Chapter 1 Introduction to materials and

family of materials

Chapter 1 (Callister)

Study outcomes: •Appreciate the development and increase in diversity of materials.•Know and define material properties•Know the five family of materials•Understand the classification system for a material .•Know the three families of processing of a material•Understand the classification system of the process.•Process property interaction•Specify a material and /or process for manufacturing of a given component

1.1 Materials , process and choice.

• Why do we need materials???

• To make something out of material you need a process.

• Process has to be compatible with the material you plan to use.

Figure 1.1 The development of materials over time. The materials of pre-history, on the left, all occur naturally; the challenge for the engineers of that era was one of shaping them. The development of thermochemistry and (later) of

polymer chemistry enabled man-made materials, shown in the colored zones. Three—stone, bronze and iron—were of such importance that the era of their dominance is named after them.

1.2 Material properties

• Mechanical properties• Thermal properties• Electrical, magnetic and optical properties• Chemical properties

1.2.1 Mechanical Properties

Some of the important mechanical property terms:1)E: Elastic Modulus indicates the stiffness of material.

For example steel has E of 207Gpa and polyethylene has1.08Gpa

2) Yield strength Strength at which permanent deformation start to occur. Examples Al alloys has 107Mpa Lead has 5.5 Mpa

3) Tensile strength :is defined as the highest value of engineering stressexamples High strength steel 3000 MPa , Al-500 MPa

4) Fracture toughness: measure of resistance to crack and fracture. Glass epitomizes brittleness;it has low K1c0.77Mpa*(m)1/2 and steel has 54Mpa *(m)1/2.

1.2.1 Mechanical Properties

5) Ductility : It is the maximum deformation to fracture

6) Hardness : It is the resistance to plastic deformation when object under load penetrates the material.

7) Resilience :It is the measure of the amount of energy that can be absorbed under elastic loading conditions and which is released completely when loads are removed.

Fig shows consequences of various mechanical properties mentioned above.

1.2.2 Thermal properties

Properties of material change with temperature. With increasing temperature it starts to creep, it may oxidize or degrade and there is loss of strength.

1) There is a limiting temperature called the maximum service temperature Tmax for use of material.

2) Thermal expansion coefficient __. Materials expand when heated but by differing amount which depend on this factor. Its unit is (C-1)

Thermal conductivity and heat capacity are the two factors responsible for the feel of the material.

Thermal conductivity λλλλ measures the rate at which heat flows through the material . Unit is W/m K.

Heat capacity Cp is the measure of the amount of heat that it takes to make temperature of material rise by a given amount .Unit is J/KUses of materials with high and low thermal conductivity and heat capacity

Thermal diffusivity : The property governing transient heat flow (when temperature varies with time) is the thermal diffusivity, a (units : m2/sec)

Various aspects of thermal properties

1.2.3.Electrical, magnetic and chemical properties

• Electrical conduction• Resistivity. It is the inverse of electrical conductivity.

The materials for conductors and insulators. • Dielectric properties

• Electric current induce magnetic fields.• Hard magnets and soft magnets and their uses• Optical properties• Products often have to function in hostile environment.

Design- limiting properties

The performance of a component is limited by certain properties of material of which it is made. Materials are chosen by identifying design limiting properties and applying limits to them.

1.3 Classifying materials

• Conventionally materials are classified into five broad families.

1. Metals2. Polymers3. Ceramic / Glasses4. Composites5. Advanced materials

Examples of each material family

• Members of each family have certain characteristics in common:

1. Metals : Have high stiffness, they are tough with usefully high fracture toughness. They are made strong by alloying ,mechanical process and heat treatment. They are reactive and so most of them corrode if not protected.the key feature that distinguishes metal from non metals is their bonding. Metallic materials have free electrons that are free to move easily from one atom to next

• Metals are mainly grouped into two categories

• Ferrous metals and alloys examples are irons , carbon steel, alloy steels , stainless steel , tool steel and die steels

• Non ferrous metals and alloysExamples are Aluminum, copper, nickel, titanium precious metals, super alloys and others alloys

Typical examples of metals and its family

2 Ceramics : They are non metallic inorganic solids. They are typically crystalline in nature and are compounds formed between metallic and non metallic elements ex Alumina, silicon nitride

The two most common chemical bonds in ceramic materials are covalent and ionic bondThey are stiff hard abrasion resistant and retain their strength to high temperatures. Most of them are good insulators. They have low K1c value.

