Fundamentals of Materials Science and Engineering

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2024年5月11日发(作者：)

材料科学导论

Fundamentals of Materials Science and

Engineering

（教案）

青岛科技大学

材料科学与工程学院

1.

Introduction

Classes of Materials

It is convenient to classify materials into broad categories for study. Many of the common characteristics of

materials within a category arise from the lowest level of structure, the nature of the atomic bond that holds

them together, and these similarities are aids to organizing our knowledge. The traditional classifications are:

• Metals

•

•

•

Ceramics (and glasses, which are usually made up of the same elements but with a different atomic

Polymers (or plastics, to use the more common name)

Composites (which combine several materials to achieve unique or economical combinations of

arrangement)

properties)

Some people (mostly those who use them) also distinguish electronic materials (semiconductors) as a

separate class. The properties of these various classes of materials are usually rather distinct. For instance,

metals are opaque to light and reflective. They are (usually) ductile, meaning that they can be bent before

they break. They are electrically and thermally conducting. On the other hand, ceramics and glasses are

usually brittle, can be transparent to light, and are good insulators. They are particularly useful at high

temperatures or in corrosive environments, since they retain their properties. Most polymers, on the other

hand, cannot withstand high temperatures. Most are insulators, and many are highly deformable (which is

the real meaning of the word, "plastic"), and some have unique elastic properties (rubber bands).

Semiconductors, of course, are distinguished by their electrical behavior. All of these property

characteristics, and the reasons they exist, are discussed in some detail in the chapters that follow.

It will be important to understand the differences between these classes of materials and how they arise from

the nature of the atomic bonds and the microstructure. But it will also be important to recognize that

comparisons are only meaningful based on similar measurement procedures. For example, mechanical

strength and ductility, sensitivity to the presence of cracks, and creep at high temperatures are measured in

the same ways for all classes of materials (of course, a high temperature for a polymer is much lower than it

is for a ceramic). The response of the materials to these tests is described in a consistent way, using the

same mathematical relationships and the same procedures for calculation.

One recurring theme in this course will be the Arrhenius relationship which describes the change in many

properties and characteristics with temperature. It applies to diffusion rates, creep at high temperatures,

viscosity of fluids, electrical conductivity in insulators and semiconductors, and more. It will obviously be to

the student's advantage to master the arithmetic of dealing with this relationship. But it will also be important

to understand that the reason this same expression appears so many times is that there is an idea behind it

that has a general validity. There is an activation energy needed to cause many processes to occur, and the

energy to overcome that barrier is obtained from thermal energy.

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