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Glossary of MinSE


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A laser is a device which achieves a finely controlled emission of coherent, monochromatic high energy radiation ranging from the ultra-violet to the infra-red wavelength range.   The most common medium in which the lasing action can be created are gases of various compositions; in surface engineering the CO­2 laser is the most popular.   The gas used comprises a mixture of 10% CO2 , 30% N2 and 60% He which  is rapidly circulated at reduced pressure between two pairs of electrodes which results in the generation of an electrical discharge and excitation of CO2 molecules;  when the excited electrons fall return to their lower energy levels photons are emitted which stimulate further photon emissions (from adjacent molecules) which are perfectly in phase and of the same wavelength (10.6 µm for CO2 molecules).    This emergent laser light has high phase contrast, can be focused to very small diameters, approximatling to the wavelength of laser light, which enables high power densities (≈103 to 1010 W/cm2) to be realised.    When coupled with appropriate substrate and/or laser beam manipulation, a wide range of interaction time, from 1 to 10-8 seconds can be obtained (diagram).  

Hungary flag lézer

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The surface zone whose composition has been modified by laser alloying.  Typically between 20 µm and 1.00 mm deep.

Hungary flag Lézer ötvözte zóna (LAZ)

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Laser treatment applied to a metallic surface which is momentarily surface melted to enable the encapsulation of preplaced or injected ceramic powder particles.   The treatment is applicable to ferrous or non-ferrous metals and alloys.  There has been a lot of interest in recent years in applying such treatments to aluminium and titanium alloys because both of these suffer from the disadvantage of responding poorly to thermochemical diffusion treatments, i.e., they develop very shallow treatments, if any.   Laser cladding offers the possibility to develop deeply hardened surfaces, up to 1 mm.  The process is analogous to electron beam cladding.

Hungary flag Lézeres bevonatolás

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A vacuum evaporation (PVD) method in which a laser beam is scanned over the surface of a solid source or target, causing evaporation through laser ablation.   The laser beam is passed through glass port in the vacuum chamber.   The process can be carried out under high vacuum conditions (≈10-6 Torr) when the substrate remains at near ambient temperature, or the substrates may be negatively biased in an appropriate atmosphere (e.g., Ar) held at ≈10-2 torr which creates a glow discharge plasma, providing substrate heating (to temperatures ≈400°C) and improving throwing power.     One advantage of using a laser is that electrically insulating materials can be evaporated; this is less easy with the more usual electron beam methods.

Hungary flag Lézeres elpárologtatás

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Also termed laser vitrification.   Achieved by surface melting with a laser beam at power densities ≈ 105 to 107 W/cm2 for  ≈ 10-3 to 10-7 seconds; cooling rates exceeding 105 K/s can be realised which suppress the usual nucleation and crystallisation processes that accompany solidification.   Instead,  amorphous or vitrified (glass) surface layers are produced.   The Nd-YAG or Excimer lasers are especially suited for laser glazing.     The latter has recently been demonstrated to improve the statistics  of  fracture (i.e., the Weibull modulus) of Al2O3 ceramics by healing surface defects.   This represents a significant break-through in materials processing.

Hungary flag zománcozás

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Any laser treatment which results in hardening, in the absence of externally applied alloying elements or second phase particles.   Hardening often results from the rapid solidification following laser melting, i.e., due to the creation of a very fine dendritic microstructure.  In some cases crystallisation is suppressed and a hard glass is produced (laser glazing).  Laser hardening can also be produced by manipulation of solid state transformations; see laser transformation hardening.

Hungary flag Lézeres keményítés

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Any surface modification resulting from the action of laser beam heating.

Hungary flag Lézeres hőkezelés

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Any laser assisted process.   A very broad term encompassing laser heat treatment, laser welding and laser cutting.

Hungary flag Lézeres eljárás

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Any surface modification resulting from the action of laser beam heating.

Hungary flag Lézeres felületkezelés

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A process applied to ferrous alloys with >0.35wt-%carbon.   Laser power density  (≈103 to 104 W/cm2) and interaction times (≈10-2 to 1 s) are adjusted to cause rapid austenitisation of the surface; the heated zone subsequently self-quenches by conductive heat loss into the steel core beneath (water quenching is not required) which remains at ambient temperature.  The resulting martensitic case can be furnace tempered, but this is not usually practised.   The process produces less distortion than, for example, induction hardening, since only a very small volume of the object is heat treated.

Hungary flag Lézer transzformációs keményítés


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