Categories of Materials

1. Categories of Materials Metals and Alloys Polymers Ceramics Composites

2. Metalsand 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

3. Metals • Possess material properties, including: • high strengthand toughness • high electrical conductance • high thermal conductance • luster • Examples • aluminum - copper - gold - zinc - iron - lead - nickel • silver - thorium - chromium - tin - beryllium

4. 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

5. 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

6. 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

7. 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)

8. 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)

9. 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

10. 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.

11. 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

12. 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

13. 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

14. 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)

15. Review Major Categories of Materials Metals and Alloys Polymers Ceramics Composites