Printer-friendly version
Glossary of MinSE


Browse the glossary using this index

Special | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O
P | Q | R | S | T | U | V | W | X | Y | Z | ALL

Page:  1  2  (Next)
  ALL

T

:

In the examples of carburised or carbonitrided steel cases, tempering is a simple heat treatment conducted at 150-200°C to relieve some residual stress and impart sufficient toughness to obviate brittle fracture.

Hungary flag megeresztés

:

The phenomenon of preferred crystallographic orientation (texture) often displayed by polycrystalline diffusion layers or surface coatings.   These are typically of fibre texture character.  The double-FCC TiN coating deposited by plasma assisted PVD methods,  frequently, but not always, has the majority of its crystals growing in the [111] direction, while TiN coatings produced by CVD, frequently, but not always, grow in the [220] direction.    Pole figures for these coatings are given below.  In both cases the TiN coatings were deposited onto "steel cutting grade" cemented carbide substrates, each depicting a classical fibre texture.   The intensity of the diffracted X-rays are expressed in "times random" units, where 1 times random equates to a randomly orineted sample.   LR and TR respectively refer to the longitudinal and transverse reference positions on the sample surface.  Many other surface treatments can produce similar effects, e.g., the orthorhombic h-Fe2Al5 phase, formed during hot dip aluminising of steel, predominantly grows in the [002] direction.  The practical implications of crystallograhic texture, for example, in regard to wear resistance, are of clear importance, but have yet to be convincingly investigated.  Texture is also sometimes referred to as preferred orientation.    Also see pole figure.  

Hungary flag Szövet

:

A coating deposited onto components or structural elements exposed to high in-service temperature (e.g.. combustion chambers,  gas turbine blades and exhaust nozzles) with the aim of thermally insulating the substrate and protecting it from oxidation and/or sulphidation.    One such coating comprises two layers, namely of a creep resistant bond coat of nickel-cobalt-chromium-aluminium-yttrium alloy and an outer coating of stabilised ZrO2 or MgO.ZrO2 (magnesium zirconate).  Also see thermal shock resistance.

Hungary flag Hőgátló bevonat

:

A general term covering many processes whereby a solid rod or powder of metal and/or ceramic is melted and propelled at an object or workpiece and resolidified.  The resulting coating or spray deposit is built-up as an array of overlapping splats of rapidly solidified metal and/or ceramic.   Thermal spray processes include; thermospraying, plasma spraying (APS and VPS), detonation gun spraying, HVAF, HVOF,  arc spraying  andwire spraying.

Hungary flag Hőráfúvás

:

Immunity of a surface treatment to degradation by heat.   For exemple, carburised cases loose strength when receiving prolonged exposure to temperatures above 250°C, while nitrided cases only start to degrade at temperatures exceeding 350°C.  However, there many specialised coatings that have been designed to provide protection above 750°C, e.g., those used in gas turbines.  See thermal barrier coatings.

Hungary flag Hőstabilitás

:

Any method of surface modification requiring heat and chemical action.  All diffusion methods fall into this catagory.   These can involve interstitial diffusion, as in carburising, nitriding and boriding,  or substitutional diffusion as in chromising and aluminising.  

Hungary flag Termokémiai kezelés

:

One of the simplest forms of spray deposition, whereby powdered coating material is gravity fed or aspirated into an oxyacetylene flame.   For metal or alloy powders, particle melting is very inefficient and the resulting coatings can be very porous.  A number of special coatings have therefore been developed which undergo an exothermic reaction during their passage through the flame,  typical of these is the 82:18 nickel-aluminium powder.   This is a nickel powder that is coated with aluminium; it is not an alloy.   The aluminium initiates an exothermic (thermite-type) reaction during spraying resulting in a coating of higher density than otherwise possible.   Thermospraying is also used as the first step in laying down fusion hard facing alloys  by the spray and fuse process. 

Hungary flag termikus hőszórás

:

A semi-schematic graphical depiction showing the influence of chamber pressure and homologous coating temperature (during deposition) on coating morphology.   The diagram is applicable to metallic or ceramic coatings produced by plasma assisted PVD and encompasses some of the morphologies originally reported by B. A. Movchan and A. V. Demchishin (Phys. Metal. Metallog., 1969, 28, (4), 83-90.) for Vacuum deposisted coatings produced at different homologous deposition temperature.     John Thornton discovered the existance of an additional morphological region "Zone T" (for sputter deposited coatings) and characterised the influence of deposition pressure on the stability of the morphological zones.   In general, it is preferable to produce most PVD coatings of the Zone T (fine-columnar) or Zone 2 (coarse-columnar) types; both are near fully dense.   PVD-ceramic coatings are invariably of these types when substrate temperatures are insufficient to produce the equi-axed Zone 3 type morphology.    Zone 1 coatings have a coarse-columnar morphology and contain significant levels of intergranular porosity and are to be avoided for most engineering purposes.   The diagram shown is adapted from J. A. Thornton, Ann. Rev. Mater. Sci., 1977, 7, 239-260.  

Hungary flag Thornton diagram

:

A situation arising when (usually) hard particles are trapped between two counterfacing sliding surfaces moving in different directions.   A fluid (gas or liquid) may also be present.   The particles cause abrasive wear of the sliding surfaces.

Hungary flag 3-test elhasználódás

:

One of the most common thin (≈5 µm) hard (≈2,000-3,000 Vickers) coatings applied to metal cutting and forming tools to convey wear resistance; usually applied by chemical vapour deposition (CVD).   Used most commonly as  one constituent of  a multi-layered, multi-phased coatings, as discussed in the comments  for titanium nitride coating.

Hungary flag Titán-karbid bevonat


Page:  1  2  (Next)
  ALL


Theme by NewSchool Learning