ENGINEERING MATERIALS&MANUFACTURING PROCESSESUNIT -II

MATERIAL

A material is that out of which anything is or may be made.

Materials comprise wide range of metals and non-metals.

CLASSIFICATION OF MATERIALS

Most engineering materials may be classified into one of the following types :-

A. Metals – 1. Ferrous _ 2. Non-FerrousB. CeramicsC. OrganicsD. CompositesE. Semiconductors

METALS

Are composed of elements which readily give up electrons to provide a metallic bond and electrical conductivity.

They play a major role in the industrial & every day life.

CHARACTERISTICS OF METALS

Lustre. Hardness. Plastic deformability. Good thermal conductivity. Relatively high melting point. Strength. Ductility. Malleability. Stiffness. Rigidity. Formability. Machinability Weldability. Castability Dimensional stability.

EXAMPLES OF METALS

Iron Aluminium Copper Zinc Magnesium

CERAMIC MATERIALS

Consist of oxides, nitrides, carbides, silicates or borides of various metals.

Are any inorganic, non-metallic solid (or super cooled liquids) processed or used at high temperatures.

Are rock, clay mineral materials Contain compounds of metallic & non-metallic

elements, such as MgO, SiO2, SiC, glasses.

CHARACTERISTICS OF CERAMICS Brittleness Rock like appearance Resistance to high temperatures Hardness Insulation (to flow of electric current) High temperature strength.

Examples of ceramics :-Sand, glass, brick, cement, silicon carbide, tungsten carbide, refractories.

ORGANIC MATERIALS

Are polymer materials composed of long chain of carbon compounds.Polymers are solids of long molecular chains.

Are either natural or synthetic or manufactured materials based chemically on carbon.

Examples :Rubber, wood, plastics, paper, fuels, lubricants,

textiles, paints, adhesives, explosives.

CHARACTERISTICS OF ORGANIC MATERIALS

Light weight Combustible Soft Ductile Not dimensionally stable Poor conductors of heat & electricity Poor resistance to temperature.

COMPOSITES

Composite materials consist of more than one Material type. Fibre glass is a familiar example, in which glass fibres are embedded within a polymeric material.

A composite is designed to display a combination of the characteristic of each of the component of the materials. Fibre glass requires strength from the glass and flexibilty from the polymer.

SEMI-CONDUCTORS

Are the materials which have electrical properties that are intermediate between the electrical conductors and insulators.

Electrical characteristics of these materials are extremely sensitive to the presence of minute concentrations of the impurity atoms, whose concentrations may be controlled over very small spatial regions.

PROPERTIES OF ENGINEERING MATERIALS

Material Property is a factor that influences qualitatively or quantitatively the response of a given material to impose stimuli & constraints, e.g., forces, temperature, etc.

Properties render a material suitable or unsuitable for a particular use in industry.

The material property is independent of the dimension and shape of the material.

TYPES OF MATERIAL PROPERTIES

Mechanical properties. Thermal properties. Electrical properties. Magnetic properties. Chemical properties. Optical properties. Physical properties. Technological properties.

MECHANICAL PROPERTIES

These include those characteristics of material that describe its behaviour under the action of external forces.

Can be determined by conducting experimental tests on the material specimen.

PROPERTIES OF METALS Metals are elements that have atoms

arranged in rows. The electrons are easily released from metal atoms so that layers of metal atoms exist in a 'sea' of electrons.

Examples of Metals are gold, copper, lead, zinc, iron, magnesium, sodium, calcium and mercury.

Physical Properties of Metals

Physical Properties of Metals include shiny lustre, greyish - silver colour, hardness, good heat and electricity conductivity, high melting and boiling points, malleability (can be hammered into a sheet) and ductility (can be pulled into a wire).

Some exceptions to these are the metals - sodium and calcium (very soft), gold and copper (yellowish colour), and mercury (low melting and boiling points).

Chemical Properties of Metals

Chemical Properties of Metals

Some metals are more reactive than others. This is because very reactive metals lose electrons easily. Metals such as sodium are very reactive and are explosive in air. Metals such as gold are very unreactive, and therefore do not corrode or tarnish in air.

