Amorphous critical cooling rate

Using the fluxing technique, Lau and Kui [33] determined that the critical cooling rate for forming a 7-mm diameter bulk amorphous Pd4QNi4()P2o cylinder was 0.75 K/sec. From this value, they estimated that the steady-state nucleation frequency was on the order of lO" m s. On the other hand, Drehman and Greer [34] estimated that the steady state nucleation frequency at 590 K is 10 m" s, which is also the maximum... 

Figure 80 shows the relation between A x and the critical diameter dc for the formation of an amorphous phase for Mg-Cu-Y alloys obtained by copper mold casting. There is a clear tendency for dc to increase with increasing AT. Furthermore, the critical cooling rate (Rc) for the formation of an amorphous phase has been evaluated to be as low as 80-... 

From equations (10) to (23), the time-temperature-transformation (ITT) curve can be obtained. The critical cooling rate Rc necessary for amorphous phase formation with a melt quenching method can be evaluated from TTT curve calculated and ap>proximated as follows... 

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. 

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