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Importance of Materials in Manufacturing

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Importance of Materials in Manufacturing

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What is manufacturing?
- Transformation process
- behavior of the material when subjected to the forces, temperatures, and other processes that determines the success of the operation.

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atom - the basic structural unit of matter
atoms - positively charged nucleus and surrounded by a sufficient number of negatively charged electrons so the charges are balanced

Elements - 2 families
1. Metals - left and center of the table
2. Nonmetals - right side
Between them - transition zone containing metalloids / semi-metals

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Atoms are held together in molecules by various types of bonds

Primary bonds - associated with formation of molecules
Secondary bonds - associated with attraction between molecules

Primary bonds are much stronger than secondary

Primary bond - Covalent and Ionic
Strong atom-to-atom attractions that involve exchange of valence electrons

Secondary bond - Dipole-dipole, London Force and Hydrogen Bond.

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Atoms of 1 element donate their outer electron(s), which are in turn attracted to atoms of some other element to increase electron count in the outermost shell

Properties:

Poor ductility

Low electrical conductivity

Example:

NaCl

MgO

CaCl

CaO

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Outer electrons are shared between 2 local atoms of different elements

Properties:

High hardness

Low electrical conductivity

Example:

Diamond

Graphite

Water

Ammonia

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Sharing of outer shell electrons by all atoms to form a general electron cloud that permeates the entire block

Properties:

Good conductor

Good ductility

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Attraction forces between molecules

No transfer or sharing of electrons in secondary bonding

Bonds are weaker than primary bonds

1. Dipole forces

2. London forces

3. Hydrogen bonding

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Molecule compromised of 2 atoms with equal and opposite electrical charges

Each molecule therefore forms a dipole that attracts other molecules

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Attractive force between non-polar molecules. Atoms in molecule do not form dipoles

However, due to rapid motion of electrons in orbit, temporary dipoles form when more electrons are on one side

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Occurs in molecules containing hydrogen atoms covalently bonded to another atom(e.g.,H2O)

Since electrons to complete shell of hydrogen atom are aligned on one side of nucleus, opposite side has a net positive charge that attracts electrons in other molecules

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A crystal system where the unit cell is in shape of a cube.

Structure in which atoms are located at regular and recurring positions in 3 dimensions

Unit cell - basic geometric grouping of atom that is repeated

The pattern may be replicated millions of times within a given crystal

Characteristic structure of virtually all metals as well as many ceramics and some polymers

When a monomer are arranged in a neat orderly manner, the polymer is crystalline.

An amorphous solid is a solid in which the molecules have no order and arrangement.

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body-centered cubic. Example: Chromium, Iron, Molybdenum, Tungsten

face-centered cubic. Example: Aluminum, Copper, Gold, Lead, Silver, Nickel

hexagonal close packed. Example: Magnesium, Titanium, Zinc

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often arise due to inability of solidifying material to continue replication of unit cell.

Imperfections (defects) can also be introduced purposely. E.g., addition of alloying ingredient in metal.

a) point defects
b) line defects
c) surface defects

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involving either a single atom or a small number of atoms

vacancy

ion-pair vacancy

interstitialcy

displaced ion (Frenkel Defect)

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Connected group of point defects that forms a line in the lattice structure

Most important line defect is a dislocation, dislocation can take 2 forms:

Edge dislocation - Edge of an extra plane of atoms that exists in the lattice

Screw dislocation - Spiral within the lattice structure wrapped around an imperfection line, like a screw is wrapped around its axis.

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extend in 2 directions to form a boundary

E.g:
External : the surface of a crystalline object is an interruption in the lattice structure
Internal: grain boundaries are internal surface interruptions

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when a crystal experiences a gradually increasing stress, it 1st deforms elastically

a) original lattice
b) elastic deformation, no permanent change in positions of atoms

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If the stress is higher than forces holding atoms in their lattice positions, then a permanent shape change occurs

Plastic deformation (slip), in which atoms in the crystal lattice structure are forced to move to new "homes“

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in the series of diagrams, the movement of the dislocation allows deformation to occur under a lower stress than in a perfect lattice

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Good news in manufacturing - the metal is easier to form.
Bad news in design - the metal is not as strong as the designer would like

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A second mechanism of plastic deformation in which atoms on one side of a plane (the twinning plane) are shifted to form a mirror image of the other side.

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Formation process of crystalline structure

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grains - millions of individual crystals that may contain in a block of metal

the structure is called polycrystalline

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Example: Water and air

A metal loses its crystalline structure when melted

Some engineering materials have non-crystalline forms in their solid state

Glass

Many Plastics

Rubber

Features

1. Absence of long-range order in the molecular structure

2. Differences in melting and thermal expansion characteristics

Difference in structure between crystalline and non-crystalline materials :-

Crystal structure is regular, repeating; non-crystalline structure is less tightly packed and random

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Characteristic change in volume for a pure metal (a crystalline structure), compared to same volumetric changes in glass (a non-crystalline structure)