Metallic Materials

Metallic materials are a general term for metallic elements or materials whose primary component is metal and which exhibit metallic properties. This group includes pure metals, alloys, intermetallic compounds, and special metallic materials. Metallic materials have played a central role in the development of human history, giving their names to periods such as the Bronze Age and Iron Age following the Stone Age and forming the fundamental material basis for the advancement of civilization. Today, they remain indispensable in countless fields including engineering, construction, medicine, transportation, and technology. They are generally known for properties such as good thermal and electrical conductivity, ease of shaping, high strength, and impact resistance. These materials are used not only in their pure form but also widely as alloys, created by combining different metals or metals with non-metals to enhance specific properties.

Classification

Metallic materials are primarily classified into three main groups based on their chemical composition and properties: ferrous metals, non-ferrous metals, and special metallic materials.

Ferrous Metals

This group includes metals and alloys whose primary component is iron (Fe). Industrial pure iron (containing more than 90% iron), cast iron (containing 2% to 4% carbon), and steel (containing less than 2% carbon) are the most well-known examples of this category. Structural steels, stainless steels, heat-resistant steels, and specialized alloys developed for various purposes also belong to the ferrous metals class. Broadly speaking, elements commonly used in iron alloys such as chromium (Cr) and manganese (Mn), as well as their own alloys, are also considered part of this group.

Non-Ferrous Metals

This is a broad category encompassing all metals and their alloys except iron, chromium, and manganese. This group is further classified into light metals (aluminum, magnesium, titanium), heavy metals (copper, zinc, lead, nickel), precious metals (gold, silver, platinum), metalloids, rare metals, and rare earth metals. The alloys of non-ferrous metals generally exhibit higher strength and hardness compared to their pure forms. Additionally, they have higher electrical resistivity and lower temperature coefficients of resistance. Common examples of this group include aluminum, copper, brass, bronze, and titanium alloys.

Special Metallic Materials

This category includes advanced technology materials developed for specific structural or functional purposes. These include amorphous (glassy) metallic materials produced through rapid solidification (quenching), as well as semi-crystalline, microcrystalline, and nanocrystalline structured materials. Additionally, alloys with special functions such as invisibility (stealth), hydrogen resistance, superconductivity, shape memory, high wear resistance, and damping, along with metal matrix composite materials, are included in this group. These materials exhibit performance beyond that of conventional metals and are used in fields such as aerospace, space, electronics, and biomedical engineering.

Properties

The wide range of applications for metallic materials stems from their diverse mechanical, physical, and chemical properties. These properties are determined by the material’s atomic structure, crystal arrangement, and chemical composition.

Mechanical Properties: One of the most prominent characteristics of metallic materials is their high mechanical strength. Properties such as tensile strength, compressive strength, fatigue resistance, and fracture toughness make them preferred for load-bearing structural applications. Standard tests such as the tensile test at room temperature (according to TS EN ISO 6892-1 standard) are used to determine the mechanical behavior of materials. These tests reveal critical values such as the elastic modulus, yield strength, and ultimate tensile strength. Hardness, ductility (ability to undergo plastic deformation), and toughness (resistance to fracture) are also important mechanical properties.

Physical Properties: Due to their metallic bonding structure containing free electrons, metallic materials generally exhibit good electrical and thermal conductivity. Their densities vary significantly from material to material; for example, aluminum is light, while lead and gold are quite dense. Ferromagnetic metals such as iron, nickel, and cobalt and their alloys display strong magnetic properties and are used in the production of permanent magnets.

Chemical Properties: Corrosion is the deterioration of metallic materials through chemical reactions with their environment. Corrosion resistance is one of the most important factors determining a material’s service life and reliability. Certain metals such as stainless steel and titanium are highly resistant to corrosion due to the formation of a thin, dense, and protective oxide layer on their surface (e.g., chromium oxide or titanium oxide). This passive layer protects the underlying material from environmental effects.

Common Metallic Materials and Alloys

Some of the most frequently encountered metallic materials in industry and daily life include:

Cast Iron: Cast iron has excellent fluidity due to its high carbon content (2%–4%), making it ideal for producing complex-shaped parts by casting. It possesses good wear resistance and compressive strength due to the presence of graphite. It is widely used in applications such as manhole covers, kitchenware, machine housings, and engine blocks.