• Typical examples of ceramics are• Structural clay products (bricks, roofing ,

wall tile etc)• Refractories, cements, abrasives, cutting

tools• Graphite , sand

3 Glasses : Are noncrystalline solids. Commonest are borosilicate glasses and sodalime. Lack of crystal structure suppresses plasticity. They are hard and remarkably corrosion resistant . They are excellent insulators and transparent to light. But like ceramics they are brittle .

• Uses : flat glass for windows, container glass (bottles) pressed and blown glass (Dinnerware), glass fibers (home insulation)

4 Polymers : are organic solids based on long chain of carbon atoms. They are characterized by low density and low moduli E. They are easy to shape. Few polymers have useful strength above 1500C the polymer is a long chain of covalent bonded atoms and secondary bonds then hold group of polymer chains togetherIndustrially important polymeric materials are plastics plastics can be subdivided into two groups thermoplastics and thermosetting plasticsExamples of thermoplastics are polyethylene, polypropylene, polystyrene and polyvinyl chlorideExamples of thermosetting polymers include alkyds, phenolic resins, epoxies, polyurethanes and unsaturated polyesters

5 Composites (Hybrids): a composite is usually defined as a combination of two or more distinct materials, each of which retains its own distinctive properties, to create a new material with properties that cannot be achieved by any of the components alone Ex concrete is mixture of Portland cement and aggregate

• Composites are said to have two phases. The reinforcing phase is the fibers, sheets or particles that are embedded in the matrix phase.

• Typically reinforcing materials are strong with low densities while matrix is usually ductile or tough material.

• Typical examples are reinforced plastics. Metal matrix composites, ceramic matrix composites etc

• Advanced materials:They are members of the above families but

with specific applications e.g electronic, bio materials and nanomaterials

The taxonomy of the kingdom of materials and their attributes. Computer-based selection software stores

data in a hierarchical structure like this.

MemberSub-Class

ClassFamilyKingdom

Material

Ceramics

Metals

Polymers

Hybrids

Advanced

SteelCu alloysAl alloysTi alloysNi alloysZn alloys

1000

2000

3000

4000

5000

6000

7000

6013

6060

6061

6063

6151

1.4Process and its classification� A process is the method of joining, shaping or finishing a

material. The choice of material limits the choice of process.

The first row contains primary shaping process below it secondary process, followed by family of joining and finishing

• Primary process creates shapes. The six primary process are listed :like casting , molding, deformation methods , powder methods, methods for forming composites, special methods.

• Secondary process: modifies the shapes and properties. Like machining which add features to already shaped body, heat treatment which enhances surface or bulk properties.

• After secondary process comes joining and surface treatment

• Sand casting : it consists of following steps• Placing a pattern having the shape of

desired casting in sand to make an imprint• Incorporating the gating system• Filling the resulting cavity with molten

metal• Allowing the metal to cool until it solidifies• Breaking away the sand mold • Removing the casting

• Investment casting / lost wax process: • The pattern is made of wax by injecting wax into

a metal die in the shape of pattern• The pattern is dipped in slurry of refractory

material. After initial coating has dried, the pattern is coated repeatedly to increase the thickness

• Then the mold is dried in air and heated to remove wax by keeping in inverted position

• Nos of molds are made and joined to form a tree to increase the production rate.