Chemical Reactions of Metals

3 Chemical Reactions of Metals Metal + Acid ------ Salt + Hydrogen Metal + Oxygen----- Metal Oxide- Metal+Water----- Metal Hydroxide +

Hydrogen

MECHANICAL PROPERTIES

Strength Hardness Toughness Brittleness Ductility Malleability Elasticity Plasticity Rigidty Machinability Hardenability Resilience Fatigue Creep

Strength

It is the ability of a material to resist deformation under the action of tensile, compressive or shear force.

The strength of a component is usually based on the maximum load that can be borne before failure is apparent.

The most common measure of strength is the yield strength.

HARDNESS

It is the ability of a material to offer resistance to penetration or indentation. It is also the ability to resist wear, abrasion, scratch or cutting.

TOUGHNESS

It describes a material’s resistance to fracture under impact loading. It is often expressed in terms of the amount of energy a material can absorb before fracture.

Toughness is not a single property but rather a combination of strength and ductility.

BRITTLENESS

It is that property by virtue of which a material breaks easily under action of shock loads without appreciable amount.

It indicates the lack of ductility. For example glass, ceramics and cast

iron are brittle materials.

DUCTILITY

It is a measure of the amount of deformation of a material can withstand before breaking.

It is also the ability of a material by which it can be drawn into wires.

MALLEABILITY

It is the ability of a material by which it can be rolled into sheets.

Malleability is the ability of a material to exhibit large deformation subjected to compressive force whereas ductility is the ability of a material to deform upon the application of tensile force.

Aluminium, Copper and gold have good malleability.

ELASTICITY

It is the property of a material to regain its original shape after the removal of load.

When a material is subjected to an external load of such magnitude that deformation continues only with increase in load, and on removing the load it regains its original shape, then the material is said to have elasticity.

PLASTICITY

It is the property of a material by virtue of which it undergoes permanent deformation.

When a material is subjected to an external load of such magnitude that deformation continues with no apparent further increase in load, the material is said to have become plastic. In this region the material experiences permanent deformation and does not return to its original shape when the load is removed.

RIGIDITY

It is also known as stiffness. It is the property of a material by virtue of which the material resists elastic or plastic deformation under applied loads.

MACHINABILITY

It refers to the ease with which a material can be removed during various machining operations. It describes the property of a material when it is cut.

Materials with good machinability require less power to cut, resulting in good surface finish and longer cutting tool life.

HARDENABILITY

It indicates the degree of hardness that a material can acquire through a hardening process. It is the capability of a material to get hardened by heat treatment.

It determines the depth and distribution of hardness induced by quenching.

RESILIENCE

It is the property of a material to absorb energy when it is deformed elastically and then, upon unloading, to have this energy recovered. In other words, it is the maximum energy per volume that can be elastically stored.

FATIGUE

It is the strength of the materials when subjected to cyclic or rapid fluctuating load conditions.

Owing to fatigue a material fails at a stress level much below that under static loads.

The maximum stress to which the material can be subjected without fatigue failure is known as the endurance limit.

CREEP

It is the progressive deformation of a material under a constant static load maintained for a long period of time. It is a slow, temperature-aided, time-dependent deformation.

It occurs in three stages known as primary, secondary and tertiary stage.

FERROUS MATERIALS

Ferrous materials contain iron. Ferrous materials are the most important metals/alloys in the

metallurgical and mechanical industries because of their very extensive use.

The widespread use of ferrous alloys is accounted for by the following three factors:

(1) Iron containing compounds exist in abundant quantities within the earth’s crust;

(2) Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying and fabrication techniques; and

(3) Ferrous alloys are extremely versatile, in that they may be tailored to have a wide range of mechanical and physical properties.

DIFFERENT TYPES OF FERROUS MATERIALS Cast Iron

(1) Grey cast iron(2) White cast iron(3) Malleable cast iron(4) Ductile cast iron

Steel

(1) Mild Steel(2) Plain carbon steel(3) High carbon steel(4) Alloy steel

NON FERROUS MATERIALS

Materials which do not contain iron are non-ferrous materials.METALS ALLOYS1..Copper 1.Brass2.Zinc 2.Bronze 3.Aluminium 3.Gun-Metal 4.Lead 4.Duralumin 5.Tin 6.Nickle 7.Chromium