Metallography Glossary

Hard particles used for grinding and polishing. Common abrasives include silicon carbide, aluminum oxide, and diamond.

Equipment used for sectioning samples using rotating abrasive wheels. Suitable for a wide range of materials and sample sizes.

A sectioning method using rotating abrasive wheels to cut through materials. Versatile and suitable for a wide range of materials and sizes.

A heat treatment process where a material is held at an elevated temperature to allow precipitates to form, strengthening the material.

A metallic material composed of two or more elements, at least one of which is a metal. Alloys typically have improved properties compared to pure metals.

A heat treatment process that involves heating a material to a specific temperature and slowly cooling it to soften the material, relieve stresses, or alter microstructure.

A feature in a microstructure that is not part of the true material structure but is introduced during sample preparation. Examples include scratches, contamination, relief, and smearing.

A standardized system for describing grain size in materials, using numbers from 1 (coarse) to 14+ (very fine). Higher numbers indicate finer grains.

A face-centered cubic (FCC) phase of iron that exists at high temperatures. It can transform to ferrite, pearlite, or martensite depending on cooling rate.

A microstructure formed by transformation of austenite at intermediate temperatures. Consists of ferrite and cementite with a characteristic acicular (needle-like) or feathery appearance.

A hardness testing method using a spherical indenter. Expressed as HB. Good for softer materials and rough surfaces.

The tendency of a material to fracture without significant plastic deformation. Opposite of ductility.

A mounting method where liquid resin is poured into a mold and allowed to cure at room temperature or with minimal heating. Ideal for delicate, heat-sensitive samples.

Cubic Boron Nitride blade - a cutting blade with CBN particles bonded to the edge. Used for sectioning hard materials like tool steels.

A hard, brittle phase of iron carbide (Fe3C) that forms in steel. Its appearance in etched microstructures depends on the etchant: appears dark with nital, light/white with picral.

A fine oxide polishing suspension used for final polishing. Produces excellent surface finishes with minimal damage.

A polishing artifact where hard particles create trailing marks resembling comets. Caused by improper polishing technique or contaminated abrasives.

A mounting method where resin pellets are heated and compressed under high pressure to form a solid mount. Fast (5-15 minutes) and produces hard, durable mounts.

Foreign material introduced to the sample surface during preparation. Can include abrasive particles, polishing compounds, or other debris.

A fluid used during sectioning to reduce heat generation and prevent damage to the sample. Also helps remove cutting debris.

A fracture or separation in a material. Can be surface-breaking or internal. Critical defect that can lead to failure.

An abrasive wheel used for sectioning samples. Available in various diameters and abrasive types.

A lubricant and coolant used during sectioning to reduce friction, heat, and tool wear. Helps produce cleaner cuts.

Imperfections in material structure such as inclusions, voids, cracks, or dislocations that can affect material properties and performance.

A tree-like crystal structure that forms during solidification. Dendrites have a main trunk with branches extending outward.

A thin cutting blade with diamond particles bonded to the edge. Used in precision wafering for low-damage sectioning.

A polishing method using diamond abrasives in various particle sizes (typically 9 μm, 3 μm, 1 μm, 0.25 μm) to remove grinding scratches and prepare the surface for final polishing.

Diamond particles suspended in a liquid carrier (water or oil-based) for polishing. Available in various particle sizes.

A line defect in the crystal structure of a material. Dislocations enable plastic deformation and affect material properties.

The ability of a material to deform plastically before fracture. Measured as percent elongation or percent reduction in area.

Electron Backscatter Diffraction - a technique used in scanning electron microscopy to determine crystal orientation, grain boundaries, and phase identification.

The ability of a mount to maintain sharp edges and interfaces during grinding and polishing. Important for analyzing coatings, edges, or interfaces.

Energy-Dispersive X-ray Spectroscopy - a technique used in SEM to identify and quantify chemical elements in a sample.

An etching method using electrical current to enhance the etching process. Used for some stainless steels and other materials.

A chemical reagent used to etch (chemically attack) a polished sample surface to reveal microstructural features. Different etchants reveal different features.

The process of applying chemical reagents to reveal microstructural features. Etching attacks different phases and grain boundaries at different rates, creating contrast.

