Metals, ceramics, polymers and composites

Traditionally, materials have been divided into three major groups - metals, ceramics and polymers. Metallic materials are made up of pure metals, for example, titanium, iron or copper, and a vast number of alloys, including the historically important alloys bronze, brass and steel. Ceramics bring to mind porcelain, silicon carbide, glass and synthetic gemstones such as ruby and zirconia. Polymers are mainly compounds of carbon and include the familiar materials poly(vinylchloride), polyethylene and nylon as well as important biological molecules such as DNA. 

In addition to these major divisions, two others should be mentioned - composites and biomaterials. Composites are important materials that are combinations of compounds from more than one of the groups listed above. They are of importance because they have superior engineering properties to the separate compounds. For example, glass fibre (ceramic) 

Biomaterials are naturally occurring materials with important properties, such as wood, silk and bone. They are invariably composites, made of more than one material type. Because of the superior properties of many biomaterials, much effort is placed into trying to recreate these materials synthetically, as biomimetics. 

At first sight, metals, ceramics and polymers have little in common. This is because of two main factors - the chemical bonding holding the atoms together and the microstructure of the solids themselves - that are quite different in representative examples of each material. However, the difference is illusory. Many ceramics can be considered as metals, for example the ceramic superconductors. Many polymers show electronic conductivity greater than metals and have use in lightweight batteries and electronic devices. The material in this and later chapters will allow these apparent anomalies to be understood. 

Roughly speaking, about three quarters of the elements can be regarded as metallic, and metals form 

---

D. Designing with metals, ceramics, polymers and composites... 

This book has been written as a second-level course for engineering students. It provides a concise introduction to the microstructures and processing of materials (metals, ceramics, polymers and composites) and shows how these are related to the properties required in engineering design. It is designed to follow on from our first-level text on the properties and applications of engineering materials," but it is completely self-contained and can be used by itself. 

Processes), (ASM), Special Issue Penton Publishing (1994). Basic reference work-up dated annually. Tables of data for a broad range of metals, ceramics, polymers and composites. 

These categories are applied to a variety of engineering materials, which can be classified into metals, ceramics, polymers, and composites. Table 1 indicates the application of different processes to different materials. 

Bar chart of room-temperature density values for various metals, ceramics, polymers, and composite materials. 

Bar chart of room-temperature resistance to fracture (i.e., fracture toughness) for various metals, ceramics, polymers, and composite materials. (Reprinted from Engineering Materials 1 An Introduction to Properties, Applications and Design, third edition, M. F. Ashby and D. R. H. Jones, pages 177 and 178, Copyright 2005, with permission from Elsevier.)... 

---