Materials Science: Structure, Properties, and Classification
Introduction to Materials Science
Introduction
Materials Science examines how materials are formed and their properties. Its objective is to provide criteria for selecting the most appropriate materials for engineering applications.
Materials are substances that make up everything. Since the beginning of civilization, materials and energy have been used to improve living standards. The production and processing of new materials are fundamental to our economy. Engineers continually seek materials resistant to high temperatures for jet engines and new materials for faster electronic devices.
The study of materials involves:
- Material Structure: Understanding how materials are formed. Composition and structure significantly influence properties and behavior. Engineers and scientists must understand atomic structure to control and tailor material properties for specific applications. Material structure is examined at five levels:
- Macrostructure: The structure at a macroscopic level (greater than 1000nm), including porosity, surface coatings, and microcracks.
- Microstructure: The structure at a scale of approximately 10 to 1000nm, including grain size, distribution, orientation, and defects.
- Nanostructure
- Atomic structure: Atoms and their arrangements, the building blocks of matter. Understanding atomic structure and bonding is essential for material selection and development.
- Atomic arrangements of short and long range
- Crystal Structure: Atoms group together to solidify. Solids are classified as:
- Crystalline materials: Atoms are grouped in defined patterns (crystals).
- Amorphous materials: Atoms are grouped randomly without a defined pattern.
- Semi-crystalline materials: Materials have both crystalline and amorphous regions.
Figure 0.1. Structure of crystalline silica SiO2 (a) and amorphous (b). - Material Properties: Properties depend on atomic structure, crystalline structure, and microstructure. Material properties quantify behavior or reaction to external stimuli.
- Structure-Property Relationship: Properties generally depend on material structure. For example, the modulus depends on atomic bonding, magnetic properties on crystal structure, and mechanical properties on microstructure. Materials Science studies these relationships at all levels.
- Material Processing: Manufacturing processes often change material geometry, leading to associated changes in properties.
Classification of Materials
Materials are generally classified into five groups based on their properties or structure:
- Metals: Atoms are bonded by metallic bonds with free electrons, resulting in high electrical and thermal conductivity. Metals have high mechanical strength, stiffness, and ductility. Alloys (combinations of metals and nonmetals) enhance properties.
- Ceramics: Chemical compounds between metallic and nonmetallic elements (oxides, nitrates, carbides). Atoms are connected by ionic bonds, leading to low thermal and electrical conductivity. Ceramics are strong, hard, but brittle, and resistant to corrosion.
- Polymers: Organic compounds based on carbon, hydrogen, and other nonmetals. They consist of long chains with covalent bonds within molecules and weak bonds between molecules. Polymers have low density, are flexible, and easy to deform.
- Composites: Physical mixtures of two or more different material types (e.g., metals with ceramics, metals with polymers, ceramics with polymers). Composites aim to achieve specific properties from their components, such as low weight and electrical conductivity.
- Semiconductors: Essential for electronics, with electrical properties between conductors (metals) and insulators (ceramics). Their electrical properties can be controlled by impurities. They are very fragile.