Categories of Materials

Metals and AlloysPolymersCeramicsComposites

Metals and Alloys Metals are pure elements which comprise

about three-fourths of the periodic table Few are used in their pure form because of:

Hardness; too hard or too soft Cost; scarcity of element Engineers need certain characteristics that

can only be accomplished by a blending of basic elements

Metallic materials include alloys, which are combinations of metals and other elements

Metals

Possess material properties, including: high strength and toughness high electrical conductance high thermal conductance luster

Examples aluminum - copper - gold - zinc - iron - lead -

nickel silver - thorium - chromium - tin - beryllium

Alloys Consist of materials composed of two or

more elements, at least one being a metal

This combination of elements gives the material a combination of properties from each element

Examples Steel- iron, carbon and impurity elements

such as boron copper or silicon Brass - copper, zinc Stainless Steel - nickel,iron

Types of Metallics:Ferrous Metallics - iron and alloys which contain at

least 50% iron (e.g. wrought iron, cast iron, steel, stainless steel)

Nonferrous Metallics - <50% iron, metallic elements other than iron (e.g. copper, lead, tin, zinc, titanium, beryllium, nickel)

Powdered (Sintered) Metals (ferrous or non-ferrous) Sometimes called sintered metal. A process of

producing small (powdered) particles which are compacted in a die and then “sintered” (applying heat below the melting point of the main component)

Examples: trigger on gun, gears, bearings, carbide tool inserts

Polymers

Polymers Chain-like molecule made of many

(poly) smaller molecular units (mono”mers”)

Chaining (polymerization) is responsible for the formation of natural fibers, wood, lignin, rubber, skin, bone and the tissues of animals, humans and insects

Plastics

Plastics Human-made polymers Plastics are workable or moldable

• Thermosetting plastics are formable once (e.g. epoxy, phonelic, polyurethane)

• Thermoplastics can be heated repeatedly and formed into new shapes (e.g. polyethylene, nylon, Plexiglas)

Elastomers Elastomer

amorphous (shapeless) structure consisting of long coiled-up chains of entangled polymers

can be stretched at room temperature to at least twice its original length and return to its original shape after the force has been removed

Process to strengthen an elastomer: vulcanization a chemical process used to form strong bonds

between adjacent polymers to produce a tough, strong, hard rubber (automobile tires)

Ceramics Crystalline compounds combining

metallic and non metallic elements The absence of free electrons make

ceramics poor electrical conductors. Because of the strength of the

bonding, ceramics have high melting temperatures

Ceramics(continued)

1.Clay Products Inorganic material which is shaped,

dried and fired.Examples: brick, floor and wall tiles, drainage

tile, roof tile, sewer pipe, chimney flue, china, and porcelain.

Ceramics(continued)

2.Refractory Materials Ceramics designed to provide acceptable

mechanical or chemical properties while at high temperatures.

Most are based on stable oxides such as carbides, nitrides, and borides.

An example of a refractory is the machinable all-silica insulating tiles on the U.S. space shuttle

Ceramics(continued)

3.Electrical and Magnetic Applications

Ceramics are used as resistors and heating elements for furnaces (silicon carbide)

Semiconductor properties: Thermistors- as they heat-up allow current to

flow. Rectifiers- allow current to flow in one direction Clay based ceramics for high-voltage insulators

Ceramics(continued)

4.Glass Based on silica with additives that alter the

structure or reduce the melting point, optimize optical properties, thermal stability and resistance to thermal shock

5.Cermets

Combinations of metals and ceramics(oxides, nitrides, or carbides) bonded together in the same way powdered metallurgy parts are made.

Examples: crucibles, jet engine nozzles

Composites

Laminar or Layer Composites - alternate layers of materials bonded together. (e.g. plywood, safety glass, Formica, bimetallic strips)

Particulate Composites - discrete particles of one material surrounded by a matrix of another material. (e.g. concrete, asphalt, powdered metals and ceramics)

Fiber-Reinforced Composites - composed of continuous or discontinuous fibers embedded in a matrix of another material. (e.g. Kevlar, rayon, steel reinforced tires, fiberglass, graphite-epoxy)

Review

Metals and AlloysPolymersCeramicsComposites

Major Categories of Materials