symmetry in lattice.
This solid solution has uniform distribution of solute and solvent
In this type, the solute atoms do not occupy any fixed
positions but are distributed at random in the lattice structure of
solvent. The concentration of solute atoms vary considerably throughout
transported to the center, where they are able to avoid
ion, and act as nuclei. Castings that consist mainly of uniform
substitute the atoms of
temperatures.
In this type, the solute atoms substitute the solvent atoms in
an orderly manner, taking up fixed positions of symmetry in lattice.
This solid solution has uniform distribution of solute and solvent
In this type, the solute atoms do not occupy any fixed
positions but are distributed at random in the lattice structure of
derably throughout

9. HUME-ROTHARY RULES:
 These are the rules which govern the formation of Solid Solutions.
 In other words, only when these rules are satisfied, a substitution solid
solution is formed.
1.Crystal Structure Factor:
‫ــ‬ For complete solubility of two elements, they should have the same type of
crystal lattice.
‫ــ‬ For example ,Au-Ag solution, both should have FCC structure.
2. Rela ve Size Factor:
‫ــ‬ The atoms of the solute and solvent should have the same atomic size
approximately.
‫ــ‬ This factor is satisfied if the difference of atomic radii of two elements is
less than 15%
3. Chemical-Affinity Factor:
‫ــ‬ For a substitution solid solution to be formed, two metals should have less
chemical affinity.
B. Greater is the chemical affinity, lesser is the chance of forming a solid
solution.
‫ــ‬ If two elements are farther apart in a periodic table, chemical affinity is
more.
4. Electro-negativity:
‫ــ‬ Higher the electro-negativity, greater is the chance of forming an
intermediate phase rather than a solid solution.
‫ــ‬ Electro-negativity is the tendency to acquire electrons.
5. Rela ve Valence Factor:
‫ــ‬ Among two metals, which have satisfied all the above rules, the metal with
lower valence tends to dissolve more of a
metal of higher valence and vice-versa.

10. Interstitial Solid Solution
- These are formed when atoms of small atomic radii fit into the
interstitial spaces of larger solvent atoms.
- Atoms of elements such as carbon, nitrogen, boron, hydrogen, etc.
which have radii less than 1 A° are likely to form interstitial solute
atoms and may dissolve more readily in transition metals such as
Fe, Ni, Mn, Cr, etc. than in other metals.
- Intermediate phases are those phases whose chemical compositions are
intermediate between the two pure
metals and generally have crystal structure different from those of the base
(parent) metals.
- An alloy can be made up of a solid solution phase entirely or can exist along
with an intermediate phase.
- An intermediate phase here is nothing but a compound and is made up of
two or more elements of which at least one of them is a metal
- A compound is a chemical combination of positive and negative valence
elements. i.e., atoms of different elements
are combined in different proportions and are expressed by chemical
formulae like H2O, NaCl, etc.
- When a compound or intermediate phase is formed, the elements lose their
individual identity and properties to
a good extent and the compound will have its own characteristic physical,
mechanical and chemical properties.
- There are three most common intermediate alloy phases:
i. Intermetallic or Valence Compounds
ii. Interstitial Compounds
iii. Electron Compounds

11. Intermetallic or Valence Compounds
- When alloy phase are exclusively metal-metal systems, they are called
intermetallic compounds.
- These are formed between chemically dissimilar metals and are combined by
following the rules of chemical
valence.
- The combination is usually non-metallic and show poor ductility and poor
electrical conductivity and have
complex crystal structure.
- Examples for intermetallic compounds: Mg2Pb, Mg2Sn, CaSe, Cu2Se
Interstitial Compounds
- These are similar to interstitial solid solutions except that they have more or
less a fixed composition.
- Example: Fe3C.
- The interstitial compounds are metallic in nature, have high melting points
and are extremely hard.
Electron Compounds
- These are of variable compositions and do not obey the valence law, but
have a definite electron to atom ratio.
Example: Cu9Al4
- Each Cu atom has 1 valence electron and each Al atom has 3 valence
electrons.
- So 13 atoms which make up the compound have 21 valence electrons with
electron to atom ra o being 21:13
- Electron compounds have properties same as those of solid solutions – wide
range of compositions, high ductility and
low hardness.