• Then molten metal is poured into these molds which take the shape, and once solidified they are taken out

• Die casting/ permanent mold casting: in this two halves of the mold is made of materials such as cast iron steel or refractory metals

• The molds are clamped together by mechanical means

• Deformation methods : ex rolling , forging, drawing, extrusion

• Rolling :It is process of reducing thickness or changing cross- section of long work piece by compressive force applied through a set of rolls

• Main products are flat plate, sheet and foil in long length, production of seamless tubing's.

• Rolling may be carried out at room temperature (cold rolling) or at elevated temperature (hot rolling)

• Forging is the process by which metal is heated and is shaped by plastic deformation by suitably applying compressive force. Usually the compressive force is in the form of hammer blows using a power hammer or a press.

• Forging refines the grain structure and improves physical properties of the metal. With proper design, the grain flow can be oriented in the direction of principal stresses encountered in actual use. Grain flow is the direction of the pattern that the crystals take during plastic deformation. Physical properties (such as strength, ductility and toughness) are much better in a forging than in the base metal, which has, crystals randomly oriented.

• Extrusion : It is a process of forcing a billet through a die, in a manner similar to squeezing toothpaste from a tube. Almost any solid or hollow cross section may be produced by extrusion.

• Typical products made by extrusion are railings for sliding doors, tubings having various cross sections.

• Drawing is an operation in which the cross section of solid rod , wire or tubing is reduced or changed in shape by pulling it through a die

• Products are wire and wire cablesWelding electrodes, springs , paper clips, spokes for bicycles, stringed musical instruments etc.

• Deep drawing . Basically a sheet forming process. Main products are beverage cans, kitchen sinks, automotive fuel tanks etc.

• Molding methods ( mainly for shaping plastics)

• Injection molding: in this process the granules or pellets are fed from the hopper to the rotating screw system or hydraulic plunger. The granules / pellets are heated and are forced into a split die chamber.

• Typical products include cups , containers, electrical and communication components, toys etc.

• Blow molding: it is modified form extrusion and injection molding process together . The blow molding process begins with melting down the plastic and forming it into a preform. The preform is a tube-like piece of plastic with a hole in one end in which compressed air can pass through. The parison is then clamped into a mold and air is pumped into it. the air pressure then pushes the plastic out to match the mold. Once the plastic has cooled and hardened the mold opens up and the part is ejected

• Powder metallurgy uses sintering process for making various parts out of metal powder. The metal powder is compacted by placing in a closed metal cavity (the die) under pressure. This compacted material is placed in an oven and sintered in a controlled atmosphere at high temperatures and the metal powders coalesce and form a solid. A second pressing operation, repressing, can be done prior to sintering to improve the compaction and the material properties.

� in a broad manner the process universe can be classified as three families : shaping , joining and surface

treatment.

The taxonomy of the kingdom of process with part of the shaping family expanded. Each member is characterized by a set of attributes. Process selection involves matching these to the requirements of the design.

Examples of families and class of manufacturing

Process property interaction

� Processing change properties. • If you hammer a metal it gets harder; if you heat it

softens.• Plastic bags when drawn to fibers , its strength increases

by a factor 5• Soft stretchy rubber is made hard and brittle by

vulcanizing

1.5 Material property charts

Data sheets do not allow comparison, perspective. For these we need• Material bar-charts and Material bubble charts� A bar chart is simply a plot of one property for all materials

A bar chart of modulus .It reveals the difference in stiffness between the families

A bubble chart of modulus and density. Families occupy discrete areas of the chart.

Bubble chart : two properties are plotted. Scales are logarithmic. Each family distinctly separated and occupies a characteristic field

� Material property charts are used as core tool because• They give an overview of physical , mechanical and

functional properties of materials, presenting information in a compact way

• They reveal aspects of physical origins of properties• They become a tool for optimized selection of materials

to meet design requirements and help understand the use of materials in existing products.

• Exercises pg 26 and 27(Ashby)Solve E2.1, E2.2,E2.4 and E2.5..