Engineering materials - Classification, properties and applications

It is important to choose the right material for any job that we pursue. Not choosing the right material can cause unintended consequences like metal whiskers growing on metallic parts. These consequences can lead to bigger disasters. Hence, it is important to understand the classification of materials. And understand their properties and applications.

Contents

Classification of engineering materials

We can classify all engineering materials into two broad categories of metals and non-metals. These two categories further classify as follows:

Metals and Alloys
- Ferrous
  - Cast Iron
    - Grey cast iron
    - White cast iron
    - Alloy cast iron
    - Malleable cast iron
    - Nodular cast iron
  - Steel
    - Alloy steel
    - Stainless steel
    - Mild Steel
    - Carbon Steels
      - Medium Carbon steel
      - High carbon steel
  - Wrought iron
- Non-Ferrous
  - Copper
  - Aluminum
  - Brass
  - Bronze
  - Lead
  - Silver
  - Zinc
  - Tin etc.
Non-metals
- Leather
- Rubber
- Polymers
  - Thermo-setting polymers
    - Phenolform
    - Aldehyde (Bakelite)
    - Polyesters
    - Epoxy resins
  - Thermoplastics
    - PVC
    - Polythene
    - Acrylic
    - Resins
- Wood
  - Softwoods
  - Hardwoods
    - Temperate hardwoods
    - Tropical hardwoods
- Ceramics
  - Traditional ceramics
    - Refractories
    - Abrasives
    - Glass
    - Cement
    - Concrete
  - Advanced Ceramics
    - Electroceramics
    - Electronic Substrate package ceramics
    - Piezoelectric ceramics
    - Magnetic ceramics
    - Optical ceramics
    - Conductive ceramics
    - Advanced Structural Ceramics
    - Nuclear ceramics
    - Bioceramics
    - Wear-resistant ceramics
    - Automotive ceramics
- Composites
  - Metal matrix composites
  - Ceramic matrix composites
  - Polymer matrix composites
- Semiconductors
  - Intrinsic semiconductors
  - Extrinsic semiconductors

Let’s get some information on some of the materials listed above.

Rubber is used in packaging material and as an electrical insulator.
Ceramics are non-metallic solids made up of inorganic compounds like nitrides, oxides, and carbides. It possesses electrical, magnetic, chemical and thermal properties. These materials are used in electronic controlled devices, computers, and aerospace field. Example: Glass and Aluminum oxide and Silicon carbide.
Organic polymers consist of carbon, in chemical combination with hydrogen, oxygen or other non-metallic substances. These are formed by a polymerization reaction in which simple molecules are chemically combined into long-chain molecules. These are used in packing, insulating materials, covers, etc. Example: Cotton, Nylon, Terylene, PVC, etc.
Composites are the mixture of materials like metals and alloys and ceramics, metals and organic polymers, ceramics and organic polymers. These are used in electrical devices and airplane parts. Example: Plywood, fiber, cement, and concrete.
We use leather in bell drives and washers.
Semiconductors are materials whose conductivity lies between that of conductor and insulator. These materials are generally hard and brittle. They are the building blocks of modern digital electronics. We use them to make devices like diodes, logic gates, flip-flops and latches, microprocessors, etc.
Mild steel is plain carbon steel containing carbon percentage between 0.15%-0.3%. It is easily forgeable, malleable, and ductile. We can weld it pretty easily too.
When special properties are required, some of the alloying elements are added in carbon steel. These elements are nickel, chromium, vanadium, etc. The steel obtained by adding alloy elements is known as alloy steel.
Grey cast iron is an alloy of carbon and steel. Additionally, it also contains iron. Its composition is Carbon (2.5%-3.8%), Silicon (1.1%-2.8%), Manganese (0.4%-1%) and Phosphorous (0.15%).
Cast iron has a high resistance to wear. It has low ductility. And low impact strength when compared with steel. Its machinability is better than steel. Grey cast iron is recognized by the presence of carbon in the form of graphite flakes.
Copper has a high resistance to corrosion. Moreover, pure copper is one of the best conductors of electricity. Copper is reddish-brown in color.
Aluminum is also another good conductor of electricity. It is highly malleable and ductile. It forms useful alloys with copper, zinc, and iron. Aluminum has a very high resistance to corrosion compared to steel.
Composites are a combination of two or more materials with compositional variables. They show properties different from their individual constituents. The composite material is better than any of the individual components as regards to their strengths, heat resistance and stiffness.
Wood consists of strong and flexible cellulose fibers. Plywood is the composite of thin sheets of wood. It hs grains of alternate sheets perpendicular to each other and bonded together by a polymer in between them.
RCC has steel rods embedded in the concrete mix which is a composite of cement, sand aggregate, and water.

