Materials Glossary

Anion

A negatively charged particle. Anion can be a single atom or a particle consisting of several atoms.

Atom

The smallest particle of a chemical element, in which the characteristic properties of that element are still preserved. An atom is the basic unit of a material structure. The atom contains a nucleus composed of protons that are positive electric charge and neutrons that are electrically neutral. Around the nucleus, there are negative electric charge electronics in motion. The number of electrons at the outer level, as well as the number of electron levels, affects the following properties: the chemical affinity of the material, the interatomic bonds that this material tends to bind (for example, ionic metal-non-metal bonding), the mechanical properties, the electrical properties, and the optical properties.

Atomic nucleus

The atomic nucleus is the dense area at the center of an atom consisting of protons and neutrons. The atomic nucleus is charged with a positive electric charge and it has a very small volume relative to the dimensions of the entire atom. The atomic nucleus was discovered by the British physicist Ernest Rutherford in 1911.

Cast iron

Iron alloy is a group of iron-carbon alloys made from pig iron, it contains more than 2 wt% carbon and 1-3 wt% silicon. Cast iron tends to be brittle, excluding malleable cast iron alloys. It has a relatively low melting point, good fluidity and castability, noble wear resistance, and good machinability. It is used for various applications such as machines and automotive industry parts.

Crystal

Crystal is the common three-dimensional structure of solid materials; it has an orderly structure with periodicity. The basic shape of the arrangement of atoms in the solid crystal is called a lattice. The lattice is made up of a collection of unit cells that repeat themselves in an orderly way. A crystal can be composed of metal atoms when there are metallic bonds, ions when there are ionic bonds, or molecules when there are covalent bonds. The process of crystal formation is called crystallization.

Dendrites

In metallurgy, dendrites are tree-like branches of crystals created when molten material solidifies. Dendritic solidification gives a high ratio of surface area to volume and therefore the dendritic configuration allows for fast evacuation of heat and hence rapid solidification.

Diffusion

Diffusion is the motion of matter (atoms, ions, and molecules). It usually accrues from an area of high concentration to an area of low concentration. Diffusion exists not only in gases and liquids but also in solids. While in gas and liquid the atoms are free to move, in the solid there are strong bonds between the atoms, which slows down the diffusion process so that at low temperatures the rate of diffusion is very limited. The laws of diffusion are the same for the solid, liquid, or gas states of matter, but the mechanisms of diffusion are different. The activation energy for volume diffusion is greater than the activation energy for surface diffusion or diffusion at the grain boundaries.

Electrically charged body

A body in which the number of electrons is less than or greater than the number of protons. A positively charged body is a body that has fewer electrons relative to the number of protons. A negatively charged body is a body that has fewer electrons relative to the number of protons. A neutral body is a body in which the number of electrons is equal to the number of protons, so it is not electrically charged.

Electron

A subatomic particle in an atom with a negative electric charge. The electron is in constant motion around the nucleus. The electron is assumed to be an elementary particle because it has no components or substructure. The electron mass is approximately 1/1836 of the proton mass.

Fracture toughness

In fracture mechanics, fracture toughness is the mechanical property that is used in order to describe the ability of a material to resist fracture. The larger the area under this stress-strain curve, the more resistant the material is to cracks propagation.

Free electron

A free electron is an electron that is attracted to the nucleus by relatively weak forces and is, therefore, free to move from atom to atom.

Grains (crystal grains)

The solidification of a liquid during cooling is not carried out at once in the entire volume of the material. It starts at certain points in the liquid, usually in areas of imperfections. From these areas, the solidification process progress until all the material becomes solid commonly in random crystallographic orientations. Therefore, most crystalline solids are composed of many small crystals, called grains, of varying size and orientation, forming a polycrystalline microstructure. In engineering materials, the size of the grains usually ranges from tens of nanometers to hundreds of microns. The surface between the grains is called a grain boundary. The grain boundaries are considered two-dimensional (2D) defects in the crystalline structure, because the periodic pattern of the crystals is broken at the grain boundaries.

Gray cast iron

Gray cast iron is a brittle iron-carbon alloy that contains 2.5-4 wt% carbon and 1-3 wt% silicon. Usually, its microstructure contains graphite flakes surrounded by ferrite or perlite matrix. The advantages of gray cast iron are good resistance to vibrations and abrasion. Gray cast iron is the cheapest material among industrial metallic alloys.

Hardness test

A test based on the penetration of a hard body with a certain geometry (such as pyramidal diamond), called an indenter, into the material being tested by applying a load on the specimen for a certain time. The hardness values represent the resistance of the examined material to penetration and are calculated from the size of the indentation trace left in the material (plastic deformation) after the removal of the load at the end of the test. The softer the material, the greater the indentation trace will be. Microhardness test is a method used for measuring a material’s resistance to penetration when the test specimens are quite small or thin, or when the material is heterogeneous.

Heat treatment

Heating or cooling at different rates in order to obtain the desired properties by controlling the microstructure. As a result of heat treatment, a wide range of physical and mechanical properties are obtained in different materials. The materials are divided into three typical groups: those that do not respond to heat treatment, those that respond to quenching treatment (steels, titanium alloys), and those that respond to aging treatment (aluminium alloys and super-alloys).

