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Glossary of MinSE


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C

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The erosion of a surface caused by the collapse of vacuum bubbles formed in a fluid. A condition which frequently affects ship propellers and impellers.
Hungary flag Kimaródás
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(i) An obsolete term denoting carburising; (ii) A general term used to denote any surface diffusion method that results in the formation of a surface layer containing interstitial or intermetallic ccompounds. See diffusion coating and diffusion metallizing.
Hungary flag Cementálás
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Polishing of a metallic surface by immersion in a bath containing oxidizing substances which levels and brightens the surface by preferentially dissolving projecting surface irregularities.
Hungary flag Kémiai polírozás
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Less commonly termed chemical vapour plating, thermochemical plating or gas plating. A reactive gas phase deposition process in which one of the reactants (typically a metal halide) is in the vapour state, prior to admittance into the reaction chamber. (Note: a vapour differs from a gas in that it can be condensed by the application of an external pressure. Conversely a gas, being above its critical vapour pressure, cannot be condensed in the same way.) CVD can be carried out at atmospheric or sub-atmospheric pressures. For the production of carbide and nitride ceramics, reactions are of the general form:-
MClx + H2 + N2 ---> MN + xHCl
The kinetics of reduction of metal halides like TiCl4 mean that the CVD of TiC, TiN, Ti(C,N) and Al2O3 requires temperatures ≈1000°C at atmosphreic (760 torr) or sub-atmospheric pressure (≈50 torr). However, by ionising the reactive gases in a radio frequency (RF) glow discharge, the kinetics of reaction can be accelerated to enable deposition at substrate temperatures ≈500-600°C.
flag Kémiai gőzöléses fémbevonatolás
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Micro-fracturing or breaking away of fragments of a brittle coat especially at an edge or a corner.
flag Kémiai adszorpció
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Micro-fracturing or breaking away of fragments of a brittle coat especially at an edge or a corner.
flag Forgácsképződés
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Thermochemical diffusion treatment involving the enrichment of plain carbon steel surfaces with chromium, to impart corrosion and wear resistance. Chromising is generally carried out between 850 and 1050°C for durations up to 12 hours, which produces chromised layers ranging in thickness from ≈10 to 150µm. The constitution of the chromised surface layer depends upon the carbon content of the steel. For steels with 0.3 wt-% C, the chromised layer is essentially ferritic (the chromium remains in solution). Steels containing 0.4 wt-% C show evidence of intergranular carbide precipitation, while steels with higher carbon contents exhibit layers enriched in massive carbide deposits of the same type, i.e., (Fe,Cr)7C3 and (Fe,Cr)23C6. The Vickers microhardness of chromised steel surfaces increase linearly from ≈600 to 1800 kg/mm2 for steels with carbon contents ranging from 0.2 to 0.8 wt-%. The higher the carbon content of a steel, the thinner the chromised layer thickness (for a given chromising temperature and time). Chromising can be conducted using various media. See pack chromising and gaseous chromising.
flag Krómozás
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An electroplating process in which chromium is deposited from a chromic acid solution in the presence of silicofluoride and/or sulphate catalytic anions. Chromium is generally subdivided into 'hard' and 'decorative' plating methods. Hard coatings (2 to 250 µm) are thicker than decorative coatings (<2µm) and are used for engineering application, often in conjunction with a sub-layer of nickel. Various types of hard chromium exist, including microcracked chromium, microporous chromium, porous chromium and crack-free chromium. The latter can only be produced in thicknesses up to 2.5 µm, whereas, the porous or cracked chromium deposits can be up to ≈150 µm. Indeed, it is essential that the microdefective coatings have a minimum thickness ≈80-120 µm in order to confer adequate corrosion resistance. Micro-cracked chromium has a Vickers hardness of 800 to 1000 kg/mm2, while crack-free chromium has a Vickers hardness ≈425 to 700 kg/mm2. There is a lack of hardness data for microporous chromium and porous chromium. The former should not contain less than 15,000 pores per square centimeter; this favours a lateral corrosion path, delaying downward penetration. The formation of micropoorous chromium is achieved by a specialised plating method involving the use of suspended inert particles. Porous chromium plating is, however, developed by an etching procedure after electrodeposition of the chromium; this coating has a coarser distribution of pores. These are designed to retain lubricant, in sliding and bearing type applications. Chromium itself is a base metal; it is the external chromium oxide layer which provides the observed tolerance to atmospheric corrosion. For an excellent review see J. K. Dennis and T. E. Such: 'Nickel and Chromium Plating', 3rd ed; 1993, Cambridge, Woodhead Publishing.
flag Krómozás
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Most commonly achieved by roll bonding two dissimilar metals together above their recrystallisation temperature (hot working), e.g., austenitic stainless steel can be clad to mild steel, producing corrosion resistant steel sheet at a fraction of the cost of solid stainless steel.
flag Plattírozás
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(i) - verb - The action of creating a coating, e.g., by a plasma torch; (ii) - noun - A surface covering, usually of very different constitution to the substrate, which renders an improvement in corrosion or wear resistance.
flag Bevonatolás

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