Properties of engineering materials

The different material properties are:

Mechanical properties
Physical properties
Electrical properties
Chemical properties
Thermal properties
Magnetic properties

Mechanical properties

The mechanical properties of material define the behavior of materials under the action of external forces. These properties are:

Strength: It is defined as the ability of materials to sustain load without distortion. The stronger the material, the greater the load it can withstand.
Stiffness: This is the ability of a material to resist deformation.
Elasticity: It is the property of a material due to which deformation caused by applied load disappears completely on the removal of the load. Alternatively, you can state is as follows. It is the property due to which material regains its shape and size after the removal of an externally applied force.
Plasticity: This is the ability of a material to undergo some degree of permanent deformation without rupture or failure. It is the opposite of elasticity.
Malleability: It is the property due to which it can be deformed into thin sheets. This can be done by rolling or hammering action without fracture. Gold has the highest malleability. Copper, aluminum, silver, and nickel are some other metals that exhibit malleability.
Ductility: It is the property due that shows the extent to which a material can be drawn into wires or elongated before a fracture takes place.
Toughness: It is the measure of the amount of energy a material can absorb before failure takes place. Ductile materials are tougher than brittle materials.
Weldability: It is the property of the material which indicates the ease with which two similar or dissimilar metals join together. It is the ability of a material to get welded.
Machinability: This is the measure of the ease with which a material can be machined or finished.
Fatigue: This is a form of failure that occurs in components subjected to dynamic and fluctuating loads.
Hardness: It is the property of a material due to which it offers resistance to penetration and scratching. Hard materials resist wear and scratches. Diamond is the hardest material.
Brittleness: It is the property of materials due to which it breaks without too much permanent distortion. This property is the opposite of ductility.
Creep: This is the slow plastic deformation of metal under constant loads. Usually at high temperatures. Metals generally show creep at high temperatures whereas plastics, rubbers are temperature sensitive to the creep.
Resilience: This is the capacity of a material to absorb energy elastically. This property is important in the manufacturing of springs and shock absorbers, etc.

Application of engineering materials

We’ll look at the applications of the following types of metals and their subtypes.

Steel
Cast iron
Copper
Aluminum

Mild Steel

It is a good shock absorber, hence used to make manufacturing screws.
Universal beams
Case hardening steel
Gears

Grey Cast Iron

Machine tool structure i.e Frame, bed.
Frames for electrical motors.
Cylinder blocks and heads for IC engine.
Lathe machine and drilling machine.

Medium Carbon Steel

Used to manufacture crankpins, crankshafts
spline shafts, gear shafts, and axles.
Also, anchor boats, Axe saw plates, hammers, valve string, and self-taping screws.

High Carbon Steel

Used in punches and dyes, railway rails, lift leaf springs, and saws for cutting steel and broaches.

Alloy Steel

Nickel steel is used to manufacture IC engine valves, turbine blades, clock pendulum, measuring instruments.
Vanadium steel is used to make springs, gears, shafts, and various other tools.

Copper

Used to make household utensils.
Used in the manufacturing of electrical cables and wires.
Used in motor windings.
Used in condensers and boilers.

Aluminum

Since it has a high resistance to corrosion, it is used to make reflectors and telescopes.
Used to make foil as food packaging.
Used in the manufacturing of piston, electric cables, kitchen utensils, automobile parts.