Ionic material (salt)

Consists of alternating positive and negative ions, held together by strong ionic bonding. Examples of ionic materials are Sodium chloride (NaCl), known as cooking salt, potassium-fluoride (KF), and sodium carbonate (Na₂CO₃).

Interstitial defect

A point (zero-dimension) crystallographic defect, where an atom of an identical or of a dissimilar kind, occupies an unoccupied site in the crystal structure. When the interstitial atom is of the same type as the atoms already exist in the crystal, the defect is called a self-interstitial defect. On the other hand, small atoms such as hydrogen may occupy normal interstitial sites in some crystals, such defect is called interstitial impurity.

Iron

Iron (symbol Fe, ferrum in Latin) is a shiny gray metal, with a density of 7.874 (g/cm³) at room temperature. It is a good conductor of electricity and heat and in addition, iron is strongly attracted to a magnetic field below 770^oC. Iron is s very ductile and malleable material, however, it corrodes when exposed to water and oxygen.

Isotopes

Isotopes are different atoms of the same chemical element, but with a different number of neutrons. Different isotopes of the same chemical element have the same chemical properties yet, their physical properties, such as density, melting point, boiling point, etc, are different. For most elements, one isotope is particularly common and others are quite rarer.

Neutral atom

An atom where the number of electrons is equal to the number of protons.

Noble gases

A family of stable elements that do not tend to form chemical bonds. All noble gases are gaseous, and they constitute the eighth column in the periodic table. Commonly noble gases are highly unreactive excluding in the case of particular extreme conditions. This family includes helium (He), neon (Ne), argon (Ar), krypton (Kr) xenon (Xe), and radon (Rn).

Non-metal elements

Elements that lack the characteristics properties of metal. Nonmetals tend to have a rather low melting point, low density and they are electrically and thermally insulating materials. The elements hydrogen, helium, nitrogen, oxygen, fluorine, neon, chlorine, argon, krypton, xenon, radon, bromine, carbon, phosphorus, sulfur, selenium, and iodine are all non-metals.

Phase diagram

A graphical illustration of the physical states of a material under different conditions such as temperature, pressure, and composition. An equilibrium phase diagram is a chart used to illustrate the conditions at which thermodynamically dissimilar phases (solid, liquid, or gas) occur and exist at equilibrium. A binary phase diagram illustrates the physical state when more than one pure component is present. It shows the different phases formed in dissimilar mixtures of two elements over a range of temperatures. In the case of a binary phase diagram, the compositions change from 100 % (atomic or weight %) of element A on the left side of the diagram, through all conceivable mixtures, to 100 % of element B on the right side of the diagram.

Plastic deformation

As a material elongates beyond the elastic range, the stress is no longer proportional to the strain and plastic deformation occurs. At the interatomic level, plastic deformation in metals is caused as a result of dislocations glide or slip, when atomic bonds are broken due to the movement of dislocations in the material, and new bonds are formed. In the plastic realm, when we remove the effort, the material will not return to its initial state.

Quenching

In metallurgy, quenching is a heat-treating process in which steel is heated to the austenitic temperature and then the workpiece cooled rapidly in water, oil, or air to achieve certain material properties. Quenching is frequently applied to harden carbon steel by martensite transformation.

Self-diffusion

Self-diffusion is the motion of pure matter atoms, in which all the atoms are identical. The motion of the atoms can be monitored by inserting radioactive isotopes of the same material (same atomic number).

Strain hardening

Strain hardening (also called work hardening) occurs because of dislocation generation and movement when metal is strained beyond its yield point. Increasing stress is essential to produce further plastic deformation. Strain hardening results in a metal that is harder and more difficult to deform.

Time Temperature Transformation (TTT) phase diagram

When the cooling of material is fast, the binary phase diagram does not provide enough information about the material because it lacks a timeline. The TTT diagram, also known as isothermal transformation diagrams, shows the different phases that exist for one specific composition by showing plots of the temperature versus time (usually on a logarithmic scale).

Vacancy defect

A point (zero-dimension) crystallographic defect, where an atom is absent from one of the lattice sites. Vacancies occur naturally in all crystalline materials. Vacancies exist mainly due to thermal vibrations of the atoms at high temperatures. The concentration of vacancies increases when the temperature is increased.

White cast iron

White cast iron is an iron-carbon alloy that contains 2.5-4 wt% carbon and less than 1 wt% silicon. When the Si concentration is low and the cooling rates are relatively high, most of the carbon will appear in the form of cementite and not in the form of graphite. The fracture surface of this alloy looks bright hence the name white cast iron. This alloy is very hard and brittle, and therefore, it is difficult to work with. The uses of white cast iron are only for cases where very high hardness and good abrasion resistance are required, for example, roller skates, or grinding balls in grinders.

X-ray diffraction

X-ray diffraction (XRD) is a nondestructive testing (NDT) analytical technique that provides information about the crystallographic structure. X-ray is an electromagnetic wave, with a wavelength on the order of the distance between crystalline planes. XRD method measures the spacing between layers or rows of atoms. XRD analysis is used for phase identification, finding the crystal structure of unknown materials, and determination of the orientation of a single crystal or grain.