Time—temperature-transformation state

A molten metal alloy would normally be expected to crystallize into one or several phases. To form an amorphous, ie, glassy metal alloy from the Hquid state means that the crystallization step must be avoided during solidification. This can be understood by considering a time—temperature—transformation (TTT) diagram (Eig. 2). Nucleating phases require an iacubation time to assemble atoms through a statistical process iato the correct crystal stmcture... 

For a number of applications, particularly those associated with conditions of continuous cooling or heating, equilibrium is clearly never approached and calculations must be modified to take kinetic factors into account. For example, solidification rarely occurs via equilibrium, amorphous phases are formed by a variety of non-equilibrium processing routes and in solid-state transformations in low-alloy steels much work is done to understand time-temperature-transformation diagrams which are non-equilibrium in nature. The next chapter shows how CALPHAD methods can be extended to such cases. 

Boey, F., Lee. T. H., and Sullivan-Lee, P High pressure autoclave curing of composites effect of high pressure on glass transition temperature, J. Mater. Sci., 29, 5985-5989 (1994). Gilham, J. K., Time temperature transformation (TTT) state diagram and cure, in The Role of the Polymeric Matrix in the Structural Properties of Composite Materials (J. C. Seferis and L. Nicolais, eds.). Plenum Press, New York, 1983, pp. 1127 145. 

Fig. 10 Thermodynamic and kinetic basis for solute depletion in the case of a binary alloy consisting of solvent A and solute B. (a) Binary equilibrium phase diagram with complete miscibility in the liquid state, partial miscibility in the solid state given by existence of a terminal solid solution. Cs is the composition along the solvus line. is the overall composition of the alloy, (b) Time-temperature-transformation diagram for precipitation of in an a matrix for the alloy shown in (a) with overall composition,...

The kinetics of solid-state phase fiansformations are often summarized in time-temperature-transformation (TTT) diagrams. Figure 6.30 illustrates the consuiiction of a TTT diagram using the fiansformation kinetics for the system in Figures 6.26 and 6.28. The TTT diagram shows the time required to achieve certain amounts of transformation as a function of the temperature of the transformation. 

The kinetics of solid-state phase transformations are often summarized in time-temperature-transformation (TTT) diagrams. The ITT diagram shows... 

Discuss the kinetic and thermodynamic factors governing liquid-solid and solid-solid phase transformations. Explain and predict nucleation, growth, and time-temperature-transformation (1 IT) processes in solid-state systems both qualitatively (through diagrams) and quantitatively (through equations). 

Fig. 3. Generalized time-temperature-transformation (TTT) cure diagram. A plot of the times to gelation and vitrification during isothermal cure versus temperature delineates the regions of four distinct states of matter liquid, gelled rubber, gelled glass, and ungelled glass. From Ref. 12.

For determining the efficiency of the developed composites, the experiments on the fire resistance by exposiue of a sample to open flame using the universal Bunsen biuner were conducted. With a help of the pyrometer C-300.3, measuring the moment of achieving the limit state, time-temperature transformations on the nonheated siuface of the sample were registered. 

Figure 14.3 Generalized time-temperature-transformation cure diagram showing four distinct states liquid state, gelled rubbery state, gelled glassy state, and ungelled glassy state in the cure of thermoset. (Reprinted from Enns and GUlham, Journal of Applied Polymer Science 28 2567. Copyright 1983, with permission from John Wiley Sons.)...

The glass transition as a reference state can be used to explain all transformation in time, temperature, and structure composition effects between different relaxation states for technologically practical food systems in their nonequilibrium nature. Among others, specific examples include reduced activity and shelf stability of freeze-dried... 

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