A mixture of two or more phases that form simultaneously from a liquid at a specific composition and temperature. The lowest melting point composition for that system.

A transformation where a single solid phase decomposes into two or more different solid phases at a specific temperature and composition.

A body-centered cubic (BCC) phase of iron that contains little or no carbon. It is soft, ductile, and magnetic at room temperature.

An individual crystal within a polycrystalline material. Grains are separated by grain boundaries and their size significantly affects material properties such as strength and toughness.

The interface between adjacent grains where atoms are less regularly arranged. Grain boundaries can affect material properties and serve as sites for phase transformations.

A measure of the average size of grains in a material, typically expressed as ASTM grain size number or average grain diameter. Smaller grain sizes generally correlate with higher strength.

The process of removing sectioning damage and preparing the surface using progressively finer abrasives. Creates a uniform scratch pattern that can be removed during polishing.

Equipment used for automated grinding and polishing of samples. Can be manual or fully automated with programmable parameters.

A measure of abrasive particle size. Lower grit numbers indicate coarser abrasives (larger particles), while higher numbers indicate finer abrasives. Common grit standards include FEPA, ANSI, and JIS.

The sequence of progressively finer grit sizes used during grinding. Typically progresses from coarse (120 grit) to fine (600-1200 grit).

A measure of a material's resistance to deformation, typically measured by indentation. Common scales include Rockwell (HRC, HRB), Brinell (HB), and Vickers (HV).

Equipment used to measure material hardness by indentation. Types include Rockwell, Brinell, Vickers, and Knoop testers.

Controlled heating and cooling processes used to alter material properties. Common treatments include annealing, quenching, tempering, and aging.

The use of software to automatically measure and analyze microstructural features from digital images. Can quantify grain size, phase fractions, etc.

An etching method where the sample is fully immersed in the etchant solution for a specified time.

Non-metallic particles or compounds embedded in a metal matrix, typically oxides, sulfides, or silicates. Inclusions can affect material properties and machinability.

A method for measuring grain size by counting the number of grain boundaries intersected by test lines.

A microhardness testing method using a diamond indenter with an elongated pyramid shape. Good for thin samples and small areas.

The degree to which an image is enlarged when viewed through a microscope. Expressed as a ratio (e.g., 100x means 100 times larger than actual size).

A hard, brittle phase formed by rapid cooling (quenching) of austenite. It has a needle-like or lath-like appearance and provides high hardness but low ductility.

A class of materials characterized by metallic bonding, high electrical and thermal conductivity, and typically good ductility and strength.

A specialist who prepares and examines metallographic samples. Skilled in sample preparation techniques and microstructural analysis.

A microscope designed for observing polished and etched metallographic samples. Typically includes reflected light illumination and various magnification options.

The study of the microstructure of metals and alloys using microscopy. Involves sample preparation (sectioning, mounting, grinding, polishing, etching) and microscopic examination.

A scientist or engineer who studies the physical and chemical behavior of metals and alloys, including their structure, properties, and processing.

The internal structure of a material as observed under a microscope, including grains, phases, grain boundaries, and other features that determine material properties.

A sample embedded in resin material, creating a standardized shape for easier handling during grinding, polishing, and analysis.

The process of embedding a sample in resin material to create a standardized, easy-to-handle mount. Makes samples easier to process through grinding, polishing, and analysis.

A container or form used to hold the sample and resin during mounting. Can be reusable or disposable.

Equipment used for compression mounting. Applies heat and pressure to form solid mounts from resin pellets.

A heat treatment process where steel is heated above the transformation temperature and air-cooled to refine grain structure.

A microscope that uses visible light to observe samples. Standard tool for metallographic analysis at magnifications up to 1000x.

Final polishing using fine oxide suspensions (typically colloidal silica or alumina) to create a mirror-like, scratch-free surface. Removes any remaining fine scratches from diamond polishing.

A lamellar microstructure consisting of alternating layers of ferrite and cementite. It forms during slow cooling of steel and provides a balance of strength and ductility.

A distinct region in a material with uniform chemical composition and crystal structure. Materials can contain multiple phases (e.g., ferrite and cementite in steel).

The percentage or fraction of each phase present in a material. Measured using image analysis or point counting methods.

