Critical quenching rate

The writing process, that is, the transition crystalline — amorphous, is caused by briefly (<50 100 ns) heating up the selected storage area (diameter (( )) ca 0.5—1 Hm) by a laser pulse to a temperature above the melting point of the memory layer (Eig. 15, Record), such that the film locally melts. When cooled faster than a critical quench rate (10 -10 ° K/s), the formation of crystalline nuclei is suppressed and the melted area sohdifies into the amorphous (glass-like) state. 

In order to obtain maximum properties after quenching, the quenching rate must exceed a certain value called the critical quenching rate which depends on the alloy it ranges from... 

Because of the low critical quenching rate of these alloys, thin semi-products can be quenched by forced-air quenching. 

For certain alloys, the hot rolling or extrusion temperatures are on the same level as the solution heat treatment temperatures. If the critical quenching rate is suflhciently low, it may be possible to quench immediately after hot working. This is current practice for several extrusion alloys of the series 6000 (6060, 6005A, 6106) that are press-quenched by forced air-cooling or water spray. These tempers are referred as T1 (quenched and naturally aged) and T5 (quenched and artificially aged). 

Corrosion testing Corrosivness Crevice corrosion Crevice corrosion Critical quenching rate... 

For the continuous cooling of a steel alloy, there exists a critical quenching rate, which represents the minimum rate of quenching that produces a totally martensitic structure. This critical cooling rate, when included on the continuous transformation diagram, just misses the nose at which the pearlite transformation begins, as illustrated in... 

Figorc 11J8. Calculated critical cooling rates for suppression of various phases in (a) Ag-Si and (b) Au-Si from Kambli et al. (1985). Horizontal bars indicate experimental glass-forming range by laser quenching. 

Since any quenching action is a bimolecular process, it is essential that the molecules M and Q should be in relatively close contact, but not necessarily in hard sphere (van der Waals) contact. Theoretical models lead to the distance dependence of the quenching rate constants as exponentials or sixth powers of r, the centre-to-centre distance of M and Q. Since these distance dependences are very steep, it is convenient to define a critical interaction distance r at which the quenching efficiency is, this being the distance at which 50% of the molecules M decay with emission of light (or undergo a chemical reaction) and 50% are quenched by some nearby molecule Q. 

Critical cooling rate, Rc minimum quenching rate of a melt that results in a glassy product... 

Adhesion. Successfiil combination of coextruded film layers has been described in terms of rheological compatibility, surface tension and melt viscosity at processing temperature, interfacial behavior at the surfaces between layers, chemical interaction between two combined materials, crystallinity, and shear compatibility between components of the composite (67). Critical factors in layer bonding are polymer fiinctionality (chemical composition), melt temperature, time in contact at temperature, viscosity of the joining layers, layer thickness, thermal stability, orientation, quench rate, and moisture sensitivity. 

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