12. C. Flaws (faults) found in casts, how & why they happen
Casting defects may be defined – those characteristics that create a deficiency or
imperfection to quality specifications imposed by design and service requirements.
- Even in modern foundries the rejection rate – as high up to 20% of the number of
casting produced.
-Hence all efforts must be taken to bring down the percentage of rejection.
- For this to happen one should have sound knowledge of principles of casting,
casting design, potential defects, causes, remedies for same, inspectional methods,
testing methods

13. BASED ON NATURE OF DEFECTS
Surface defects : may be visible on surface
incorrect shape & size, laps, flashes, poor surface finish.
- Internal defects : these are present in interior of cast. Can be revealed
through NDT techniques.
- Incorrect chemical composition – formation of undesirable microstructure.
- Unsatisfactory mechanical properties – low quality, poor percent of usage.
BASED ON CONTRIBUTING FACTORS
-Defects caused by pattern making and moulds: results in incorrect
dimensions, poor surface finish, flash, mismatch.
- Defects – improper gating & risering results in cold shut, misrun, inclusions,
pulls, shrinkage cavities.
-Defects caused – molten metal results in cold shut, metal penetration,
porosity.
CAUSES FOR DEFECTS
- Unsuitable and unsatisfactory raw materials.
- Application of unsatisfactory casting principles.
- Use of improper tools, equipment, appliances or patterns.
- Unprofessional management.
- Unsatisfactory setting up of procedures, poor work discipline, lack of training
.CASTING DEFECTS ,FACTOR

14. CASTING DEFECTS ,FACTORS RESPONSIBLE FOR THEM AND REMEDIES
1 .CORE SHIFT
2. WRAPED CASTING
3. SWELL
4. FIN
5. BLOW HOLES
6.PIN HOLES
7.GAS HOLES
8 .SHRINKAGE CAVITY
9.HOT TEAR
10. INCLUSIONS
11. MISRUN AND COLD SHUT
12. EXPANSION SCABS
CORE SHIFT
- Results in mismatch of the section.
- Usually easy to identify.
- Can be repaired provided with in tolerable limits.
- Misalignment of flasks is a common cause.
- Can be prevented by ensuring proper alignment of pattern, die parts,
molding boxes.

15. WARPED CASTING
- Warpage - Undesirable deformation in a casting.
- Large cross sections or intersections are particularly prone to warping.
- Can be reduced by proper casting design, judicious use of ribs.
- Cannot be eliminated but allowances can be
given along with machining allowance, to remove by machining.
SWELL
- Swell- enlargement of the mould cavity by metal pressures, results –
localized or overall enlargement of castings
- Caused due to insufficient ramming of the sand.
- Also due to rapid pouring of molten metal.
- Also due to insufficient weighting of mould
- Remedies – avoid rapid pouring, provide sufficient ram on sands , proper
weighting of moulds.
FIN
-A thin projection of metal – not a part of cast.
- Usually occur at the parting of mould or core sections.
- Causes - Incorrect assembly of cores and moulds, improper clamping,
improper sealing.
- Remedy is proper clamping of cores and mould.

16. BLOW HOLES
- They are entrapped gases.
- This is result of gases from mould, molten metal and steam sand.
- Remedy is to provide sufficient permeability, making vent holes, use
minimum quantity of water.
- Also use of dry sand moulds, use of no bake sands.
SHRINKAGE CAVITY
- It is a void or depression in the casting caused mainly by uncontrolled
solidification.
-Remedy is apply principles of casting, provide adequate risers, feeders, which
supply the molten metal to compensate the shrinkage.
HOT TEAR
- If the mould surface is rigid, it restrains solidifying casting from contraction
and resulting in development of cracks or tear, also called pulls.
- Remedy is avoid excessive ramming.
- Controlled ramming should be done.

17. 5. Discussion :
A. What is meant by segregation how and why does it happen? How can it
be prevent?
The solubility of each alloy in the other is dissolved in the molten state (ie in
the liquid phase) indefinitely, ie, the decomposition is complete or limited.
However, some metals do not show any kind of mutual degradation in the
liquid state (copper lead, lead Iron). In this case, the molten is formed in the
form of two layers depending on the variation in density. At the hardening of
molten alloys, the atoms are distribut
reciprocal acts between their components.
This can be prevented using different production methods and molding
methods
1. Use metal metal powders and use pressure in the forma on of the required
piece, for example the rotary column supports in the engine
2. When we teach the cas ng we move this molten in order to prevent the
isolation process by relatively large recycling devices
B. Define dendrites, columnar grains, equi
A. What is meant by segregation how and why does it happen? How can it
The solubility of each alloy in the other is dissolved in the molten state (ie in
the liquid phase) indefinitely, ie, the decomposition is complete or limited.
e metals do not show any kind of mutual degradation in the
liquid state (copper lead, lead Iron). In this case, the molten is formed in the
form of two layers depending on the variation in density. At the hardening of
molten alloys, the atoms are distributed according to the nature of the
reciprocal acts between their components.
This can be prevented using different production methods and molding
1. Use metal metal powders and use pressure in the forma on of the required
rotary column supports in the engine
2. When we teach the cas ng we move this molten in order to prevent the
isolation process by relatively large recycling devices
B. Define dendrites, columnar grains, equi-axed grains
A. What is meant by segregation how and why does it happen? How can it
The solubility of each alloy in the other is dissolved in the molten state (ie in
the liquid phase) indefinitely, ie, the decomposition is complete or limited.
e metals do not show any kind of mutual degradation in the
liquid state (copper lead, lead Iron). In this case, the molten is formed in the
form of two layers depending on the variation in density. At the hardening of
ed according to the nature of the
This can be prevented using different production methods and molding
1. Use metal metal powders and use pressure in the forma on of the required
2. When we teach the cas ng we move this molten in order to prevent the

