Detachment of surface particles by rubbing.

Crack opening

Width with a defined distance between the two side margins of the crack.

Crack’s apex

Sharp and extreme tip of the split.

Crack arrest

Point where the crack stops advancing.

Breaking appearance

Shape of the break identified at a visual inspection.

Fatigue bands

Set of bands that reveal the stop and progress of fatigue failure.


Brazing consists in connecting metal pieces without melting them, using a filler metal. The filler metal penetrates by capillarity between the pieces to be assembled.


The force able to overcome the resistance of the material up to the point of deforming it or fracturing it.


Micro-vacuums between grains.

Linear expansion coefficient

The thermal expansion of the bodies is a typical property of the materials, which consists in varying its dimensions as the temperature increases. The thermal expansion is quantified by a specific coefficient of thermal expansion according to the physical variation of the body that correspond to: coefficient of volumetric thermal expansion; surface thermal expansion coefficient; coefficient of linear thermal expansion.

Isostatic pressing

In conventional compaction techniques, the pressure is applied uniaxially, so that the resulting structure is inhomogeneous or is not uniform in all directions. In isostatic pressing, the pressure is hydrostatic and is applied at room temperature (cold isostatic pressing – CIP) or hot (hot isostatic pressing – HIP). It is made through a fluid that is not mechanical, but is a pressure that is exerted in all directions.

Cathodic corrosion

Corrosion for impressed currents. The modifications of the corrosive medium caused by the current flow from the corrosive medium to the metallic material (cathode) result in a spontaneous corrosion of the material itself, in an alkaline environment.

Contact corrosion

Localized corrosion that occurs in the area in which two different materials are in contact with each other.

Widespread corrosion

Corrosion of the material that affects the entire surface and for which the thickness of the dissolved material is on average equal.

Electrolytic corrosion

Chemical decomposition produced by an electric current.

Galvanic corrosion

Corrosion due to use of a continuous electric current.

Localised corrosion

Corrosion which affects, at the macroscopic scale, only a part of the surface of the metallic material.

Dry corrosion

Corrosion of a metallic material that occurs at high temperatures in the absence of water or other solvent.

Wet corrosion

Corrosion that occurs in the presence of water, or other solvent, in the condensed state.


Phenomenon of a chemical-physical nature that causes the gradual decay of the characteristics of the material, with the contribution of the surrounding environment.

Anodic corrosion

Corrosion due to electrical flow that occurs when the dissociation of the metallic material (anode) passes to the corrosive medium (cathode).

Atmospheric corrosion

Corrosion due to atmospheric condensation on the metal surface.

Uniform corrosion

Diffuse corrosion that affects the entire surface of the material and where the dissolved thickness is the same in all points.


Wear of the tool due to the creep of the processed material.


Microscopic or macroscopic discontinuity of a metal in which two dimensions are definitely more relevant than the third (length-depth-width). The presence of this discontinuity, in a solicited artifact, implies the increase of local stress at the top of the crack.

Capillary crack

Very thin split.

Grinding crack

Cracks usually in spiderweb-like shape generated by overheating induced by the wheels.

Surface crack

Crack that appears at the surface and affects limited external layers.

Thermal shock cracks

Cracks due to temperature changes (too drastic cooling or too rapid heating).


Process (usually involuntary and unwanted) of carbon removal from the carbide, in case it is placed in contact with certain atmospheres, generally at high temperature. Decarburization involves a serious metal defect called phase-eta.


Shape variation due to mechanical or thermal causes.


The density (correctly called specific mass) of a body is defined as the relationship between the mass of the body and the volume of the same body.

Defect from use

Anomaly caused by an incorrect use of the piece.

Finishing defect

An anomaly, usually dimensional, caused by the last stages of processing.


The hardness can be defined metallurgically as the resistance of a material to the penetration of a harder body. The hardness test is a conventional, static and non-destructive test performed by subjecting a non-unified test piece (it must have parallel faces) to a stress.


EDM is the process by which a part is ground using the erosive properties of electric shocks.


Removal of particles from the metal surface due to the abrasive action of a liquid or gas.

Cross breaking force

The transverse breaking force is determined by placing a standard sample (for ASTM B-406, ISO 3327) between two supports and loading it up to the breaking point. The value obtained is called the transverse breaking force or cohesion force and is measured in relation to the weight that caused it to break. This test detects the load on the single area of ​​the unit and is expressed in psi or N / mm2.


Insufficient toughness of the material in relation to its usual characteristics.


Appearance of surfaces that delimit the breaking of a piece.

Fatigue fracture

Fracture characterized by fatigue stress. It is distinguished by the presence of concentric resting lines at the triggering point and by a culminating crash zone.


Abrupt increase in sliding friction between two mechanical parts in relative motion, which causes blocking and sometimes welding.


Presence in the metal of an unwanted percentage of unwanted elements.

Grains enlargement

Increase in shape of the grains constituting the hard metal matrix. The anomaly is often caused by excessive sintering temperature or prolonged heating.


Small roundish hall opening to the outside.

Resistance to fatigue

The mechanical elements are often subject to stresses that change in time in a cyclical way, that can be identified in a succession of alternating maximum (peaks) and minimum (valleys) load stories


Contraction of the metallic mass following sintering.


Release of the internal bonds of molecular cohesion with detachment of the parts of certain surfaces.

Compression rupture

Breakage caused by a mechanical action that tends to alter the size of a body, so as to reduce its volume by bringing the particles that compose it together.


Breakage with splinters (sharp or pointed fragments).


Sintering refers to the compaction and transformation of materials reduced to powders into an indivisible compound. This heat treatment is carried out at a temperature lower than the melting point of the material. This operation (also called sintering or metalloceramic or powder metallurgy) is performed to obtain compact products. Thanks to sintering it is possible, starting from powder materials, to obtain objects with specific shapes and sizes that can be subjected to mechanical and thermal treatments.

Decarburized layer

Carbon depletion on the surface of a metal during heating in an oxidizing atmosphere.


Simple stress that occurs in the generic section of a structural element under the action of two forces on the orthogonal plain to its geometric axis, resulting in a torque.


Progressive mechanical deterioration of a metallic surface which is in moving contact with other solid material that causes parting of metallic particles.


The term comes from the trade name of a range of high hardness alloys: the word derives from the first letters of the German expression “wie Diamant”, or “hard as diamond”.