What Are Materials?

Materials are the physical substances from which devices, structures, and systems are constructed. In engineering and applied science, the term refers to any solid-phase substance whose properties are deliberately selected or modified to meet a performance requirement, spanning metals, ceramics, polymers, semiconductors, composites, and biomaterials. The study of materials examines the relationships among a substance's composition, atomic structure, microstructure, and observable properties, with the goal of enabling rational selection and design rather than trial-and-error substitution.

Materials science and engineering draws from physics, chemistry, and multiple engineering disciplines. Ohio State University's materials science overview describes the discipline as linking atomic-scale understanding to macroscopic performance, with practitioners working across synthesis, characterization, processing, and failure analysis. IEEE research regularly engages materials questions because performance limits in power systems, semiconductors, sensors, and structural applications are ultimately set by what the underlying materials can do.

Classes of Engineering Materials

Metals and alloys are the oldest class of structural and electrical engineering materials. Their combination of high electrical and thermal conductivity, ductility, and strength makes them essential for wiring, structural frames, and rotating machinery. Ceramics are inorganic, non-metallic solids characterized by high hardness, high melting points, and electrical insulation; alumina, silicon carbide, and silicon nitride are used in electronics substrates, cutting tools, and thermal barrier coatings. Polymers span a broad range from elastomers to engineering plastics; their low density, chemical resistance, and ease of forming make them preferred for insulation, packaging, and lightweight structural components.

Semiconductors occupy a critical position in the materials hierarchy because their electrical conductivity can be controlled precisely through doping, temperature, and applied field. Silicon remains the dominant semiconductor for integrated circuits, while compound semiconductors such as gallium nitride (GaN) and silicon carbide (SiC) are used in power electronics and high-frequency devices. Composites combine two or more distinct materials to achieve properties neither constituent provides alone; carbon-fiber-reinforced polymer (CFRP) laminates exemplify the approach, delivering high specific stiffness alongside electrical insulation.

Structure and Microstructure

A material's properties are determined at multiple scales. At the atomic scale, the type of bonding (metallic, ionic, covalent, or van der Waals) governs baseline electrical and thermal conductivity, stiffness, and reactivity. At the microstructural scale, grain size, phase distribution, dislocation density, and defect concentration control strength, toughness, and resistance to fatigue. MIT's Department of Materials Science and Engineering highlights semiconductor microstructure research as a central activity linking atomic design to device performance.

Oxidation is a microstructural concern in many engineering contexts: metals exposed to air form oxide layers that can be protective (as with the alumina scale on aluminum alloys) or corrosive (as with scale spallation on steel at elevated temperatures). Managing oxidation through alloying additions, protective coatings, or inert atmospheres is a routine part of materials processing for aerospace, power, and electronic components.

Processing and Performance

Processing converts raw materials into the forms and microstructures needed for service. Casting, rolling, forging, powder metallurgy, thin-film deposition, and polymer extrusion are among the routes used to shape and consolidate materials. Post-processing steps such as heat treatment, surface finishing, and coating modify the microstructure and surface condition to achieve target properties. The choice of processing route affects grain size, residual stress, and phase composition, all of which feed into service performance. Purdue University's materials engineering program characterizes materials engineers as working from material design through fabrication, testing, and failure analysis.

Applications

Materials have applications in a range of fields, including:

• Semiconductor substrates and dielectrics for integrated circuit fabrication
• Structural alloys and composites for aerospace and automotive structures
• Insulating and conducting materials for power transmission and storage
• Biocompatible materials for medical implants and diagnostic devices
• Materials handling systems in manufacturing and industrial processing