Steel and Stainless Steel: Steel is an alloy of iron and carbon, with carbon content below 2%. Its mechanical properties can be varied over a wide range by adding other alloying elements (chromium, nickel, molybdenum, etc.) and applying heat treatments. Stainless steel is a type of steel containing a minimum of 10.5% chromium. Chromium forms a self-repairing chromium oxide film on the surface that prevents rusting. Austenitic stainless steels (e.g., 304, 316L) are used in household products, industrial piping, and medical implants; martensitic stainless steels are used in knives and turbine blades; and ferritic stainless steels are used in boiler components and similar applications.

Aluminum and Its Alloys: Aluminum, known for its low density, good corrosion resistance, and high strength-to-weight ratio, is a modern engineering material. It is obtained from bauxite ore in nature. It is widely used in the aerospace and space industries, the automotive sector (for vehicle weight reduction), and the packaging industry. Advanced alloys such as aluminum-lithium have been specifically developed for aerospace applications.

Titanium and Its Alloys: Titanium is lighter than stainless steel yet offers comparable strength. One of its most important properties is its nearly complete inertness to bodily fluids and high biocompatibility. For this reason, it is widely used in orthopedic implants (hip and knee prostheses), dental implants, and surgical instruments. The Ti6Al4V alloy is the most commonly used titanium alloy in both biomedical and aerospace sectors due to its high corrosion resistance and static/dynamic strength.

Copper and Its Alloys: Copper is known for its high electrical and thermal conductivity and is used in electrical wiring and heat exchangers. Alloys such as brass (copper-zinc) and bronze (copper-tin) are preferred for piping systems, valves, bearings, and decorative purposes due to their corrosion resistance and mechanical properties.

Zinc: Zinc is the third most commonly used non-ferrous metal after aluminum and copper. Its low melting point makes it suitable for casting processes. Its most common application is as a protective coating (galvanizing) to prevent steel from corrosion. It is also a component of brass alloys and is used in battery production.

Production and Forming Methods

Metallic materials undergo various production and forming processes from raw ore to final product. These methods determine the final shape, dimensions, and mechanical properties of the material.

Casting: This process involves melting the metal, pouring it into a mold, and allowing it to solidify. It is suitable for the mass production of complex-geometry parts. Different types include sand casting, precision casting, die casting, and permanent mold casting.

Plastic Forming: These are processes that apply forces to induce permanent shape changes in the material. These methods typically reduce or eliminate the need for chip-forming manufacturing. Major plastic forming methods include:

• Rolling: A process in which metal is passed between rotating rolls to reduce its cross-section and shape it. It is used to produce sheets, plates, strips, rails, and various profiles (angles, I-beams).
• Forging: The shaping of material under compressive forces within open or closed dies. It is commonly preferred for components requiring high strength and toughness.
• Extrusion: A method in which a cylindrical metal billet is forced through a die under high pressure to produce long, constant-cross-section profiles (pipes, rods, rails). It is common for materials that easily deform, such as aluminum.
• Drawing: A process in which the material is pulled through a die to reduce its cross-section, used in the production of wires, rods, and tubes.

Powder Metallurgy: An advanced manufacturing technique in which metal powders are compacted under high pressure and then sintered (bonded at high temperature) to produce solid parts. It enables the production of complex shapes with high precision and superior properties.

Welding: The joining of two or more metal parts using heat, pressure, or both. Methods such as electric arc welding, TIG (Tungsten Inert Gas) welding, and MIG-MAG welding are widely used in the assembly of metallic materials.

Advanced Metallic Materials

Advanced metallic materials are high-value-added materials requiring advanced technology and offering superior properties compared to conventional materials. These materials are engineered at the atomic level during production to achieve desired characteristics such as toughness, hardness, temperature resistance, and corrosion resistance. Important examples include nickel-, cobalt-, and titanium-based superalloys (for high-temperature applications), intermetallic materials, ultra-high-strength steels, and shape memory alloys (which return to their original shape at a specific temperature). These materials play a crucial role in enhancing countries’ technological advancement and economic competitiveness.