A polycrystalline can be a metal or
a solid and can consist of many crystalline parts. These are randomly
orientated with respect to each other. These types of metals’ have a low
strength and do not depict the required properties you would want to achieve in
a metal. For this reason, alloys are created by melting two or more metals
together. Metals can be classified into two major groups and these are ferrous & non-ferrous metals.
contain iron as their base material and can be split into two groups; steels
and cast iron. The most commonly used non-ferrous metals in engineering
include, pig iron, cast iron and wrought iron. Steels on the other hand include;
plain carbon steels and alloy steels.
Cast iron is primarily an alloy of
iron and carbon with around 2-4.5% carbon. However, this does not only include
carbon but also includes a small amount of silicone, sulphur and phosphorus
too. Cast iron is obtained by re-melting pig iron with coke, limestone and
steel scrap in a furnace. Pig iron is the raw material for the production of
all kinds of cast iron and steel products.
The properties of cast iron include:
– weak in tension. Which means it
cannot be used to make bolts.
– low in cost
– it can be easily cast
– high compressive strength
– high wear resistance
– good corrosion resistance
Cast iron can also be classified as grey, white,
mottled, nodular and malleable cast iron. It is usually used for machine beds
such as lathe machine’s, automotive cylinder blocks and heads, sewage pipelines
& water pipes.
Non-ferrous metals do not use iron
as a base material. Examples of this type of metal can be; aluminium, copper,
brass, bronze, magnesium, zin, lead etc. Aluminium
is a metal which is prepared from a clay mineral – bauxite. Bauxite is hydrated
aluminium oxide. Aluminium has a very good resistance to corrosion. It is
ductile, malleable and allows for good conduction of heat and electricity. When
it is mixed with small amounts of other metals, it becomes very hard. Aluminium
is lightweight and for this reason, it is widely used in transportation,
construction, electrical and consumer goods. It also has a good strength to
weight ratio. In transportation, it is ideal for aircraft, trains and automobiles.
Within the construction industry, aluminium is generally used in high rise
buildings and bridges. Again, the light weight ensures it is easier faster and
more convenient to work with. Since aluminium is more ductile than copper, this
enables it to be formed into wires much more easily and also protects the wires
from the elements. It is generally used for long distance power lines. Lastly,
aluminium is used in everyday consumer goods, from tin foil, cans, cooking
utensils, furniture, gadgets and smartphones. It is non-toxic, heats well, is
resistant to rust and cleans well.
Ceramic materials are
non-metallic. They are of a solid nature made of inorganic compounds. The
compounds which make up a ceramic can include; oxides, nitrides, borides and
– A oxide is a binary compound of
– A nitride is a binary compound
– A boride is a binary compound
– A carbide is a binary compound
Ceramics do possess exceptionally good properties
such as; electrical, magnetic, chemical and thermal properties examples
include, glass & cement. In industry, aluminium
oxide is a ceramic material which can be used in grinding wheels and
abrasives. Silicon carbide is also a
ceramic which can be used for cutting tools. Applications for ceramic materials
can also include nuclear engineering, electronic control devices, and
structures and can be used in the aerospace field too.
Plastics are commonly known as
polymers. They can be hard, rigid and can easily be moulded into different
shapes and colours. Plastics are extremely light and have good corrosion
resistance. They are easily mass produced too, an example of this can be the
invention of the plastic bag. Over the years, plastics have become preferable
over other materials, this is due to the combination of properties which exist
in them. Like metals, plastics can be classified into two groups; thermos-plastics and thermo-setting plastics.
Thermo-plastics can be softened over and
over again by heating them and these can be shaped into many various shapes. On
the other hand, once thermo-setting
plastics are heated, the effects are non-reversible and they do not soften
with the application of heat. Applications include; bottle tops, wheels,
switches and camera bodies.
Composites commonly include any
products made from a blend of two or more base materials. Manufacturers can mix
the best properties of each component by mixing multiple materials together.
Carbon fibre consists of a thin crystalline filament of carbon and these are
used as a strengthening material in resins and ceramics. Carbon fibre is 5
times tougher than steel and has improved weight savings however, this comes at
a cost. The material itself can withstand moisture without rusting, enhance
durability & also has a high strength tow weigh ratio. This can be used in
many industrial processes from flight structures, turbine fan blades, drive
shafts and seat structures etc.
a material various physical and mechanical properties have to be taken into
consideration. A material selection
chart is achieved by plotting one material property on each axis of the
chart. Below are several examples of material selection maps from Mike Ashby. I
have decided to include maps which support the 5 main areas of material
The below chart shows Young’s modulus (E) against
the density of a material. This chart provides selection for materials which
can be used for light and stiff components.
(2017). online Available at:
Accessed 20 Dec. 2017.
The below chart is used for the design of light
and strong structures. It is evident that metals are the highest in density but
not all metals have a high yield strength.
(2017). online Available at:
Accessed 20 Dec. 2017.
third chart which I have chosen to look at is the cost of a material which is high
in strength. From the chart, it is obvious that there is positive correlation
between the price of a material (per volume) and its strength. We can see this
from the graph below:
9: Grantadesign.com. (2017). online
Accessed 20 Dec. 2017.
is very important in all parts of engineering. Selecting the best material for
a certain application can be a complex job. When selecting a material, cost can
come into the equation and as an engineer it may result in more sales.
Approximately 50% of the manufacturing cost will be the cost of the raw
materials. Likewise, the choice of a lighter material may be used on transport
and may provide an increase in fuel economy as well as a reduction in CO2
emissions. As mentioned above, materials can be grouped into several
categories; Metals (non-ferrous and ferrous), ceramics, non-metals and
composites and each material is usually defined by its properties. If an
adequate material selection is not done, it may result in critical failure.
The material selection process needs to be an
overall procedure and can be referred to as cost, durability and the intended
lifespan of a product. When choosing a material 5 key areas should be looked at:
properties of the materials
Wear of materials
Corrosion of materials
The ability to
manufacture the materials
Cost of the materials
When a certain design is going to be used, the mechanical properties of a material
need to be thoroughly researched before producing the end product. Quite often,
the designer will need to get involved with the material selection process and
an engineer may be needed to take charge in choosing the correct material in
order for the end product to be fit for purpose. In mechanical engineering,
this is a major concern, manufactured parts need to withstand various loads and
temperature variations. Mechanical properties include; strength, elasticity,
degradation, wear, impact resistance, surface finish & aesthetics.
Wear and corrosion are concerning factors for engineers, so when they are
selecting materials, they must have a sufficient resistance to both to be able
to last. Various types of wear include abrasion, adhesion and corrosion. Abrasion can include two surfaces which
slide across one another – this is called two body abrasion. Another form of
abrasion is three body, unlike the two body this is where particles move
between the two surfaces and removes the material from either one or both
surfaces. To reduce wear, machined parts must be properly lubricated. When materials
are making contact with one another, this is called adhesion and materials must be compatible with each other. As a
general rule of thumb, materials should not be able to dissolve into each other,
not be identical and should also include one metal from the B-subgroup. A
B-subgroup refers to the periodic table, these are metals and can be referred
to as transition metals and can include the likes of platinum and nickel.