Small holes or depressions in the polished surface, often caused by preferential etching or removal of inclusions.

A method for measuring grain size by counting the number of grains within a known area.

A manual method for determining phase fractions by counting points that fall on each phase in a grid overlay.

The final step in sample preparation that removes grinding scratches and creates a mirror-like surface suitable for microstructural analysis. Typically uses diamond or oxide abrasives.

A fabric pad used on polishing wheels to hold abrasives and provide appropriate surface texture. Different cloths have different nap levels and properties.

A synthetic pad used for polishing, typically with a specific texture or nap designed for different polishing stages and materials.

A rotating disc used for polishing samples. Holds polishing cloths or pads and rotates at controlled speeds.

A material composed of many small crystals (grains) with different orientations. Most metals and alloys are polycrystalline.

The presence of voids or pores in a material, typically expressed as a percentage of void volume to total volume.

Small particles of a second phase that form within the primary phase, typically during aging or heat treatment. Precipitates can strengthen materials.

A sectioning method using thin diamond or CBN blades to make precise, low-damage cuts. Ideal for delicate materials, thin sections, and applications requiring minimal damage.

Equipment used for precision sectioning with thin diamond or CBN blades. Produces low-damage cuts ideal for delicate materials.

The complete sequence of steps required to transform a raw material sample into a specimen suitable for microscopic examination. Includes sectioning, mounting, grinding, polishing, and etching.

Rapid cooling of a material from high temperature, typically in water, oil, or air. Used to form hard phases like martensite in steel.

The formation of new, strain-free grains in a deformed material during heating. Occurs at temperatures above the recrystallization temperature.

A polishing artifact where different phases or features stand above or below the polished surface due to different removal rates. Can be minimized with proper polishing technique.

A synthetic polymer material used for mounting samples. Types include phenolic, epoxy, acrylic, and polyester resins.

A hardness testing method using different scales (HRC, HRB, etc.) based on indenter type and load. Quick and widely used.

A linear mark or groove on the polished surface, typically from previous grinding steps that were not fully removed.

The pattern of scratches left on a sample surface after grinding. Should be uniform and oriented in one direction before moving to the next grit.

The process of cutting a representative sample from a larger workpiece using abrasive or diamond cutting equipment. The first step in metallographic sample preparation.

Scanning Electron Microscope - a type of electron microscope that produces high-resolution images of sample surfaces. Provides higher magnification than optical microscopes.

A polishing artifact where soft material is smeared across the surface, obscuring the true microstructure. Common in soft materials like aluminum and copper.

A heat treatment where alloying elements are dissolved into solid solution by heating, followed by rapid cooling to retain the solution.

A steel alloy containing at least 10.5% chromium, providing excellent corrosion resistance. May also contain nickel and other elements.

An alloy of iron and carbon, typically containing less than 2% carbon. May also contain other alloying elements.

An etching method where the etchant is applied to the sample surface using a cotton swab or similar applicator.

Transmission Electron Microscope - an electron microscope that transmits electrons through thin samples. Provides very high resolution and magnification.

A heat treatment process where quenched steel is reheated to a temperature below the transformation range to reduce brittleness and adjust hardness.

The maximum stress a material can withstand while being stretched before failure. Also called ultimate tensile strength (UTS).

The ability of a material to absorb energy and deform plastically before fracture. Combines strength and ductility.

Equipment used in castable mounting to remove air bubbles from liquid resin before curing. Ensures porosity-free mounts.

Equipment that uses vibration to polish samples. Eliminates subsurface damage and produces superior surface finishes, ideal for EBSD preparation.

A hardness testing method using a diamond pyramid indenter. Expressed as HV. Suitable for a wide range of materials.

An empty space or cavity within a material. Can be introduced during processing or form during service due to damage.

A thin blade with diamond or CBN particles used in precision wafering. Much thinner than abrasive wheels.

Wavelength-Dispersive X-ray Spectroscopy - a technique for elemental analysis with higher resolution than EDS but slower analysis.

A microstructure characterized by needle-like or plate-like phases that form along specific crystallographic planes. Often seen in titanium alloys and some steels.

The increase in hardness and strength of a material due to plastic deformation. Also called strain hardening or cold working.

The stress at which a material begins to deform plastically. The point where permanent deformation occurs.