MATERIALS SCIENCE AND ENGINEERING

Transcription

1 MATERIALS SCIENCE AND ENGINEERING materials science - the discipline that involves investigating the relationships that exist between the structures and properties of materials materials engineering - the discipline of designing or engineering the structure of a material so as to produce a pre-determined set of properties

2 WHY STUDY MATERIALS SCIENCE? answer: Many an applied scientist or engineer (mechanical, civil, chemical, or electrical) will at one time or another be exposed to a design problem involving materials.

3 SOLID MATERIAL PROPERTIES mechanical properties - determine how a material is deformed in response to an applied load or force (eg elastic modulus, shear modulus, hardness, ductility, maleability) electrical properties - determine how a material responds to an imposed electric field (eg resistivity, dielectric constant, dielectric strength) thermal properties - determine how a material conducts or stores heat energy, or how its dimensions change in response to temperature changes (eg specific heat, thermal conductivity, linear coefficient of expansion) magnetic properties - determine how a material responds to an imposed magnetic field (eg magnetic susceptibility) optical properties - determine how a material transmits or reflects light (eg index of refraction, reflectivity) deteriorative properties - determine how a material chemically reacts with an existing environment

4 FOUR COMPONENTS OF MATERIALS SCIENCE AND ENGINEERING processing structure properties performance example: All disks shown are made of aluminum oxide (Al 2 O 3 ). The leftmost disk was grown as a single crystal. Its monocrystalline structure is responsible for its being optically transparent. The second disk was produced by a process which allowed the growth of numerous, small, interlocking single crystals, making it optically translucent. The disk on the right was produced by a process which allowed the growth of numerous, small, interconnected crystals and microscopic voids, making this material optically opaque.

5 METALS materials, normally composed of metallic elements, having significant numbers of conduction electrons (1) extremely good electrical/thermal conductors (2) not transparent to visible light (3) polished surfaces appear lustrous (4) strong, yet deformable examples: steel, cast iron, aluminum, brass, titanium

6 CERAMICS compounds whose molecules are composed of metallic and non-metallic elements (1) very poor electrical/thermal conductors (2) resistant to high temperature environments (3) resistant to harsh chemical environments (4) hard, but very brittle examples: metal oxides, metal carbides, clay minerals, cement, glass

7 POLYMERS typically organic compounds based on carbon, hydrogen, and other non-metallic elements; they have very large molecular structures, usually with some repeating submolecular unit (1) low densities (2) may be extremely flexible and ductile (3) low electrical and thermal conductivities (4) shock resistant (5) corrosion resistant examples: plastics, rubbers, adhesives

8 COMPOSITES engineered materials that consist of more than one material type; they are usually designed to display a combination of the best characteristics of each of the component materials, or to produce a characteristic not observed in any of the constituents (1) low density (2) high strength (3) good ductility (4) high temperature resistance examples: plywood, fiberglass, concrete

9 SEMICONDUCTORS materials whose electrical properties are intermediate between conductors and insulators; their electrical characteristics are very sensitive to minute concentrations of impurity atoms (1) not resistant to high temperatures (2) not corrosion resistant (3) engineerable electrical characteristics examples: silicon, germanium, gallium, arsenic

10 DIFFERENT MATERIALS - SAME USE

11 MATERIAL TYPES METALS - materials, normally composed of metallic elements, having significant numbers of conduction electrons (1) extremely good electrical/thermal conductors (2) not transparent to visible light (3) polished surfaces appear lustrous (4) strong, yet deformable examples: steel, cast iron, aluminum, brass, titanium CERAMICS - compounds whose molecules are composed of metallic and non-metallic elements (1) very poor electrical/thermal conductors (2) resistant to high temperature environments (3) resistant to harsh chemical environments (4) hard, but very brittle examples: metal oxides, metal carbides, clay minerals, cement, glass POLYMERS - typically organic compounds that are chemically based on carbon, hydrogen, and other non-metallic elements; they have very large molecular structures, usually with some repeating submolecular unit (1) low densities (2) may be extremely flexible and ductile (3) low electrical and thermal conductivities (4) shock resistant (5) corrosion resistant examples: plastics, rubbers, adhesives COMPOSITES - engineered materials that consist of more than one material type; they are usually designed to display a combination of the best characteristics of each of the component materials, or to produce a characteristic not observed in any of the constituents (1) low density (2) high strength (3) good ductility (4) high temperature resistance examples: plywood, fiberglass, concrete SEMICONDUCTORS - materials whose electrical properties are intermediate between conductors and insulators; their electrical characteristics are very sensitive to minute concentrations of impurity atoms (1) not resistant to high temperatures (2) not corrosion resistant (3) engineerable electrical characteristics examples: silicon, germanium, gallium, arsenic