18. Dendrites
- In metals, the crystals that form in the liquid during freezing
generally follow a pattern consisting of a main branch with many
appendages. A crystal with this morphology slightly resembles a
pine tree and is called a dendrite, which means branching.
- The formation of dendrites occurs because crystals grow in defined
planes due to the crystal lattice they create.
- The figure to the right shows how a cubic crystal can grow in a melt
in three dimensions, which correspond to the six faces of the cube.
- For clarity of illustration, the adding of unit cells with continued
solidification from the six faces is shown simply as lines.
-Secondary dendrite arms branch off the primary arm, and tertiary
arms off the secondary arms and etcetera.
crystal growth and grain formation
- nuclei → crystals → grains
- polycrystalline – solidified metal containing many crystals
- grains – crystals in solidified metal
- grain boundaries – the surfaces between the grains
- two major types of grain structures:
(1) equiaxed grains – crystals grow about equally in all
directions, commonly found adjacent to a cold mold
wall
(2) columnar grains – long, thin, coarse grains, created
when metal solidifies rather slow in the presence of a
steep temperature gradient. columnar grains grow
perpendicular to the mold surface

19. C. How do you think the grains will be of a cast that has been cooled and
formed form in a metal mould
The metal mold is a good conductor of the heat and the process of cooling the
mold leads to the formation of a large number of nuclei throughout the
molten and thus will be a large number of nuclei, but it will be small size, that
is due to consumption of molten by this large number of nuclei and it will
hinder the other one During the growth so that can not grow to a large size
Because of the fact that the cooling homogenous throughout the template in
the sense of the same degree of thermal gradient during the molten, it leads
to the fact that these crystals regular shape so that it can also be called
crystals equal axes
D. How can faults in casts be considered an advantage? I e point defects,
Atom atoms are different from the atoms of the spatial network Host -
All solid materials are not pure but contain some impurities and the purity
may reach 99.99%
These alloys are usually alloyed and not impregnated with the first type of
metal or metals. In all cases, the sentence has the characteristic
characteristics of the metal case, namely metallic luster, retractable,
Bronze, for example, copper alloy Cu and tin Sn tougher than copper, making
it so important so called the era of the use of the Bronze Age. It is well-known
alloys brass and brass composed of copper and zinc, stainless steel, which
consists mainly of iron and carbon, and enters the manganese and nickel and
other
The alloys are heavier than the pure metals involved, and their electrical
conductivity is much lower, as is their thermal conductivity, and their melting
points are lower than the melting point of the main metal. The mobility
depends on the degree of arrangement in the alloy, and the hardness changes
depending on the heat treatment.

20. E. If we have here different structured metals (fcc , bcc, cph)
no BCC FCC HCP
1 High resistance
resistance
Low coefficient of
elasticity
crisp
2 elasticity high
coefficient
Low resistance
resistance laboratory
Bombing
3
High Hall Low hardness
Low resistance
resistance
4
Limited formability
Four atoms in each
cell
5 High tensile
resistance
Good flexibility
6 Each cell consists of
two atoms
F. What are the differences between "twin bands" & "slip bands"?

21. G. What factors affect dislocations?
1. Total forces of attraction between ions and electrons along
The plane completes slip if this slip occurs simultaneously in one
Foolish. So the real strength of metals is only a small part of it
Which was calculated on the assumption that the slip occurred one place
Sudden movement.
2.As the shear modulus in metals is usually within the range of 20 000-150 000
mpa, this is difficult to reconcile with shear stress in the 0.5 to 10 mpa
H. How many types of dislocation are there , what are the differences
between them ?
-screw dislocations :1.
Is one of the types of linear faults produced by the successive transmission of
atoms to the surface
The outer spiral or spiral around the line of convergence has been
accompanied by some
Tensile and compression stresses that affect the mechanical and physical
properties of the materials
Solid. Or is the displacement of part of the crystal grid for another part in a
manner Spiral

22. -:edge dislocation2.
It is the introduction of a half-row of external atoms to the perfect
crystallization to limit the edges of the edge part
Of the level or is the lack of part of one of the atomic layers and then the
displacement of levels
Close to filling the vacuum and the line of the outlet that has a greater
capacity compared with the crystal parts
Because the network above the outlet line is in compression
Below the take-off line is a tension state (tension) and an abnormal interstitial
vacuum may occur below
The takeoff line acts as an incubator to collect atoms or chemical impurities